5 is better but only .5% better but that extra valve costs almost 20% more. For a cylindrical bore and equal-area sized valves, increasing the number of valves beyond five decreases the total valve area. The following table shows the effective areas of differing valve quantities as proportion of cylinder bore. These percentages are based on simple geometry and do not take into account orifices for spark plugs or injectors, but these voids will usually be sited in the "dead space" unavailable for valves. Also, in practice, intake valves are often larger than exhaust valves in heads with an even number of valves-per-cylinder. 2 = 50% 3 = 64% 4 = 68% 5 = 68% 6 = 66% 7 = 64% 8 = 61%
Great explanation! Found your channel from youtube's "recommended" section and I've been binge watching your videos while I do a full top to bottom rebuild on a 200 exc 2 stroke engine in my closet (I have a workshop set up in there, lol). If you've already done this forgive me but what about a video about desmo valves? I still don't quite understand it even after looking at pictures, it seems to be something all the ducati guys ramble on about but I want to know if there's actually any tangible benefit. Thanks Matt! Keep bringing on the videos.
Why are there no valves that take up more surface area? Like a 3 post with a valve bridge that is shaped like a half moon, or maybe a 2 post with a valve bridge rectangular shape. I understand possible strength issues, but with materials being the way they are today they should be able to overcome that.
for ages round valves and round seats were a thing that could be made with machine tools available. we could do other shapes now but there are a few constraints on that. sharp corners are hot spots and fatigue points. round valves rotate in use which keeps them wearing evening / not wearing.
I assume both cylinders are the same size . in the two valve example the cylinder looks smaller. Two circles will always give you more area than one big one ?
The Yamaha thought they were slick with the 660 engine by putting 5 valves on a SOHC. Then switched back to the classic 4 valve SOHC and haven't changed since. Am I right to assume that the change was a reliability issue with the extra valve not inline with its other intake valves or do you think it was just a decision based on production cost? I just found it kinda weird that they were relying on one cam shaft to work efficiently with rocker arms at three different linear points
Great comment - I don't have all the answers, but I would guess that it was a cost decision. All the prototypes would have ekked out any masvie production failures. They're pretty tight with their money these days - matt
F1 for example ditched 5 valve after they switched to pneumatic valve springs. Only reason they used 5 valves was due to valve float at 14-15k rpms and when pneumatic springs came that issue was gone they just ditched it. It was extremely hard to control the flow etc of 5v so they couldnt extract anything out of 5v so they just ditched
The day that Camless engines become common I can easily imagine 6 valve or 5 valve per cylinder engines becoming more common because they are actuated by air or fluid pressure instead of a cam.
Probably 5, being that you can use the same size for intake and exhaust (wich gives you the maximum usable area on the head) and still have the higher % of intake needed, you could even use only one of the intake valves at low speed and have better performance.
This probably will not work but I thought of inlet and exhaust being a half circle that way you can have just one big valve for inlet. Maybe it would be weak and a poor seal just a thought. Great videos Iam addicted lol. I have learnt alot to. Iam a landscape gardener use alot of machines. I used to think two strokes was the best due to weight, power and simplicity. However i have a 4 stroke Honda GX 25 strimmer yes its heavier but engine life lasts longer more low down torque powerful too..
I'm not sure if it's ever been tried since I don't know what to call it, but what about a single big valve that was half of the combustion chamber in the shape of the chamber? Two stems to keep it straight and such. I figure you can get into flow, stress, and manufacturing issues with that design but I was always curious.
Hi sir, greetings from Brazil, I want to you if valves of same types, inlet out Exaust, have delay from opening of close from each other or they open the same time.
Excuse me, the keyboard from my phone, again. I want to know if an engine have 2 valves for intake or exaust, these 2 intake valves open in same time? Or they have a delay?
My GW250 has 2 valves per cylinder, very oldish design it seems but it is a budget commuter. I was kinda surprised when I found out my 2010 FZ1 has 5 per cylinder
Yeah the Fazers always have 'detuned' YZF engines. The fazer 600 has the old R6 engine. The R1 engine I was talking about is in the FZ1. It was from 1998 to 2006 they ran with 20 valves instead of the usual 16. The performance benefits weren't what they hoped The competition was still running 16 valves so they scrapped the idea. Valve numbers is obviously based on cost as well, so for cheap commuters it makes sense. 2 valves, 4 springs, job done.
