Hmm does anyone know what the difference is in the F20C US and F20B Japan, im guessing its compression or its the SIR style motor.

 

The JDM engines have slightly higher compression and slightly higher horsepower due to the use of a thinner head gasket.

 

Just to add, they did this for the NA cars because on average we have a lower octane fuel available to us.

P.S. As one of my teachers would always say, Fans have motors, Cars have engines

 

Are you for certain the higher compression in the Japan spec engine is from the use of a thinner head gasket? I know on the Japan spec ITR engine they use different shaped pistons to achieve higher compression. I just want to know if you are positive about that because that would be great for those of us who want a cheap and reliable way to up the compression rather than having to worry about stock pistons smacking into the valves on an overrun.

 

I don't think anyone knows for sure exactly what the differences are, and if they do...they're keeping quiet. The JDM headgasket is certainly thinner, but it's not the only thing that adds to the higher compression. This has been looked at as a possible pony maker in the past, do a search on it.

 

The head gasket is the difference between the JDM 11:7:1 versus our 11:1:1 compression.

 

"having to worry about stock pistons smacking into the valves on an overrun"

you will always have to worry about this... the F20C is an interference design.