964 crank in SC case
 

Hi guys,
I see on the rod thread, that Henry uses a 964 crank with the rod bearing journals machined down to SC sizes.

I wanted to know if anyone else has tried this, and what rods did they use.

I am sure that the SC rods could be used, with JE pistons(still to order) made to accept the longer rods and SC small end.

Any comments, as well as problems that would be encountered in the case with the longer stroke.

Is the extra 2mm stroke worth the extra effort, or should I just look for a 3.2 or turbo crank. I will also be using 98 mm barrels.

Thanks

my 2 cents-

you could machine down the 964 journals and use SC rods. you could. but it will cost a lot of money to machine the crank, and I've heard the 964 crank is a piece of s*!% compared to SC or 3.2, yet it's still $1000(?). I heard Andial built/rebuilt a 930T w/ a 964 crank (was it a long-stroke 3.5L w/ 98mm P/C?... I can't remember) three times because the thing kept grenading.

There is no substitute for cubic inches, but for the effort/cost involved, I would be more inclined to use a 3.2 crank/rods and 98mm P/C for a relatively easy and relatively inexpensive 3.36L. Still pretty fast, especially if you spend your extra money (saved on the crank mod) on twin plugs.

I actually have a 3.2 crank spare if you're interested...

Re: 964 crank in SC case
 

There really is no need to put 3.0 rods on a 3.6 crank. The new GT3RSR cranks already comes that way. Prices are amazingly reasonable.
Sell the low rpm 964 crank and take the difference that you would spend on machine work and end up with a new race crank.
The 964 crank is not really designed to spin so the stock rods with ARP bolts will work for most applications. If you want to spin it there are aftermarket rods for that. I don't much like the 964 crank because of the lack of counter weights and the need of a harmonic balancer.
The only early case 930 Andial engine that I have disassembled that use a 964 crank also used 100mm pistons and Carrillo rods. 3.5 liter displacement.
If you run a full length 3.0 rod with a 964 crank you need to run barrel shims and build custom pistons. The result of barrel shims causes an overall dimension change that has it's own set of challenges.
If you use a 930 crank with 3.0 rods the engine will spin higher rpm and No custom pistons are necessary. You just use 3.6 pistons.

Henry,
Approximately how much $ is a GT3RSR crank from the factory?

What happens if you run a 964 crank without the harmonic balancer? Is the long term diagnosis fatal? Seems the factory did it in race cars, but I would imagine they inspect or tore down the engines at regular intervals? Have you ever seen a broken 964 crank?

I certainly recognize that the factory installed a harmonic balancer for a reason and that resonance can result in build up of stresses at specific rpms. Just curious about your experience.

Or is the harmonic balancer used to reduce engine vibrations for the comfort of the occupants?

Finally, does balancing of the rotating assembly have benefits so as to remove the harmonic balancer?

Thank you,

Doug

In order:
1) It's hard to get a retail price on GT3 RSR parts because PCNA don't want to sell them. I will tell you that $2500 will get you one from Supertec.

2) I have seen some cracked main webs on 3.6 cases running 964 cranks with no harmonic balancers. I don't have enough experience to say that the cracks were caused by harmonic vibrations but it seems like a reasonable conclusion. Once again RPM may be the determining factor.
Factory race engines do not use the production 964 crank.

Interesting information - as always!

I realize unless you have enough data points, it is very hard to draw a very specific conclusion.

Thank you,

Doug