Currently Im running 13:1 compression I want to up my nitrous to a 30hp shot. Rather than changing out the piston can I go to thicker head gasket to bring it down? or do you think running 114 octane would be enough or maybe higher? Im at 20 right now and its workin really good. Would 12:1 be safer and is there a way figure what the compression is if I go to a thicker gasket?

 

There are formulas to figure out compression ratios, even some online calculators to help like this one. But you have to know a few measurements such as the Head CC, deck height/piston dome CC.

So the easy way is to call your parts supplier. Another issue you may have is that since you piston is from HPR but your head is KMS, the head CC measurements may have changed if KMS changed the combustion dome. If KMS did remove material from the combustion dome, then you would be running a lower compression ratio then you think (the piston is compressing the same amount of fuel and air into a larger area = lower compression ratio).

The simple answer is yes, a thicker gasket would lower your compression ratio. It is my understanding that HPR only makes one 105.5 bore piston, but with gasket changes you can go from 13:1 to 11:1.

 

Scott's right. I have a 12.1 piston and HPR gave me a gasket to reduce it to 11:1. I'm sure he can set you up with whatever you need.

 

I dont think he did anything to the dome but Im going to call to be sure. Thanks for the link, very cool.

 

Stock base gaskets are .020 or 1/2 mm

On a stock bore for every extra gasket added - compression will go down .5
On a 105.5 bore for every extra gasket added - compression will go down .6