Dual Mass Flywheel versus Lightweight Flywheel

[Lyn]

Have any of you tried a lightweight flywheel in your 3.6 or 3.8 997s? I know that the change causes transmission "rattle" noise at idle speeds, but I'm interested on the effect on drivability. Does the lighter flywheel make it more difficult to drive smoothly at low speeds, or does the quicker throttle response offset the negatives??

[JFP in PA]

Have any of you tried a lightweight flywheel in your 3.6 or 3.8 997s? I know that the change causes transmission "rattle" noise at idle speeds, but I'm interested on the effect on drivability. Does the lighter flywheel make it more difficult to drive smoothly at low speeds, or does the quicker throttle response offset the negatives??

You also need to do a search on problems associated with the use of single mass flywheels on these engines. Porsche even release a tech bulletin about not using them due to loss of torsional and harmonic dampening, which is what the dual mass is there for. Some engine builders will not use them unless the engine is first properly rebalanced. I know someone will chime in and tell you that they have had one for years and not had problems, but I can assure you that is not always the case, and the results can be disasterous.

This is what happened to a 3.6 X51 engine that was not rebalanced before using a light weight single mass flywheel, if you want to read more about it, start here:

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

[Silver_TT]

JFP is spot on. Do not replace your dual mass flywheel. The harmonic dampening it provides is key....and a potential recipe for a very expensive disaster if you remove it.

Also, I previously owned a 3.6L manual transmission and never noticed a rattle at idle. Are you sure this is the dual mass flywheel causing the noise?

[JFP in PA]

JFP is spot on. Do not replace your dual mass flywheel. The harmonic dampening it provides is key....and a potential recipe for a very expensive disaster if you remove it.

Also, I previously owned a 3.6L manual transmission and never noticed a rattle at idle. Are you sure this is the dual mass flywheel causing the noise?

I think he is referring to the rattle and noise you get after switching to a single mass lightweight flywheel, which is a common complaint, and an indication of the loss of dampening.

[Silver_TT]

Indeed....you are correct (as usual)!

[Lyn]

Thx to all for stepping in with your knowlege and comments. That's what the Forum is for and I really appreciate the collective input.

[logray]

Continuing from JFP's post above...

"...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." - Jake Raby from http://www.flat6innovations.com/index.php/broken-crank