I'm a mechanical engineer, just graduated. I'm currently working on a website (it's taking a long time) and I'm going to have a post on being an engineer vs technician/mechanic. It really boils down to do you want to get into design, or do you want to get your hands dirty, it's difficult to have both. That's why I made this channel, so I could learn a little more myself.
I'm in school for industrial Manufacturing and controls, and work maintenance Technician at CocaCola, we have lathes, mills, tig, mig, stick, almost anything ever needed. I have a 3d printer and design my own parts or frames needed. I do enjoy my job it doesn't pay as good as I could possibly get but I design and maintain as needed and enjoy doing it!
@@bigpapa3708 I'm doing the same program..I love it..I think Manufacturing has alot of overlap with engineering..I seem to enjoy stuff like print reading more than I enjoy stuff like gcode.
Why not go tell putin to stop killing innocent children civilians,and wildlife,I’ve never had a issue with Russian people on the whole, even if during the 1980’s in the military Russia was our main concern, I don’t get why your ppl don’t kick Putin out of power I don’t get how he claims to get 90% of the votes, ? it’s like Russia has blinders on its ppl or something, ? Had a Russia friend here till the war, and she said even her parents believed putins lies, even over their own daughter who showed them proof of his crimes..maybe it’s like the fools here in the USA who still support trump after his crimes ,lies and tax scams, god help us if he ever gets back in office again..take care, and let others know that 30k Russian troops have died already, sad maybe truth might help ya guys.. @@hepcat93
What is the current design of the "hemi" head if not hemispiracle? Emissions, aside is the current "hemi" a better design than that of the 60's hemi head?
Thanks for watching. Basically a flat cylinder head has a lot of surface area but doesn't add any volume. A sphere is the best possible shape for maximizing the ratio of volume to surface area; ie it has a large volume and relatively low surface area. This means less heat lost. Also, it doesn't have corners like a flat head, which can create heat spots and unusual stresses.
Trump took alot out of the more educated segment of our population. Ignorance is bliss, his sycophants never understood the danger. Part of the reason he openly loves the uneducated.
I know practically nothing about cars and looked this up to try to understand the hype about hemi engines. My husband went on a small rant about them but I didnt quite get what he was trying to express. This video is AMAZING, thank you for making this. If you aren't an instructor you should be. 🤯
Awesome! I would head to my website (howdoesacarwork(dot)com) and go to Lesson 1. There I've organized my videos into a logical manner. Or simply go to my channel and start with the engines playlist. Let me know if you have any questions along the way!
Thanks for watching. I've got a detailed answer to your question on my website FAQ (see link in the description). Though to be honest, most comes from the good ole' interwebs.
@@JoseMartinez-jw2dy Hemi rams are great, I've owned 2 cummins powered rams in the past (still have one) but rented a hemi ram for a week and was amazed at how quiet & quick it was. But I still love my diesels. I think the only way I'd buy a hemi RAM is if I could do so while keeping the Cummins. The Hemi is truly great but so is that Cummins. And I love my Cummins. The Hummin' Cummins, 6 in a row make 'er go!
Honda inline 4's are pretty straight forward and easy to work with. Plenty of space and intelligently laid out. But there are probably a good amount of simple engines to work with out there. Not really on newer cars though, electronics keep getting jammed in there!
Just getting started eh? Fantastic. Well the first ones I took were statics, dynamics, and solids. Statics one semester, dynamics and solids the next. The good thing about mechanical engineering is every semester you'll take a class that you'll swear is the most difficult you've ever taken. And it's true too!
Should be added that the Hemi (compared to the Wedge design) allowed for bigger valves as they are opposite of each other and not in line like the Wedge. Along with straighter and larger ports gave the HEMI a huge advantage in air flow. The Hemi really shines in high rpm operation or supercharged to move alot of air.
*"These disadvantages are exactly why the hemispherical design was displaced by the Wedge type"* Was under the impression that wedge predominance was merely because it's so much easier to package a wedge-shaped combustion chamber, with parallel valves, in a pushrod engine. Generally OHC engines aren't constrained in that manner and thus generally don't use that combustion chamber geometry. Also thought the high surface area/volume ratio and acute angle between piston and head led to excessive emissions.
punjabimunda5555 this. They also have less inertia each and thus will be less likely to float at a given rpm than one larger valve, even if you don't consider the rocker arms and pushrods
12 years late to your class but I am glad you are still preaching :D I'm not a car person, a motorbike guy in fact, but since an engine is an engine, I've been gaining a lot of insight from your videos, in other words, your passion.
It's funny how you have such a profetional thumbnail on such an old video. You really care about your old videos and update their thumbnails, witch is nice.
Just watched this in May 2023. This by far excedes the info to the lay person, what the "HEMI" is and and the old (flat) and new (pent). Learned a lot in just a few mins. Other clips don't show you the diff's and just show a pic of the head (w/no ref's to others).
Two sparkplugs per cylinder are used in basically every aviation piston engine.This is done primarily for redundancy, but increases power output, too. This also allows to check if the ignition system is working, if shutting off one set of sparkplugs reduces rpm (=> less power) slightly everything works fine. If nothing changes, the engine has been running on the other set only.
Higher compression ratios yield greater efficiencies. Of course, the law of diminishing returns is always in effect. Cost goes up, and does difficulty with using low octane fuels. Mazda currently holds the record (in my head) of highest CR on 87 octane gas, of 13:1. Very impressive.
@PirateXzibit Yes. You'll always have at least two valves in four stroke engine. (The four strokes being intake, compression, power, and exhaust.) One valve lets the air come in the cylinder, the other valve allows the air to leave. Watch my video on gasoline vs. diesel, it will help a lot on understanding this. Also, most modern engine use four valves (two for intake, two for exhaust) as this allows for better airflow and higher efficiencies.
The idea with the pentroof is that only one spark plug is needed for complete combustion. If possible, it's better to just have one, so that's part of the goal of cylinder heads.
Cooler air is more dense so it allows for more fuel to be burned (more power). Heat is important for lubrication purposes - reducing friction and frictional losses, but there's plenty of wasted energy that the engine creates which can be used to keep it warm.
As the valves are located perpendicular to the crank centerline, the Hemi simply gives a shorter, straighter shot at the valves. Thanks for your videos.
Wow, first time watching one of your older videos from about six years ago. Still very good IMO. In hindsight, showing the valves in the block for the flat head may have helped a bit with the overall explanation about the designs. And, you skipped the wedge head completely - the hemi was considered an improvement on that design if I remember correctly. This was the first time I noticed inaccurate terminology coming from you... you referenced the "weight" of the hemi's piston when you actually were referring to a property (inertia) of its "mass" when describing the work the crankshaft needed to do to move the piston. Regardless of my negative comments your white board and coloured markers have been of great value to a lot of people including me. I have frequently offered links to your videos when someone has asked "How does 'that' work?" Keep up the great work.
HEMI's of today aren't like they used to be, they're much closer to the pentroof design. That said, 2 valves per cylinder has faded out of most manufacturers, and likely remains simply because of cost, or perhaps they can effectively market it.
@EngineeringExplained I used to think the same thing, having only had a quick intro to the different type of cylinder heads. And as an aspiring engineer i am extremely excited to have stumbled upon your channel! Thanks for the vids!
Paul Paulie *They're BMHNMH Just plain wrong. Convex piston heads were just an addition to the original Hemi design, which in fact denotes hemispherical cylinder heads. Vernard Pugh There always has to be a DICKHEAD in the world who can't cope with facts and gets upvoted for behaving like a clown. "LMFAO".
