915 to 930 gearbox help.

[porschekrest]

Hi everyone, I am going from 915 to 930 gearbox on a 3.2 motor platform. I have found a 87-88 3.2 flwyheel meant for a g50 gearbox, does anyone know if this flywheel also works if I use a short bellhousing 930 gearbox with the correct clutch for a short bellhousing 930? I ask because 87-88 is supposed to be factory short bellhousing g50 correct? Unless I am misinformed...

[porschekrest]

I will elaborate, my 3.2 has 3.3 pistons and cylinders and a large turbo. It also has a custom efi system using the original motronic mounts and trigger wheel on the 915 flywheel. So I need a flywheel that works for a short bellhousing 930 setup but still has the trigger teeth like found on 3.2 motors. So the only two I know of are the 915 flywheel and the g50 flywheel 87-88. I am hoping the g50 3.2 flywheel would work with a 930 short bell, hope someone knows the answer to this.

[scottrx7tt]

Wouldn’t it be easier to run a toothed wheel on the crank pulley?

[porschekrest]

Yes and I know that is the only other solution but it ads extra cost.if I have to buy new sensors wheel and sensor mount, versus using the original sensor and everything even more so if I need a new flywheel, if the g50 one cannot be used then i am sure a new or custom new flywheel prices are not far off.

[porschyard]

The problem you will run into with a G50 flywheel on a SBH 930 box is it's a stepped flywheel.
All of your 930 flywheels 75-88 and also 72-86 915 are flat flywheel's.
On a flat Flywheel the press.plate sits on the same surface level as the disc.
This apply's to 915 and 930.

On a G50 Flywheel the G50 press. plate sits on a "step"approx. 11 mm higher than the disc surface. A 3.0 turbo press.plate (SBH) will not work on a stepped Flywheel.

I am wondering if you can machine the step on the G50 flywheel flush with disc surface and then you would be able to use a 3.0 press plate as the bolt pattern is the same.
(just thinking out loud here).

The stand off distance from the crank flange to disc surface is as follows
( I did a quickie measurement so not 100% accurate but gives a good idea)

915 72-86 = approx.20 mm
930 = 23mm ( i measured an 87 3.3) I would think all 930 75-88 would have same dimension but dont take my word for it.
G50 =20mm to the disc surface but 31mm to press.plate seat.

I included pics of a 915 72-83, 915 84-86, a 930 and G50 flywheels.
I will take a closer look at the G50 flywheel and try to see if machining the steps out will work.

Richard



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[porschekrest]

I see exactly what you mean about the stepped lip on the g50 flywheel, from looking at the flywheels I had access to, this is the only difference I found also,and the bolt pattern for the PP. I figured the same conclusion as you, that a machined lip should allow the SHB type PP to be used. too bad the 915 flywheel (84) looks like it cannot be used because I think the 915PP bolt pattern would almost sit where the 240mm disc contact surface would be.

[porschyard]

So scratch the machining the lip idea, i just went out and did a quick measurement
and the G50 is about 12-13 mm narrower than a 930 press.plate so it does not look like that will work.

The 915 is 225 mm versus 240 for G50 and 930 so its out of the question.
I think your best bet is a custom unit by Patrick.

If that's not possible your last option is a 930 clutch and flywheel package and like Scott said go to a crank pulley trigger setup.
Good luck

[porschekrest]

danm....haha okay. Thanks guys.