Found out the hard way....964 has a different hole pattern than earlier engines....

[Dennis Kalma]

Just thought I would let everyone know...

Got my 964 Carrera Cup flywheel which I was hoping would be the answer to fitting my 6 speed G50 to my '89 Carrera project car (got to do a lot more stuff like trim the bell housing etc).

Anyway, besides a few other issues, I tried to match up the 964 flywheel and it has 9 evenly spaced holes with an indexing dowel pin, while the earlier 911's have 9 unevenly spaced holes, two of them being closer together, I guess to get the same result as the 964's dowel pin....namely, make sure the flywheel is always in the same relationship to the crankshaft.

I suspect that the 964 needs the precision as it picks up the EFI engine speed sensor signal from the notches on the outside of the flywheel, while the earlier engines just need orientation for balance purposes.

And to add insult to injury, the aluminium Ruf pressure plate is a tad larger than the recess in the outer edge of the flywheel it is intended to fit into....about 2 or 3 millimetres larger diameter. I suspect that I still do not have the flywheel that matches that fine pressure plate.

Anyway, anyone want to buy a Porsche single mass flywheel for a 964?

Sigh

Dennis

[89turbocabmike]

I feel your pain Dennis, you are certainly charting new waters.

A couple years ago when simply trying to replace my G50 turbo flywheel after the rubber center let go on the disc, I ordered a new flywheel from Porsche. It arrived, I put the old and new flywheels face to face and everything looked the same... the holes lined up.........Cool I'm good to go. Couple days later I've got the new cams in......You know the engines out, while your in there Anyway get ready to put the engine back in and try to mount the flywheel to the crank...hmmm, the holes don't all match, spin around, try old flywheel, it matches, put flywheels "face to face", they line up? what up here?......wait a minute I need to compare the flywheels in same orientation..duh. New flywheel has the offset hole opposite?! According to Porsche, a batch of flywheels were drilled wrong side up! Seemed to explain why all six similar flywheels sitting in Porsche's US warehouse including mine looked like they had been previously opened(and probably returned without explanation?), but curious as i would expect they have premade fixtures for machining. Anyway, I feel your pain, I've obviously still got issues some two years later

It's a cool project, you gotta work through the pain. Think of all the 6spd conversions waiting to be born in the future!

[BReyes]

Good Luck. What years did the 6spd start?

Regards,

[Dennis Kalma]

If I understand my documentation correctly, the 6 speed started with the 993....it is an extended housing (of about 63mm greater length) on the 5 speed G50 transmission. There is a large rubber doughnut with cast in assembly that will need to be removed as well. Theory is that shortening the bellhousing as people have been doing when they fit the 5 speed G50 to 915 equipped cars will save 28mm, plus there is some space (around 40-50mm) in front of the transmission, using part of that plus moving the engine back slightly ought to do the trick. Issue right now is to get a flywheel/pressure plate/ring gear combo that will allow the bell housing to be cut back (I want to make absolutely sure before I start machining it).

Dennis

[MBruns]

The crank bolt pattern is the same on all the 9 bolt flanges from the 78 3.0 thru the 993, I dont have a 996 here to check but the 996 GT3 RS has the same pattern, the only difference is the locator dowl pin, Sounds like you have a flywheel that was machined wrong (see if it lines up if you flip it backwards) and the dowl is between the bolts, the other change was how the pilot bearing mounted either to the crank via 3 allen bolts or pressed into the F/W
Mike Bruns JBRacing.com

[Dennis Kalma]

Curious. I am matching the Carrera RS flywheel to the 915 flywheel that came off of my donor engine (930/03, '79 vintage) and a used Turbo Flywheel (3.3) and neither of them match the holes. In fact, if you look at the Turbo and 915 flywheels you can see there are two holes closer together....

I will take some pics tonight and post them...be interesting if Porsche had machined the thing wrong! TurboCabMike's experience seems to suggest that there have been problems in the past....

Dennis

Dennis

[MBruns]

I bet its wrong, we run a 964 based 3.8 with a 993 6 speed, although we use a 5 1/2" 3 disc clutch the flywheel will fit all the 9 bolt cranks including the 930, and they only go on one way with or without the dowl pin
Mike Bruns

[Henry Schmidt]

Off sets, clutch diameter, pilot bearings all change over the years but I would be surprised to hear that the bolt pattern changed.
I don't work on later model engines but Porsche rarely changes this type of dimension.