Effective clearly explained, thank you I appreciate it. I am not a car person but as an educator I very much appreciate the time you took and the visuals that you used I know that this was over 13 years ago and that you might’ve moved on to greater things but I have to tell you you have a great beginning and I’m proud of that.
Americans grew up with these cars and trucks. It's a part of our history. Someone said it themselves,, nostalgia.. But at the end of the day, we are all driving Camerys to work lol
Agreed! As a Mopar fan boy who owns a Charger R/T, I was about to chime in and correct you! The R/T comes equipped with the 5.7 L. The early SRT8s came equipped with the 6.1L. The current SRT8s come with the 6.4 L, otherwise referred to as the "392" (392 cubic inches). Love your videos man. I'm an engineer and it's awesome to see a fellow engineer educating others who may not be engineers but are curious and eager learners! Keep it up my friend!
Thanks for sharing. A powerful truck isn't my style, but to each his own. I prefer the practicality and handling of a hatch, though there's plenty a truck can do that a hatch cannot. Your truck would disappear before I got to second gear, my poor little 1.8 liter.
There are two types of comments 1. How inefficient and outdated the Hemi is 2. How people own one because Murica I have one because I don't have a choice
I respect the amount of knowledge this person has on his videos about car engines. The down side is that his videos are a little boring so I never finish whatching them completely.
Here in Australia, we had slant-6 HEMI's in Chrysler Valiant Pacers and Chargers, in 245 and 265, and they were powerful enough to go toe-to-toe with the V8's (this was long before the days of turbo 6's). What is it about their design that allowed them to have the same output as the V8's, which were 351 Windsor/Cleveland, and 350 Chevy/308 Holden at that time frame?
Blake, maybe being an "Over square" engine may be the answer you're looking for. Also a big RT38 charger fan this way. A shame nobody thought about using a 4 speed box for Mt Panaroma.
Of course, now they have multi-spark ignition, delivering a barrage of smaller sparks for a longer period of time, allowing more power and better efficiency because more of the fuel is burned in the cylinder thingie. But, please correct me if I'm wrong. I love your videos, and your dry-erase graphics. Nothing extra. What I really like is that you expect the viewer to understand you and you don't dumb down or oversimplify or give weird analogies. Engineers are like physicists that speak English. You are clearly a good engineer. Thank you.
The problem with knocking is that the air/fuel mix is detonated at an inopportune time. 2 ignitions with planned timing, and equal timing, will work out just fine.
Good video.Also, about the Surface to Volume ratio (S/V ratio), the more surface you have the more carbon build up you are likely to have if you cant burn all your fuel.This encourages detonation/pre-ignition and bad for emission standards.Just my two cents.Again,Good video! Thanks for sharing.
Thank you very much!! you're such a good guy. You always take time to answer requests.Cool video as usual. And please don't reply every time cause you're such a busy guy.
Two spark plugs are a little bit unusual, but not unheard of. Mazda's rotary engine (i.e. wankel) used 2 per rotor, but that's a completely different animal. A more common engine was Ford's 2.3L 4 cylinder that had 2 spark plugs. Other manufacturers did it too. Pretty much same reason why Chrysler is doing it today. Emissions and Combustion.
The new Hemi's remind me sort of the early Hemi's The Chysler FirePower Hemi's. About 17 years ago, I worked a place in El Segundo, CA where we made plenty of Hemi pistons for for both the Gen 1 and Gen 2 Hemi's. The Gen 2's are massive!
The real doktorbimmer Yep, it's the flat top pistons of the new Hemi's that reminded me of the Fire Power Hemi's. That's putting combustion chamber aside. It's just the piston design that reminded me. Speaking of the Fiat-Hemi's just being a brand name, have you seen the Australian "Hemi" 6's? That's pretty liberal use of the "Hemi" name for marketing purposes. I saw one of those in Vegas at Mopars at the Strip car show. I have to admit, that 6 did sound pretty mean though.
Yes, the Hemi's main advantage was its ability to really get going like a hound from hell in the upper revs with its insane head-flow. But, like you mention, under 4500 revs, a 440-6 was a serious force, and that sort of stump-pulling grunt has a very impressive feel to it during normal driving. It's what makes my 250hp Dakota feel much faster than a 250hp Camry. But, if you were serious about going to the strip and doing some racing, the Hemi was the best. And it STILL dominates top fuel!
@JayBird90210 It would be a challenge, indeed, however there is a video that explains it very well. I couldn't offer the visualizations that are shown in this video: (/watch?v=6EfuRJrseD4). At about 45 seconds they go into how the advancing and retardation of the cams works. It's brilliant.
I guess I will be the oddball out here.... I have a 2008 Forenza, and I can tell you, OHV has one big advantage over OHC. My timing belt came off at 135k miles and ruined my valves. Had to get another Forenza, rip off the valve cover, and replace the whole unit (That was fun, BTW). OHV doesn't really have that problem, per se, although it theoretically could happen. I don't see why OHV is obsolete per se, everything that can reduce costs and make it simpler to manufacture, as the Russians say, "Quantity has a quality all its own".
You're right about the 440 RB having poor intake runners & is often times sophisticated by the carb. 350-600 cfm carb on an engine which the each intake runner will flow over 200 cfm (more than one piston end up short) usually still had 500 tq. Although the 383 RB with a 4 barrel was a good package. Smaller displacement meant it revved quicker because of the lighter internals and were more consistent because they came with hydrolic lifters instead of solid lifters like larger hi po engines.
No need to ask for replies. Yes, heat is unwanted as it represents wasted energy, but the reaction of combusting gasoline and air results in a great temperature gain, increasing pressure as well. This pressure drives the piston down, rotating the crank.
A modern hemi engine does not breath better then a 4 valve design, in fact the greatest weakness of the 5.7 (which is not in a srt as stated) is its lack of airflow through the valve.
I have a Alfa Romeo. It has a hemispheric chamber with a two camshafts in overhead. It's very efficient. I already see the Lancia Delta integrale engine with 4 valves in overhead and Hemi chamber.
Ok? Yes they are disadvantages. The same supercharger would make more power on a stock 2018 Mustang engine that it does on a Demon. That engine is 307 ci
Can you explain the surface area thing.... Got a hard time figuring this... The surface area of a dome would be greater than a flat disk of the same diameter.... Not quite a car guy but it's been 2 evenings in a row watching your videos... Seriously awesome stuff man
The 5.7 was only ever an R/T engine. The Srt8 was the 6.1 hemi, aka the early hellcat🔥🔥👍 Thanks for the explanation though I've always wondered what part of the engine is actually hemispherical and you explained it extremely well! Again, thanks man!
all of these comments saying they're outdated, yet when maximum launch and straight line speed is concerned...you don't use anything else. makes you think...
the real advantage of the hemi was/is moving the exhaust valve to the outside. This freed up the intake valve and runner, and created a straight exhaust shot. It's all about the flow in and out of the cylinder the chamber shape has little to do with it. The more air you can get in and the quicker you can get it out the more power you will make, it's about building a better air pump.
Dodge Plymouth and Chrysler put the Hemi on the map,. An incredibly efficient motor at making horsepower back in the day The true hemi engines built by the DPC were hard to beat !!
