Engine/Transmission (1998.5 - 2002) Help with Compression Issues/Calculation

[Partyat33]

My engine recently ingested a washer and I had to do a full rebuild. Not thinking too clearly I put in SO pistons in my HO engine. I have been doing a little research and the only real difference in the pistons is the bowl is approximately . 080" larger in diameter. The problem is that my compression is really low. I have a . 020 over head gasket, the block was decked . 007. Also note I went . 020 over on the pistons to allow a clean bore from the damage. I did a little math on this but don't seem have have all the variables.



A little help please.





Dennis

 

[Joseph Donnelly]

You lost roughly one point of compression, but without all the measurements, I can't be more exact.

 

[BDaugherty]

Do you mean that your compression ratio is low, or that your actual measured compression is low? What are your symptoms and/or gauge readings?

 

[Vaughn MacKenzie]

The SO pistons took you down to 16. 3:1 and the thicker gasket would put you very roughly around 15. 5 accounting for shaving the block. Why did you do a . 020 gasket, a stock one should have been fine.

 

[Partyat33]

I did the 20 over to compensate for the block shaving and the lower the compression cause I am running so much boost with the twins. Can I use a stock gasket with . 007 shaved off the block ?

 

[DAWG-1]

I would not recommend a stock gasket with an HO motor. I had approx . 007 off my head and the valves just kissed the top of the pistons. I was lucky and didnt have any bent valves. I put a . 020 gasket on and no clearance issues. I also had one of the first Piers cam. Sam