The A12GX engine manifold has extra-large inlet ports, taller and wider than the A14 oval ports




The A12 engine has round ports, same width as A14, but the A14 are taller (oval shape)


This is what happens when you use the GX manifold on an A12 engine:

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  port mismatch.jpg (53.93 KB)


  round port.jpg (125.63 KB)

Even with that severe port mismatch, the engine will start and run. But considering a) the price you can sell the GX manifold for and b) the performance loss you'll have, it makes sense to not use this combination


Option 1: upgrade the head:
* obtain a real A12GX head, or an A12T head from a B210 modified to suit
or
* A14/A15 oval port head can be port-matched to the GX manifold. It can't be ported out to the match the GX head, but the entrance to the ports can be enlarged to meet the GX gasket, making a smooth transition between the little A14 ovals and the monster GX oval





Option 2: sell the GX manifold and get an A12 round-port manifold for twin SU carburetors, such as Lynx D1000 or Lynx M042 or M137. Yes, these are a bit rare these days, but no more rare than a GX manifold

But say you don't care about the performance. Yes, the twin carbs will look cool and sound cool. So maybe you have a GX manifold and want to run it on your stock A12

How well does it run? Dunno, but a couple of club members reported that the engine does run. If you try this, let us know how well it runs, particularly at slow cruising speeds (in city traffic, for example) and at high speeds. Are there any unusual flat spots or bucking/hesitation at certain RPMs? Give us a report