+The real doktorbimmer I would never use the term "Famous" for something that MOST people never knew existed. It was only after Chrysler set many world records did the general public realize what a HEMI was. The fact is once it was made famous by Dodge Plymouth Chrysler, the others came forward waving their arms saying "we made one"
Jaguar won le mans a number of times with their XK motor in the 1950's. Hemi head, DOHC 6 cylinder. They didn't make the hemi famous only because they didn't name it HEMI.
Hemispherical cylinder heads have been used since at least 1901;[1] they were used by the Belgian car maker Pipe in 1905[2] and the 1907 Fiat 130 HP Grand Prix racer.[3] The Peugeot Grand Prix Car of 1912 and the Alfa Romeo Grand Prix car of 1914 both were four valve engines also, Daimler, and Riley were also using hemispherical combustion chambers. Stutz, beginning in 1912, used four-valve engines
@@tonym3675 They copied century old designs and someone elses v8 design . Chrysler just trademarked the name "Hemi" , not "Hemisherical" Still not bad from 2 guys from Ford who had a bicycle making company !
Hmm, I have a video on intake manifolds, that's really all that you'd need to know. They perhaps just created two so that each cylinder bank had it's own manifold, perhaps due to space, or some other concern.
All SRT8's now have a 6.4L or 392ci Hemi engine (challenger, charger Jeep grand Cherokee). but you are correct the 5.7 Hemi only comes in the lesser RT package NOT the SRT8 models.
Minor correction SRT does not use the 5.7 that would be an RT Daytona RT, or a base model with a v8, SRT used the 6.1 and now are currently using the 392 (6.4) in their SRT larger vehicle models
I like your videos man but disagree with the DOHC vs Push-rod view. Yes, a DOHC is more efficient due to its valve curtain size but they are also heavier, larger (top to bottom thereby affecting hood design) and far more complex engines that introduce more things that can go wrong.
DOHC 4v in a V-engine without VVt and VVL is actually simpler than pushrod design and has less moving parts. Judging by the engines available in Europe pushords don't seem to have any advantage in reliability over DOHC. And since DOHC is more efficient a smaller engine can be used for the same performance... with better economy. Important in a place where people do care about fuel costs.
It may have fewer moving parts... but only if you equate low stress low movement parts like pushrods and rocker arms to high stress high movement parts like timing belts and camshafts.
The ford CVH engine was also a hemi, but it had the valves at a compound angle to each other so it was also an overhead cam configuration with the hydraulic valve setup.
Hey, I want to expand my knowledge beyond learning from listening to someone. I'm more of a hands of guy, If I wanted to rebuild/fix an engine, which one would you suggest? I'm not loaded with money and would like to keep the price lower but I want to have an engine I can have pride in and maybe get a profit out of it. Thanks. I really enjoy your videos! Keep it up!
I only just now got around to watching this and there are just too many errors in this video, its more like what I would expect to see out of an outdated kid’s schoolbook. Many of the comments are off topic as well, so here is a summary of my opinion: -Overhead cams actually have been made to work on Hemi engines. In the US a Dual overhead cam 426 Hemi was actually produced and fitted into two Chrysler race cars in 1964 to counter Ford's Single Overhead Cam race engine. Ford was not allowed to use that engine so Chrysler never bothered to put it into production. -Hemi heads are superior to pent repp heads because they give a much better flame front in actual production engines. The drawings in the video illustrate schoolbook dogma on the subject. In the real world the piston dome is extremely tall in hemis which allows for one spark plug to give an ideal omnidirectional, shallow, flame front. -Pent roof are a low cost knock off of Hemi heads, they doesn't combust the mixture as well as hemi but are easier to manufacture ad assemble than a hemi. -Four valve per cylinder heads can flow more air than two valve per cylinder heads even though the valves are smaller die to "curtain area". The amount of air the valves can flow is the diameter times the lift. If you add up the curtain area on a 4 valve its significantly greater than on a 2 valve (on the same engine). A 4 value can open ad close its valves much quicker and with greater control because each (smaller) valve weighs a lot less and so can move faster. It also reduces the stress on the valve train because of the lighter weight (they can also rev higher without heavier valvesprings). -The cylinders in an engine may be perfectly round however the chambers in the head have a roof that od not round, its actually part round and part flat (hence its called pent roof and not round roof). -Racing engines do not explain why certain designs are used for street engines, each has difference requirements for their usage and race engines have some vert strict restrictions due to their own politics. Racing engines also have budgets higher than street engines, sometimes costing as much as an entire street car so these comparisons just are irrelevant and invalid. -As for those of you perplexed about heat loss and combustion chamber shape, keep in mind this video is incorrect, the drawings are incorrect and the explanation is correct only on the most basic level but its also incorrect because it is not illustrating what real world engines are like. Once you take into account that the advantage of the hemi is actually the ability to use hemi pistons then you’ll see that the surface area calculations in the discussion area are also incorrect. The hemi’s advantage is mostly in the uniform and somewhat omnidirectional flame front and its more complete evacuation of the exhaust gasses, the thermal efficiency is possibly a little better but its still relatively poor just like most other comparable street engines. -Hemi engines are still in production, most engines use pent roof because its performance has gotten a lot closer to hemi and its noticeably cheaper to manufacture. -Ralph Nader never married, never had a daughter so he did not attack the Corvair because of his child’s death. -Chrysler; Toyota (I had one), Peugeot, Jaguar, Lancia, Lotus (“Big Valve”), Mitsubishi, Ford (Aftermarket and racing), Porsche (911), Aston Martin and BMW have or had hemi head engines. Stuz had a 4 valve per cylinder hemi head engine back in the early 1900s, so its not impossible just costly to produce, verified by Aston Martin’s 4 valve hemi V8 with double overhead cams and Alfa-Romeo’s 24V hemi. -Cross-Flow is more likely than not to be simply a marketing term used to get the public to believe that hemi is inherently better that other designs. There is no way the “flow” actually matters because once the fuel air mix is combusted, the resulting gasses are all pushing outwards omnidirectional, the have no memory of which direction they are supposed to go nor do they have uniform inertia in one single direction (towards gas, they are simply pushed out mechanically by the piston. -Hemi combustion chambers are inherently more efficient so you can make more power or enjoy better fuel economy, depending on how you design it. There have been street engines designed for both those reasons (but not at the same time. -Hemi engines are not obsolete, they are still superior to pent roof designs, as usual the cheaper to produce pent roof (and wedge) design has been selected by manufacturers to save them a few bucks. Of course Chrysler is still producing Hemis in quantity, so intuit sense its also not obsolete. -Some but not all Hemis use two spark plugs. there are non-heme designs that use more than one spark plug per cylinder, there is no relationship between being a hemi and two plugs, its a design choice by the manufacturer. -Despite disadvantages in the past, semis have been made to work better over time, just as pent roof being improved over time. Since the two designs now are so similar to almost appear to be merged, their thermal efficiency and power output is now very close. -Calculated or theoretical comparisons are fun but do not affect us as consumers because can’t go to a car dealer and ask for a certain engine to be fitted with or without a hemi head. Calculations and theoretical differences don’t show up in the street today in any noticeable way because there are dozens if not hundreds of different factors that a manufacturer has to compromise on that any math that is discussed here is purely for entertainment purposes. -Most engines are not hemis simply because of cost. Its much more expensive to make a hemi than a wedge or a pent roof. All of these designs now have a squish area that helps get a good burn because all these designs have been improved since they were first invented. -Increasing the stroke of an engine does not increase compression ratio, it increases displacement -One poster stated that they purchased a SRT 392 Hemi because Toyota does not make a 485 HP engine, well in fact they do. Toyota’s high horsepower street car offering is known as the Lexus LF-A which features 552 HP. (Ouch!) -Rotary is no match for something like a Chrysler Hemi, it does not make as much power, wears out quickly (especially apex seals) and has poor emissions, all of which is why its already been put on the extinction list and why Mazda abandoned eh RX-8 a few years ago. -All else being equal a hemi will make more maximum horsepower, but when have we ever seen everything song equal? -Changing the shape of the piston does not alter h compression ration, all else being the same. To change the compression ratio you have to squeeze the mixture more or less either by using a position with a taller dome or a head with a smaller chamber (both of these increase the ratio, reverse the process if you need to decrease the ratio). -Subaru pent roof is not a hemi. The automotive industry makes a clear distinction that pent roof heads are not hemi heads. Although they look extremely similar today, there is a huge difference in manufacturing them and there is still a packaging and performance difference between them. -There are plenty of pent roof engines whose pistons look pretty much like a highly domed hemi piston. It works very well and is why I previously noted that hemp and pet roof designs are now very close to each other in physical aspects as well as performance.
