Valve Float! What Is It, And How To Avoid It | Engine Masters | MotorTrend
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- Опубліковано 24 лип 2022
- We all know valve float as the evil that lurks beyond the redline, the dreaded robber of horsepower and destroyer of valves. But what is it really? What does it look like when it happens? And how can you put it as high in the RPM band as possible?
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Valve float, valve bounce or valve lofting are all different things and can have different causes, including spring pressure, harmonics and cam lobe design. There is a great video on youtube taken with a high speed camera under the rocker cover and shows valve bounce which is what I believe we are talking about in this video.
that vid you are talking about is one of the coolest vids on you tube for engineers.
Post a link to that video I'm sure I'm not the only one who wants to see it
Downshifting to 1st at 100mph might cause some float.. among other things.
Or missing a shift
2nd or 3rd at 100 would destroy everything
Money shift
More rpm more hp
Otherwise known as money shifting as stated already
The person i bought my 67 el camino from had a auto shut off on the ZL1 engine. It had trick heads, had roller rocker arms, triple valve springs and steel retainers. Victor jr manifold, 750 holley carb. Solid lifter cam 500" lift + 260° duration. 4.56 posi rar 1 ton axles and 4 speed. Lots of fun.
No titanium valve? I guess I missed the valve choice discussion. Mushrooming stems or what?
Think i missed something as well
rapid wear constant adjustment. no good for a street engine.
And 100 bucks a valve vs 12
Bronze valve guides, dlc or nitride coated stems to not gall, and sometimes special lash caps to keep the roller from eating the top if the stem. And price… Always the price.
quite some years ago i had an Alfasud which has a flat 4 overhead cam per bank motor boxer motor just like a Subaru, it could rev to well over 8,000 rpm as it only had a 54mm stroke , one day i experienced valve float at around 6150rpm no misfiring just a strange sensation while reving , i didn't know it was valve float at the time , a friend of mine who worked at an Alfa dealer told me what the problem was he said that probably some retainers had split causing a loss of spring tension on the valves he said because of the flat 4 design the pistons were closing the valves affected ! , luckily there was no damage to the pistons or valves i could see once i had the heads removed Phew close call , he overhauled the heads and found that 2 valve retainers had cracked/split in the cone part of the retainer where the valve stem collets are seated causing a loss of valve spring tension , i fully understand why spring tension on a Valve is important as your video has pointed out cheers
Engine Masters PRO Sessions 🙂thanks Guys!!
Ahh, valve float. One of my favorite things about 2-strokes and rotaries is the sheer "who cares" factor with rpm. It's a neat experience to feel the power nose over, and then hold it wide open for two minutes, knowing that it's just resonance timing and the engine has 4,000 more rpm of mechanical overhead. Just... make sure you have good premix that day, lol.
My dad had an 83’ CJ7 with the inline 6 and it used to float the valves going up hills, had over 300k miles on it too
What a remarkable clip. Thanks for explaining this issue great!
Such a great basic video thank you for this 🙏🏻
So informative. Thank you.
Very informative!
I have a panhead harley that I've owned for over 40 years, am running a ridiculous big cam, and use the stock FL valve springs (way to light seat pressure for the cam) and I rely on the valves floating as a rev limiter, but having it for as long as I have, I don't abuse it, also the light pressure on the valve train has the benefit of not wearing stuff out fast, I do weird things with my vehicles but would never do on a customer's bike, car whatever, but for myself I go way out in left field, and it works for me
I respect that. Cheers
Great show. Thanks
Nice, thanks for sharing!
Thank you for all of your knowledge
Eng Masters is the best car show , Tell use about the intakes on the shelves behind you. Thanks
Thank you techno hippies I learned a lot
Preventing valve float is also why Ducati motorcycle engines sound like, as one person put it, "a Cuisinart full of clarinets" -- actually looking at the system as implemented breaks my brain with the linkages involved, but short version, the top end works kinda like the bottom-end rotating mass -- the valve stems are pushed /and/ pulled by the cam, no springs, so no float, but it's very noisy and probably a bit harsh on parts without the tolerance buffer that a spring provides. But when you need a twin to make twice the revs of the tested V8, and thus fire each cylinder ... not gonna lie, but I must've slept through the session of physics class covering the square-cube law. A 1.3L twin is working a lot harder per cylinder to bet to 12kRPM than a 5L V8 at 6k, that's just basic math, right?
