Ben,
I am sort of used to the difference in slang from American English and other types of English but what is a 'dizzy'? I am not familiar with that word as an automobile part. It seems it has to
be something that spins around so I will assume it is a crankshaft, Correct?
Personally, I am partial to short stroke/big bore motors. I had a head from an early 1200 that had a very small combustion chamber. It came on a wrecked 1971 1200 and when I put it on my A12,
it had 260 pounds of compression. That relates to 14:1 compression ratio. I built an A14 engine with an A12 crankshaft in it. I had to shave .100 inch off the top deck of the block and still,
the piston didnot reach the top of the cylinder. I calculated that the .100 less cylinder wall height would have 8:1 compression with that head. It came out correct with 140 pounds (8:1)
compression. This engine had every racing part that I could come up with inside it but stock bearing and cylinder wall clearances. At first, I used a stock intake and Carb and a tuned exhaust
headerwith 3" pipes. When i first drove it, it was pretty mild but this was only to break in the motor at fairly slow RPM's. When I put the turbo on it, it came off the line very slowly but
then it came on very strong when it got up in its torque range and the little sedan would kick ass on most vehicles that ever come up along side it. It would get 9,000 RPM's through 1st, 2nd
and 3rd but it would only pull 8100 RPM's in 4th gear, but the sedan was pushing a lot of wind resistance. I only got to drive this motor for less than 1000 miles as my exwife screwed me out
of it and it ended up going to the crusher.
Long stroke motors do not get the RPM's as fast or as many as a short stroke motor. NISMO told me they didd not sell forged racing pistons for the A15 motor and that I should build an A14
engine. They had had too many problems with the stress of high RPM A15 pistons and 6500 RPM's was as much as could ever reliably be gotten from the A15.
You are correct in assuming the A15 head would have less compression on the A14 block. For turbocharging, it would be ok but it would have less power in drivability mode than thr A14 head.
A15's were not made for power but for more torque. Hope this helps you some.
Mareo