Billy bob you are very knowledgeable with engines and disagree with the video. I’ve learned from the vid and from your novel of comments. Thanks a lot my good dude
That's actually a really good question. I noticed this when messing around on a couple beaters. When I asked my dad about it (he's been a mechanic for 40+ years), he suggested that the single valve could have a larger valve stem as opposed to the thinner 2 valves. Therefore, a thicker valve might mean more reliability at the higher RPM's of muscle cars. Could this be a possibility?
Yeah not a "true hemi" but as much of a hemi as a modern one. Hemispherical heads are great and that's why we don't use flat headed combustion Chambers. I'd say that honestly it was a great effort by Ford but they just didn't stack up. my only note is that this video kinda discredits the engine... It's what top fuel cars are running and making 10000-12000 hp with only 500 cubic inches. They arent practicle, but they also aren't bad.
George Withrow All racing is confined by rules. Regulations dictate specific engines, so that's what's used. Engineers do the best they can within the guidelines of the sport.
Top fuel is not using the vintage hemi design as is. The blocks, heads and valve springs are all technically state of the art. Saying it is backward is like saying the traverse leaf spring in modern corvettes is obsolete. Corvettes have been doing well in le mans. If you think a car needs irs, 4 valves and ohc to win races, you're probably european, or read road and track too much...lol
The real doktorbimmer my lawnmower would disagree with that last statement, hek y r we arguing over this outdated internal combustion rubbish, P85D anyone?
Having a push rod engine is not a bad thing or old tech. Most modern face cars use them because it provides a lot lower of a center of gravity then DOHC or SHOC two valves isnt a bad thing either you get a lot more low end torque with two valves and torque is way mor important then horsepower in cars or trucks so all arguments of pushrods and 2 valves being bad is invalid. and by the way hemis are made to make power high in the rpm band thats just how they were designed. the 2 spark plug thing is so that they burn all the fuel possible to make the most power not about emissions
It not outdated to me. It's typically greater displacement counter acts its less than ideal volumetric efficiency. Sure the Fords 5.0 liter coyote can make as much peak horsepower as GM's 6.2 LT engine but below peak it cant match the torque . Chevy has won le mans with a naturally aspirated 5.5 liter pushrod 8 times against turbo six and 8's cylinders so I beg to differ
I'm a mechanical engineer, just graduated. I'm currently working on a website (it's taking a long time) and I'm going to have a post on being an engineer vs technician/mechanic. It really boils down to do you want to get into design, or do you want to get your hands dirty, it's difficult to have both. That's why I made this channel, so I could learn a little more myself.
Hey there from the year 2019 dude and thank u for ur channel xD and hello from Russia
PS. God bless the Internet xD xD xD
I'm in school for industrial Manufacturing and controls, and work maintenance Technician at CocaCola, we have lathes, mills, tig, mig, stick, almost anything ever needed. I have a 3d printer and design my own parts or frames needed. I do enjoy my job it doesn't pay as good as I could possibly get but I design and maintain as needed and enjoy doing it!
@@bigpapa3708 I'm doing the same program..I love it..I think Manufacturing has alot of overlap with engineering..I seem to enjoy stuff like print reading more than I enjoy stuff like gcode.
Hey love your content. I'm in the navy considering trade schools or mech e in a few years when I get out. I would love some advice from you.
Why not go tell putin to stop killing innocent children civilians,and wildlife,I’ve never had a issue with Russian people on the whole, even if during the 1980’s in the military Russia was our main concern, I don’t get why your ppl don’t kick Putin out of power I don’t get how he claims to get 90% of the votes, ? it’s like Russia has blinders on its ppl or something, ? Had a Russia friend here till the war, and she said even her parents believed putins lies, even over their own daughter who showed them proof of his crimes..maybe it’s like the fools here in the USA who still support trump after his crimes ,lies and tax scams, god help us if he ever gets back in office again..take care, and let others know that 30k Russian troops have died already, sad maybe truth might help ya guys.. @@hepcat93
Hence they still slap "Hemi" tags on the side of Dodges without a true hemispherical head. It's simply a marketing term now.
What is the current design of the "hemi" head if not hemispiracle? Emissions, aside is the current "hemi" a better design than that of the 60's hemi head?
still hemis in 2021 lol
Why should they still use 2 spark plugs today?
All heads are hemispherical with dual spark plugs. Wdym. Not as pronounced as the original hemi. Trying not to drink all the fuel.
Thanks for watching. Basically a flat cylinder head has a lot of surface area but doesn't add any volume. A sphere is the best possible shape for maximizing the ratio of volume to surface area; ie it has a large volume and relatively low surface area. This means less heat lost. Also, it doesn't have corners like a flat head, which can create heat spots and unusual stresses.
You've come a long way in 8 years!
Ikr, I was like damn he came a long way
Yeah, came from looking 18 to 40
Oou7i9iio9jnto to
Trump took alot out of the more educated segment of our population. Ignorance is bliss, his sycophants never understood the danger. Part of the reason he openly loves the uneducated.
I know practically nothing about cars and looked this up to try to understand the hype about hemi engines. My husband went on a small rant about them but I didnt quite get what he was trying to express. This video is AMAZING, thank you for making this. If you aren't an instructor you should be. 🤯
I've driven several hemi's & always impressed by the power & understand the entire engine, currently saving up for a Challenger Hemi
You've come a long way my man! One of my favorite channels over the years. Glad you're helping us all get a little smarter everyday.
Awesome! I would head to my website (howdoesacarwork(dot)com) and go to Lesson 1. There I've organized my videos into a logical manner. Or simply go to my channel and start with the engines playlist. Let me know if you have any questions along the way!
I'd prefer to have the word "Hemi" on my hood than "Pentroof" lol
Thanks for watching. I've got a detailed answer to your question on my website FAQ (see link in the description). Though to be honest, most comes from the good ole' interwebs.
They're engine's on steroids. Some call them hemiroids.
No wait 🤔
Every dodge owner has left the chat
Lol...that's classic....
Hemiroids because they are a pain in the ass ;)
Literally XDDD
Helephants ;-)
I would still take a hemi any day..Those badges that say HEMI on the side of the Dodge Rams look cool and give the truck an extra 10bhp.
Rieksfier, no, what you really need is a big pair of truck nuts hanging from the back.
