OK,Here are some pic's of a few heads that are being presented as GX heads. The one's on the right are mine, one is a standard A12 head, nothing special, the other with the dual sidedraft manifold is an H72 A14 head.

The one's on the left (bottom of image) are the one's for sale. The guy isn't sure as he bought these in a lot purchase of A series engines for a Morris minor project. He was kind enough to bring to Seattle up from Oregon the set of 13" mag I'd bought off his neighbor (small world).

Can you guys identify these heads so he really know's what he has, I think he'd really appreciate it.

Comp head left, standard A12 right









comp/GX head left, H72 w/dual manifold right









Sorry for the sideways photos, they're oriented properly in photobucket, not sure why they appear this way. Both his head have round intake ports, valves are same diameter as my standard A12 head, both Intake & Exhaust ports were the same as well. Both of his had heart shaped chambers. I thought GX heads had oval ports only. No cast numbers on the heads at all & no bump up of the intake runner in the casting either.

what are they?

Thanks, Evan

they dont appear to be a gx head.

If they are round port they are definately not gx.

they are all a12 heads by the looks of it as they are using the a12 stud pattern.

The presence of the additional oil hole & round ports on US heads tells me that all three first saw life bolted to a standard Datsun 1200 engine. [If it had been Australia, they might also have been A10 [1000] heads.]

None of these three heads are either GX, or factory Datsport/Nismo competition heads.

These are not from the later [1974 onward] A12's but specifically from the 1200 engine.
This manifold stud pattern was used on all round port heads from the A10, 1200 & A12 engines.

What he has there is known as the H production cylinder head. These were a standard A12 head with the heart shaped combustion chamber. They were listed as a legal alternate for SCCA H Production race cars. They were also used on some Improved Touring cars but most prepped heads got the bigger valves so that made them illegal for IT. Get the valve measurements, likely 37mm Int and 30mm Ex. Also check the stamping number it's an oddball, something like H53 or something weird like that. I used to have an old motorsports catalog with the number but couldn't find it.

As for how much they are worth, the trick is finding someone in need of one, I was using one about 3 years ago before I went back to the GX set up, I sold mine for $250. Rob Walker out of San Diego ran a 1200 in SCCA H Prod but I haven't seen his name in the results for a while. The vintage guys all go with race heads. Either way it's a neat part for USA drivers as you get a head that flows well and doesn't have the brake master interference problem.

Tom

Quote:Most interesting.
Identical to the typical A12 head except it has heart-shaped combustion chambers.
Why was this a "legal alternative"?
Did some Datsun 1200s come with this head?


As everyone has pointed out, none of them are GX heads, which have large oval ports. The A14 head there will have smaller oval ports than a GX.
GX ports

Thanks for all the input, I'm sure the owner (Dave) will be plleased to know this much.

I looked for stamping #'s & there were none on the head at all. I did mic the valves & they were identical to my stock valve diameters - I didn't write them down but Tom's right, they were approx. 29mm & 37mm.

The heart shaped chambers were the only difference I could find. The intake ports were the same size as my stock head, I'd of assumed they'd of been larger but were not.

Out of curiosity, how much difference would a head like this make over a stock head or a H72 oval port head on an A12 block, any ideas?


Evan

Valves:
A12: 35 mm & 29 mm (including GX engines)
A14: 37 mm & 30 mm (both stock and "competition" heads)


We discussed the compression ratio previously. I think the figure was 3% (going from 9:1 to 10:1), if carb and distributor curve are modified to match Premium gasoline. That means instead of 69 hp, you might get 71 hp. Definite gain, worthwhile advantage for racing.

The Nissan Motorsports catalog said this head came on some A12's in the USA, therefore SCCA deemed it a legal alternate. Peter Zekert might know or a guy named Ron Johnson who used to work for motorsports. I seem to recall numbers on the head in an oddball location......look carefully.
As for power if it has the race valves and flow work I would imagine if you put on a 32/36 weber it'd be worth about 8-10HP maybe a little more. I seem to recall ITC 1200's using this head rated at around 85HP. Sooooo if you put on a single side draught weber (clears brake master on LHD cars) a hotter cam and that head you could probably get to 95-100 at the crank? Not bad for an A12. Full race A12's make 140 at the crank and H Prod cars were something like 110-115.

Tom