Quote:While it is clear from your location details & the stroke measurement in your first post, that you are refering to the 1974 US model B210's A13 engine, it is desirable that you are aware that there are in fact two different A series A13 engines.

The B210 engine is a one year only, ... US-only, version & is the first of the tall blocks, however there is also an Asia-only version from about 1980 which is little more than a later type A12 with a 76mm bore instead of the A12's 73mm bore.

In fact, the US only A12A engine that saw life in the US model 210 car [B310] is also little more than the same A12, but with a 75mm bore, which means that there are three versions of the short stroke engine, being A12, A12A & A13.

When writing, or even reading about the A13 engine, just be aware that there are two completely different versions within the same A series family.

The morris 998 engine is RPM limited due to small valves and shared ports.

It has 65 bore and 77 stroke, which is a much more modern bore-stroke ratio than the early british engines.

The longer-stroke BMC engines e.g. 1275 made power at higher RPMs.

the stock morry engines here have about a 65mm odd bore size and a super long stroke and produce nice low end but suck balls at above 4000rpm.

This shows the torque increases matches the increase in displacement.

The effect on torque (given equal displacement) between bigger-bore/shorter-stroke and smaller-bore/longer-stroke is not much. The A13 stroke is only 10% longer than A12 stroke. In the old british cars, the stroke was twice as long (or longer) than other cars, hence it had a larger effect.

In racing, in or OEM fleet averages -- where even a small advantage is chased -- it may make a measureable and worthwhile difference.

From what I have able to find
A12 61.5 ft-lbs torque
A13 69.4 ft-lbs torque
A14 74.9 ft-lbs torque
A15 80? ft-lbs torque

ddgonzal,
Do you know the torque for the 1974 A13 vs the 1973 A12? At the same bore that would tell me the effect on torque due to the crank throw.

Yes, Nissan has done so.

Nissan offered two production A13s:
* 1974 A13 is a stroked A12 (North America market)
* 1980 A13 is a bored A12 (Asia markets)

For 1973 A12 vs 1974 A12
* A12 1171cc: 68 HP
* A13 1288cc: 75 HP

The performance was equal although though 1974 car was about 15% heavier. The torque was considerably more.

The higher peak HP was due to larger ports (small oval ports, instead of round) and enlarged intake and exhaust manifolds. Carburetor was the same size. Exhaust pipe was 1.5" on both.

Has anyone had an A12 and a similar A13 on the same dyno? I'd like to see how the additional 7mm of stroke in the A13 helps the torque numbers.

Thanks, Peter