Building the best engine? (12A Shortblock)
 

Okay, so I know thet pretty much the 12A shortblock over the 1st gen span has been the same... The differences I know of are:

Series 1 engines don't have some internal passages that the Series 2 and 3 engines do because they lacked the ACV. But the Series 1's have provisitions for the Thermal Reactor that the Series 2 and 3's don't. (What those provisitions are, I don't know. Are they passages or different mounting bolt locations or something?)

Series 2 and 3 engines have the lip around the spark plug hole, so you need a socket that fits in there.

Somewhere along the way, the rotor weight was changed, along with the flywheel weight. Which year had the lowest rotating mass???

Are there any other changes that were made?

Which parts would make the best performing stock engine?

I know for a fact that the SA engines had two little exhaust ports below the main ones, that aren't on the later models...

Jeff

83-5 engines have the lightest rotors, by a good bit.

http://www.mazdatrix.com/faq/rotorwgt.htm

Series 1 rear side housings have no provision for a oil pressure sender. However they have a thicker, stronger casting...especially around the oil filter mount area.

UK or Jap spec 81-85/6 (we had 1st gens in early 86 still) 12a's also have bigger ports than the US ones ... they give around 115 hp as standard with the "cooker" type exhaust converter

As for flywheels, 81-82's have the lightest at 23 pounds. Lucky for me:)

79-80 are 30 pounds, 83-85 are 26.

http://www.mazdatrix.com/faq/flywheel.htm

Euro spec 1st gens were close to the UK ones. 105hp for 1979-80, and 115hp for the later ones (81-85) In Germany that was 113hp, though. Rotors were lighter on the 113/115 models. Oilpressure sender was added.
Exhaust was, however, the same. We never got cats on the 1st gen for exemple. If I'm not mistaken even the early 2nd gens didn't come with cats overhere. And we never get the 150hp convertible (verts were always Turbo overhere), but that's not 12A related :-)
I think using the later 12A components, would make a better motor. You'd have lower rotating mass, and an easy way to use a oil pressure sender.

Re: Building the best engine? (12A Shortblock)
 

not sure exactly what you're asking here ... but to me, it would seem that if you get an '83-'85 engine, then have it blueprinted, balanced (with a performance flywheel) and carefully built (maybe some really mild porting) and very calculated mods (the oil system) ... then you should have what i think you're asking for.