SoloRacer

CMW Racing out of California lightened and knife edged my crank - I believe they dropped 13 lbs out of it. My flywheel also was lightened. The car is not difficult to drive at all. I have never stalled it - even the first time I drove it after the engine rebuild.

cpt_koolbeenz

I have found that with a more aggressive clutch and a lightened crank it is easier to stall the engine... But it is not hard to get used to...

However, I still stall my car sometimes when starting out in 2nd gear in the snow though!

RKD in OKC

Landjet...

Yes, stock journal sizes and is ready to drop in.

The crank has 20,000 miles on it, a few autocrosses, but no track.

When Lindsey Racing pulled it out the #4 rod and rear main bearings were worn a little, but no visable damage to the crank. They sent it out to their crank guy to make 100% sure it was OK. It passed with flying colors with the crank guy. Was planning to use it until talked into going to 2.8 L since I was going to have to buy pistons anyway due to cylinder damage. Cylinders were Nikasiled and Chrome rings were used, not a good combination after about 18-20,000 miles.

RKD in OKC

OK, I've talked to some people...

The stalling/lightened rotational mass thing is an older model 911 thing NOT a 944 Turbo thing. Their motronics did not have an idle mixture adjustment like ours, and it also did not have an idle stabilizer. So, if you reved down to quickly or loaded to quickly at idle, it would die.

My 944 Turbo with knife-edge crank, alumunium flywheel, and sport clucth was much easier to start rolling than my stock 2001 Boxster S. Stalls getting rolling were not uncommon in my Boxster S and I NEVER had that problem on my 944 Turbo, NEVER.

In my humble opinion... MYTH BUSTED

MPD47

Biggest reason I stalled a Boxster first time I drove it. I couldnt hear or feel it. Stock, with a helmet on, you cant hear the engine till it's over 6000rpm, and even then you need to know what you're listening for. They desperately need some harder motor mounts, an intake, and an exhaust.

RKD in OKC

Try to get a boxster rolling by just slowly letting the clutch out, then try the same with your 944 Turbo. It ain't just not being able to hear it.

333pg333

That was always the theory. Less inertia, less torque, but by how much??? Also lightened fly contributes to this.

RKD in OKC

Your theory of less inertia, less torque applies to models where the inertia is used to perform work. The only time the rotational mass of a motor performs work is when you are trying to decelerate the motor, ie letting out the clutch, engine braking, and technically slowing down between cumbustion strokes. Once the rpm of the engine must increase to accelerate the car, any torque required to increase the rpm of the flywheel is not available to accelerate the car. So lightened crank and flywheel increase the torque available to accelerate the car.

Given two dragesters of equal power to weight ratio and unlimited clutch and tire grip. The one with the lightest rotational mass will be slower off the line, but will catch and beat the dragster with heavier rotational mass. Which one has more torque?

333pg333

Interesting theory and I'm not going to argue in absolutes as I don't have definitive data either way. My point being that it was always the preconception that having a certain amount of inertia through the weight of the aforementioned internals lent itself to more tq. Your example of the dragsters seems to agree in that the one with the more tq leads early only to be overtaken by the one with the ability to rev higher...I think. I'm happy to be proved wrong however, and do expound your theory more if you so choose.
Moreso, I agree that it stands to make more sense that the lighter the internals, the easier it is to rev therefore producing power. Equally so, the heavier the internals the more power is required to get them moving. However what if once you do get them moving they then develop more power through the greater inertia
due to their extra weight? So at some point the advantages of both setups are shown and probably cross over. It's quite interesting and over my head but possibly proveable (?) in a control situation. The only thing is at what weight differences does the crossover take place?

RKD in OKC

Here is some physics...

http://www.physicsnews1.com/question_15.html

333pg333

Physics huh? Don't start confounding me with the truth now will you? Anyway as I said I'm happy to be corrected as in fact I was just passing on the theory. I can't lay claim to it.

hally

anyone have dyno charts showing before and after with a lightened flywheel?

Douglas Sorrells

Can anyone comment on the seat of the pants feel knife edging the crank gives in a 951 with some modest mods?

thanks d

Chris Prack

I see cranks like this and I wonder. I have used one crank that was cut down like the cranks in this thread.

The whole idea is that the crank is balanced with the weight of the connecting rod, pin and piston in mind. It's not just hack some weight off and call it improved. IMO this is done blindly all too often by someone who does not have the proper understanding of what they are doing.

Now Porsche does some "interesting" things with crank weights. If you look at the crank in a GT3RS motor. The crank is light with small counter weights. They counter this by using Ti rods and small 2 ring pistons.

The crankshaft in a 944 is huge. It has large counterweights and weighs 58lbs. Why? Why does it have to weight 58lbs.? The crankshafts also suffer from less than ideal oiling. The common "fix" for this is not a solution but a mild improvement. The oiling hole in the rod journal is in the wrong place.

Lightening the crank is more complex. You need to get weight out of the rod end first then move to the counterweight. For every ounce out of the small end you can get two ounces out of the big end.

Currently I have a crank out to a manufacture to have it redesigned. New material, proper oiling and less mass.

TRP951

a new custom crank huh sounds cool but then all I see is $$$$$ and that makes me go I wish I had more money haha