Yamaha is done with 5 valve its all 4 valve now... and four valve is great for most normally aspirated engines but once you start adding pressure you are generally better off with two valves for durability
yamaha should know, they started it. Genesis. one of the few times bikes lead the way for f1 and one of MANY times yamaha pushed some wild innovation out into the consumer market.
The old engines were the 1st big fours (superbike) needed to compeat with the British bikes. They still drag race em today with massive piston blocks. The newer engines didn't have any competition so not as well built. I love big and old well built.
My old CB250 had 4 valves per head. Most motorbikes and cars are at least 8 valves per head now. 16 per head isn't unusual. When you say valves per head when you mean valves per cylinder there's a big difference :D
could you name a few f these engines with valves in the cylinder, just so i can start doing some research, i mean right now i'm picturing poppet valves with angles in the end and a square shaft or something to keep it from rotating and not seating, also you look like 25 or something, less than 30
4+ valves per head is only good for race-cars and motorcycles. 2 valves is much better for a normal family car because of lover fuel consumption since you never rev it high enough to get any benefit of the extra valves... Only reason 4 valves is so popular on regular cars is fashion....
Top vids man. These along with the Haynes motorcycle manual are quickly getting me up to speed! Cheers
5 is better but only .5% better but that extra valve costs almost 20% more. For a cylindrical bore and equal-area sized valves, increasing the number of valves beyond five decreases the total valve area. The following table shows the effective areas of differing valve quantities as proportion of cylinder bore. These percentages are based on simple geometry and do not take into account orifices for spark plugs or injectors, but these voids will usually be sited in the "dead space" unavailable for valves. Also, in practice, intake valves are often larger than exhaust valves in heads with an even number of valves-per-cylinder.
2 = 50%
3 = 64%
4 = 68%
5 = 68%
6 = 66%
7 = 64%
8 = 61%
Great explanation! Found your channel from youtube's "recommended" section and I've been binge watching your videos while I do a full top to bottom rebuild on a 200 exc 2 stroke engine in my closet (I have a workshop set up in there, lol). If you've already done this forgive me but what about a video about desmo valves? I still don't quite understand it even after looking at pictures, it seems to be something all the ducati guys ramble on about but I want to know if there's actually any tangible benefit. Thanks Matt! Keep bringing on the videos.
Yes the desmo video is coming this weekend
Why are there no valves that take up more surface area? Like a 3 post with a valve bridge that is shaped like a half moon, or maybe a 2 post with a valve bridge rectangular shape. I understand possible strength issues, but with materials being the way they are today they should be able to overcome that.
Good question - ATTL
for ages round valves and round seats were a thing that could be made with machine tools available. we could do other shapes now but there are a few constraints on that. sharp corners are hot spots and fatigue points. round valves rotate in use which keeps them wearing evening / not wearing.
5 is best, 4 is almost the same, and more than 5 is worse, and less than 4 is worse. 4 is cheaper than 5, so that's what it is now
SOHC 2 valve is life.
I assume both cylinders are the same size . in the two valve example the cylinder looks smaller.
Two circles will always give you more area than one big one ?
please explain for your viewers who do not know why four vavles are superior to two valve at partial lift. which is extremely important.
The Yamaha thought they were slick with the 660 engine by putting 5 valves on a SOHC. Then switched back to the classic 4 valve SOHC and haven't changed since. Am I right to assume that the change was a reliability issue with the extra valve not inline with its other intake valves or do you think it was just a decision based on production cost?
I just found it kinda weird that they were relying on one cam shaft to work efficiently with rocker arms at three different linear points
Great comment - I don't have all the answers, but I would guess that it was a cost decision. All the prototypes would have ekked out any masvie production failures. They're pretty tight with their money these days - matt
Can you do a video on valve maintenance on a Honda NR 750 ?,... I'll set aside a free week for the video ..thnx !!!!!
Yeah I'll jump right to it lol
Audi and Ferrari also had 5 valves engines
But its not worth it
It depends what you mean by not worth it
F1 for example ditched 5 valve after they switched to pneumatic valve springs. Only reason they used 5 valves was due to valve float at 14-15k rpms and when pneumatic springs came that issue was gone they just ditched it. It was extremely hard to control the flow etc of 5v so they couldnt extract anything out of 5v so they just ditched
5 valves don't float anymore than 4 would. The difference is valve mass.
4 valve with variable valve lift and variable valve timing is better than 5 valves i think
I prefer 2v per head. Produces more usable torque, at a more usable RPM.
I always heard 2v allows more low down torque than 4v but never seen any source. Do you have any source to back up this claim?
