I am trying to get my compression down, not for boost but to run some heads I have with too small of a cc. The stock MLS is .054 and I need to get my CR down from 11.3 with these heads, to around 10.9. I wanted to see if there was a thicker gasket what it would be and if having valve reliefs cut into my flat top pistons would do that for me. I thought FI guys would know best. My 408 I just ordered the right pistons, this motor I changed plans after parts were ordered.

 

Sometimes reducing your compression will bump you out of the optimum quench zone. Having good quench will reduce the engines tendency to detonate, maybe more so than lowering the compression. Find out what your quench is with a stock gasket.

 

How would I do that? The heads I have are a 62 cc chamber Dart 225 and with the flat top pistons it would be like 11.3 with the .054 compressed MLS. This is way over my head so what ever info you need I will give to the best of my ability. I have found that GM makes a 5 layer and Fel Pro makes a 6 layer but I can't find any compressed thickness of these. Also if the bore of my block is 4.00 and the head gaskets are 4.030 what affect would that have?

 

How much are your pistons coming out of the cylinder?

Take that number and subtract it from your gasket thickness for your quench.

If your pistons are in the hole you would add that amount to your gasket thickness to determine your quench value.

Of course if your engine would be zero decked then your compressed gasket thickness would be the quench.

 

Ok, well the motor will have to be assembled. Is that something that can be changed? From what I was playing with I would need the gasket to be .060 thick, have -2 cc dish in pistons, and the piston come out .018 to yeild a CR of 10.9. Does that sound right? Would having 2 cc of valve relief cut into the piston be the same as a 2 cc dish? Would getting 2 cc dish of valve clearence be a problem on stock LS2 pistons? Thanks for the help guys. If that will work would my quench be acceptable at .042?

 

Depending on your camshaft overlap the 11.3 may be fine. I have 11.5 and run 31* timing on 93.

 

Who did your tuning because I am also in Alabama? 50, -1, -79 Is what was on the email attachment Pat G sent me for my overlap. He said that 11.3 would be too much for the weight of my truck and the intended purpose of a DD and a tow vehicle

 

I do my own tuning. But for a true tow vehicle and not being able to tune it yourself as issues arise then no, I wouldn't try that much compression.

 

Retarding the cam will lower the DCR which will help. You don't want to retard the cam too much if you are looking for low end towing power.

 

I want as much low end power as possible