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mbufkin

Dual mass vs single mass flywheel

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I am having the clutch replaced on my 1999 Carrera 2 and the shop doing the work has recommended replacing the dual mass flywheel with a single mass flywheel. Can anyone explain the advantages and disadvantages of this option?

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I am having the clutch replaced on my 1999 Carrera 2 and the shop doing the work has recommended replacing the dual mass flywheel with a single mass flywheel. Can anyone explain the advantages and disadvantages of this option?

The dual mass flywheel is the only source of harmonic dampening in the engine, removal of that capability can lead to serious issues, like cracked (or worse) crankshafts. These engines are not particularly well internally balanced from the factory, so the dual mass dampening is rather important. More than one leading Porsche engine builder has recommended against using single mass flywheels unless the entire engine components and the flywheel are properly rebalanced as a unit.

A second consideration is how well the single mass itself is balanced; we have seen several that were 10 grams (and more) out as delivered. These flywheels are also difficult to have accurately balanced; only a handful of machine shops can do a proper job. And even after one is correctly rebalanced, they still can be a bit of a pain to drive on the street due to clutch chatter related issues.

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I agree with JFP in PA, but would like to add that when you go to a single mass flywheel you are reducing the weight of the flywheel significantly. This has a benefit of a slightly faster revving engine. If the ECU is not tuned for it, you may have a stalling problem when coming to stops.

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Before you take that shop's advice you might want to read this:

http://www.flat6innovations.com/broken-crank

I believe this is what JFP was referring to. Specifically (and these are Raby's words).......

I feel that this failure was attributed to by a couple of things-1- The engine was "upgraded" to a lightened flywheel. This new flywheel was installed onto the existing stock engine without being balanced to that assembly. This created an imbalance in the rotating mass AND it did away with the factory dual mass flywheel.2- The dual mass flywheel was removed to alow the single mass lightened unit to be installed. This eliminated ALL MEANS OF HARMONIC DAMPENING!! The crankshaft was forced to absorb ALL harmonics from the engine and transaxle when the dual mass unit was removed..So- adding the light weight flywheel was a double negative, not only did it create imbalance, it also eliminated the harmonic dampening of the dual mass arrangement. Due to this I feel that adding a lightweight flywheel to any existing engine is not a wise decision, and that they should only be added when the entire rotating mass can be balanced and indexed to accomodate the lightweight unit. This means engine disassembly, so I'd only add one of these when doing one of our performance upgrades so the entire assembly can be precisely balanced.

Edited by ferrugia

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Definately replace with dual mass flywheel. Check this video out under the videos portion on the menu above.

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Video CLICK HERE

Edited by kbrandsma

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IIRC the experts say stick with the dual mass even if your engine has been balanced to within very fine tolerances, unless perhaps you are building a race car.

If you've gone so far as to tear the engine down and have it profesionally balanced to within say a gram or less, I would say the benefit of having it balanced (along with the others you probably made while you were in there) are likely to far outweigh the benefit of a lighter flywheel.

Remember there is not normally a harmonic underdrive pulley either.

Are there cars on the road with LWFW that don't have problems, sure, but I guess if you want a better insurance policy stay with the DMFW.

FWIW, my dual mass was off by at least 20 grams from the factory (not to mention crank and rods were a few grams off each). That 20 grams out at 5 or 6 inches at 7000RPM is a huge power zapper! Of course, went with micropolish crank and R&R rods (pre-balanced) and everything came to within a gram. Didn't knife edge or anything though. I bet I could safely raise the rev limit!

Edited by logray

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Speaking as the owner of that particular 2 piece crankshaft (now a 20k doorstop), I would also recommend staying with the dual mass FW. I had the LW balanced as well, but Jake still recommends against using it. My car is strictly track, but the small potential increase in performace does not outweigh the cost of a rebuild. I am concentrating on getting the ROI to a sane level and am at 4k track miles and the engine is performing flawlessly.

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Speaking as the owner of that particular 2 piece crankshaft (now a 20k doorstop), I would also recommend staying with the dual mass FW. I had the LW balanced as well, but Jake still recommends against using it. My car is strictly track, but the small potential increase in performace does not outweigh the cost of a rebuild. I am concentrating on getting the ROI to a sane level and am at 4k track miles and the engine is performing flawlessly.
Finally! I've searched the web over, top to bottom, looking for someone, ANYONE, who had even a single failure caused by a LWFW. Now I've finally found one. ONE mind you, amidst literally hundreds of people confirming they've been running their LWFW for years and hundreds of thousands of miles without issue.

Oh, there are plenty of people saying "I know a guy who installed a lwfw and it broke his crank", but in every instance they credit Jake raby as their only source (except JFP, who also credits several porsche engineers as saying it's a bad idea).

Anyway.....
Thanks for posting here as the owner of that infamous crankshaft. I was beginning to think it was all made-up! Haha

Sent from my SM-G930T using Tapatalk

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Generally speaking, people rarely own up to it on public forums when they make a $20k mistake... You've been warned ?

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