Proud to own a 2012 ram 2500 with a hemi, nothing comes close to it
@@JoseMartinez-jw2dy Hemi rams are great, I've owned 2 cummins powered rams in the past (still have one) but rented a hemi ram for a week and was amazed at how quiet & quick it was. But I still love my diesels. I think the only way I'd buy a hemi RAM is if I could do so while keeping the Cummins. The Hemi is truly great but so is that Cummins. And I love my Cummins. The Hummin' Cummins, 6 in a row make 'er go!
@@Soupy_loopy wth😆😆
Gay
Honda inline 4's are pretty straight forward and easy to work with. Plenty of space and intelligently laid out. But there are probably a good amount of simple engines to work with out there. Not really on newer cars though, electronics keep getting jammed in there!
Just getting started eh? Fantastic. Well the first ones I took were statics, dynamics, and solids. Statics one semester, dynamics and solids the next. The good thing about mechanical engineering is every semester you'll take a class that you'll swear is the most difficult you've ever taken. And it's true too!
Should be added that the Hemi (compared to the Wedge design) allowed for bigger valves as they are opposite of each other and not in line like the Wedge. Along with straighter and larger ports gave the HEMI a huge advantage in air flow. The Hemi really shines in high rpm operation or supercharged to move alot of air.
*"These disadvantages are exactly why the hemispherical design was displaced by the Wedge type"*
Was under the impression that wedge predominance was merely because it's so much easier to package a wedge-shaped combustion chamber, with parallel valves, in a pushrod engine. Generally OHC engines aren't constrained in that manner and thus generally don't use that combustion chamber geometry.
Also thought the high surface area/volume ratio and acute angle between piston and head led to excessive emissions.
Perfect explanation!
Incorrect, two slightly smaller valves are always more efficient in moving air than one bigger valve
punjabimunda5555 this. They also have less inertia each and thus will be less likely to float at a given rpm than one larger valve, even if you don't consider the rocker arms and pushrods
punjabimunda5555 only if its dohc if its pushrod bigger valves are better
Seeing this video in late 2019 is just great. Jason seems really young here lol. Comparing how much the show has improved since then, kudos!
I think the skyactiv engine is absolutely awesome. Efficient engine running on 87 octane? Pretty cool.
12 years late to your class but I am glad you are still preaching :D I'm not a car person, a motorbike guy in fact, but since an engine is an engine, I've been gaining a lot of insight from your videos, in other words, your passion.
loved the video, great job explaining. I appreciate Dodges efforts, look at the demon. That's my kind of car
Good question. It also alters the compression, I should have a video on it eventually actually, a few people have requested it.
It's funny how you have such a profetional thumbnail on such an old video. You really care about your old videos and update their thumbnails, witch is nice.
Just watched this in May 2023. This by far excedes the info to the lay person, what the "HEMI" is and and the old (flat) and new (pent). Learned a lot in just a few mins. Other clips don't show you the diff's and just show a pic of the head (w/no ref's to others).
Two sparkplugs per cylinder are used in basically every aviation piston engine.This is done primarily for redundancy, but increases power output, too. This also allows to check if the ignition system is working, if shutting off one set of sparkplugs reduces rpm (=> less power) slightly everything works fine. If nothing changes, the engine has been running on the other set only.
+The real doktorbimmer did you not watch the video? LOL
Higher compression ratios yield greater efficiencies. Of course, the law of diminishing returns is always in effect. Cost goes up, and does difficulty with using low octane fuels. Mazda currently holds the record (in my head) of highest CR on 87 octane gas, of 13:1. Very impressive.
At 3:35 you said that the srt8 have the 5.7 but think that you meant rt because the earlier ones had the 6.1
@PirateXzibit Yes. You'll always have at least two valves in four stroke engine. (The four strokes being intake, compression, power, and exhaust.) One valve lets the air come in the cylinder, the other valve allows the air to leave. Watch my video on gasoline vs. diesel, it will help a lot on understanding this. Also, most modern engine use four valves (two for intake, two for exhaust) as this allows for better airflow and higher efficiencies.
The idea with the pentroof is that only one spark plug is needed for complete combustion. If possible, it's better to just have one, so that's part of the goal of cylinder heads.
Like watching these originals from the early days. Gives good perspective of your journey.
Awesome video man. You taught me a lot, but the SRT was 6.1 until a few years ago, now they're 6.4. 5.7 is the RT model. Thanks man. Good video.
Ryan Foster ... 5.7 is actually badged HEMI
@@fernandomoreno4911 Yes, but it is not used in the SRT model. It is in the R/T :>
Cooler air is more dense so it allows for more fuel to be burned (more power). Heat is important for lubrication purposes - reducing friction and frictional losses, but there's plenty of wasted energy that the engine creates which can be used to keep it warm.
The by-product of a Hemi engine, is a lot of horsepower
Not really, the 5.7l Hemi makes 90hp less than the 5l v8 in a ford mustang.
Mostly lots of emissions.
As the valves are located perpendicular to the crank centerline, the Hemi simply gives a shorter, straighter shot at the valves. Thanks for your videos.
Wow, first time watching one of your older videos from about six years ago. Still very good IMO. In hindsight, showing the valves in the block for the flat head may have helped a bit with the overall explanation about the designs. And, you skipped the wedge head completely - the hemi was considered an improvement on that design if I remember correctly. This was the first time I noticed inaccurate terminology coming from you... you referenced the "weight" of the hemi's piston when you actually were referring to a property (inertia) of its "mass" when describing the work the crankshaft needed to do to move the piston. Regardless of my negative comments your white board and coloured markers have been of great value to a lot of people including me. I have frequently offered links to your videos when someone has asked "How does 'that' work?" Keep up the great work.
Holly crap. I couldn’t believe it was you 😂 you have come a long way
HEMI's of today aren't like they used to be, they're much closer to the pentroof design. That said, 2 valves per cylinder has faded out of most manufacturers, and likely remains simply because of cost, or perhaps they can effectively market it.
My understang the modern MopAR hemi has poly spherical shaped combustion camber similat to MOPAR V8s of the late 50, early '60s.
@EngineeringExplained
I used to think the same thing, having only had a quick intro to the different type of cylinder heads.
And as an aspiring engineer i am extremely excited to have stumbled upon your channel!
Thanks for the vids!
Well explained, I have a RAM 5.7 Hemi that I recently acquired.
Can you elaborate more on that claim? Thanks!!
There still hemis just semi hemis..closer to pentastar heads
Tony P HEMI does not mean the cylinder head is curved it means the piston head is curved
there always has to be a DICK in the world (Oh its not a claim, its a fact.) LMFAO
Paul Paulie
*They're
BMHNMH
Just plain wrong. Convex piston heads were just an addition to the original Hemi design, which in fact denotes hemispherical cylinder heads.
Vernard Pugh
There always has to be a DICKHEAD in the world who can't cope with facts and gets upvoted for behaving like a clown. "LMFAO".
Effective clearly explained, thank you I appreciate it. I am not a car person but as an educator I very much appreciate the time you took and the visuals that you used I know that this was over 13 years ago and that you might’ve moved on to greater things but I have to tell you you have a great beginning and I’m proud of that.
Americans grew up with these cars and trucks. It's a part of our history. Someone said it themselves,, nostalgia.. But at the end of the day, we are all driving Camerys to work lol
Kalyn Griffin I ride a motorcycle. But whatever I don't have another vehicle so rain or shine. It's 2 wheels
I'm not charger all the way
Nope. I drive a 16 392 hemi charger every day
Camry's are a Hemi type engine and my 1998 BMW is a Hemi type engine !
