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PORSCHEV
Joined: 02 Nov 2002 Posts: 1901 Location: Cedar Lake Nova Scotia, Canada
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Posted: Thu May 08, 2008 1:40 am Post subject: Lightening The Flywheel |
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I sent my flywheel to the machine shop to get lightened. I had pics from the board as others had done it to try an ensure it was done properly. Once the material was removed the machined said it kept running out of true. Thats when he discovered that it was cracked! I am glad he found it...otherwise it could have been my legs.
It was my spare and once I saw that I cam to the conclusion there is no way I would lighten one in the same fashion. Too unsafe!
Just my opinion. _________________ 1976 924
5 lug conversion, 17'C2 wheels,custom body work,327 vette engine.
1978-#53 "D" track racer. |
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Chrenan
Joined: 15 Jan 2003 Posts: 3903 Location: Canada
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Posted: Thu May 08, 2008 2:27 am Post subject: |
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Does anyone know how safe the stock bell housing is? If the flywheel was to come apart, would it go through the bell housing? I would think yes, they stock flywheel is a heavy beast and the bell housing is pretty light material, but I've never heard of such a horror story. _________________ 1987 951 - M193 Version for Japan |
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Slam
Joined: 07 Jan 2005 Posts: 1689 Location: Wainwright, Alberta, Canada
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Posted: Thu May 08, 2008 2:33 am Post subject: |
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Didn't Lakefield (??) make scatter shields? Doubt they'd do anything for a P-car.
edit: 'twas Lakewood. _________________ '84 944 - kid blew motor
'83 944 - resting comfortably. For 12 years
'87 944 - sideswiped by trucker
'80 924 - gone
'78 924 - gone
'77 924 - rusting comfortably |
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ideola
Joined: 01 Oct 2004 Posts: 15548 Location: Spring Lake MI
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Posted: Thu May 08, 2008 2:49 am Post subject: |
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My legs are worth the $309 it costs to purchase a Fidanza. _________________ erstwhile owner of just about every 924 variant ever made |
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Rasta Monsta
Joined: 12 Jul 2006 Posts: 11723 Location: PacNW
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Posted: Thu May 08, 2008 2:50 am Post subject: |
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They make a 931 unit? Linky?
*Answered my own question*
In looking at their app guide, it appears that a 931 unit is all they make, although in the pressure plate column, it says CALL. . .not sure what that means.
FWIW, Fidanza Part # is 199241. _________________ Toofah King Bad
- WeiBe (1987 924S 2.5t) - 931 S3
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ideola
Joined: 01 Oct 2004 Posts: 15548 Location: Spring Lake MI
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Posted: Thu May 08, 2008 3:02 am Post subject: |
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Yes, they make a 931 unit, and it is compatible with both SI and SII (since it is the ring gear on the pressure plate that is used for the starter). The ring gear on the flywheel is only required by the SII 931 for the DITC crank sensor. So even though it is superfluous for an SI application, there is no need for two different units. Apparently, it is cheaper to make a single part with a ring gear, than two parts, one with & one without.
As for the "call for info", that is specifically if you want to order the friction surface replacement parts. If you're buying one new, you can just order one up. I just called the guys at UltraRev about this last week. _________________ erstwhile owner of just about every 924 variant ever made |
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Rasta Monsta
Joined: 12 Jul 2006 Posts: 11723 Location: PacNW
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Posted: Thu May 08, 2008 3:19 am Post subject: |
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Wow, nice link. That pic is thexthy!
I wonder what (if any) timing markings are on it? _________________ Toofah King Bad
- WeiBe (1987 924S 2.5t) - 931 S3
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Benino
Joined: 30 Jan 2003 Posts: 505 Location: Vista, CA (San Diego County)
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Posted: Thu May 08, 2008 3:27 am Post subject: |
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Lots of us have lightened the flywheels and I haven't heard of anyone having one shatter. There is less metal, so obviously it's not as strong, but also there is less weight spinning around, so less centrifugal force.
The flywheel isn't just spinning on it's own. It is bolted around the edge to the pressure plate, which absorbs a lot of that centrifugal force.
