Why doesn't anyone make a near-normal weight single mass flywheel?

[Gilles]

[QUOTE=Cloudsurfer]Engine harmonics. There's a reason why I'm running an RSS dampened front crank pulley on my engine with an AASCO flywheel.

Cloud,

How long ago did you installed yours?

I called RSS a couple of months ago inquiring for a dampened front crank pulley for the Cayman and they told me that the only one they offer was for the GT3 or (911..?)

I was planning to install the AASCO LWFW but also wanted the dampened front pulley, how do you like your combo..?

I am currently using the BBI pulley (non dampening)

[Cloudsurfer]

[QUOTE=Gilles]

Originally Posted by Cloudsurfer

Engine harmonics. There's a reason why I'm running an RSS dampened front crank pulley on my engine with an AASCO flywheel.

Cloud,

How long ago did you installed yours?

I called RSS a couple of months ago inquiring for a dampened front crank pulley for the Cayman and they told me that the only one they offer was for the GT3 or (911..?)

I was planning to install the AASCO LWFW but also wanted the dampened front pulley, how do you like your combo..?

I am currently using the BBI pulley (non dampening)

I've got a few thousand on the motor with the AASCO and RSS pulley. Hasn't blown up yet and drives great

[JoeFromPA]

JFP -

Thanks so much. That is exactly the type of information I was looking for...

I'm guessing that Porsche uses a metallurgy in their crankshaft that allows them to break under such stresses. This isn't a criticism; they designed the crank to be used with a specific flywheel and provide longevity.

Perhaps it is the specific application of a solid-mass aluminum+steel flywheel that's less than 1/2 the weight of the stock dual-mass flywheel on this particular crankshaft....I haven't seen/heard cranks breaking as even a concern when switching back and forth between single mass/dual-mass on an otherwise stock rotating assembly.

Reading Jake's comments, I understand now why a vendor hasn't chosen to develop a 25+ pound single-mass flywheel for these engines. It's just not a choice they want to entertain, given the available options.

[Cloudsurfer]

Originally Posted by JoeFromPA

JFP -

Thanks so much. That is exactly the type of information I was looking for...

I'm guessing that Porsche uses a metallurgy in their crankshaft that allows them to break under such stresses. This isn't a criticism; they designed the crank to be used with a specific flywheel and provide longevity.

Perhaps it is the specific application of a solid-mass aluminum+steel flywheel that's less than 1/2 the weight of the stock dual-mass flywheel on this particular crankshaft....I haven't seen/heard cranks breaking as even a concern when switching back and forth between single mass/dual-mass on an otherwise stock rotating assembly.

Reading Jake's comments, I understand now why a vendor hasn't chosen to develop a 25+ pound single-mass flywheel for these engines. It's just not a choice they want to entertain, given the available options.

This isn't a problem that only affects Porsches. Any engine crankshaft is prone to failure from harmonics if those harmonics excite the crank at any of its resonant frequencies. Plenty of kids have learned this the hard way by removing the harmonically damped crank pulleys on cars and replacing it with an un-damped, underdrive pulley with disastrous results.

For that matter, it's not just internal combustion engine crankshafts that are prone to this. Many aircraft turbine engines have specific speeds (which are only seen during start up/ shut down on most engines) that absolutely have to avoided, as they are the resonant frequency speeds of the shaft. This can be a problem during a "hung start," when, if the pilot does not abort the start sequence, the engine could be left at one of these critical RPMs for longer than the time it takes to simply "spin through" it on the way up or down, with very severe consequences.

It is worth noting, however, that the cranks in these engines are NOT forged.

For whatever reason, Porsche chose to not utilize a harmonic damper on these engines, at least until the M97 3.8 came out, and thus the dual mass flywheel is of critical importance.

On most cars, this isn't a huge deal as the car already has a harmonic damper on the other end of the crank.

I'm of the opinion that you CAN run a single mass flywheel IF you put some damping back into the equation with a dampened front pulley. If the engine is internally balanced that's obviously a huge benefit which will lessen the loads that need to be damped in the first place.

As to making a "heavy" single mass flywheel, there would be absolutely no reason to bother. If you want a heavy flywheel, keep the stock dual mass. If you want a single mass flywheel, it may as well be lighter and enhance the free-revving capabilities of the car.

[JoeFromPA]

Hey Cloud,

Thanks for your response. Perhaps my experiences lie in engines that are harmonically balanced elsewhere, perhaps not.

As to your statement, "As to making a "heavy" single mass flywheel, there would be absolutely no reason to bother. If you want a heavy flywheel, keep the stock dual mass. If you want a single mass flywheel, it may as well be lighter and enhance the free-revving capabilities of the car."

My original thought was that alot of boxsters get 5-10k a year on them in terms of mileage. A flywheel on a car driven such yearly distances in a normal driving scenario (i.e. few long high rpm clutch slipping events) should last a very long time. And, if it's single-mass, could be re-surfaced and last indefinitely.

Instead, from what I can tell, we see boxsters with fine clutches but flywheels that are out-of-spec or no longer engage right because their damping mechanisms are wearing out from age.

So my thought was: Why not create a similarly weighted single-mass flywheel so that boxsters that accumulate normal-driving mileage at a low rate can expect a normal lifespan from their clutch/flywheels once they replace the OEM unit.

Sounds like it's still possible, but would need to be paired with some additional dampening mechanisms.