Compression Ratio??

[G-U-NOT]

Ok, so I did a compression test on my 3.1 today because I was curious to see what its at now that I rebuilt the engine with thinner head gaskets, plus it looed like someone already had the heads milled down!!
All cylinders were between 175 psi and 180 psi....
Does anyone know what that is in ratio form??

[bszopi]

There is no way to convert dynamic compression to static compression.

[G-U-NOT]

So how do I figure out what the ratio is then??

[bszopi]

You'd have to measure everything. Most of it could use stock values, but since you think the heads have been milled, you'd have to actually CC them.

[G-U-NOT]

Well Im not positive about the heads... thats just what they looked like when I had them off to sandblasted them!

Lets just say that the combustion cambers are still the factory size....
I used head gaskets from a 3.1L Camaro, which are .020" thinner than my stock ones! What would my CR be then??

[bszopi]

http://60degreev6.com/CR_Calculator

[ForcedFirebird]

Well Im not positive about the heads... thats just what they looked like when I had them off to sandblasted them!

Lets just say that the combustion cambers are still the factory size....
I used head gaskets from a 3.1L Camaro, which are .020" thinner than my stock ones! What would my CR be then??

You are crazy for using the RWD gaskets. The pistons protrude .020" out of the block and the RWD gaskets are only .040" thick. This gives you a quanch of a mere .020" and probably will have piston contact in higher RPM's. Ask SuperDave.

[G-U-NOT]

Nah its fine.
I've aready had it up to 5k and no problems so far!!
Runs good, sounds good....

[ForcedFirebird]

Nah its fine.
I've aready had it up to 5k and no problems so far!!
Runs good, sounds good....

You won't know until you take it apart, or chip a pston/bend a valve.

http://60degreev6.com/forum/showthread.php?t=38702&highlight=3500+piston+contact

[johnnymossville]

Are you running a 3.1 or a 3100? If you are running a 3.1 and using the iron head gaskets your CR should be around 9.37:1. You may not have valve to piston clearance problems, but like ForcedFirebird says you really won't know until you take it apart or over rev it and something very bad happens. I agree with Forced also on the fact that your quench values will be less than ideal.

[Superdave]

Gen2 pistons don't pop out of the block, the .040" Camaro gaskets are fine... esp with a stock cam.


All heads have that milled look.. because they were surfaced at the factory

[ForcedFirebird]

Gen2 pistons don't pop out of the block, the .040" Camaro gaskets are fine... esp with a stock cam.


All heads have that milled look.. because they were surfaced at the factory

DOH, wasn't thinking he had a Gen2 :P

[tetnus shot racing]

I'd like to add a question to this post... I have the Gen 2 3.1 also. Is the amount of dish in the stock piston necessary? I'm looking to increase compression, and that much of a dish seems foolish. My engine as of right now is completely stock, and I'm doing a complete overhaul... I haven't checked the "factory" or "stock" valve to piston clearance, but I was hoping to use flat top pistons with valve reliefs for clearance. I'm sure that the change would lead to substantial compression increase, right? Too much compression for alum heads? Does any of the hi-perf piston manufacturers already make something for this?

Any help would be appreciated. I've been trying to figure these questions out for a while...

[Superdave]

I'd like to add a question to this post... I have the Gen 2 3.1 also. Is the amount of dish in the stock piston necessary? I'm looking to increase compression, and that much of a dish seems foolish. My engine as of right now is completely stock, and I'm doing a complete overhaul... I haven't checked the "factory" or "stock" valve to piston clearance, but I was hoping to use flat top pistons with valve reliefs for clearance. I'm sure that the change would lead to substantial compression increase, right? Too much compression for alum heads? Does any of the hi-perf piston manufacturers already make something for this?

Any help would be appreciated. I've been trying to figure these questions out for a while...

you can use the 3.1 Camaro pistons, they're basically flat tops (12cc dish). they bring the compression up to 11:1

[torq455]

http://60degreev6.com/CR_Calculator