A15 cranks are forged.

If there exists a cast A-series crank, maybe someone can post a photo of it. An unmodified crank will show a thin cast line or a thick forging line.

yes i did read that artical all i am asking is how much tourque will i be loosing going back to the a14 or will i gane some back through balencing the crank

Good question - who has the peak torque@rpm figures in front of them. A14 and A15 - I thought I had this info...but don't.

I vaugely remember that the difference in torque between and A14 & A15 was fairly minimal...don't seem to have the numbers anymore.

A torque plot of each would be even nicer.

Quote:Sure, all things being equal it would be 7% or less ... so if you don't want the best, using an A14 won't be too far off.

The torque may not be much different, but the torque curve would be significant adding power throughout the low and mid ranges. Some A14s have less power, some more than other A14s due to cam changes, and I expect the cams are different with the A15s. Build 'em up the same and see what you get.

Well rb20, I can see you haven't got the answer you are looking for. Thats mainly because its impossible to answer unless you consider EVERY modification, gear ratio, etc.

The extra 6.5% stroke of the A15 will give you approximately 6.5% extra torque throughout the rev range until you run into breathing restrictions with the head and induction. With standard ports and carbs, the A15 will provide more torque until say 4,000 rpm. But due to the extra capacity of the A15, it will become short on breath at a lower rpm than an A14 will. Hence, an A14 will rev harder. Since power is a measure of both torque and rpm, it can be predicted by the flow properties of the head and induction setup. You may have noticed, a lot of american Chev/ford/dodge aftermarket manufacturers rate their products in HP. Eg, you can buy a set of heads which are stated to flow 600HP, not 250cfm.

If you look at the specs of the stock motors, you will notice they are basically the same power rating. I'm pretty sure the A14 just pipped the A15. This is with the same induction system and head ports, valve sizes etc. I think the difference (although small) is due to a cam change. But thats just a guess. Any performance datsun needs a cam change, a lightened flywheel and tidy-up job done on the intake ports anyway!!

If the crank is out of unbalance, it will vibrate at high rpm. People (such as myself) balance a crank to reduce unwanted stresses on internal components due to things whirling around out of balance. It also reduces friction and can enable a bit more power to reach the wheels. A lot of people run A-series without balancing the cranks and they claim to still rev them over 7000rpm. If I was building a decent road machine, I don't know if I'd bother balancing an A-series.

that sheds a little more light on the subject
my mane concern is to build the bottem end as strong as i can afford on my budget to give me more pice of mind
with my supercharged setup
and as i have a good a14 sitting in my shed i was going to build it up while still runing my a15

This would be a bit of extra effort but should end up with more power,

put the A14 in the car while you build up the A15.

6.5% bigger got to be better.

yeh well that wasalso a thaught.
wich ever motor i do not use will probebly end up in a 1000 coupe

Source an a15. There out there you just got to find them. I picked up a complete one for $20 just the other week.