Still amazed at Formula 1 engines.
Ye Olde Desmodronic systeme
But they still dont make power so kinda pointless. If it wasnt for favorable rules you would never see another one on a racetrack
I learned the hard way about desmo service. Lol
@@ryanwalker9472 I pity the man (apparently you) who had to work in that ridiculousness.
Is their a lighter spring with a faster return rate, like maybe do away with the damper or thinner outer and heavier inner. I remember some of the old Isky,s worked well and smoothed out like it didn't rob power. Just a thought. Mike
Boy you were made for the camera!Always interesting listening to you David,
Thank you for the awesome content
Valve float is also a function of the spring harmonics, should have talked about BeeHive springs. Beehive springs have less of an issue with harmonics and you are able to use less spring pressure to control the valvetrain
And for certain engines like Buick, they clear the top at the rocker better.
if beehives are better why do the nascar guys never use them?
@@davidgalea6113 its the difference between "loft" and "float".
The idea was to ski jump the valve off the nose and have it catch on the slope. Beehives provide more stability, but loss power because they dont promote the ski jump.
Mind you, this can be done with a solid flat tappet. Try this with a roller cam (especially a needle roller) and the roller destroyes itself from being unable to take the landing impact...
@@crd-nz_001 they used flat tappets in the cup engines and they used rollers in the nationwide engines.. today both series use roller lifters.. my point was that you rarely see the beehive springs on high rmp engines...usually it is the double/ triple springs. probably not the best option if you are going above 8000...
@@davidgalea6113 hard to get enough pressure as no room for multiple springs.
Floating a valve is my biggest fear in my old Chevy. I’ve got a 1978 Big 10 with the 454 and 400 turbo trans. It’s all original parts, and at 128k lol
Probably fine with that 400 lift cam and a redline of something in the 4000rpm range
@@taylorsrus9543 if I put a cam in it I might see 4000 rpm but it doesn’t care for more than 3500 lol
Be ok long as you don't hold down while they float
I'd be more concerned about how the locks and retainers are doing at that age.
first time i learned about it was in a r32 in the back seat watching it bounce at 8 was also hauling on a back road
Do you need more valve, spring pressure when under boost?
Nice
You guys need to do a Free Valve conversion.
Great Info guys. David, are you going to go back to long hair too? Love to see you sport a mullet! Thanks for sharing and Cheers from Motown/Dearborn.
"boing" Absolutely perfect.
Why no Ti valves? No explanation for why this is bad?
Why did he state don’t use Titanium values?
I missed that part.
Always great information in the show.
me too!
Yeah! Maybe it's a reference to the ls7 valve drop issue?
Now do one for us on valve adjustment
Did dulcich get new jibs or something??? Looks a lil different
Can you test Koenigsegg's Free Valve (no-spring) heads on that engine?
You boys need to play around with the same concept but on a modern overhead cam engine.
Sure, to see the benefit of design but doesn't demonstrate the issue with pushrod engines.
Try out the ultimate, Formula 1 pneumatic valvetrain!
Can this be tested on a chassis dyno?
Do you guys have an email address I can use?
I’m having a RPM issue that I can’t resolve.
New engine build all roller and I can’t power past 5800rpm.
After 6000rpms the engine makes this horrible cackling noise and just loses power AFR goes rich.
Built to handle 7000 rpm expecting 6500.
I’m guessing valve float but could it be an ignition distributor issue?
I’m using an MSD ready to run distributor.
Got it, now if I can find a place that sells upgrades for my rotary
🐸
If Dulcich had blonde hair he would look like Dave Mustaine lol
I was gonna write that same comment haha.
Why no Ti valves? They are fantastic at high rpm and allow for more aggressive cam profiles. The other I would like to see are Sodium filled valves for higher cylinder pressures.
maybe because fatigue
Sodium filled valves? Not in my engine please.
