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Difference between H89 and H75 heads?
Quite a regular
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2009/11/4 12:43
From Byford
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Hi all.
Need some info on the differences between an A14 H89 head and H75?

any help appreciated

Posted on: 2010/10/27 12:52
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Re: Difference between H89 and H75 heads?
No life (a.k.a. DattoMaster)
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check out the <----------- Tech section...

Posted on: 2010/10/27 12:56
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Re: Difference between H89 and H75 heads?
No life (a.k.a. DattoMaster)
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From East New Britain, Papua New Guinea
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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.

Posted on: 2010/10/27 14:18
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Re: Difference between H89 and H75 heads?
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From Hawaii, USA
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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
Open in new window

Attach file:



jpg  H89 combustion face.jpg (61.73 KB)
174_5cdbab3523af8.jpg 640X480 px

jpg  H89 closed combustion chambers.jpg (53.68 KB)
174_5cdbab4fc73a0.jpg 640X480 px

jpg  H89 heart-shaped combustion chambers.jpg (58.83 KB)
174_5cdbab58e0dad.jpg 640X480 px

Posted on: 5/15 7:04
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Re: Difference between H89 and H75 heads?
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... continued

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

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Attach file:



jpg  H89 primary casting mark.jpg (71.84 KB)
174_5cdbad0e3023a.jpg 640X480 px

jpg  H89 secondary casting mark '019'.jpg (74.41 KB)
174_5cdbad160c3ec.jpg 640X480 px

Posted on: 5/15 7:11
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Re: Difference between H89 and H75 heads?
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... continued

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

Attach file:



jpg  H89 front face -- 5-bolt pattern.jpg (50.06 KB)
174_5cdbb01c8680b.jpg 640X480 px

Posted on: 5/15 7:22
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Re: Difference between H89 and H75 heads?
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... continued

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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Attach file:



jpg  H89 port face - regular size ovals port & small water passages.jpg (64.28 KB)
174_5cdbb23c4a79f.jpg 640X480 px

Posted on: 5/15 7:31
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