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Re: H89 vs gx head
No life (a.k.a. DattoMaster)
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like 1st version of FIA heads for the L series the GX heads for the A series
were too large for anything down low or midrange. Nissan rectified this for
the 2nd version of the FIA heads with smaller ports same valve sizes and
improved overall performance and even peak hp. A series werent developed
as much as the L series for competition with the AY as the last effort.
In the 80s the A15 sunnys did very well, in fact better than 1200s.

Posted on: 5/20 6:15
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Re: H89 vs gx head
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I have compared the a14 and a12 valve sizes a12 is 35mm a14 is 37mm dosnt sound like much but side by side theres quite a difference.

If the h92 being similar to a h89 made more power then the gx head then the valve size is definitely a limiting factor.

Not sure why datsun did this?

Gx head with a14 valves or even larger would make use of the larger ports

Posted on: 5/20 13:03
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Re: H89 vs gx head
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Quote:
Gx head with a14 valves or even larger would make use of the larger ports
Nissan Competition sold exactly that

This reminds me that during the 1960s/early 1970s all the manufacuters were doing the same thing. Remember the Ford Cleveland 351? The ports were "too big" so Ford Australia combined the best of the features to make the ultimate street head. Chevrolet went through similar learning curve

Posted on: 5/20 18:03
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Re: H89 vs gx head
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I agree with D, the GX head with the huge ports likely is a bit much for most A series builds that aren't a full race setup.

Posted on: 5/20 21:36
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Re: H89 vs gx head
No life (a.k.a. DattoMaster)
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the Cleveland 4v heads vs 2v is a good example DD
Seems they had to use smaller valves to get some
decent lower down airflow to suit 1170cc gx models.
Full race applications with 1300cc bigger valves etc.

What still surprises me is that the little roundport
was used in big bore 1600cc 80s Sunnys with lots of
"learnt" architectural changes from years of development
they never resembled anything from the factory.
Maybe it was cheaper to start with a round port a12 head
to get what they wanted than to waste a GX head or
buy a gx head vs a roundie.

http://www.pitroad-ts.com/tuning/Ts-cup/miya-z/a12a-2.JPG

http://www.pitroad-ts.com/tuning/Ts-cup/miya-z/miyaz-6.JPG

Posted on: 5/21 1:58
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Re: H89 vs gx head
No life (a.k.a. DattoMaster)
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Posted on: 5/21 2:23
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Re: H89 vs gx head
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Hi D

Is that a round port with a raised roof and built up floor?

Looks like a nice port.

Are the valve guides cut down?

Posted on: 5/21 11:50
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Re: H89 vs gx head
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In the not too distant future I'm hoping to try a few different standard heads on a 'control' engine in a car on a dyno to see what figures each one makes.

I'm also hoping to port a round port using the info from the book 'performance 4 stroke tuning' by A. Graham Bell to see how it goes vs standard.

I don't know of any places near me to test them on a flow bench unfortunately, would be much better I'm guessing, less variables and whatnot.

Surprised after all these years that noone has done it before and posted the results in tech wiki.

Posted on: 5/23 9:54
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Re: H89 vs gx head
No life (a.k.a. DattoMaster)
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Yes to all A12dato and supposedly 1 or 2 mm thinner stemmed valves


They might show the porting of these beast but most of it was closely
guided secret hence no info available to most of the world. It keeps
their business going but also few can do this kind of specialty work
on heads and the camshaft grinds used to make them work not disclosed.

I would like to see a square inlet port like on chevs and some other
aftermarket heads not just round port units. The inlet manifold plenum
would be nice to adapt to an A series since they are a copy of the
cosworth units used in formula for and other formula classes.
Itbs are good but they still need a good plenum to hold the pulses
and frequencies to keep torque flat rather than all over the place
as is common with itbs just open to open air.

Posted on: 5/23 11:35
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Re: H89 vs gx head
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A long time ago... in a galaxy far far away

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Posted on: 5/23 11:42
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