Hey guys i have a quick question for you all. I just rebuilt my motor with wiseco 8.8:1 pistons. THe car runs great except for the fact that i dont have the money for a turbo yet. My problem is I did a compression check today and the freakin compression is a strong 235 in each cylinder. This seems extremely high considering the stock compression is between 170-225. I am not the sharpest tool in the shed but i would think that the compression would be much less than 235. I have heard that thicker head gaskets can force the motor to run higher compressions and i am running a 3 layer cometic gasket but 235 seem rediculous. what should my compression be and is this compression safe to boost? Any input would be greatly appreciated.

Originally posted by seancrosariol
I have heard that thicker head gaskets can force the motor to run higher compressions

False. A thicker head gasket will lower compression by adding volume to the top of the cylinder.

As far as where you should be, I don't know, maybe someone can chime in on that one. When you installed the pistons, what shape did the surface have? Were they slightly dished, flat, or slightly popped up?

Yeah sorry that makes sense about the head gasket. The wesico pistons were slightly dished.

that sounds a little high, are you at really low altitude?

Piston rings gapped incorrectly? Maybe check and see if oil is getting into the cylinder, as that would cause a false high reading. Other than that just make sure to do the test with the car warmed up, and with the throttle open.

there is definetly no oil getting past the rings. I have been religiously pulling the plugs and inspecting them. i live at the beach so i am at sea level but i find it hard to believe that the compression would be this high due to sea level altitude. THe only thing that i can think of is i have an obx intake manifold coupled with a head that is extrude honed head, more aggressive cams, and larger valves. THis is the only explanation i can think of that the cams and valves are packing the cylinders full of air. If i am wrong or this sounds way off base please tell me. Also could adjusting the timing reduce the compression?

that could explain the extra 10-15psi, still seems a touch high but you've got a pretty built engine there that's gonna be flowing a ton of air.

Edit: how much did the extrude honing cost?

about 600 bucks but well worth every penny. cna i just switch the cams out for a different grind to lower the compression or is this motor safe to boost the way it is?

Compressions tests measure the seal of a cylinder. Static compression will influence the final number, butt eh number is in no way indicative of static compression.

Your numbers say you've got a healthy, well sealed motor. Do whatever you want with it.