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| Re: H89 vs gx head |
Subject: Re: H89 vs gx head
by Rallytwit on 2019/5/16 16:31:51
The GX head was designed for a motor with a 73mm bore whilst the H89 was used on a motor with a 76mm bore. For street use perhaps the smaller valves are optimal for that bore?
By the time the bores were enlarged for the A12A / A14 & A15 Nissan likely wouldn't want to spend the money for the tooling to put the larger valve seats in the head.
The Cherry N10 prep manual specifies 38/32mm valves for racing so again I suspect someone worked out what was optimal for the combo of Bore, Cam & RPM range.
Naturally this is all pure speculation on my part.
To further muddy the waters; for a brief time I used the so called H-production round port head on my car. It had been expertly ported and was set up for a Weber DGV downdraft. The motor pulled every bit as well as it did with the standard GX twin carb set up.
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