Hi,I am hopping someone can give me a bit of advice on which way to go to build an engine for my 1200 ute. Currently have an A14 stock with twin hitachis but it is getting a bit tired. I have a buch of bits to build a new engine for it but am not sure what combination I should use.

I have a GX head flow tested to 122HP, a stock A15 which ran well but was very smokey under acceleration, also have an A14 bottom end Blueprinted, balanced, mild cam, over sized pistons but had been run over fueled, (twin 45mm webbers) so deglazed the bores.

So I am not sure wether to just put the gx head on the A15, (and hope it was just valve stem seals) or else to try and fix the A14 which has had more work done to it?

Also I'm not sure if my twin hitachis will fit the GX head as the ports appear to be a bit higher.

Any info would be of great help.

Thanks Geoff.

Hi Geoff, I recommend skipping the A-series. Go with an L20B, SR20 or CA18. L18 or L20 will be less expensive than hopping up the A14/A15 and even a stocker will have about 100HP!

Everyone feels there hot engine "got a bit tired" after a while. It's normal to get used to it, no longer as exciting.

If you wish to stay with the A-series, the A15 will defintely give you more power under the curve than A14 when built the same (same cam, same piston type e.g. flat-tops). Peak power will be the same, but lower RPMs will have more power with the extra displacement.

A12 GX cylinder head has bigger ports than A14T head. So look for a GX inlet manifold to match the head.

Hi David, Thanks for the advice, will stick with the A series as ultimate HP is not the goal, also less work than converting to another engine type and my 60L gear box would not fit either.

Sounds like the A15 will have better low down power which is good for my ute.

Thanks
Geoff

pm sent

Always remember that while the 1200 & A12 GX heads have larger ports than the A14/15, it also has smaller valves than the A14/15.

The ports in the A14/15 head are not all that much smaller than the GX, so on balance the original A14/15 head is not such a bad choice in many applications.

usually,
*smoke on initial acceleration, and long deceleration = valve stems (high manifold vacum),
*smoke when driving under load or normally = rings

Go for a h89 head.

Ok, Am a bit confused now. The A15 I have has a H89 head on it, but the GX head is ported has larger valves and double valvle springs, I would have thought this was the best choice? I'm not sure if the a14T manifold can be matched to it?

Also would the mild cam from the A14 fit in the A15?

Thanks
Geoff.

Don't be confused.

* For high-revving engine (6000-7000 RPM), use the GX head with the stock dual valve springs. To rev higher reliably, you need racing dual valve springs.
* For medium revving engine say 6000 RPM max, use the stock A14/A14 (H89) head.

You can't port the A14T twin carb manifold to match. You might be able to port-match where the gasket meets, but the runners will still be smaller than the GX manifold.

With both heads, careful porting can extend the peak rev power of both heads. But it must be done correctly. Otherwise just port the bowl area and smooth out the bowl-to-seat area for increase power at the same RPMs.

For 8500 RPM, throw away the twin Hitachis and fit dual Webers/Mikunis/Dellortos. Use the GX head, pay to have professional porting, and pay to fit the larger A14 valves, and aftermarket dual-valve springs.

Remeber, there is no "best choice" there is only options. Depends on what you want.