Pushing it...

[MPFab]

Nah, I don't mind talking about it here. Boost can and does affect valve float. Boost pressure is trying to push the valves open at any given time. If the springs are marginal for the operating rpm, boost pressure can easily cause float. I'm pretty sure the valve springs I have in my Evo, have seat pressure guidelines depending on the boost pressure you intend to run.
Also, have you ever held a factory spring in your hand? I have. It possible to compress them a good bit using your thumb and index finger.

 

[Colin]

I thought boost pressure definitely affects valve closure forces. Not only on the intake side which seems most easy to comprehend, but also on the exhaust side (maybe even more so) due to the severely increased back pressure created from high boost at high rpm.

Boost is being applied to the area of the valve head, so the forces rise pretty quickly as boost is raised, at least that is my understanding. I'm sure there is ONE way to find out. opcorn:

Boost pressure certainly affects the intake valve while it's opening, but as the compression stroke begins (and the intake valve begins to close) the pressure in the combustion chamber should be roughly equivalent to the pressure from the intake manifold. In other words, when the intake valve starts to close after the piston begins returning upwards towards the head from BDC the boost pressure from the intake manifold (pushing the valve into the combustion chamber) is equal to the boost pressure in the cylinder (pushing the valve back into the head). The forces balance.

On the exhaust side, remember the pressure in the combustion chamber during the exhaust stroke is significantly greater than the pressure on the exhaust manifold side.

 

[Preloader]

If the compression pressure/boost balance forces so well, then a valve spring that just works at n/a pressures at 6k rpm will gladly operate at 30 psi at 6k rpm according to that principle. I'm oversimplifying to extract the point.

I understand that compression pressures are much higher than the intake boost pressure near TDC, and that 30psi won't easily overcome that. But we aren't talking about boost overcoming a seated valve. we're talking about float, which, at the upper rpm, has to do with very short time events for valve timing. To open and close. Adding any additional force to those time events could really interfere when a valve spring is already struggling to do it's job at 23psi.

I'm not claiming to be an authority on this subject, just joining in on the fun with info that I have either read in auto books or read off of the infallible internet.

 

[Colin]

If the compression pressure/boost balance forces so well, then a valve spring that just works at n/a pressures at 6k rpm will gladly operate at 30 psi at 6k rpm according to that principle. I'm oversimplifying to extract the point.

I understand that compression pressures are much higher than the intake boost pressure near TDC, and that 30psi won't easily overcome that. But we aren't talking about boost overcoming a seated valve. we're talking about float, which, at the upper rpm, has to do with very short time events for valve timing. To open and close. Adding any additional force to those time events could really interfere when a valve spring is already struggling to do it's job at 23psi.

I'm not claiming to be an authority on this subject, just joining in on the fun with info that I have either read in auto books or read off of the infallible internet.

I'm on forums for friendly/fun discussions with fellow enthusiasts as well! If my words come across as confrontational I assure you that's not the case.

You're first paragraph, while I agree is over simplified, is correct. If an NA valve spring works at a given rpm then so should it work in a boosted application at the same rpm. The reasoning for this is the cylinder pressure at BDC of the intake stroke should be equal (or greater) than the intake manifold pressure -regardless of pressure in the manifold. There is more pressure pushing the valve in the head than pushing it into the cylinder.

I'm aware we're talking about valve float, but when the valve goes to close it doesn't have a net of 30psi resisting it. It's true the 30 psi in the intake side is exerting a force to hold the valve open, but the key is at this point the cylinder has been filled with 30+ psi as well -which is now pushing the valve back in!

Does this make sense? If you increase the pressure on both sides of the valve it balances out. 30 psi is pushing the valve from both ends after the cylinder fills, it's no longer a one sided force.

 

[Colin]

I want to point out a caveat here. If the cylinder isn't able to properly fill with (at least) the same pressure in the intake manifold during the intake stroke then the forces won't balance -however if the cylinder isn't properly filling then there's another problem.

This phenomenon could be exaggerated by increased boost pressures, and while stiffer valve springs might help -that's not solving the real problem.

 

[CheapFuneral]

I would think the biggest issue is not at stock rpms, if you look he's still got more horses he just rpms


If I die, bury me in my truck, because it's never been in a hole it can't get out of!

 

[Preloader]

I want to point out a caveat here. If the cylinder isn't able to properly fill with (at least) the same pressure in the intake manifold during the intake stroke then the forces won't balance -however if the cylinder isn't properly filling then there's another problem.

This phenomenon could be exaggerated by increased boost pressures, and while stiffer valve springs might help -that's not solving the real problem.

While now I do understand how you are arriving at the net balance premise between cylinder and manifold. I think the time events at 6k (intake valve opening and closing 50 times a second) rpm very likely don't allow 30psi to fill into the cylinder. I believe the valve is attempting to close before that happens.

A valve spring happily closing at 5,500 rpm under 30 psi, has a whole new battle at 6,300 rpm.

While we know the stock head wasn't engineered to flow the volumes/pressures that Morgan is abusively pushing through it, and will likely benefit greatly from some porting and obviously camming...... I think the valve springs are already passed their employed duty where he is at.

