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and finally the feature listed above, wet vs dry intake manifold

* H75: dry manifold, with no water passages in the cylinder head manifold face
* H89: wet manifold, with small water passage below intake ports

Wet design allows use of disconnected exhaust manifold. Carb hot spot provided by water temp, instead of by exhaust gas hitting the bottom of the intake. Either system works but it means the intake manifold is different, and needs a matching exhaust manifold

H75 manifold face. No water passages (for dry-type manifold)

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  H89 port face - regular size ovals port & small water passages.jpg (64.28 KB)

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Front head face
* H75: anyone know? Have a photo?
* H89: 5-bolt allows use of high- or low-mount right-side alternator

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  H89 front face -- 5-bolt pattern.jpg (50.06 KB)

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Of course the front casting marks:
* "H75"
* "H89"
The secondary casting mark (rear mark) varies

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  H89 primary casting mark.jpg (71.84 KB)


  H89 secondary casting mark '019'.jpg (74.41 KB)

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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  H89 combustion face.jpg (61.73 KB)


  H89 closed combustion chambers.jpg (53.68 KB)


  H89 heart-shaped combustion chambers.jpg (58.83 KB)

Mostly the combustion chamber CCs and the water cooling holes to the manifolds, I think H75's are a dry manifold head?

Apart from that once you machine them down past the excess alloy surrounding the combustion chamber, they perform just as well as a H89, I think so anyway.

check out the <----------- Tech section...

Hi all.
Need some info on the differences between an A14 H89 head and H75?

any help appreciated