There's a reason why you don't see them any more, and there's a reason why they are never used in racing. High cylinder pressure? What does that have to do with sodium filled valves? I'd take either Inconel or Ti for that application.
sodium is for boosted applications not for revving
I ran comp 911 springs in my 5400 rpm 454 and at 5550 they floated, I put in pac hotrods springs and no float, still singles but oval wire with a flat tappet X268 comp cam
comp xe cams are more modern flat tappet cams. they need a pretty decent spring. 911s are lightweight vs what they really call for.
never heard of oval wire springs. where do you find them?
Only if Grateful Dead was still around these guys would totally fit in
This is an old episode at this point. When does the next episode drop on MotorTrend+?!?! I'm feening. I have an idea for an episode: "426 Hemi vs 427 Chevy vs 427 Cammer. Which wins Daytona?"
Funny what you get away with when young. I used to know my 81 f150 with a BBF would pull a mud pit in a higher gear was it wouldn't rev any higher in gear then neutral lol.
try rhoads lifters
Most change rockers for more valve lift not for weight.
So what would be the rotational speed of the cam in relation to the crank? Are they the same?
In a 4-stroke engine it's always half of crankshaft speed.
1:2 ratio
He literally starts out by saying this. Have you ever worked on an engine?
Valve float shift light with out the light.
It's great. Not blinding you at night.
But what do I now maybe 🤔 the crypt keeper mullet is in ..
I wish they had a heart with the 👍👎... great video, thanks for the info. You guys are the best.👍👍👍
You mentioned all the new LS engines use beehive springs, but credit where credit is due...Mopar used them in all their Magnum engines starting in 1992.
And Mercedes in 1954. What's your point?
The technology comes from military aircraft engines developed in the early 1900’s.
@@thebigpicture2032 My comment was not to discuss the origins of the design. The commentary would seem to imply the LS, and GM in particular, was breaking new ground by using the design, when the first large scale application would seem to be the Magnum series.
Why not run a titanium valve?
For race motors yes
Freiburger, you need to get one of those caps that has long hair attached to it, just so you fit in with the other guys.
Your conclusion was:(among other things) ...-and don't use a titanium valve. Why?Longevity? How about titanium retainers? Otherwise, a great channel!
My small block 600+ hp 480 torque still pulls at 8200 i keep it at 7200 most mostly 65 6800. However its built rigjt
lol nice
I wonder if anyone has tried a system for opening and closing valves that uses heavy duty electronic solenoids/actuators that can be controlled by a computer module similar to an engine ECU? I remember the crappy Cadillac 8-6-4 disaster, but that is not exactly the same as what I'm talking about. With electronically controlled valves, you wouldn't need a camshaft, lifters or pushrods, hence no valvetrain rpm limit, just a bottom end rpm limit. You could literally change lift and duration on the fly and never worry about valve float. Less moving parts, less weight, it would be interesting to see someone try it if it already hasn't been done.
könidsegg has freevalve system witch is basically what you are saying it has not been ina a car alrdy but is going into the gemera with a 600hp 3cyl
I have a 1984 Lincoln town car thats got CFI. Anything past half throttle makes no difference its like i only have less than half a pedal. Tried literally everything. Whats your thoughts?
probably where the fuel cutoff is at. what RPM is it happening at? they design stuff from the factory so you cant blow it up like that trying to rev it to the moon
@@KingJT80 its not really at a specific rpm its just in general past half throttle really makes no difference than half throttle. Itle rev to the moon in park its more of a lack of throttle response. Ive done everything i can think of. New injectors new tps new distributor everything. New iat new ect plugs wires the works.
Us Australians call it, "valve Bounce" a harmonic inbalance, be amazing to see it in ultra slow motion. Hint hint. Lol here's a great video idea, a sectioned cylinder head, where vales are exposed. Then test them at high RPM's, using a slow motion camera, hint hint you can thank me later loolz
I agree with what you said about not buying Chinese junk. But I say buy Aussie, Canadian or US goods and then Taiwanese is decent especially for certain things.
Crazy a guy teaching class about valve float LOL
I have a question.
Why would my engine builder use 1.6 rockers on the intake and 1.5 on the exhaust?
I can run 1.6 on all of them if I want to.
