I am looking at running a light weight rotating assembly (flywheel, crank, etc). I'm doing this to lessen the shock on my transmission (less momentum hitting the tranny). Since this is going into a 1987 944 porsche, the transmission it will have is limited to about 400hp so I can never drop the clutch.

My question is this, will I notice much difference with speed, rev up, or acceleration if I drop 50 grams on each piston or 2-3 pounds off the crank? The price difference is quite significant so I want to know that it is justified. This will be a road racing car that might see a drag track once or twice in its life. It won't see over 500rwhp.

 

If possible I'd run a t56 transmission instead of the Porsche tranny. By lightening the rotating assy it will rev quicker, but won't really lessen drivetrain shock for you. Your best bet would be to build the motor you want, then short shift and slip the clutch a little so you come in under the rpms that the motor is building power.

If you have any questions you could pm me and I might newborn to lead you in the right direction.

 

Why wouldn't it lessen the drivetrain shock? There is less momentum being transferred to the transmission if there is less weight in the rotating assembly. How much effect will revving quicker have? I mean....two pounds off of a pretty small radius isn't that much is it? It seems my money would be better spent taking two pounds off the wheels since it has a larger radius.

Note: yes it is possible to put a t56 in it but it takes buttloads of cash or intense fabricating skills. It is not an option for me. (I may attempt to fit an audi transmission in the car eventually but we'll see.)

 

Oh, lightening the assembly will lessen the shock to the tranny, but I'm not sure how much....I still think driving style would have more to do with tranny life than the lighter assembly...hopefully more people will chime in

 

I think your going about this the wrong way.

Lightening the flywheel and drivetrain will lessen the shock but you will have to slip the clutch more.

I know a guy that built a custom triple disc clutch for his f-body and it is considerably lighter than stock and has a very small moment of inertia. He has to slip the clutch a bit just to get going.

It does rev super fast almost like a super-bike when in neutral. A lighter rotating assembly in the motor would just be expensive and would maybe free up some power but I think there is money better spent somewhere else. If the car is going to be road raced and wont see much street time, go with a light weight clutch assembly with a small moment of inertia and light flywheel. It will rev quicker, but how much of that will translate into actual acceleration difference I don't know.

Lighter wheels always helps but if you want less drivetrain shock, you need to for a way to lessen the amount of speed the clutch has to compensate for when taking off from a dead stop. This will save the transmission a bit but at the expense of the clutch. From what I can remember when by buddy owned a 944 he told me clutch jobs on those cars was a PITA.

When the car is sitting still and the clutch goes to engage, slipping the clutch allows the car to get rolling first lessening the amount of difference the clutch has to take up resulting in less of a shock.

I know this information is sort of all over the place, but you didn't really say what the car will be used for.

Hope this helps

 

Get something like the Quartermaster 7.25" button clutch (my flywheel/clutch assy weighs 16lbs), and then just turn the crank counter weights down. If you have the money then get the journals turned down for honda bearings, this will require more expensive rods though. Every little bit will help, especially rotating mass, with rev'ing easier and faster. Doing these things will be great on the road course and terrible for leaving the line at the drag strip.