I don't claim to be an expert but my a15 revs to 8000 rpm very easy every race meeting. It's balanced though

I had no idea my simple (minded) comments would raise such heated debate!
By the way jb1200, good job on those parts. To answer your original question again, it sounds like you made the right choice. Looking forward to seeing this hotrod sometime!

This is getting very interesting....Love it! This motor I built is from a 310GX(us version so this was badged as 310GX and was front wheel drive)and really all that was retained was the short block. The head is a true GX head from an unknown origin, meaning I got it while swapping parts and can't figure out what it really is other than it has dual valve springs and oval ports, water jacket ,and dual SU manifold and carbs came with it. Also have GX header(I was told anyhow by a few 1200 nuts that I showed it too at the time)It is shorter than the headers that dimlight65 posted pics of.There is a head pipe that came with it with a three bolt flange and two to one collector.Btw..when I was comparing motor parts to the a14 it seems like the rods were the same but the pistons had the wrist pins in different places to achieve the shorter length with the longer stroke. Actually this is fitted into the a14 block as it was in better shape after sitting around waiting for me to put the parts together. Both blocks measured the same deck height. A 1200 racer told me he used the A12A since it pulled harder out of the corners so this was my thinking in using the A15. Sorry for the long post but I've been the lone 1200 here for too long and it gets lonely

excuse me

where can I get some of these adjustable cam gears you mentioned ???

Ah you guys aren't thinking this out straight.

First of all, the A15 stroke is very short compared to other hi-revving engines.

Secondly, the bore-to-stroke ratio is more interesting in its effects.

Lastly, as mentioned, there is no replacement for displacement.

From the half-logic I keep hearing one might begin to think the A10 is the best "peformance" a-motor -- since it has the shortest stroke!

One of the reasons the A14 is favored by racers is because of class rules. Which doesn't apply to street cars.

The A15 head has the same size ports as the A12 GX head. The biggest effect on feel is the torque comes on sooner due to the bigger CCs, then levels off sooner as it's flowing more air than an A14. it's partly psychological and partly due to the factory tune -- unless anyone's taken objective measurements (for example, timed both 0-100 km) this is all just guessing as to whether a stock A14 is "faster" than a stock A15.

Getting adjustable cam gears and advancing [edit: retarding] it a little should perk an A15 up in the high-rpm section (has anyone tried this?) along with advancing the dizzy timing and richening the jets a little. The late 70s motors generally were a little weaker in those areas to gain lower emissions. Disconecting the EGR valve and air pump should also help performance.

I totally agree. 5mm is significant. The rod length is same for A15 as A14. The rod to stroke ratio is similar to Ford's 302 engine in the A15. Nobody would consider that to be a non-revver, but the bore to stroke ratio is much smaller in the A15. I would expect that to have a compound effect. Who has got a A15 with dual carbs and big cam and can tell us what it's like to drive?

Without researching all the physics behind it, I reckon 5mm extra stroke will make a significant difference. I know it doesn't sound like much, but picture the thing turning 50 times every second (that's only 3000rpm) and you'll start to get an idea of the increased inertia caused by moving the crank journal and rod big end 5mm frurther away from the crank centreline. Piston speeds are increased dramatically travelling 10mm further for each stroke (ie 20mm further for each crankshaft cycle), and rod angularity is increased placing greater loads on it and the piston skirt. Although this may be offset by using a longer rod, I suspect the A15 rod is more than likely shorter to allow for the increased stroke and to improve torque. If my tenuous grasp of physics is correct, shorter rods will increase the max piston speed as well.

youd have to admit theres a big diffence in engine charachteristic between the a-12 and a-15, Yes?

well i see the a-14 as the inbetweener cause the a-12 will rev like all hell and go if you keep the revs up there, but down low its a slug

The a-15 exactly the opposite it launches from low revs and never really reaches high revs

the a-14 gives a happy medium where you can use torque down low but also let it scream

it obviously depends on how the engine is built (cam choosen ect. ect.) but in general thats the way i look at it.

I know we all say that the A-15 doesn't rev like the A-14, but really, does a 5mm longer stroke make THAT much difference? Also, is 100cc really that much more displacement in the "no replacement" argument? Sorry to be so pessimistic about the "conventional wisdom." I'm just not sure it really is that big a deal. I could be wrong though.

i reckon it strongly depends on the intended use of the car as a non reving a-15 would be nowhere near as good in a race application but for a road car and engine life an a-15 is probably better because you dont have to rev the crap out of it to get somewhere quickly