Basically, will valve float happen at the same rpm range when the car is in neutral compared to climbing an incline? Just wondering if the rpm at which float happens on the dyno would be the same under various loaded conditions in the car

Valve float is a result of the valve springs inability to overcome the weight of the valve train components beyond a given frequency or RPM. The profile of the camshaft will have an effect but with it being constant, I would say engine load would have zero effect.

I have no data to back this up, but I would agree with TJP. If you are having an issue that varies with load, I would suspect fuel delivery probelms.

When free-winding in Neutral the rpm will increase quicker and might possibly allow a higher rpm before valve float. When the rpm increases more slowly under load valve float might occur sooner.

Ok thats what I was thinking to but wasnt sure. Except what Mr K said, I hadnt thought of that

Load doesn't matter, just happens quicker with cold tires......


Ed

an engine on a dyno is under a load, it's not the same as free revving in neutral.

I'll rarely and politely disagree with you John.
I will agree that when free winding in neutral one may attain a higher RPM before the "FLOAT" is apparent, but the laws of physics say it has to happen at the same point / RPM.

Higher load = higher combustion temperatures = higher valve temps = higher valve spring temps/oil temps =

Yes, the engine could go into valve float much sooner pulling a heavy load up a long grade vs. winging it in your driveway out of gear.

There are many more factors influencing physics than speed, acceleration and mass.

Anybody that has ever had a bad set of valve springs for a while knows that they get worse as the engine warms up.

What about the idea that under load you're pulling a lot more air fuel in, creating higher chamber pressures which would help 'push' the valve closed?

Same idea about how you can't seat the rings on a fresh motor by just blipping the throttle. You need the load to create the higher pressures.

To answer your question.......Just think of the machine used by builders and engineers to test valvetrain performance.

if you even suspect valve float fix that problem right away before you break something in the valve train ruining the motor

This.

"creating higher chamber pressures which would help 'push' the valve closed?"

That would only be the case if valve was "floating" at peak opening, which is also the moment I suspect there is the closest to equal pressure on BOTH sides of the valve, resulting in minimal "push". Can't believe air flow velocity/force on back side of intake valve is a significant factor

As I see it, for example, 2" intake =3.14 Sq in, if cylinder fill was at a vacuum, and intake track at NA atmospheric pressure or zero vacuum, intake back side valve pressure at max would be 3.14x14.7, or close to 50lbs of loss of valve spring closing pressure, and this case will never be incurred, I suspect, and this effect will always be much less. and rpm/load dependent.

Valve float, when the lifter doesn't stay on the top of the cam lobe at max lift at max RPM is one thing, hydraulic lifters pumping up causing the valves to stay open on the heel of the cam in another issue also.
Which problem are you trying to deal with

Isn't the Spintron more for measuring valvetrain dynamics in a nominal test environment? Wouldn't troubleshooting in the car be a bit different in the way of the break-fix mentality behind diagnosis?

It's also used for testing component compatibility, designing springs, cam lobes, etc.

They usually(never?) don't even have any kind of rotating assy in the bottom end, much less an induction system.

When I visited Comp Cams a number of years ago(they have 2 Spintrons), there were several "motors" from a variety of engine builders there for some spintron testing/developement.
These were all very well established big name builders.

A few of those were combos where the builders had been fighting some sort of valve train issue on the dyno or in the car and had been unsuccessful thus far, so some Spintron testing was going to be used to try and pinpoint just what the problem was.

I guess my point is......even some of the bigger names in the industry use the Spintron to figure out what's really going on with the valvetrain........and the Spintron has no provision for creating the combustion pressures and shock wave tuning inside the manifold.......so it's unlikely those things have a big impact on the results.

Another way to look at it is........if you're having a valvetrain stability issue.......I highly doubt it's the combustion pressures or the tuning pulses inside the manifold that are the cause of the problems.

GOOD QUESTION

But I understand the sky will be GREEN tomorrow, I've actually read some articles that say it always has been We were just taught that it was blue.
So back to the OP's valve float question. Wing it in neutral until makes noise and stops.
Repeat the process SEVERAL times with the IDENTICAL Motor under laboratory conditions with various temperatures, humidity levels, Ambient as well as engine temps, and report back. Do not forget with or without proper crankcase venting, oil viscosity, grade of hill, rear end gears, transmission ratio, UHH and phase of the moon due to it's gravitational pull on my septic tank and valve train. With all of that data collected We will then be able to continue to comment on the silly question.

OPPS forgot one variable, What type of valve covers ??
HMM, original, reproduction, aluminum (cast, billet, or sheetmetal)

What is the surrounding temperature ?? IE: under hood, Dyno room, Maybe no hood ??

octane of fuel??

I come here to relax, enjoy and try to help. Some of the suggestions responses make me question why I continue to do so

Just wondering if the rpm at which float happens on the dyno would be the same under various loaded conditions in the car

Missing the simple part here.... if it floats on the dyno there is a problem that needs fixed before it even hits the car.

If it floats on the dyno its time to look cross eyed really hard at your engine builder.


For what 99.9% of us here do, spec and check the right parts and valve float will never happen.

It's one thing to disagree and offer up your opinion but insinuating to anyone that disagreed with you in this thread that we are too stupid for you to even attempt to correct and then threatening to take you ball home. lol

Instead why don't you explain why we are so dumb. With as many posts as you have if you were going somewhere to do something more important it would have happened years ago lol.