SpeedPro Forged Pistons/Comp. ratio

[eastwoodad]

Does anyone know what compression these pistons yield with an uncut block and heads?

I have seen the specs somewhere that show the dish cc and what not. What specs do I need and how do I determine the compression ratio.

Also, did steel head gaskets come stock on the turbo engines? What compressed thickness?


Thanks,
Aaron

 

[J-B Racing]

7.8

 

[Nick Micale]

There are MANY factors that determine compression ratio when rebuilding and engine. The piston dish is only one factor, but the replacement piston is "usually" the same a stock. This must be checked prior to machining and assembly if you want a specific ratio, or just want to know.:smile:

The 1984-5 engines used a steel shim gasket at 0.018" installed thickness. For 1986-7, a composition gasket of 0.060" was used.

 

[eastwoodad]

Nick,

Well I am looking for about 9 or 9.5 to 1 with a steel headgasket. I am building this engine N/A with N20 for right now but I want the flexability to decrease compression by adding a thicker gasket for a blow-thru turbo/supercharger down the road.

As I understand it, generally, a .010 cut on the heads is 1/2 point and a .010 cut on the block is about 1/4 point of compression. Is this accurate?

Thanks,
Aaron

 

[fuzzyGN]

Nick,

As I understand it, generally, a .010 cut on the heads is 1/2 point and a .010 cut on the block is about 1/4 point of compression. Is this accurate?

Thanks,
Aaron

Not accurate. If anything it is the other way around but shaving the heads .010 doesn't yeild much at all. Decreasing the head gasket thickness or shaving the block makes much more of a difference but I still don't think .010 cut will give half a point compression. There are many on-line compression calculators that will help you out.

 

[eastwoodad]

I may have it backwards then...hmmm

 

[eastwoodad]

Here's what I found out, for anyone who cares.....

It takes close to .030 on the heads or gasket thickness to yield 1/2 point of compression. Also 1cc on the heads is roughly 1/10 point of compression. Again these are general guidelines. Hope this helps somebody!!

Aaron