3.9 g6 GXP flywheel

[robertisaar]

NVH has become a huge thing lately. and by lately, i mean starting in at least the early 90s.

i can see why GM would want to make their cars as seamless to operate as possible, and assuming you don't exceed the capacity of the DM flywheel, it works great.

us enthusiasts tend to break things though.

[Joseph Upson]

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.

As I mentioned earlier, the F40 becomes a very noisy transmission at idle speeds below ~800 rpm without the dualmass flywheel. The vette community has lodged the same noise complaint upon eliminating their dualmass flywheel. That along with advancing technology probably has the most to do with it and the fact that the 6 speed transaxle hasn't been around for a decade yet in a GM vehicle. It has other benefits as well, it makes learning to drive a manual shift car easier as the clutch engagement is very smooth.

I can't imagine harmonics being more critical for the F40 than all the trannies before it that didn't have the benefit of a dualmass flywheel especially in the Fiero community where nearly every engine GM has made since the car was made has been mated to one of its manual trannies using a solid flywheel.

Did I mention the dualmass unit weighs 25 lbs by itself and it's also a perishable item like a clutch disc.

[pocket-rocket]

People are too prissy to drive real cars. They need to be all sleek and tidy and plush and girly. Anyone that doesn't want to deal with engine and drive line noises should only be allowed to buy something like a Prius or an Aveo or something like that, not something with enough power to break stuff. Hence my title, lol.

[NateD4]

Well, I had a really nice reply typed up but I took too long and I got logged out and poof it disappeared into nowhere land.


Actually the importance of the dual mass flywheel over conventional has to do with the ability of the flywheel to reduce the total torque experienced by the transmission. It does this by absorbing a pulse and then releasing it over a longer period of time. It thereby exposes the transmission gears to less total torque. This allows the designer to design a gear which sees less extreme stress fatigue cycles. This then allows them to be less conservative on their designs. So they can either make the gears with less metal or they can up-rate the torque they can handle all the while still offering the customer a 100K mile warranty.

This is how the new F40 can handle nearly 300 Ftlbs and the old Getrag 282 and 284 can not. Yet, there is only a small change in weight. Of course if you dont' mind cutting into the fatigue life of the parts you can push the transmissions well beyond their ratings.

The best comparison I came up with is crumple zones of cars or shock absorbers and a really bumpy road. The dual mass flywheel imply spreads the high energy pulse of the energy out over a longer period of time and exposes the entire drive train to a lower peak value but a higher average value.

Hope this makes some sense.

I had all the math typed out and a really good explanation but its floating around in the nether somewhere.

NVH is probably only a small part of why they do it, though today it appears to be more and more important.


Here is a video of a valve spring that actually has a high speed vibration after the valve closes you can see the spring dissipating the energy as it vibrates a few times. Keep in mind this is happening at 7000 RPM.

http://www.youtube.com/watch?v=i_NpzU4pGjc

Interestingly enough something very similar happens with a flywheel every time a piston fires.... it actually winds up the crank and causes the crank to oscillate a few times. The flywheel mass on a conventional flywheel actually resists this and prevents the crank from properly damping the vibration. This also causes higher stresses in the crank and the transmission.

[NateD4]

Pocket Rocket,

So you drive a miniature motorcycle?

[NateD4]

Joseph,

I think its as much about warranty as it is about noise. Though with the Gov't mandating higher mileage they need 6th gear for cruise and lower RPM... they also then need to make sure they don't annoy the customer with vibration at low RPMs. It really is a perception thing in that regard. (though the stuff I mentioned about load rating matters)

GM is competing with other companies that do worry about things like noise and harshness so they need to stay competitive.

Also its a win win for GM and Sachs if they can sell you a part that wears out at 100,001 miles. They sell you service and a new part.

But that doesn't meant they can't be rebuilt and repaired. You just have to know how and know the right shops with the right equipment.

[robertisaar]

there is at least one 284 that's holding up to 700 ft/lb...

however, there is also a F40 that pushes 500 ft/lb via a LS7...

obviously, both have had work done to them.



stock transaxle meant for stock engine: hard to break it(unless you're trying). we start moving beyond 240/240, that's when things get hairy. cryo the internals and either figure out a way to make the dual-mass last or get a good single-mass.

personally, i'm liking the LQ1/2006 F40 combo.

[bszopi]

Well, I had a really nice reply typed up but I took too long and I got logged out and poof it disappeared into nowhere land.

OT, but this will be fixed the next time I upgrade the site software. The latest version has an auto-save feature built into the editor, so you shouldn't loose long posts anymore.

[pocket-rocket]

Pocket Rocket,

So you drive a miniature motorcycle?

