i think your biggest mistake was not letting the gaskets season in before boosting over 40 psi.....according to swamps you need to drive conservatively 10k miles before boosting over 40 psi or so....under that 10k miles and its a gamble if they will hold or not....there are a few write ups and threads about this over on the army if you want a good read.....i know it sucks but removing the heads on a stroke is supposedly not a good thing to do unless you have to because you then have to wait to play.....just the nature of the beast.....also i would not re use the arp's.....get some h11's......

 

Again...

Please tell me how that extra 40# pushed the head gasket that was holding a few thousand?

Boost has no direct reference with cylinder pressure.

You'd be more accurate to say, "I think you blew your gasket because you didn't leave the chip in stock for the first 10k or more."

 

so youre saying that the 52 psi of air wasnt going into the cylinder? exhaust back pressure comes from driving the turbo right? im asking not being sarcastic.....its my understanding that the new gaskets are still soft and need time to harden (season) to hold the boost in.....thats why you can run up to 60-70 psi on stock head gaskets with studs when the heads have not been removed.....they recommend you go to fire rings once the heads have been removed and if your are going to be exceeding 60 psi or so.....52 psi doesnt sound like a ridiculous amount of boost to be pushing on stock gaskets with studs as long as the heads havent been removed....

 

while you to go back and fourth..here is my take,right or wrong, builders that race their truck didn't put 5000-10000 miles before the race and most in a small class don't use fire rings, now, i wish I had of but "it is what it is"..
I believe my failure is do to the type of gaskets or prep of the block and heads..Eather way, this will be fixed..I am concerned about the back pressure and the damage it could/would cause..
At first, the truck would hit 50psi of boost and hold,but at 52 it decided not to..
now, would it be beneficial to change to the 1.10 exhaust housing??that is what I am trying to figure out..

.91 housing--spools quicker,tows very well,egts are in check-----back pressure high @WOT in performance tunes (rarely used)

1.10 housing--spools slower, towing unknown,EGTs unknown-----lower back pressure

now the best thing to do is try both and pick one,which is whats going to happin...I am just trying to get more knowledge inregards to back pressure and its effects..

 

thats because in the race type world engines get rebuilt all the time....they dont worry about longevity....

not arguing just fact searching like yourself....

 

Theres been lot of failures with those gaskets, period. Theres also been failures with o-rings if not machined correctly. On the valves, if you think you have to machine them I would go with after makert stainless or something that are built thinner and made for heat. You really need to buy two sets of gaskets and clay the pistons and measure the clearence to tell. Thats the only way to know. How much did you take off the block and heads? You are right on gaskets, they should work the first time regardless if done right. You could check your bolts for strech but after four times, I mit be inclined to change also. Go with the larger housing.

Chet

 

The gaskets actually bond to the head and the block, and harden to a point. That's why guys can get away with swapping head bolts for studs on factory assembled engines, because they're never cracking that bond.

Now on boost/back pressure/cylinder pressure... We're talking several thousand psi when combustion starts. Two things that directly cause a rise in cylinder pressure; more fuel - more timing.

Boost and back pressure will rise according to where you set timing, and where you set pulse width.

Lots of timing, and lots of PW = lots more cylinder pressure.

All other things equal, the more you retard timing, and increase PW, the more you'll see back pressure rise, as less fuel is injected and burned during that optimal window of time in crank rotation, and more fuel is simply chasin the piston down the stroke, creating heat and smoke and more drive pressure.

The less timing you use, the less cylinder pressure you can expect.

So, while timing and fuel affect cylinder pressure, back pressure and ultimately boost, are a product of the combination of the first two values, rather than values that affect cylinder pressure themselves.

Cylinder pressure PSI is thousands, and boost/BP is tens. If you've blown a head gasket do you think the thousands of PSI from the combustion event did it? Or the tens from the compressor/turbine that is driven by that combustion event?

 

Every single shop I know of that is worth it's name is recommending fire rings as soon as the factory bond is broken between the head and block, when the engine is receiving even a small hybrid.

It just takes to many miles driving normal, keeping cylinder pressures down, to achieve a bond capable of holding elevated pressures.

I would guess that with yours popping at 3500 miles, that your gasket had been working its way toward blowing since the first time the engine went WOT. I promise it had nothing to do with the extra 2 pounds of boost. They had just had as much as they could handle, and that time goin WOT was the final straw.

Like I said, high back pressure alone won't hurt a thing other than the turbo. There is some valve overlap on the stock cam profile, so high back pressure isn't gonna allow a complete expulsion of the burned gasses in the cylinder, but that alone won't hurt anything.

Do fire rings, bolt it back together, and see what your PW is. Might be that a slight trim on PW will lower your BP and make your turbo a little happier.

 

Just for the sake of clarity in the conversation... What turbine do you have on that turbo?

What injector are you using?

 

E-mail Cory, Ziggy, he'll give you the skinny. He dyno'd over 600hp and know o-rings that I know about. Could be wrong, but not the last time I read his build.

Chet

 

I will have to go back and look to get the turbine specs...
injectors are 238/100


I was there when he dyno'd and I believe you are correct...

 

where is a good place to look at fire rings/gaskets???

 

I know Black Widow had/has them. Good luck bud, been watching your horror stories.

 

WOP, or whoever they are now, has them.

Swamps has 'em. Carson Staufer (sp) as well.

I think Beans machinist was gettin things together to do them too.

 

And 52 pounds of boost on 238's is pretty high... Seems like guys are normally in the mid 40's with those.

Might trim up your PW, I think you're just hittin the turbo hard.