The day that Camless engines become common I can easily imagine 6 valve or 5 valve per cylinder engines becoming more common because they are actuated by air or fluid pressure instead of a cam.
Probably 5, being that you can use the same size for intake and exhaust (wich gives you the maximum usable area on the head) and still have the higher % of intake needed, you could even use only one of the intake valves at low speed and have better performance.
This probably will not work but I thought of inlet and exhaust being a half circle that way you can have just one big valve for inlet. Maybe it would be weak and a poor seal just a thought. Great videos Iam addicted lol. I have learnt alot to. Iam a landscape gardener use alot of machines. I used to think two strokes was the best due to weight, power and simplicity. However i have a 4 stroke Honda GX 25 strimmer yes its heavier but engine life lasts longer more low down torque powerful too..
watch this - ua-cam.com/video/FmPRkXzPcaw/v-deo.html
I'm not sure if it's ever been tried since I don't know what to call it, but what about a single big valve that was half of the combustion chamber in the shape of the chamber? Two stems to keep it straight and such. I figure you can get into flow, stress, and manufacturing issues with that design but I was always curious.
Great question, will do a video on it - matt
Hi sir, greetings from Brazil, I want to you if valves of same types, inlet out Exaust, have delay from opening of close from each other or they open the same time.
Sorry mate - I don't understand what you mean - try typing it into google translate
Excuse me, the keyboard from my phone, again. I want to know if an engine have 2 valves for intake or exaust, these 2 intake valves open in same time? Or they have a delay?
Same time dude - generally. Very few engines have had valves of the same cylinder that open at different times.
The Workshop thanks
My GW250 has 2 valves per cylinder, very oldish design it seems but it is a budget commuter. I was kinda surprised when I found out my 2010 FZ1 has 5 per cylinder
Yeah the Fazers always have 'detuned' YZF engines. The fazer 600 has the old R6 engine. The R1 engine I was talking about is in the FZ1. It was from 1998 to 2006 they ran with 20 valves instead of the usual 16. The performance benefits weren't what they hoped The competition was still running 16 valves so they scrapped the idea.
Valve numbers is obviously based on cost as well, so for cheap commuters it makes sense. 2 valves, 4 springs, job done.
Why are valves all circular ? Surely it would make more sense to have two valves both being semicircular in shape ? That would use the maximum area ?
JAMP0T1 hes actually done a video about it check it out
Communist Hippie yeah nah he did the video since and it makes sense tbh
Yamaha is done with 5 valve its all 4 valve now... and four valve is great for most normally aspirated engines but once you start adding pressure you are generally better off with two valves for durability
yamaha should know, they started it. Genesis.
one of the few times bikes lead the way for f1 and one of MANY times yamaha pushed some wild innovation out into the consumer market.
1970's Honda 750/4 sohc 8 valves with rockers top speed = 123mph
1980's Honda 750/4 dohc 16 valves with shims top speed = 125mph
wow fucking wow lol
Yeah but does the engines acceleration change, its not all about top speed!
The old engines were the 1st big fours (superbike) needed to compeat with the British bikes. They still drag race em today with massive piston blocks. The newer engines didn't have any competition so not as well built. I love big and old well built.
4 are the way..Still i see the 3 is efficent too
"imaginary invisible line"
damm...
7:42 valve went from VALVE to *VALVE*
Wr 450 has 5 valves too
Yes - I have a video.....
ua-cam.com/video/eEZOXSeaM0I/v-deo.html
same for the SZR 660 with one cylinder
Sounds commonsense to me !
My old CB250 had 4 valves per head. Most motorbikes and cars are at least 8 valves per head now. 16 per head isn't unusual. When you say valves per head when you mean valves per cylinder there's a big difference :D
the ferrari 360 has a 5 valve head
so did the Yamaha R1 for a while and other bikes and cars have.
ok got u ko
could you name a few f these engines with valves in the cylinder, just so i can start doing some research, i mean right now i'm picturing poppet valves with angles in the end and a square shaft or something to keep it from rotating and not seating, also you look like 25 or something, less than 30
my wr250f has 5 valves
didn't I say everything I s fuxked cause problems are -
4+ valves per head is only good for race-cars and motorcycles. 2 valves is much better for a normal family car because of lover fuel consumption since you never rev it high enough to get any benefit of the extra valves... Only reason 4 valves is so popular on regular cars is fashion....
no its not, it all about volumetric efficiency
all is not right