Agreed! As a Mopar fan boy who owns a Charger R/T, I was about to chime in and correct you! The R/T comes equipped with the 5.7 L. The early SRT8s came equipped with the 6.1L. The current SRT8s come with the 6.4 L, otherwise referred to as the "392" (392 cubic inches). Love your videos man. I'm an engineer and it's awesome to see a fellow engineer educating others who may not be engineers but are curious and eager learners! Keep it up my friend!
Your channel is chalk full of extremely factual information! Awesome work, and thanks!
Finally, I can sleep at night. (Or during the day, for you)
Thanks for sharing. A powerful truck isn't my style, but to each his own. I prefer the practicality and handling of a hatch, though there's plenty a truck can do that a hatch cannot. Your truck would disappear before I got to second gear, my poor little 1.8 liter.
There are two types of comments
1. How inefficient and outdated the Hemi is
2. How people own one because Murica
I have one because I don't have a choice
1. When did "[h]emi" become some sort of brand?
3. Why do you believe you "don't have a choice"?
Raging Bull
Robert Duncan
Maxx Fordham! What happened to 2?😂😭
I was matching my numbers to his, that which I had questions about. So I skipped *his* 2 because I didn't have a question about it.
I respect the amount of knowledge this person has on his videos about car engines. The down side is that his videos are a little boring so I never finish whatching them completely.
Here in Australia, we had slant-6 HEMI's in Chrysler Valiant Pacers and Chargers, in 245 and 265, and they were powerful enough to go toe-to-toe with the V8's (this was long before the days of turbo 6's). What is it about their design that allowed them to have the same output as the V8's, which were 351 Windsor/Cleveland, and 350 Chevy/308 Holden at that time frame?
Blake, maybe being an "Over square" engine may be the answer you're looking for. Also a big RT38 charger fan this way. A shame nobody thought about using a 4 speed box for Mt Panaroma.
The HEMI-6 was a wedge head... not a hemi.
Of course, now they have multi-spark ignition, delivering a barrage of smaller sparks for a longer period of time, allowing more power and better efficiency because more of the fuel is burned in the cylinder thingie. But, please correct me if I'm wrong.
I love your videos, and your dry-erase graphics. Nothing extra.
What I really like is that you expect the viewer to understand you and you don't dumb down or oversimplify or give weird analogies.
Engineers are like physicists that speak English. You are clearly a good engineer.
Thank you.
they put the valves in those positions to increase the airflow in and out of the combustion chamber
The problem with knocking is that the air/fuel mix is detonated at an inopportune time. 2 ignitions with planned timing, and equal timing, will work out just fine.
Good video.Also, about the Surface to Volume ratio (S/V ratio), the more surface you have the more carbon build up you are likely to have if you cant burn all your fuel.This encourages detonation/pre-ignition and bad for emission standards.Just my two cents.Again,Good video! Thanks for sharing.
Thank you very much!! you're such a good guy. You always take time to answer requests.Cool video as usual. And please don't reply every time cause you're such a busy guy.
Two spark plugs are a little bit unusual, but not unheard of. Mazda's rotary engine (i.e. wankel) used 2 per rotor, but that's a completely different animal. A more common engine was Ford's 2.3L 4 cylinder that had 2 spark plugs. Other manufacturers did it too. Pretty much same reason why Chrysler is doing it today. Emissions and Combustion.
The new Hemi's remind me sort of the early Hemi's The Chysler FirePower Hemi's. About 17 years ago, I worked a place in El Segundo, CA where we made plenty of Hemi pistons for for both the Gen 1 and Gen 2 Hemi's. The Gen 2's are massive!
The real doktorbimmer Yep, it's the flat top pistons of the new Hemi's that reminded me of the Fire Power Hemi's. That's putting combustion chamber aside. It's just the piston design that reminded me.
Speaking of the Fiat-Hemi's just being a brand name, have you seen the Australian "Hemi" 6's? That's pretty liberal use of the "Hemi" name for marketing purposes. I saw one of those in Vegas at Mopars at the Strip car show. I have to admit, that 6 did sound pretty mean though.
The Nash for several years had two plugs per cylinder. They called it Twin Ignition.
Cool username, I was actually just researching that engine yesterday. And yes, some had the chamber on the side to start ignition.
HEMISPHERICAL DOME DESIGN MEANS THE FASTER YOU GO THE FASTER IT WANTS TO GO,IN AND OUT IN THE CYLINDER,FIGHTER PLANE ENGINE FIRST
Yes, the Hemi's main advantage was its ability to really get going like a hound from hell in the upper revs with its insane head-flow. But, like you mention, under 4500 revs, a 440-6 was a serious force, and that sort of stump-pulling grunt has a very impressive feel to it during normal driving. It's what makes my 250hp Dakota feel much faster than a 250hp Camry. But, if you were serious about going to the strip and doing some racing, the Hemi was the best. And it STILL dominates top fuel!
Thank you ☺️ for this clip 👌🏻 quite informative
@JayBird90210 It would be a challenge, indeed, however there is a video that explains it very well. I couldn't offer the visualizations that are shown in this video: (/watch?v=6EfuRJrseD4). At about 45 seconds they go into how the advancing and retardation of the cams works. It's brilliant.
I guess I will be the oddball out here.... I have a 2008 Forenza, and I can tell you, OHV has one big advantage over OHC. My timing belt came off at 135k miles and ruined my valves. Had to get another Forenza, rip off the valve cover, and replace the whole unit (That was fun, BTW). OHV doesn't really have that problem, per se, although it theoretically could happen. I don't see why OHV is obsolete per se, everything that can reduce costs and make it simpler to manufacture, as the Russians say, "Quantity has a quality all its own".
"Quantity has a quality all its own" I agree with this wholeheartedly, I think most have forgotten this way of thinking.
You're right about the 440 RB having poor intake runners & is often times sophisticated by the carb. 350-600 cfm carb on an engine which the each intake runner will flow over 200 cfm (more than one piston end up short) usually still had 500 tq. Although the 383 RB with a 4 barrel was a good package. Smaller displacement meant it revved quicker because of the lighter internals and were more consistent because they came with hydrolic lifters instead of solid lifters like larger hi po engines.
I'll just stick with my elephant thanks.
_100th likee_
No need to ask for replies. Yes, heat is unwanted as it represents wasted energy, but the reaction of combusting gasoline and air results in a great temperature gain, increasing pressure as well. This pressure drives the piston down, rotating the crank.
The biggest benefit of the HEMI that's not mentioned here is that it *BREATHES BETER* on both the intake and exhaust
A modern hemi engine does not breath better then a 4 valve design, in fact the greatest weakness of the 5.7 (which is not in a srt as stated) is its lack of airflow through the valve.
Your explaining of this topic was good , even that srt-8 is the same design w/ 16 plugs total , it is a 6.1 or 6.4 (newer) (392) , the r/t is the 5.7
could you please explain Lee Harvey Oswald's Carcano bolt action rifle- and how the single shooter of theory is impossible
My 2014 jeep Cherokee has a 5.7 liter hemi. Runs great and i love the way it sounds with the dual exhaust. Growls...
Hmm, tough to tell sarcasm on UA-cam. I'll just continue: Yeah how did Google know my videos were car related?
I have a Alfa Romeo. It has a hemispheric chamber with a two camshafts in overhead. It's very efficient. I already see the Lancia Delta integrale engine with 4 valves in overhead and Hemi chamber.
