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Lightening The Flywheel
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PORSCHEV  



Joined: 02 Nov 2002
Posts: 1901
Location: Cedar Lake Nova Scotia, Canada

PostPosted: Thu May 08, 2008 1:40 am    Post subject: Lightening The Flywheel Reply with quote

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.
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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: 3899
Location: Canada

PostPosted: Thu May 08, 2008 2:27 am    Post subject: Reply with quote

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.
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Slam  



Joined: 07 Jan 2005
Posts: 1689
Location: Wainwright, Alberta, Canada

PostPosted: Thu May 08, 2008 2:33 am    Post subject: Reply with quote

Didn't Lakefield (??) make scatter shields? Doubt they'd do anything for a P-car.

edit: 'twas Lakewood.
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ideola  



Joined: 01 Oct 2004
Posts: 15505
Location: Woodstock IL

PostPosted: Thu May 08, 2008 2:49 am    Post subject: Reply with quote

My legs are worth the $309 it costs to purchase a Fidanza.
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Rasta Monsta  



Joined: 12 Jul 2006
Posts: 11378
Location: PacNW

PostPosted: Thu May 08, 2008 2:50 am    Post subject: Reply with quote

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.
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Toofah King Bad

  • Red (1987 924S) - Pro44/Spec944
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ideola  



Joined: 01 Oct 2004
Posts: 15505
Location: Woodstock IL

PostPosted: Thu May 08, 2008 3:02 am    Post subject: Reply with quote

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.
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Rasta Monsta  



Joined: 12 Jul 2006
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Location: PacNW

PostPosted: Thu May 08, 2008 3:19 am    Post subject: Reply with quote

Wow, nice link. That pic is thexthy!

I wonder what (if any) timing markings are on it?
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Benino  



Joined: 30 Jan 2003
Posts: 497
Location: Vista, CA (San Diego County)

PostPosted: Thu May 08, 2008 3:27 am    Post subject: Reply with quote

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.
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Rasta Monsta  



Joined: 12 Jul 2006
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Location: PacNW

PostPosted: Thu May 08, 2008 3:29 am    Post subject: Reply with quote

But they do let go. . .I have read sports car racing rules requiring shields around the bellhousing for this reason. Maybe PCA?
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Benino  



Joined: 30 Jan 2003
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Location: Vista, CA (San Diego County)

PostPosted: Thu May 08, 2008 3:39 am    Post subject: Reply with quote

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.
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Benino  



Joined: 30 Jan 2003
Posts: 497
Location: Vista, CA (San Diego County)

PostPosted: Thu May 08, 2008 3:42 am    Post subject: Reply with quote


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Martijnus  



Joined: 29 Dec 2006
Posts: 2019
Location: Netherlands

PostPosted: Thu May 08, 2008 6:09 am    Post subject: Reply with quote

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!
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PORSCHEV  



Joined: 02 Nov 2002
Posts: 1901
Location: Cedar Lake Nova Scotia, Canada

PostPosted: Thu May 08, 2008 6:15 am    Post subject: Reply with quote

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.
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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: 2801

PostPosted: Thu May 08, 2008 12:10 pm    Post subject: Reply with quote

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: 497
Location: Vista, CA (San Diego County)

PostPosted: Fri May 09, 2008 3:11 am    Post subject: Reply with quote

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.
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