Based on that and also on the crossection diagram I made to ensure the friction surface remained thick enough before having mine lightened (I posted that diagram here a while back) I feel it is sufficiently strong. It is made as thick and heavy as it is primarily to make it easy for crappy drivers to be able to handle the manual transmission, not because it needs to be that thick for strength. _________________ 1980 Porsche 924 N/A USA
1980 Porsche 924 turbo USA
1987 Porsche 944S USA |
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Rasta Monsta
Joined: 12 Jul 2006 Posts: 11723 Location: PacNW
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Posted: Thu May 08, 2008 3:29 am Post subject: |
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But they do let go. . .I have read sports car racing rules requiring shields around the bellhousing for this reason. Maybe PCA? _________________ Toofah King Bad
- WeiBe (1987 924S 2.5t) - 931 S3
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Benino
Joined: 30 Jan 2003 Posts: 505 Location: Vista, CA (San Diego County)
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Posted: Thu May 08, 2008 3:39 am Post subject: |
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Rasta Monsta wrote: | But they do let go. . .I have read sports car racing rules requiring shields around the bellhousing for this reason. Maybe PCA? |
Yeah. You can take anything too far. That's why I made the diagram. I didn't make anything even as thin as the thinnest point on the unmodified flywheel. So actually, since it's got less weight, I relieved some stress on those thinner parts. It's safer now than before. _________________ 1980 Porsche 924 N/A USA
1980 Porsche 924 turbo USA
1987 Porsche 944S USA |
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Benino
Joined: 30 Jan 2003 Posts: 505 Location: Vista, CA (San Diego County)
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Posted: Thu May 08, 2008 3:42 am Post subject: |
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_________________ 1980 Porsche 924 N/A USA
1980 Porsche 924 turbo USA
1987 Porsche 944S USA |
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Martijnus
Joined: 29 Dec 2006 Posts: 2019 Location: Netherlands
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Posted: Thu May 08, 2008 6:09 am Post subject: |
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Benino wrote: | Rasta Monsta wrote: | But they do let go. . .I have read sports car racing rules requiring shields around the bellhousing for this reason. Maybe PCA? |
Yeah. You can take anything too far. That's why I made the diagram. I didn't make anything even as thin as the thinnest point on the unmodified flywheel. So actually, since it's got less weight, I relieved some stress on those thinner parts. It's safer now than before. |
that demands a test!
bench test the terminal velocities and you've got my vote! _________________ "Rule: Turbo's make torque, and torque makes fun." (C. Bell)
924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment |
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PORSCHEV
Joined: 02 Nov 2002 Posts: 1901 Location: Cedar Lake Nova Scotia, Canada
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Posted: Thu May 08, 2008 6:15 am Post subject: |
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Just to clarify the crack wasn't the radius either..it was 3/4 of the circumference. It was VERY visible due to the fact it had sat around for so long. The machinist was doing pretty much what your diagram shows. The crack was about 3/4 inch into the original radius. _________________ 1976 924
5 lug conversion, 17'C2 wheels,custom body work,327 vette engine.
1978-#53 "D" track racer. |
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emoore924
Joined: 13 Apr 2004 Posts: 2815
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Posted: Thu May 08, 2008 12:10 pm Post subject: |
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If you want to know the timing marks on the Fidanza, PM me. I have one sitting in the basement I can have a look at... |
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Benino
Joined: 30 Jan 2003 Posts: 505 Location: Vista, CA (San Diego County)
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Posted: Fri May 09, 2008 3:11 am Post subject: |
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Martijnus wrote: | Benino wrote: | Rasta Monsta wrote: | But they do let go. . .I have read sports car racing rules requiring shields around the bellhousing for this reason. Maybe PCA? |
Yeah. You can take anything too far. That's why I made the diagram. I didn't make anything even as thin as the thinnest point on the unmodified flywheel. So actually, since it's got less weight, I relieved some stress on those thinner parts. It's safer now than before. |
that demands a test!
bench test the terminal velocities and you've got my vote! |
That would be a really fun test to run! It would be kind of expensive though as I don't have any extra flywheels and would have to pay to have one lightened. _________________ 1980 Porsche 924 N/A USA
1980 Porsche 924 turbo USA
1987 Porsche 944S USA |
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