I’m just not sure why he did what he did.
He’s a hard guy to get ahold of or I would ask him.
He built me a 383 stroker running “according to his Dyno” 500hp 520tq
Cam 234/242
Intake cam lobe 374 with 1.6 rocker = 598 lift
Exhaust cam lobe 382 with 1.5 rocker = 573 lift
The heads have 205 intake 160 exhaust valve.
Using a comp roller cam and comp short travel hydraulic lifters.
According to Comp the springs he used are to weak and that why my valves a floating at above 5800rmps
So I’m planning on installing the right springs and a stud girdle and installing those ultra pro magnum roller rockers.
Just not sure if I should change that set up from 1.6/1.5 to 1.6/1.6
Oh and the heads “according to Brodix” are good for a 640 lift.
Any explanation for that set up?
i know this is an old video. but your cam spec math is not accurate. if i figured my cam like that it would be 1135 lift. your measurement is from the cam base to top of lobe. the equation is gross lift minus lift from centerline of cam to top of lobe and then multiplied by rocker ratio.
2 things; why did the engine not make more power when it was flowing more air and it was lame to throw the Ti comment in with no explanation.
Exactly
Ok, you added spring stiffness to resolve this particular engine's valve float problem: so what is the limiting factor to adding even more spring stiffness and running to higher RPM's?
Or making it DOHC.
If the valve springs are too stiff, the rockers and push rods will self destruc because they are working too hard. What's the limit on RPM? It's a big block Chevy, you spin it any faster than 5500 the pan gets full of piston skirts REAL quick.
Heavy valvesprings rob power
@@reesewilliamson3346 Also switch to solid lifters if want life at higher RPM's.
For a daily, just build for low to mid to avoid a grenade.
@@SoI_Badguy I thought they prevent floating?
Valve bounce, what is it? The old school rev limiter 🤣
I've dyno'd where the graph dropped at about a 70 degree angle. Interestingly enough, a .060" valve shim fixed it.
Spring shim?
Reason is that you had too much free spring when compressed. Obviously it will also increase pressure, but what few seem to think about is how a spring that is too tall affects control even if the pressure is correct. Never let it be more than 0.070 between bind and open height. About 0.030-0.040 is what you want and that's a big part of why so many have issues. Probably one of the most overlooked issues in valvetrain setups.
@@goratgo1970 Guess so.
That background music! Sounds like a guy is going to ring the door asking to clean the pipes. It is also TOO LOUD!
just like max piston speed . there's a maximum valve speed for every setup . even the ducati system has a limit .
If you don’t want to float take off your water wings lmao jk thanks for sharing buddy great video
I Like to know What would happen if you had too stiff of a valve spring.
I think it might wipe out the cam. Or break a lifter depending on the setup...
It really depends on the specific situation.
Sometimes you will just be down on power and wear out things slightly faster. Sometimes almost nothing. Other times you might break rocker studs, bend pushrods, wear out valve stem heads, tulip valves, crack seats, collapse lifers, destroy lifter rollers, etc. etc. etc.
It depends...
With my 4.10 gearing I really wanted to plan my build very carefully. Overkill? You bet. Expensive? Oh yeah. This build lightened my wallet, which encouraged me to eat less and lighten myself. Next up, the car (68 Barracuda fastback) gets a diet to bring her down to 2,900-3,000 lbs. with me in it.
Valve float? Not in my little 3.580" stroke Chrysler 360LA motor. I have a mild Lunati Voodoo *solid* flat tappet cam, 80 gram lifters, I did add mass to the valve train with some GOOD pushrods because the Mopar LA series cams sit kinda high and well, the geometry could be better. Comp 7228 438 lbs/inch conical valve springs, tool steel retainers, ductile iron rockers, Ferrea hollow stem intake valves. No, I am not running sodium filled exhaust valves, I want to keep the heat in the combustion chamber where it belongs rather than in the oil which would be absorbing that heat through the valve stems as the oil (Royal Purple HPS 10w30) lubricates and cools them. The plus side for that would be any water in the oil system would be boiled off rather quickly.
You couldn't *pay* me to build a motor with hydraulic roller lifters, and solid rollers are for the track.
