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Re: Difference between H89 and H75 heads?

Subject: Re: Difference between H89 and H75 heads?
by ddgonzal on 2019/5/15 7:04:07

This is a good question and we now have more information. I found some more photos to illustrate the differences

H75: Open combustion chamber
H89: Closed combustion chamber

Open (full-circle) combustion chamber is superior for lower NOx emisssions

Closed is superior for power, and superior for fuel economy. It is not due to higher compression ratio, it is due to quench and requires flat-top pistons to get the optimum power. In the JDM B310 H89 model they used dished pistons to lower the compression ratio (to reduce NOx emissions), however they are offset-dish which allowed some quench

H75 open chamber
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