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911 RSR lightweight Flywheel ... Pros/Cons

I did a quick search on the later 9 bolt RSR lightweight fly wheel but got nothing but the FS/WTB threads.

I am debating on what flywheel to use on my rsr engine build. Here is a quick spec becasue I know I will be asked what the motor will be, lol.

3.6 993 engine with RS valves, DC-40 cams with backdated mech rockers, 930 Oil pump, Crank/case mods, RR H beam rods with JE FSR 100mm pistons and topped with PMO 50 carbs. Trans will be a modified 915.

I remember threads a few years ago saying the 6 bolt RSR flywheel had issues with harmonics and bolts loosening causing the flywheel to fall off. IIRC the 9 bolt crank fixed with. Correct? So if you have run on of these flywheels I would like to hear what you thought of it. Thanks guys!
Old 12-11-2013, 04:14 AM
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I think that the issue was generally caused by a torsional vibration in the crank which caused some relative movement between the end of the crank and the flywheel. The fretting that this would generate allows the bolts to lose preload.

The driver for these resonances will be the high order gas torques that occur at relatively high rpm.

The 9 bolt crank is possibly a bit stiffer than the 6 Bolt crank so the torsional resonance is probably at bit higher frequency and the 9 bolts, of course give a much greater clamping load so relative movement between the two parts is less likely to occur.

I would also guess that these engines may not rev so highly and this in itself would solve the problem.
Old 12-11-2013, 07:31 AM
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I thought the problem was limited to the early, long stroke 2.5 liter engines used in the 911ST. No similarities between that engine and the one you want to use...

JR
Old 12-11-2013, 07:40 AM
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KTL KTL is offline
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I ran the RSR style flywheel on my racecar for a few years after I got it. Worked just fine.

225mm Lightened Flywheel- Used

If you're looking for reciprocating weight reduction, the RSR flywheel does a fair job of that. Usually the clutch is the bigger weight penalty so you want to look at that as well. Point being is the std. 915 flywheel is already pretty slim. Not exactly lightweight, but not a big fat hog like the later 3.6 dual mass flywheels.
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'79 911SC-based 3.0L 930S/934/965/911R looking thing NASA GTS-3
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Old 12-11-2013, 07:58 AM
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Nothing wrong with the RSR clutch / pressure plate / lightened flywheel setup.

Another option - Wevo / Tilton Superlite

Welcome to Windrush Evolutions - WEVO - Porsche Products
Old 12-11-2013, 08:49 AM
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Here's an article I wrote a while back on aluminum flywheels. It's not Porsche specific but it's good information. I love aluminum flywheels. I believe it's the single best modification you and make to a car for track use. It's even a lot of fun on the street. I've noticed very little downside.

Richard Newton
Old 12-11-2013, 09:44 AM
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Thanks guys. I have heard of some guys running these and complaining about stalling. Im not to concerned about the stalling. The car wont be a daily driver. Just another car in the corral. I figure Id pose the question and see what the response was. Seems like most guys run these in their track cars but has anyone driven around town in one or traffic? I had a buddy years back who had a alum flywheel in his jetta ... it took some getting used to when I drove his car. I have a light weight flywheel in my cobra but its heavier then 6-8 lbs. I figure since the rest of the reciprocating mass are getting lighter a lighter fly wheel would also help. Ill have to give PMS a call and inquire there take. The clutch is going to be a center force lightweight clutch package. I have the same clutch on my cobra and love it. I wish I could afford the wevo tilton unit but that would be a complete waste for me ... pretty much just bling, lol.
Old 12-11-2013, 11:55 AM
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KTL KTL is offline
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With that scalloped flywheel I also had a four puck spring centered disc (clutchnet brand w/sintered metal friction material) and a Kennedy stage 1 uber light clutch housing. This was their aluminum housing, aluminum "foot" sprayed with carbide friction material. I was shocked how light it was- 6 lbs.

225mm Kennedy Eng. Stage 1 Clutch- 915 trans

Point of sharing that is the combination of the clutch, flywheel and disc were pretty light for a street-based combination. I could drive it around the neighborhood on short test drives and get on/off the trailer no problem with it. What I mean by street based is the clutch was still your basic 225mm size with strap-drive operation, the flywheel was a lightened stock-like piece and the clutch disc was spring damped. So the whole thing was still plenty driveable. As long as your chip mapping is accounting for the lighter weight, it'll avoid stalling when closing the throttle. Stalling from a dead stop is operator dependent!

Mine wasn't super touchy like a true racing clutch. You could slip the clutch from a dead stop and get rolling w/out stalling due to the spring damped disc allowing for it.. Gear changes were not abrupt due to the spring centered disc. See what i'm getting at? Spring centered discs are key to keeping it driveable. Once you get into a solid hub disc, then it's that binary on/off no-slip-allowed behavior.

Now the Tilton Superlite is a whole different animal. I have one of those on the shelf for when I get the racecar back together. Those clutches are super compact low weight low moment of inertia. 5.5" dia. (140mm) and solid discs = no damping. Beautiful little thing. Good friend has a GT3 Cup with a similar style clutch. Stalls it almost every time in the pit area when backing out of his parking spot.
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'79 911SC-based 3.0L 930S/934/965/911R looking thing NASA GTS-3
Enginerded by Red Snail Racing, MotoDelta Motorsports, G2 Performance, Elbowmotions
'87 Carrera- gone 7/25/14 but never forgotten
Old 12-11-2013, 12:24 PM
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Originally Posted by KTL View Post
Good friend has a GT3 Cup with a similar style clutch. Stalls it almost every time in the pit area when backing out of his parking spot.
Love it Kevin! No DME or chip ... just carbs and a right foot. Ill look into the kennedy set up too. Any idea on the life span of the cluth when you had it? Thanks for the info.
Old 12-11-2013, 12:30 PM
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+1 what KTL said.
Old 12-11-2013, 12:35 PM
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I think the clutch disc has a good life span. The one I had in there when I got it (2010) was fairly well used since around 2004, but still had good life it in. Car was used quite a lot from 03-07 and then sat 08-09 while guy was getting out of the racing thing w/personal stuff. When I had the engine out for rebuild 2012, I had KEP look at the clutch and re-line the disc just as a matter of while in there. Re-lining the disc was like $40, which was a steal! So the clutch had a pretty long lifespan to it.

If you want the uber light one, you have to ask for the all aluminum unit. The heavier one, but still much ligher than stock, is the aluminum housing with iron friction surface. The heavy one should last forever since it's got your typical iron friction surface.
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'79 911SC-based 3.0L 930S/934/965/911R looking thing NASA GTS-3
Enginerded by Red Snail Racing, MotoDelta Motorsports, G2 Performance, Elbowmotions
'87 Carrera- gone 7/25/14 but never forgotten
Old 12-12-2013, 06:34 AM
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Old 12-12-2013, 06:34 AM
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