[JFP in PA]

Originally Posted by Gelbster

Inadvertently I think we are on a previously well researched path. Curious that no product has yet emerged. I googgled "Porsche+996 harmonic+balancer" and #1 was this = day jar view?:
Snapped Crankshaft (with pics) - 996 Series (Carrera, Carrera 4, Carrera 4S, Targa) - RennTech.org Forums
Installing M97 3.8 Harmonic Damper? - 996 Series (Carrera, Carrera 4, Carrera 4S, Targa) - RennTech.org Forums

I think one of the biggest issues was mentioned by poster #2 in that first thread; "RFM "is a retired Porsche engineer living in Belgium that worked on the design and production of the M96/97 during his career with them. He knows an awful lot about these engines, and their weaknesses.

Poster #12 quotes the following advisory from Porsche NA to their dealer network concerning warrantees and the use of single mass flywheels on their 997 GT3 cars (which they expected to be wailed on at the track):

"• The single-mass flywheel causes fluctuations and vibration in the lower rpm range, thereby reducing the smooth-running performance of the engine.
• The crankshaft is subjected to one-sided loading, causing stress peaks that can result in damage to the crankshaft.
• The one-sided loading of the crankshaft can cause the pulley to come loose, resulting in damage to the belt drive and engine.
• Any damage relating to conversion or damage that can be attributed to conversion is not covered under warranty"

Jake (and others) have also noted significant unbalanced conditions on certain brand light weight single mass flywheels right out of the box. One was a much as 15 grams out of balance, brand new. Others of the same brand were much better balanced, but still not perfect.

I don't think anyone with serious experience with engines would deny that lightweight flywheels have certain inherent advantage's over heavy units. But in this case you are dealing with a number of uncertainties; the engine has certain design elements, such as the component spacing and material of manufacture in the crankshaft, which when combined with inconsistent inherent balance characteristics of the lightweight replacement flywheel itself, can lead to a complete disaster. Some work fine, others shake the crank apart; the problem is that you don't know which engine and flywheel combinations will work, and which ones won't without doing a lot of work before trying the lightweight flywheel. This is why both some engine builders and a lot of shops back away from using them, we don't want customers coming back with two or more piece cranks.