 

[MPFab]

Here are two graphs at lower boost levels that show the power drop off a the same rpm. You can see on the higher boost graph, the drop is much more dramatic even though the boost difference between the two was only about 1.5psi



I just want to say that I would love to believe that it wasn't a spring issue. It would make my life so much easier, but being the actual guy who is pushing this platform to its limits, and has spent months now tuning, logging, and dynoing, I have a pretty substantial amount of data compiled. We can all talk theories as to why it should or shouldn't happen, but everything I have learned/experienced in the last several months points to the valve springs needing replacement for any RPM over 6,300 regardless of the turbo. More boost really seems to "put the nail in the coffin", but I would link it primarily as an issue of RPM, and secondarily an issue of boost pressure.

 

[Foxbox]

Love it.

Perfect numbers imo.

I can't wait to see trap speeds.

-Mike

 

[Blue Moon Sonic]

Well all I know is that I'm going to have fun destroying my transmission after this kit goes in and maybe by that time something stronger will come out.

 

[EPYON96R]

I dont know much about internals. Much less boosted internals. But preloader might be on to something with camming. That might be a factor in the power drop. But yes you are the one with the data. So my guess is exactly that, just a guess.

 

[MPFab]

It holds on to power too well up top to be cam related. I seriously feel like it's valve float. I will say, it's actually making great power for only 2° of timing up top. Hopefully, the next step will give me my timing back. I expect another 40-50whp with timing advance where it should be. I won't be able to run that kind of boost pressure on 93 anymore, but I ain't scurred of race gas or the corn when the need arises.

 

[Brags]

Love what your doing!! Keep it up! Looking forward to head upgrades!!!

 

[SoundWave]

Just to throw my uneducated opinions into the mix.

We've seen more than one tuner report valve float on these engines above 6300 RPM on the stock head/turbo at 24(ish) psi.

Morgan's logic that a larger turbo, pushing 30(!) psi will exacerbate this issue makes total sense to me. In a perfect engine, I agree that intake pressure and cylinder pressure should be equal with the valves closed, but keep in mind the core of the turbo 1.4 was actually an N/A engine built to charge batteries (Volt) that was later modified for full-time drivetrain status by adding a turbo and beefing it up to handle that pressure.

This is of course hearsay, but it explains some of the strange compromises GM made to produce the turbo Sonics.

I suspect head work + turbo will be the real key to making transmission destroying numbers on the GammaII.


Typoed on my iPhone

 

[Sneakerfix]

Just to throw my uneducated opinions into the mix.

We've seen more than one tuner report valve float on these engines above 6300 RPM on the stock head/turbo at 24(ish) psi.

Morgan's logic that a larger turbo, pushing 30(!) psi will exacerbate this issue makes total sense to me. In a perfect engine, I agree that intake pressure and cylinder pressure should be equal with the valves closed, but keep in mind the core of the turbo 1.4 was actually an N/A engine built to charge batteries (Volt) that was later modified for full-time drivetrain status by adding a turbo and beefing it up to handle that pressure.

This is of course hearsay, but it explains some of the strange compromises GM made to produce the turbo Sonics.

I suspect head work + turbo will be the real key to making transmission destroying numbers on the GammaII.


Typoed on my iPhone

That's not true the turbo 1.4 was out a few years before the 1.4 N/A was put to market

 

[ScarabEpic22]

Like the progress and sounds damn good!

Look at the engine move in relation to the body/fram on that pull, wonder if you're going to need beefier mounts as well...

I wasnt sure I liked how high the power peaked, then I saw the overlay with the stock dyno. As someone said, at like ~3.5k you're already above stock power levels with boost barely coming on. That's sleeper status, cant hear boost yet you'll be beating stock 1.4s left and right. Then boost hits, game over for the other guy.

Think you'll be able to lean it out a little bit, looks rich if you're actually seeing 9.5-10 on the wideband in the downpipe. Looks good for E85 though, just stick some in and go haha!


I'm going to hate the RS gearing with this much power, going to be shifting all the time. First gear will be absolutely worthless.

 

[MPFab]

Think you'll be able to lean it out a little bit, looks rich if you're actually seeing 9.5-10 on the wideband in the downpipe.

You're looking at the boost scale on the right. AFRs were mid 11s.

 

[EPYON96R]

Time to edit that sig

 

[ScarabEpic22]

You're looking at the boost scale on the right. AFRs were mid 11s.

:blankface: Dang it, assumed that was AFR not boost.

Good then, having the fueling dialed in is a big part! :banana:

 

[Colin]

Here are two graphs at lower boost levels that show the power drop off a the same rpm. You can see on the higher boost graph, the drop is much more dramatic even though the boost difference between the two was only about 1.5psi



I just want to say that I would love to believe that it wasn't a spring issue. It would make my life so much easier, but being the actual guy who is pushing this platform to its limits, and has spent months now tuning, logging, and dynoing, I have a pretty substantial amount of data compiled. We can all talk theories as to why it should or shouldn't happen, but everything I have learned/experienced in the last several months points to the valve springs needing replacement for any RPM over 6,300 regardless of the turbo. More boost really seems to "put the nail in the coffin", but I would link it primarily as an issue of RPM, and secondarily an issue of boost pressure.

Yea that graph tells quite a bit... I have the feeling the cylinder isn't effectively filling with the intake charge and there's a noticeable pressure differential. The real fix to the problem would be allowing the head to flow better -but valve springs are likely easier and should fix your dilemma.

Thanks again for not only being a pioneer but sharing all of the info as well!