I was wanting to know if I would have to have my cylinder head combustion chamber bored from 85mm to 86mm to match my block? I talked to two shops and they said it has nothing to do with anything and would be fine to use as is. This doesnt sound right to me, but im still learning. Can any of you techs help me out and steer me in the right direction. Set up is f23 short block with rsx type s pistons and the f22b dohc head.

 

its fine as is.

 

Are you talking about the small flat area near the very edge of the combustion chamber? So the 'pocket' of the combustion chamber would be the exact same diameter as the cylinder?

 

yes, so the edges line up.

 

You don't want to do that. They are there for a reason. That is called a quench area. The surface of the cylinder head runs very close to the top of the piston. This presents a lot of surface area to metal that is relatively cooler than the combustion gases. They ensure that the engine doesn't detonate by cooling the gases near the edges of the combustion chamber as the flame front compresses the unburnt fuel ahead of it. If anything, you would want to increase that quench area to try to curb detonation. One thing engine manufacturers did when emissions controls started coming around was to reduce this quench area because a lot of quench area tends to increase unburnt hydrocarbons coming from the exhaust. Which was good for emission but bad for performance.

 

Thanks for the clarification, so 1mm should be fine, but if in the future I wanted to go with a 90mm piston, do you any good shops that could modify the combustion chamber

 

If you go with larger pistons I still would not modify it, the increase in quench might be beneficial.