So not having and OHC design and not having 2 valves per cylinder are disadvantages? Tell that to the Demon
Ok? Yes they are disadvantages. The same supercharger would make more power on a stock 2018 Mustang engine that it does on a Demon.
That engine is 307 ci
Can you explain the surface area thing.... Got a hard time figuring this... The surface area of a dome would be greater than a flat disk of the same diameter.... Not quite a car guy but it's been 2 evenings in a row watching your videos... Seriously awesome stuff man
Awesome video , next.time explain the 2jz supra engine for me pls
It's an engine. Inline 6, DOHC with 4 valves per cylinder. It is built to be durable. Done.
The 5.7 was only ever an R/T engine. The Srt8 was the 6.1 hemi, aka the early hellcat🔥🔥👍
Thanks for the explanation though I've always wondered what part of the engine is actually hemispherical and you explained it extremely well! Again, thanks man!
5.7L Hemi engines are the best
Hey that’s what I have
Yep, it's been pointed out a few times below. There is also a 5.7L hemi.
all of these comments saying they're outdated, yet when maximum launch and straight line speed is concerned...you don't use anything else. makes you think...
Yeah... because of draconian rules which force you to use a 500 cid hemi engine.
Just think of how much faster theyd be with a modern design?
the real advantage of the hemi was/is moving the exhaust valve to the outside. This freed up the intake valve and runner, and created a straight exhaust shot. It's all about the flow in and out of the cylinder the chamber shape has little to do with it. The more air you can get in and the quicker you can get it out the more power you will make, it's about building a better air pump.
I probably missed something but, does two spark plugs per cylinder mean there is 16 spark plugs in some hemis?
Yes
Speaking of money pits...
Yes 16 spark plugs. Comes out to $90
@@juanrios3182 where did you find them for 90
This was such a good explanation! Thanks for making such a great video.
Dodge Plymouth and Chrysler put the Hemi on the map,. An incredibly efficient motor at making horsepower back in the day
The true hemi engines built by the DPC were hard to beat !!
+The real doktorbimmer I would never use the term "Famous" for something that MOST people never knew existed. It was only after Chrysler set many world records did the general public realize what a HEMI was. The fact is once it was made famous by Dodge Plymouth Chrysler, the others came forward waving their arms saying "we made one"
Jaguar won le mans a number of times with their XK motor in the 1950's. Hemi head, DOHC 6 cylinder. They didn't make the hemi famous only because they didn't name it HEMI.
And the hemis of today are still hard to beat. It's seen day in and day out.
Hemispherical cylinder heads have been used since at least 1901;[1] they were used by the Belgian car maker Pipe in 1905[2] and the 1907 Fiat 130 HP Grand Prix racer.[3] The Peugeot Grand Prix Car of 1912 and the Alfa Romeo Grand Prix car of 1914 both were four valve engines also, Daimler, and Riley were also using hemispherical combustion chambers. Stutz, beginning in 1912, used four-valve engines
@@tonym3675 They copied century old designs and someone elses v8 design .
Chrysler just trademarked the name "Hemi" , not "Hemisherical"
Still not bad from 2 guys from Ford who had a bicycle making company !
Hmm, I have a video on intake manifolds, that's really all that you'd need to know. They perhaps just created two so that each cylinder bank had it's own manifold, perhaps due to space, or some other concern.
Srt8's have 6.1, 6.2 supercharged, or 6.4
Dan G srt8’s have never had 6.2 supercharged
@@joshuaherring7246 they do, but they're called Hellcats.
All SRT8's now have a 6.4L or 392ci Hemi engine (challenger, charger Jeep grand Cherokee). but you are correct the 5.7 Hemi only comes in the lesser RT package NOT the SRT8 models.
Dear Sir, could You please talk
some on the Wankel engine design.
Thank You, Sincerely, Me.
.
+Kathleen Adkins About how shit they are?
Minor correction SRT does not use the 5.7 that would be an RT Daytona RT, or a base model with a v8, SRT used the 6.1 and now are currently using the 392 (6.4) in their SRT larger vehicle models
I like your videos man but disagree with the DOHC vs Push-rod view. Yes, a DOHC is more efficient due to its valve curtain size but they are also heavier, larger (top to bottom thereby affecting hood design) and far more complex engines that introduce more things that can go wrong.
DOHC 4v in a V-engine without VVt and VVL is actually simpler than pushrod design and has less moving parts. Judging by the engines available in Europe pushords don't seem to have any advantage in reliability over DOHC. And since DOHC is more efficient a smaller engine can be used for the same performance... with better economy. Important in a place where people do care about fuel costs.
It may have fewer moving parts... but only if you equate low stress low movement parts like pushrods and rocker arms to high stress high movement parts like timing belts and camshafts.
The ford CVH engine was also a hemi, but it had the valves at a compound angle to each other so it was also an overhead cam configuration with the hydraulic valve setup.
07 srt8 have a 6.1L and 2012 srt8 have 6.4L
Hey, I want to expand my knowledge beyond learning from listening to someone. I'm more of a hands of guy, If I wanted to rebuild/fix an engine, which one would you suggest? I'm not loaded with money and would like to keep the price lower but I want to have an engine I can have pride in and maybe get a profit out of it. Thanks. I really enjoy your videos! Keep it up!
I only just now got around to watching this and there are just too many errors in this video, its more like what I would expect to see out of an outdated kid’s schoolbook. Many of the comments are off topic as well, so here is a summary of my opinion:
-Overhead cams actually have been made to work on Hemi engines. In the US a Dual overhead cam 426 Hemi was actually produced and fitted into two Chrysler race cars in 1964 to counter Ford's Single Overhead Cam race engine. Ford was not allowed to use that engine so Chrysler never bothered to put it into production.
-Hemi heads are superior to pent repp heads because they give a much better flame front in actual production engines. The drawings in the video illustrate schoolbook dogma on the subject. In the real world the piston dome is extremely tall in hemis which allows for one spark plug to give an ideal omnidirectional, shallow, flame front.
-Pent roof are a low cost knock off of Hemi heads, they doesn't combust the mixture as well as hemi but are easier to manufacture ad assemble than a hemi.
-Four valve per cylinder heads can flow more air than two valve per cylinder heads even though the valves are smaller die to "curtain area". The amount of air the valves can flow is the diameter times the lift. If you add up the curtain area on a 4 valve its significantly greater than on a 2 valve (on the same engine). A 4 value can open ad close its valves much quicker and with greater control because each (smaller) valve weighs a lot less and so can move faster. It also reduces the stress on the valve train because of the lighter weight (they can also rev higher without heavier valvesprings).
-The cylinders in an engine may be perfectly round however the chambers in the head have a roof that od not round, its actually part round and part flat (hence its called pent roof and not round roof).
-Racing engines do not explain why certain designs are used for street engines, each has difference requirements for their usage and race engines have some vert strict restrictions due to their own politics. Racing engines also have budgets higher than street engines, sometimes costing as much as an entire street car so these comparisons just are irrelevant and invalid.
-As for those of you perplexed about heat loss and combustion chamber shape, keep in mind this video is incorrect, the drawings are incorrect and the explanation is correct only on the most basic level but its also incorrect because it is not illustrating what real world engines are like. Once you take into account that the advantage of the hemi is actually the ability to use hemi pistons then you’ll see that the surface area calculations in the discussion area are also incorrect. The hemi’s advantage is mostly in the uniform and somewhat omnidirectional flame front and its more complete evacuation of the exhaust gasses, the thermal efficiency is possibly a little better but its still relatively poor just like most other comparable street engines.
