3.9 g6 GXP flywheel

[NateD4]

Has anyone had any trouble with the dual mass G6 F40 GXP 6 speed manual flywheel?

I'm looking at using one in a boosted application.

[robertisaar]

Joseph Upson would be a good person to ask about this, but i believe he had his stock setup sent out to someone to have it's torque capacity tested and the results were that it could only hold up to ~10% over stock levels?

[pocket-rocket]

I've seen plenty of videos from things like VWs and Caddies dual masses going bad. Didn't Joseph bolt his together to make it one solid unit?

[Joseph Upson]

My flywheel is a modified 3.4L rwd flywheel to accept the smaller diameter ring gear. The 10% estimated increase limit margin was directly from a SACHS representative.

Here is a link to a one piece aluminum replacement that will set you back about $700

http://imageshack.us/g/17/clutchflywheel1.jpg/

[NateD4]

What did the Sachs rep tell you about the flywheels?

I'm not sure I need a replacement flywheel for the stock unless someone has record of breaking one. The stock flywheel has shock and vibration tuning 'stuff' in it.

I am planning more HP but inertia isn't a concern at present. Any other info would be great.

Thats an expensive flywheel. I've gotten quotes in the $500 range.

[robertisaar]

you won't "break" the flywheel, however, if you look up how dual-mass flywheels work, you'll see that there are springs inside the flywheel that allow the two portions of the flywheel to move independantly of each other, but once the springs start getting close to the maximum limit of their compression, there is a friction ring that will start slipping to prevent the springs from just outright failing. now, if the friction ring starts having to slip too often(under higher TQ loads than the 240 + ~10% quoted), it WILL burn out and you'll be left with a flywheel that's completely useless as it will just slip against itself all the time.

if you're a member of any diesel forum that caters to any of the cars/trucks that came equipped with a DM flywheel, you'll quickly see how much they hate them as well.

i'm not sure how feasible it is, but you MAY be able to permanantely lock the two halves together, giving you a heavy flywheel that would stand up to plenty of abuse.

[NateD4]

I didn't know there was a clutch internal to the flywheel. I thought it was rubber or urethane. The springs make sense.

maybe I should take it a part and see what makes it tick. I can probably have an aluminum one made fairly easily. My concern was that they have harmonics that will damage my trans. So I'd hate to lose the damping. Perhaps I can beef up the friction material.

[robertisaar]

http://www.youtube.com/watch?v=YnaXB8q3uzQ

that was a wonderful video for me, as i didn't exactly understand how they worked until i saw it. it doesn't show the friction ring being exceeded(or shown at all now that i think of it), but it would give you a good idea.

[Joseph Upson]

The G6 flywheel has grease in it along with any springs. The dual mass configuration for cars probably has more to do with reducing transmission noise especially due to the 6th gear than it does transmission protection. When it's replaced with a solid piece the transmission produces more chatter at idle. The corvettes do the same when a solid piece is installed.

The HO 3.9 G6 had about 10% more power at 270, but the torque increase was less at around 258 lb/ft suggesting GM was aware of the dualmass flywheel limits.

I experienced a small slip with my first motor but am not sure if it was the flywheel or the clutch though I suspect the flywheel because the stock G6 pressure plate applies enough pressure (2000 lbs) to hold well above the flywheel's expected limit.

[NateD4]

I didn't know GM made a 270 HP HO version of the 3.9. Any idea what was different?

I'm messing with an LZG with 6 speed.

As for the flywheel. Who made yours?

I have heard there is a company that will make one from 4340.

I also have an aluminum blank I can make one from. However, I think for now I will use the stock flywheel. I may pop the rivets off after what you have told me and rebuild it with ceramic friction material. Have you had one apart before?

[robertisaar]

The HO 3.9 G6 had about 10% more power at 270, but the torque increase was less at around 258 lb/ft suggesting GM was aware of the dualmass flywheel limits.

wait, i've never heard of this either?

also, if you've seen the internals to the F40, it's pretty much a guarantee the dual-mass configuration was selected for NVH reasons, not durability issues. they can take the grunt of a LS7 in a fiero with only cryo work.

