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924 n/a flywheel cross section & lightening
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Benino  



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

PostPosted: Tue Dec 04, 2007 5:28 pm    Post subject: 924 n/a flywheel cross section & lightening Reply with quote

I made a scale diagram of the cross section of the 924 n/a flywheel.

I'm planning to have mine lightened. Here is the cross section. The light gray areas are the parts I'm thinking of having removed. I think that whole area and all the way to the end is just for weight purposes, not for strength. part of the friction surface to the inside of that, is already that thin. I think the area closer to the center (which is thinner) would need more strength since it has to be able to handle the centrifugal force of the mass of the rest of the flywheel.


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!tom  



Joined: 28 Aug 2006
Posts: 1902
Location: Victoria, BC Canada

PostPosted: Wed Dec 05, 2007 6:29 am    Post subject: Reply with quote

There's also the heat capacity of the flywheel to consider. The majority of the mass that you're planning on removing is adjacent to the friction surface of the flywheel. Removing this will cause the temperature of the flywheel to increase over an un-modified flywheel when operating the clutch, due to the reduced heat capacity of the flywheel.

If your driving style is clutch friendly, this would probably not be an issue. However, I wouldn't be surprised if a lighter flywheel would lend itself to more clutch slipping than a conventional flywheel, and consequently that much higher temperatures.

Just something to consider. . .
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Dutch924-racer  



Joined: 23 Jul 2007
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PostPosted: Wed Dec 05, 2007 5:21 pm    Post subject: Reply with quote

I had my flywheel lightened. The took 1,5 KG of the back (engine side). This safe and won't effect the strength.

Ofcourse you can get more of it (by putting holes in it). But you will loose strength.
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Rasta Monsta  



Joined: 12 Jul 2006
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PostPosted: Thu Dec 06, 2007 2:57 am    Post subject: Reply with quote

So you removed material from the same area as in the pic above?
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AppleBit  



Joined: 16 Nov 2002
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PostPosted: Tue Mar 11, 2008 1:14 am    Post subject: Reply with quote

Ever get it lightened? Otherwise I'll sell ya one dirt cheap... PM me if interested.
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Martijnus  



Joined: 29 Dec 2006
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Location: Netherlands

PostPosted: Tue Mar 11, 2008 1:45 am    Post subject: Reply with quote

I've heard some stories from people who took too much off... a shattered flywheel isn't fun... so keep limits in mind

interesting thread however... I'm not interested in weight loss in this case but you never know how I think about it in a few yrs
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AppleBit  



Joined: 16 Nov 2002
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PostPosted: Tue Mar 11, 2008 1:50 am    Post subject: Reply with quote

Martijnus wrote:
I've heard some stories from people who took too much off... a shattered flywheel isn't fun... so keep limits in mind

interesting thread however... I'm not interested in weight loss in this case but you never know how I think about it in a few yrs


Yeah, the shop that took the weight down recommended only so far. I told them to do what they thought was safe.

Result:


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AppleBit  



Joined: 16 Nov 2002
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Location: Minneapolis, MN

PostPosted: Tue Mar 11, 2008 1:52 am    Post subject: Reply with quote

took it down to 15 lbs. Honestly that doesn't sound like much, but its WHERE the weight was taken off. Made a bit of a difference. The only thing better is an aluminum flywheel (I have one left for sale) - either which way a great way to add power.
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Benino  



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

PostPosted: Tue Mar 11, 2008 1:59 am    Post subject: Reply with quote

Yup. I had mine lightened. Its back in the car and working fine. It looked pretty much exactly like the picture AppleBit posted. I'm pretty sure I took some pictures of it before I installed it, but I have on my home PC.

I did pretty much exactly what I have in my cross section diagram.
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Nobbi  



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PostPosted: Tue Mar 11, 2008 2:00 am    Post subject: Reply with quote

Whats the positive effect of a light-flighwheel ?
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AppleBit  



Joined: 16 Nov 2002
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PostPosted: Tue Mar 11, 2008 2:02 am    Post subject: Reply with quote

Nobbi wrote:
Whats the positive effect of a light-flighwheel ?


+ Faster revving engine
+ Easier on the engine

- Loss of torque (minimal)
- Has to be done right or BOOM!
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Martijnus  



Joined: 29 Dec 2006
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PostPosted: Tue Mar 11, 2008 2:10 am    Post subject: Reply with quote

AppleBit wrote:
Nobbi wrote:
Whats the positive effect of a light-flighwheel ?


+ Faster revving engine
+ Easier on the engine

- Loss of torque (minimal)
- Has to be done right or BOOM!


what do you mean by "easier on the engine" ... the flywheel smoothes out the peaks in an engine iirc, especially when idling.
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"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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AppleBit  



Joined: 16 Nov 2002
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Location: Minneapolis, MN

PostPosted: Tue Mar 11, 2008 2:14 am    Post subject: Reply with quote

Martijnus wrote:
AppleBit wrote:
Nobbi wrote:
Whats the positive effect of a light-flighwheel ?


+ Faster revving engine
+ Easier on the engine

- Loss of torque (minimal)
- Has to be done right or BOOM!


what do you mean by "easier on the engine" ... the flywheel smoothes out the peaks in an engine iirc, especially when idling.


If you had a 25 lb weight or a 5 lb weight, and you were swinging it around with your arm, what would be easier?

Another idea with the less weight is it can then consume less fuel... Now this all is more like a variable along with other things....
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Benino  



Joined: 30 Jan 2003
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PostPosted: Tue Mar 11, 2008 2:35 am    Post subject: Reply with quote

Nobbi wrote:
Whats the positive effect of a light-flighwheel ?



any decrease in weight of the rotating drivetrain parts is going to mean less power lost between the engine and the wheels.
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Rich H  



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PostPosted: Tue Mar 11, 2008 2:41 am    Post subject: Reply with quote

Did you guys balance them afterwards?
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