Cylinder base gasket question again....

[Tippy]

Background of engine:

'87 3.2L with 3.4L (98mm) flat-top Max Moritz pistons (I think) and Mahle cylinders. The engine is turbocharged (1-bar).

So "Cgarr" did a fine job rebuilding my heads for my engine. He had to resurface my heads due to shipping damage though (my fault when packaging).

Craig took off 0.008" and to which I've read here, Wayne's book, and the factory manual, that once you resurface the heads, you must use 0.50mm gaskets instead of the 0.25mm ones. I know this is a 0.010" difference which makes sense.

But, just for another reference, I called my local Porsche shop. The owner is factory trained and he told me that since I have the flat-tops, I don't need the thicker base gaskets.

Is that true?

[MBruns]

You wont need them for clearance but .010 in. off the heads can make more compression than you may want for a boosted engine at 1 bar, I would add the base gasket dimension to bring it back to what you had, short of figuring out exactly what you have now by pouring and calculating that is the safe bet.

Mike Bruns JBRacing.com

[cgarr]

.21mm would bump your compression .20 with a 74.4 stroke 98mm bore engine. assuming your at about 9 right now. Do you know where its at right now? It would only be about .12 if your around 7.5 now.

[Tippy]

Originally Posted by MBruns

You wont need them for clearance but .010 in. off the heads can make more compression than you may want for a boosted engine at 1 bar, I would add the base gasket dimension to bring it back to what you had, short of figuring out exactly what you have now by pouring and calculating that is the safe bet.

Mike Bruns JBRacing.com

So he was correct in the clearance part.

Originally Posted by cgarr

.21mm would bump your compression .20 with a 74.4 stroke 98mm bore engine. assuming your at about 9 right now. Do you know where its at right now? It would only be about .12 if your around 7.5 now.

I used a CR calculator and IIRC, it was 7.5:1. All the dimensions I have are correct but the one I searched and wasn't 100% was the 90cc combustion chamber size. I too figured it would bump .20 by the calculator.

Now I have to decide if I want the bump or not....it would have a slightly better off-boost response but probably would not make up for the extra cylinder pressure on-boost.

[fred cook]

You might want to have the heads CCd. That way you would know the actual combution chamber volume. I had the same situation on a set of heads that had been cut and twin plugged. It turned out that the material removed when the second plug hole was cut actually increased the volume slightly. Good luck with your project!