No, I created my name thinking I wouldn't be interacting much with the community and made it more out of being a joke name than an actual name to be taken seriously.

The explanation makes perfect sense. The dual mass is a "buffer" between the engine and tranny so they can make a weaker tranny, basically, cutting corners for more profit. The 284 may be rated at less than 300 ft.lbs, But I highly doubt it has a harder time handling higher loads than a newer transmission.

[Joseph Upson]

I'm aware of the true nature of the dualmass flywheel regarding what it does and how it does it Nate, so no need to put yourself through the trouble of the math although I appreciate it, and warranty concerns go without saying. I'm just letting all interested know that the transmission is very noisy without the dualmass flywheel at typical idle levels. Remember I actually have one in a car. The noise can be excessive and unattractive to even the most devoted performance enthusiast. The noise offers no benefit unless you like the sound of raggedy and about to fall apart.

Another point to remember is that the noise issue maybe tied into the addition of a 6th gear and the design to accomodate it.
Also as far as modifying the flywheel, remember there is grease in it also. The design has to lend itself to the modifications mentioned. Not sure if you've seen the one from the G6 up close, but the upper hub is connected to the lower with what appears to be a similar process to how the lobes are locked into place on the camshaft. It really appears flimsy. Perhaps that's why there has been so many stock clutch system failures from what I've heard between the flywheel and the disc.

For all we know the dualmass flywheel in this application was mandatory to accomodate GM engines as the F40 as well as the 5spd F35 for the cobalt SS and redline are Saab originals from as early as 2003 that were used by GM, so if the recessed input shaft in the F40 was present from the start, the dualmass would be practical to fill the gap regardless of its scientific reasons.

[Joseph Upson]

I forgot to mention that a good part of the shock load handling attributed to the dualmass flywheel was handled by the sprung clutch hub in the earlier GM trannies as with the F40 assembly the springs in the disc are so small as not to contribute much except to help with tranny noise as explained by a clutch builder. Its nearly a solid hub.

[pocket-rocket]

I'm familiar with tranny noise. My 284 rattles at idle because of the exhaust cams being retarded 13 degrees and that modification giving the engine a lopey idle. Before the modified cam timing and the cams were set to stock and the engine idled smooth, there was no noise from the transmission. Now that Joseph mentions 6th gear, I wouldn't doubt that's the reason for the excess noise. The rattle in my is fairly easy to deal with because it's not obnoxious, but you know it's there when you stop and the radio is down.

[jdaniels]

The flywheel that Mr. Upson posted is mine, it's actually a custom unit that was tooled for me by Clutchmasters. I was on a mission to have 10x made @ $375 shipped per unit but I fell short on interest with other parties. The flywheel was sold to me for near cost, $795 shipped, due to it being a single run custom unit and all the measuring and tool setup factored into one piece. It's a wonderful unit, weighs approximately 12# and has a replaceable friction surface on it. I just installed it yesterday along with a SPEC Stage 4+ clutch (Hybrid stage 3+ with rigid hub). The unit itself is amazing, the car revs freely and power delivery is smooth. The clutch itself is very manageable and actually has the ability to slip for smooth starts unlike the pucked clutches I have tried. One thing that is Very apparent however is the noise at idle, it's exactly as Joseph says. It sounds nearly like a VW TDI idling in my opinion! Pushing the clutch in makes the noise disappear completely. Under load I don't hear the noise at all.

Anyhow, sorry for my first post to be a run on but I thought I'd chime in. Anyone with questions on the flywheel etc just let me know and I'll try to answer them.

Jon

[jdaniels]

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.

I don't think they actually ever produced the '06 GXP at all. Regardless, it was to be the same car but with a less restrictive intake and exhaust. Heard a little about the cam being bigger but I highly doubt it considering the engine code was still LZ9. Other than that, it was probably just timing advance (spark and physical via VVT) that was added to make the higher BHP number. My GTP came alive after I street tuned it with higher octane fuel and more adavance. I actually run e85 right now.

[Joseph Upson]

I don't think they actually ever produced the '06 GXP at all. Regardless, it was to be the same car but with a less restrictive intake and exhaust. Heard a little about the cam being bigger but I highly doubt it considering the engine code was still LZ9. Other than that, it was probably just timing advance (spark and physical via VVT) that was added to make the higher BHP number. My GTP came alive after I street tuned it with higher octane fuel and more adavance. I actually run e85 right now.

Glad to hear it's working out well and for further discouragement to anyone considering the stock flywheel for a performance application, I do believe I made it slip at least once as the pressure plate applies a pretty good clamping force leading me to suspect the flywheel during that one instance. I had the Kevlar disc in place at the time and upon tear down for the engine swap it didn't show any signs of abuse or overheat.