Q1 what would give best performance for a mild streeter

Q2 will A12 GX head bolt straight on to A1500 block

yes no mabee,
yes it will bolt on, performance depends on mods to either head or engine..

you would have to be very keen to get a gx head for a streeter considering they cost so much and are difficult to find. an a15 head has slightly smaller ports than a gx, but larger valves. personally i would go with the a15 head.

For a mild streeter as you specified, the A15 head will be better than A12GX. Use the GX head for a high-RPM engine. The GX ports are considerably bigger.

Yes, the GX head bolts on the A15 but won't work correctly. It will burn up the rockers unless you modify the head for oiling passage.

Ummmm, not quite.

As stated, the A15 head has smaller ports than the GX, but not all that much smaller & they are well matched to the engine for most street & a great many race applications.

The upside is that the A15 has larger valves & it usually comes with the rest of the A15 engine which saves a great deal of hunting around.

There are two A12 GX heads [actually, .... three]

The first is for the 1200 engine & it is drilled for the rocker oiling system that the 1200 engine used. The later engines fed rocker oil to the recess in the block that is also used for one of the center head bolts.
You can use the early head on the later block without any problems.

The second head was for the A12T [120Y GX] & it used the same casting as the 1200 but was not drilled for the earlier engines rocker oiling system.
This head should NOT be used on the earlier engine unless it is suitably modified to get oil to the rockers but will be fine on an A15, or any of the rear distributor engines. [1974 onward].

The third head was also for the A12T & is dimentionally interchangeable but has a slightly revised casting that removes a small boss on the distributor side that was previously used when drilling was done for rocker oiling in the 1200 head.
Naturally, this too will fit & work on the A15 engine but should not be used on the earlier engine without suitable modification.

To all practical intents & purposes, these last two are the same head.

Use the A15 head & you will not suffer any degradation in performance against the GX head & your wallet will be eternally gratefull

There was a 120Y GX?

I forgot about the early E10 Cherry A12T, it would have the same oiling passage as the A12GX.

Sunny B210 GX was trim only and didn't signify the engine type used (Single or Twin carb engines were fitted to B210 GX). Nissan only called the B210 twin carb engine 'A12T', never as 'A12 GX'.

If you can get a GX head, use it. The valve seats have enough material in them to be opened up to take the larger A14/A15 valves. So why wouldn't you? They do still pop up from time to time. A bloke I knows brother bought three heads for $200, and one of them was a GX! I picked one up for $20, but it has a small crack in it. Which is odd, because when I had it hardness tested the guy said it was harder than a brand new falcon head. I would have thought if it'd been cooked it would have gone soft...... (Unless I cooked it?)

Quote:

For the "mild streeter" that the original poster asked about :

1. Cost. It will cost more to acquire the head, then more to get the manifold and carbs, then even more to add larger valves

2. Driveability. I prefer to keep the engine under 5000 RPM it lasts a long time. This is where the A15 head is good. Continually revving over that (where the GX head has an advantage) the rings in my engines have not lasted very long, like only two years.

Quote:
My use of the name "120Y GX" was intended more as a description than as a model name for simplicity's sake.

The car itself would be a Sunny GX but I am not aware of any other factory model name that would distinguish it from the earlier 1200 GX which was also a Sunny.

None the less, I was refering to the A12T engine which I mentioned in the post with the 120Y GX name as a supporting descriptor.

This is the model that I refered to & this particular example had the A12T engine.
[Click on image for larger view.]














Quote:I would agree with every word of this 100%

Shortened ring life in high reving engines is a fact that was brought home to me many many years ago which is one reason for my obsession for the overdrive auto trans & higher geared differential for my 1200 coupe.
I dearly love the 1200 engine in that car, but I love the extra 1/2" stroke of the A15 with its resultant increase in torque even more.

That should keep the revs down at highway cruise speeds with the resultant increse in engine life.
Smoooooooooth cruisin, now that's what I call motoring.

Damn, it was ugly.