What is difference between 3.2 crankshaft and 964 crankshaft? Racers swapping them?

[BReyes]

What is difference between 3.2 crankshaft and 964 crankshaft? Racers swapping them?

Thank you.

Regards,

[Carrera3.5L]

The MAJOR difference is the 3.2L crank has a 74.4mm stroke and the 964 crank has a 76.4mm stroke.

Many people over the years have used the 964 crank in 3.0/3.2 based motors to increase displacement (modifying the pistons to help accomodate).

Ralph

[BReyes]

Its hard to think about this and watch Corvette on fire on TV in Speed GT champ seriies at Infineon.

But now there is a Kingsford BBQ charcoal commercial.

The bigger displacement sounds good. What about if run proprietary cam and high rpms? Is it better for high revving 3.2 or 3.6 to run stock stroke, shorter or longer stroke? How do you come up with the final liter size?

I think I know the theory here but looking for every lil bit of hp can get.

[Carrera3.5L]

Generally speaking, a larger bore with stock stroke increases power capability at higher rpm ranges, whereas a longer stroke with stock bore increases torque in the low and mid ranges. The 962C went from 3.0L to 3.2L not by increasing the bore but rather lengthening the stroke. It wasn't meant to gain horsepower but to increase the low and mid-range torque and to help reduce turbo lag coming out of corners.

I'm not sure what you are trying to accomplish? If trying to build a 3.6L or motor larger, you would be better suited to simply transplant a 3.6L 964/993 motor. If trying to spin the motor to higher rpms (7200>) AND still make power, you would need to ditch your Motronic and the relatively docile cams that are required. A shorter stroke would help facilitate higher rpm power, which is why all the <2.5L guys use short-stroke cranks in their rubber band motors.

I've listed many times before some of the popular and easily doable engine size combos that are available for the 3.0L/3.2L owner who doesn't wish to transplant a 3.6L. Just for clarification, your stock bore and stroke on your Carrera is 95 x 74.4.

98 x 74.4 = 3.4L
100 x 74.4 = 3.5L
98 x 76.4 = 3.5L long-stroke (generally for 930 owners)
100 x 76.4 = 3.6L
102 x 74.4 = 3.7L

Steve Wong's chip, a proper exhaust, a sport cam profile such as 964 or 20/21's and modified plenums can provide decent "bolt-on" gains (somewhere in the 235-245 hp range) but increasing displacement or an engine transplant will put a smile on your face from as low as 2,500 rpm when you accelerate that no Motronic 3.2L gets close to matching.

Ralph

[kenikh]

Why not use a 70.4mm crank, then? If you want revs, that'll do it.