Marc, I've been lurking along here for a while since I find the subject interesting but have no boosted 928 data to report... at the moment. I'd be very interested in hearing what you know about that blown gasket, like what exact part was it when installed with what prep, if known. Maybe the gasket that blew wasn't the best one for the application. Can you post pics of the head and deck, and the gasket? I find that sort of information highly fascinating, if only to satisfy my morbid curiosity and provide fodder for armchair speculation.

So, what say?

 

Marc, my GTS was running 5 pounds of boost before it was brought back to stock. Is your candidate the other GTS?

 

Bump

 

I have around 2.5 years, and probably 30k miles, on a daily driven, intercooled twin screw running pump gas and ~9 psi.

I use Cometic gaskets which were specially ordered thicker than stock.

I know I don't exactly fit the mold of what you're looking for, but it's one experience for the archive.

 

Marc,

My head gasket went last year, I don’t; have the head off yet but it will be removed in a couple weeks. Had a failed injector on the diver side and when it finally failed it would not open. So I think what happened that as it was failing, it created a lean condition in that one cylinder and the gasket went as a result of that.

Mine is a low boost (~6psi) non intercooled setup. The head gaskets were pretty new (~3 years old) made by Victor Reinz and the engine is an ’85 32V (studded from the factory).

 

Marc:

I've been running my intercooled twinscrew (424) at 7 psi for nearly 2 years. This includes 12 DE days with a wide range of temperatures. No issues or problems. I did upgrade the intercooler pump to a Deadenbear (23 gpm with 3 amp draw) and used a radiator from a 750 Yamaha with fan for the heat exchanger. My return temp from the intercooler is around 102-104 degrees.

While at the track I usually do plug together the low fuel loop (1985 MY) as a bit of safety margin.

Hope this helps.....I would like to add one more PSI if there was a pulley available.

Ken

 

My 4.5L was 7 psi of boost non I/C. After two years the right head gasket is starting to fail. Two cylinders are low on compression

Time for rebuild anyhow. The HG is 25 years old.

 

This is great info.....thanks for the honesty!

If you can also state the hp/dyno results that would be useful in calc'ing bmep.

 

Whatsa 'bmep'?

 

I had never seen this thread before.

I blew the HG on my 85 running 6psi non-IC with a FAST kit. The motor and car was in fair condition and had 129000 miles on it. When we tore the engine down, one cylinder had a scratch in the wall that my mechanic said was significant enough to allow "blow by" crank-case pressure. The damaged cylinder was exactly where the HG failed, so I have to believe there is some merit to that claim.

In the low compression motor I now run, I use the 951 HG however we are just starting to tune the car and have only run it under boost for very short runs because of going lean. Working on that now and will be running the car regularly soon with a dyno to follow.

 

In a nutshell, it's torque / displacement. So for a given displacement, an engine with a lower BMEP is not as efficient as one with a higher BMEP.

Brake Mean Effective Pressure: http://www.epi-eng.com/ET-BMEP.htm

 

so tell me, why does boost have anything to do with headgasket failure? Its the mass expansion in the cylinder that provides the power, and those combustion pressures are orders of magnatude higher than the boost levels of 4-7psi when we are talking about 1000+psi under combustion in the cylinder head combustion chamber. I cant think of any reason why the pressures with boost vs with an equal greater mass flow due to a stroker crank would be any different, besides the intake charge temp being higher with boost. are strokers blowing head gaskets too? Sure sounds like there is some kind of differerence based on all the blown HGs, but im curious as to why.

Best of luck with the Cometic gaskets. I guess they can stand up to the pressures better, for whatever the reasons.

MK

 

Mark,
Actually run the numbers on a 450 rwhp SC 5.0 engine and a 6.4 450 rwhp engine....and then compare them to the factory 300 rwhp 5.0 engine.

the factory designed head gaskets to last for 20 plus years based on a the above numbers.

does it mean if you double the bmep, the headgasket will last half as long or 1/10 as long?

I am trying to find the practical limits for stock head gaskets in a boosted application....

 

That's a good point.

Here's what I think. If the volume of air is the same in both the stroker and the boosted engine that its probalby the intake air temperature that makes al the difference. OR maybe that the N/A engien can eaiser controll the A/F ratio.

 

Just had to add to your statement a bit.