[Joseph Upson]

I didn't know GM made a 270 HP HO version of the 3.9. Any idea what was different?

I'm messing with an LZG with 6 speed.

As for the flywheel. Who made yours?

I have heard there is a company that will make one from 4340.

I also have an aluminum blank I can make one from. However, I think for now I will use the stock flywheel. I may pop the rivets off after what you have told me and rebuild it with ceramic friction material. Have you had one apart before?

There are or were pictures from the 2006 SEMA show of the G6 with the engine I spoke of in the picture gallery section on this forum with the specifics as to the upgrades.

That's not my flywheel. I sold the owner my extra flywheel and sent it to the company for him so that they could measure it in order to make the one seen in the link.

My flywheel is a modified flywheel from the 3.4L F-body cars and the like. My clutch is a G6 hub with kevlar friction material. My pressure plate is a modified HD piece to produce 2300 lbs of clamping pressure, 300 more than the stock G6 plate and several 100 more than the stock Fiero plate. It was all done by a local clutch builder, except the flywheel which required some machine work and tack welding of the ring at the flywheel flange gaps.

The stock flywheel that was staked didn't workout. It held but had broken 2 of the six bolts below the pressure plate flange. Grease came out of the holes the bolts did not go all the way through due to one pair being shorter than the others. The grease was very dense and hard to clean out of the bellhousing.

wait, i've never heard of this either?

also, if you've seen the internals to the F40, it's pretty much a guarantee the dual-mass configuration was selected for NVH reasons, not durability issues. they can take the grunt of a LS7 in a fiero with only cryo work.

I don't know what NVH means but I only attributed the dualmass flywheel to noise reduction although it also makes for a smoother start among other things. Get rid of it and you will get chatter from the F40, I promise, unless you raise the idle rpm above typical levels.

Again access the pics from the 2006 SEMA show for the HO motor in the gallery. It was not produced.

[robertisaar]

NVH = noise, vibration, harshness.

just think of a HO Q4 when you see the term.

[NateD4]

Joseph,

I did quite a bit of reasearch on these flywheels since my original posting. I see no reason I can't pop the rivets out of it and replace the friction surfaces and preload it with more pressure. I also see no good reason that I can't add a second stage spring to them for over torque use. It can all be done without changing the damping frequencies.

From what I've read some engines produce a driving frequency that is near critical frequency with the transmission components under certain driving conditions (I'd imagine these to be low RPM cruise). In which case you can probably wear transmission components out quickly.

The real benefit to these style flywheels is that they reduce the torsional vibration and thereby allow them to run at a higher torque load then otherwise possible. Basically in audio terms they clip the amplitude of the torque pulses and widen their duration (though mostly conserving the energy under the curve).

If anyone were interested I could put a bit of time into reworking one of these flywheels to handle more torque without sacrificing much of their main function.

Without more info on the gear box I couldn't quite predict how much service life people running solid flywheels are sacrificing.

As it stands I'm pretty sure I'l take mine apart and do something with the slip ring at very minimum. I can't imagine coil-binding the springs to be a huge issue. I'm working on a turbo 3900 and want to double the stock power output and add at least another 100 ftlbs torque to it... so I guess we'll see how it all works out.

[pocket-rocket]

I'm just at a loss as to why, on a naturally balanced engine they have the need to "dampen drive harmonics" with a double mass flywheel? I mean, cars have been in existence for over a century with manual transmissions and in the last decade, they suddenly need them? I wonder what the difference would be in NVH between a solid and a dual mass flywheel in a car that came with a dual mass. I'm not arguing saying they shouldn't have dual mass, and I'm sure when they work as intended they are a swell idea, but of the many videos on dual mass flywheels I saw on youtube, all of them were people having problems with them.