-Hemi engines are still in production, most engines use pent roof because its performance has gotten a lot closer to hemi and its noticeably cheaper to manufacture.
-Ralph Nader never married, never had a daughter so he did not attack the Corvair because of his child’s death.
-Chrysler; Toyota (I had one), Peugeot, Jaguar, Lancia, Lotus (“Big Valve”), Mitsubishi, Ford (Aftermarket and racing), Porsche (911), Aston Martin and BMW have or had hemi head engines. Stuz had a 4 valve per cylinder hemi head engine back in the early 1900s, so its not impossible just costly to produce, verified by Aston Martin’s 4 valve hemi V8 with double overhead cams and Alfa-Romeo’s 24V hemi.
-Cross-Flow is more likely than not to be simply a marketing term used to get the public to believe that hemi is inherently better that other designs. There is no way the “flow” actually matters because once the fuel air mix is combusted, the resulting gasses are all pushing outwards omnidirectional, the have no memory of which direction they are supposed to go nor do they have uniform inertia in one single direction (towards gas, they are simply pushed out mechanically by the piston.
-Hemi combustion chambers are inherently more efficient so you can make more power or enjoy better fuel economy, depending on how you design it. There have been street engines designed for both those reasons (but not at the same time.
-Hemi engines are not obsolete, they are still superior to pent roof designs, as usual the cheaper to produce pent roof (and wedge) design has been selected by manufacturers to save them a few bucks. Of course Chrysler is still producing Hemis in quantity, so intuit sense its also not obsolete.
-Some but not all Hemis use two spark plugs. there are non-heme designs that use more than one spark plug per cylinder, there is no relationship between being a hemi and two plugs, its a design choice by the manufacturer.
-Despite disadvantages in the past, semis have been made to work better over time, just as pent roof being improved over time. Since the two designs now are so similar to almost appear to be merged, their thermal efficiency and power output is now very close.
-Calculated or theoretical comparisons are fun but do not affect us as consumers because can’t go to a car dealer and ask for a certain engine to be fitted with or without a hemi head. Calculations and theoretical differences don’t show up in the street today in any noticeable way because there are dozens if not hundreds of different factors that a manufacturer has to compromise on that any math that is discussed here is purely for entertainment purposes.
-Most engines are not hemis simply because of cost. Its much more expensive to make a hemi than a wedge or a pent roof. All of these designs now have a squish area that helps get a good burn because all these designs have been improved since they were first invented.
-Increasing the stroke of an engine does not increase compression ratio, it increases displacement
-One poster stated that they purchased a SRT 392 Hemi because Toyota does not make a 485 HP engine, well in fact they do. Toyota’s high horsepower street car offering is known as the Lexus LF-A which features 552 HP. (Ouch!)
-Rotary is no match for something like a Chrysler Hemi, it does not make as much power, wears out quickly (especially apex seals) and has poor emissions, all of which is why its already been put on the extinction list and why Mazda abandoned eh RX-8 a few years ago.
-All else being equal a hemi will make more maximum horsepower, but when have we ever seen everything song equal?
-Changing the shape of the piston does not alter h compression ration, all else being the same. To change the compression ratio you have to squeeze the mixture more or less either by using a position with a taller dome or a head with a smaller chamber (both of these increase the ratio, reverse the process if you need to decrease the ratio).
-Subaru pent roof is not a hemi. The automotive industry makes a clear distinction that pent roof heads are not hemi heads. Although they look extremely similar today, there is a huge difference in manufacturing them and there is still a packaging and performance difference between them.
-There are plenty of pent roof engines whose pistons look pretty much like a highly domed hemi piston. It works very well and is why I previously noted that hemp and pet roof designs are now very close to each other in physical aspects as well as performance.
Very well explained!!!!
Billy bob you are very knowledgeable with engines and disagree with the video. I’ve learned from the vid and from your novel of comments. Thanks a lot my good dude
That's actually a really good question. I noticed this when messing around on a couple beaters. When I asked my dad about it (he's been a mechanic for 40+ years), he suggested that the single valve could have a larger valve stem as opposed to the thinner 2 valves. Therefore, a thicker valve might mean more reliability at the higher RPM's of muscle cars. Could this be a possibility?
Looks like you are missing a shaft in your Pentroof figure. Sorry, I am OCD.
my 2 cents is that a true hemi design will outpower other designs however at the cost of fuel economy and tricky packaging
Where does Ford's Boss 429 semi-hemi(crescent head) fall into this?
Yeah not a "true hemi" but as much of a hemi as a modern one. Hemispherical heads are great and that's why we don't use flat headed combustion Chambers. I'd say that honestly it was a great effort by Ford but they just didn't stack up. my only note is that this video kinda discredits the engine... It's what top fuel cars are running and making 10000-12000 hp with only 500 cubic inches. They arent practicle, but they also aren't bad.
@EngineeringExplained Thank you very much! I think engineering is what I am looking for.
Yeah...but saying "that thing got a pentroof?" Doesn't sound nearly as cool
you got a pentroot in there?
Right, and that energy takes the form of heat. Heat accelerates the particles in the air, increasing the pressure, driving the piston down.
What is a hemi?……. It’s a engine that chews up rocker arms & camshafts, and spits out manifold bolts! Oh yeah, and has a worthless warranty
😂😂😂😂
As someone whose dad had a 3/4 ton ram with the 5.7, I can assure this is 110% correct 😂
Great videos. Where do you aquire this wide range of knowledge? Keep it up
And by the way if hemi is such a bad way to build a motor why do most dragsters run only hemi motors ?
George Withrow All racing is confined by rules. Regulations dictate specific engines, so that's what's used. Engineers do the best they can within the guidelines of the sport.
Top fuel is not using the vintage hemi design as is. The blocks, heads and valve springs are all technically state of the art. Saying it is backward is like saying the traverse leaf spring in modern corvettes is obsolete. Corvettes have been doing well in le mans. If you think a car needs irs, 4 valves and ohc to win races, you're probably european, or read road and track too much...lol
The real doktorbimmer 9th century Chinese skyrockets and the saturn V from NASA are basically the same ,both are rockets
The real doktorbimmer my lawnmower would disagree with that last statement, hek y r we arguing over this outdated internal combustion rubbish, P85D anyone?
W
hat the hell does china or NASA have to do with hemi head engines
I am from Germany - the heavenly place where engineering is a philosophic good - and i officially aprove your channel, sir !
Having a push rod engine is not a bad thing or old tech. Most modern face cars use them because it provides a lot lower of a center of gravity then DOHC or SHOC two valves isnt a bad thing either you get a lot more low end torque with two valves and torque is way mor important then horsepower in cars or trucks so all arguments of pushrods and 2 valves being bad is invalid. and by the way hemis are made to make power high in the rpm band thats just how they were designed. the 2 spark plug thing is so that they burn all the fuel possible to make the most power not about emissions
+The real doktorbimmer I've heard that as well, the HEMI® engine of today is apparently much closer to a polyspherical design a la the '57-66 318s.
+The real doktorbimmer Interesting.
It not outdated to me. It's typically greater displacement counter acts its less than ideal volumetric efficiency. Sure the Fords 5.0 liter coyote can make as much peak horsepower as GM's 6.2 LT engine but below peak it cant match the torque . Chevy has won le mans with a naturally aspirated 5.5 liter pushrod 8 times against turbo six and 8's cylinders so I beg to differ