To 1200/110 Masters,

Could anyone tell me the difference between GX heads and regular heads?? also, I have seen oval intake ports and round intake ports...no clue why and what year they changed...need your knowledge please...

Thanks,
Cel

GX heads have oval intake ports, some non GX heads do too. GX heads should have small water ports under the ports.
GX heads use larger valves
the best way to tell for sure is to check the casting number in the valve train area.
A12 should have "180" or "H10"
A12 GX should have "H23"
A13 should have "H62"
A14 could have several different ones, such as "H72", "H74", "H98" depending upon year and emission control equipment.
the casting number will be the first 3 digits of the last half of the part number, as all cylinder haed part numbers begin with the same 5 digits

rgrinder,

Thanks for the info...you D Man!

Thanks,
Cel

just to add
GX heads also have double valve springs in them

Re: "A12 should have '180' or 'H10'"

Any chance the '180' refers to the pre-7/73 1200 head and the "H10" to the post-7/73 head???????????????????

I just came across a factory reconditioned A12 short block (serial number A12 033455) and will need to find a head for it. The dizzy is up front so I assuming it's a pre-7/73 head. I have don't know how to tell one head from the other visually, so when I go to scour the salvages yards, should I look for the '180'??

Thanks!

To add just a bit, "GX" is the twin-carb engine. The Nissan Competition cylinder heads were often called "GX" heads as well.

I believe the A12GX heads had standard size Intake valves (29mm). These same valves were used in the later round-port A12s and A13s. Not sure what size the exhausts were.

The A14/A15 stock heads have the largest valves outside of competition heads, the GX valves were not bigger.

See our tech section article A-type Cylinder Heads.

rgrinder, thanks for the info. I'll add it to the A-type Cylinder Heads article.

I'm sure there are some mistakes or missing info in the article, let me know if you have comments on it.

Been a long day at the end of a long week. Did more digging (which, admittedly, I should have done first) and found the answer to the question.

thanks!

The 1200GX cylinder head does not always have a casting number, & both the inlet & exhaust are the same size as regular 1200's, ie, 35mm inlets & 29mm exhausts.
GX valves had a diferent part number, but were domentionally identical, so it must have been the material they were made from that was diferent.
I bought my head new as a service replacement part & it has no casting number.

The genuine 1200 head has the extra drillings for the earlier rocker oiling passages. Early 120Y [A12] GX heads were the same castings, however, they did not drill the boss that was provided in the casting as these engines used the newer rocker oiling passages in the block.

I saw a pic on this site of a round port A12 head with the high compression heart shaped combustion chambers and there was no further discussion or explanation. I recently pulled my head off my A12 and found this type of head and I thought that A12s had round 360 degree chambers??