Drive pressure vs engine failure? - PowerStrokeNation : Ford Powerstroke Diesel Forum
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post #1 of 60 (permalink) Old 07-27-2008, 06:17 PM Thread Starter
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Drive pressure vs engine failure?

The quotes below come from the "head gasket failures with Hybrids" thread.

Quote:
Originally Posted by PTSUPERD
I guess other things come into play as well. (drive pressures etc.)

Quote:
Originally Posted by racehauler
Personally I don't see how drive pressure has anything to do with a head gasket failure but if someone could enlighten me I am all ears.
The boost crated due to the high drive pressure number I could buy that as being a contributing factor.
All things remaining equal higher drive pressure is going to blow a head gasket how?

Quote:
Originally Posted by Powerstroke Racer
ya, it's called uncontrolled detonation.

Quote:
Originally Posted by Powerstroke Racer
Believe me 10 psi of a particular boost number is not what will pop a head gasket.

2 things that will pop a head gasket are too much timing or too much fuel too early causing detonation which induces cp spikes and eventually you will get to a point even in a properly tuned and well running engine that there is simply not enough clamping force on the head gasket.




The thing that keeps coming to mind are the amount of engine failures with smaller turbos (stock, van, and drop in replacements). I made the comment before about drive pressures being a big factor. Seemed that at that time everyone disagreed with me and maybe still do. I wanted to bring this back up for more discussion.

One good example that comes to mind is House(Joe). Still running stock bolts and everyone knows how the truck is used. Last I remembered he was running some type of HX50 hybrid. When I started adding power I ran a van turbo for a while then tried a Phat Shaft Stroker. Both had what I considered excessive drive pressures. As much as 20 psi over boost. I then went to the K31 and now the S400. I know that there is a power limit to the stock forged rods. The majority of the failures were in the 400hp range with the smaller turbos. Most of which were running 230-240 cc injectors. I'm sure I'm over the 500 mark and so is Joe.

So the question is: Why do the trucks with BIG turbos and more power stay together longer?

Kevin

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post #2 of 60 (permalink) Old 07-27-2008, 06:30 PM
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Re: Drive pressure vs engine failure?

They don't. It just so happens that most trucks don't run big turbos....

So since the VAST majority of trucks are running "small" turbos (probably 95% of them) then obviously you're going to see the most failures with them.

Fact of the matter is, of the trucks running larger turbos the percentage of failure is almost certainly much higher.

There just aren't many of them (comparitively) so you incorrectly draw the conclusion that the small turbo is causing the failures since more trucks with small turbos fail.


Maybe someone would be kind enough to explain how 60 or 70, hell 100 psi of drive pressure is going to pop a head gasket that sees between 2000 and 3000 psi every time it hits TDC at WOT?

Residual exhaust gas increasing cylinder temps and slightly decreasing the ignition delay of the diesel fuel?

That's the only way I can see it having ANY effect on a headgasket, and the reality is, that is just TIMING of a different flavor.
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post #3 of 60 (permalink) Old 07-27-2008, 06:39 PM
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Re: Drive pressure vs engine failure?

would it make sense that the trucks runnin smaller chargers have more piston cracks that cause failures? ya know from higher egts?

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post #4 of 60 (permalink) Old 07-27-2008, 06:40 PM
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Re: Drive pressure vs engine failure?

I'd like to know too, I hate blowin crap up........My combo should have lasted much longer. I was around 400-430 hp is my guess and went boom both times.....
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post #5 of 60 (permalink) Old 07-27-2008, 06:46 PM
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Re: Drive pressure vs engine failure?

Quote:
Originally Posted by Charles View Post
They don't. It just so happens that most trucks don't run big turbos....

So since the VAST majority of trucks are running "small" turbos (probably 95% of them) then obviously you're going to see the most failures with them.

Fact of the matter is, of the trucks running larger turbos the percentage of failure is almost certainly much higher.

There just aren't many of them (comparitively) so you incorrectly draw the conclusion that the small turbo is causing the failures since more trucks with small turbos fail.
I think the best way to get the complete story from the survey is to have an additional survey for EVERYONE to fill out, not just those with blown motors. This way we'll have an idea of just how many (percentage-wise) out there are running certain combos. Then we'll have something to compare the blown engine data to.
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post #6 of 60 (permalink) Old 07-27-2008, 07:06 PM
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Re: Drive pressure vs engine failure?

Well if you just think about this, the only way that drive pressure can blow a heagasket is if it effects the compression stroke in some way. The only way I can see that happening is through cylinder reversion on valve overlap causing residual exhaust gas to mix with the incoming air, producing higher intake air temps in the cylinder prior to the injection event.

That would increase the timing of the start of ignition.....timing.

It almost always comes back to timing one way or another.
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post #7 of 60 (permalink) Old 07-27-2008, 07:08 PM Thread Starter
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Re: Drive pressure vs engine failure?

Charles I see your point. Now if you stop and think about it there is a pile of H2E's out there running then add the few 42's 45's S300's S400's and even a hand full of twins. All (or most) making more power than a BB.

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post #8 of 60 (permalink) Old 07-27-2008, 07:09 PM
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Re: Drive pressure vs engine failure?

And they blow up plenty often too.

BTW, an H2E is not a big charger. I am still not convinced that it moves more air than a 38R.
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post #9 of 60 (permalink) Old 07-27-2008, 07:09 PM Thread Starter
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Re: Drive pressure vs engine failure?

Quote:
Originally Posted by Charles View Post
Well if you just think about this, the only way that drive pressure can blow a heagasket is if it effects the compression stroke in some way. The only way I can see that happening is through cylinder reversion on valve overlap causing residual exhaust gas to mix with the incoming air, producing higher intake air temps in the cylinder prior to the injection event.

That would increase the timing of the start of ignition.....timing.

It almost always comes back to timing one way or another.

The reversion is what I brought up in the past. Yes it can be changed with timing but is it the cause?

Kevin

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post #10 of 60 (permalink) Old 07-27-2008, 07:10 PM Thread Starter
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Re: Drive pressure vs engine failure?

Quote:
Originally Posted by Charles View Post
And they blow up plenty often too.

BTW, an H2E is not a big charger. I am still not convinced that it moves more air than a 38R.
The drive pressure is what were looking at.

Kevin

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