Valve float with a roller cam can destroy roller lifters especially on a solid roller.
Hehe I keep them valves floating daily ,😂 stock 302 lives at 8grand
I've got enough valve float to unsink the Titanic
Solid lifters and good springs is the way to go
Desmodromic valvetrain is the only way to totally eliminate any valve float.
Got to cut your hair Steve. Looking like the Crypt keeper.
Explain it with OHC
Is this still common with a Dohc type motor?
Yes.
Have you guys ever tried a springless valvetrain before? What has to happen to the engine in order to do that?
It's called Desmodronic Ducati is the only company to use it
Even that needs springs, but yes, it can't float.
Desmo valves in a chevy
Dear EngineMasters/MotorTrend, how do Australian fans legally access Engine Masters, Roadkill, Dirt Everyday etc as we're GeoBlocked. Are there any streaming platforms we can use to view without breaking to law?
Thanks
Engine masters is Amazon, pretty sure the motor trend channel is on there
I pay my Mt with google pay and can watch it with a VPN... but I know others can't even have a Mt account cos of ozy credit cards etc etc
@@hot308vb That's where I'm at and Paypal is very odd, join, got account frozen, then after appeals it was unfrozen, 40 bucks went out but hadn't bought anything...hoping for the legal option 🙂
Why would you not run a titanium valve?
Great for racing, but wears too fast for the street in many cases.
Aren’t the steel rocker actually lighter. Stronger therefore less material.? At least this is what comp ultra pro magnum claims
As my mom used to say in 1970 to many RPM'S.
Whats wrong with titanium valves ?
Nothing. Each thing has its place.
thats what finnigan uses instead of using a shift light
You'll hear a engine float valves. Not a good thing. I have a camshaft that's runs up to 5500 rpm. But I still maintain the single hd springs. So yes weight is a problem. My engine will clatter at 6500rpm. Don't hurt the engine to go to 6000. Just point less on a street engine. I could have double springs. But having a soild camshaft. It will wear it down quicker with double springs. So I normally only hit 5000 in first and 5500, in the remaining gears.
Is it a diesel?
@@taylorsrus9543 no it's not a diesel.
@@taylorsrus9543 a diesel would have holes in the block before 4500
@@jradish I better go look for mine.
@@jradish a high performance diesel engine can rev well past 4500 rpms but a stock diesel engine will certainly grenade itself
Also bent pushrods!
I go back to a video I watched on a UA-cam channel complete toilet garage, 350vs LS.... LS motor chained up to a cherry picker, Had it held on limiter with no water in it for something like 7 minutes.....like laughing in the face of valve float,
So a cam with 360° of duration is not good
WHOA WAIT, why not a titainium valve?????
They are not suitable for street applications. You can read up on why in many places.
Please built me a v10 eco boost
I love these shows! Regardless of these guys turning into long-haired, hippies; they're old school GENIUSES I can trust to give me the facts I need/want to know(before blowing up my engine)
I'd like to hear their take on dual overhead cam, where we get rid of the pushrod completely AND use smaller/lighter valves. More flow and revs and better reliability?
you still need spring to control the valve return. dohc gets rid of a lot of mass' inertia you have to overcome. you want valve control though, look at f1 pneumatic...no spring weight to overcome. similar with freevalve.
Pneumatic valves literally negate these problems, these guys need to make a 1500HP 1.5L 4 cylinder, that can operate at 75k rpm
@@C_Castillo But there's the complexity and reliability versus power-gains consideration, same as DOHC.
@@dgholstein these guys have literally been trying to make more power, in the 80s 1.5L 4cylinder engines were dumping out 1500HP, they have no excuse , they’ve blown up engines for a lot less, they just need to make a 75k RPM monster or something that tops at least 1k HP theyre so called “engine masters” they should be able to do it easily.
@@C_Castillo 75k?
Losing control of your bowels is way cheaper but you have more fun achieving valve float, lol so to speak!
Aping tension
My motto is when the valves float shift
the background music is loader than you
Mr. D I respect your knowledge and work ethic plus you're a Mopar guy. But dude clean up your act.
Haha yeah, valve float means time to shift. I'm down with that.