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.
#108370, "RE: Compression Question" In response to Reply # 0
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?
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#108383, "RE: Compression Question" In response to Reply # 2
that sounds a little high, are you at really low altitude?
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#108386, "RE: Compression Question" In response to Reply # 3
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.
#108389, "RE: Compression Question" In response to Reply # 4
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?
#108406, "RE: Compression Question" In response to Reply # 5 Apr-13-08 02:50 PM by RoninEclipse2G
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?
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#108411, "RE: Compression Question" In response to Reply # 6
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?
#108412, "RE: Compression Question" In response to Reply # 7
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.
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