quote Originally posted by fieroguru: Joseph Upson has said that the 3.9L flwheel is a torque limiting design. For his turbo 3.9 swap, he ended up pinning it to eliminate the torque limiting feature. His current flywheel is from a RWD 2.8, that came with a 148 tooth ring gear, but that ring gear would not fit inside the tranny, so he turned down the ring gear landing to fit the 142 tooth one. In the mall, Joseph Upson and some other G6 guys were putting together a group buy for an alumimun 1 piece flwheel that was essentially a copy of the 3.9 flywheel for around $350 The other concern I would have with using the stock G6 flwheel, is it has a raised pressure plate and I am not sure if any of the after market clutch manufacturers will support that application... until they do, you might be stuck running a stock clutch that is probably marginal at best for a stock LS4.

While the dual mass flywheel does limit torque a bit, I don't think it would be a problem on a stock LS4, or one with only DoD delete, and LS1 cam. Joseph's turbo 3.9 is making more torque/power than a stock LS4. Now, a built LS4 making much more power might have some issues. The only thing I'm really wondering about with the 3.9 flywheel is if the bolt circle diameter is the same. It is the same 6 bolt style as the LS4, but I don't know if the diameter is the same on the circle.

I'm not sure the pressure plate design on the G6 flywheel is a big issue. At least, I've been able to find aftermarket clutches for it. No flywheels, but a clutch at least. And from the 6 speed thread it seems like the stock clutch is probably plenty good for a stock street LS4. I probably wouldn't recommend tracking it with that setup, but should be fine for normal everyday street driving.

quote Originally posted by fieroguru: Probably the best/lowest cost solution is for someone to manufacture blank flywheels for the F40. The 2.5, 2.8, 3.1, 3.4, 3.4TDC, 3400, 3500, 3900, 3800, 4.9, N*, and LS4 could all use the same basic flwheel design, just with the proper center bore, crank pattern and imbalance for those that need it.

(from a guy who hasn't measured a dam thing related to this task)
Instead of making an entirely new flywheel, is it possible to make an assembly to stack on top of the flexplate? The assembly would consist of:
- a hub that would stack on the OE flexplate. The crank flange bolts would go through the hub and the flexplate.
- a flange that would bolt to the hub. The bolts would come through from the engine side and thread into the flange. The side of the flange opposite the engine would be the clutch friction surface. The flange would be 5/16-3/8" thick steel. The OD would be large enough to bolt the pressure plate to it and the ID would be large enough to for the sprung hub of a clutch disk to slip inside.

I bet the whole assembly could fit inside 15 lbs. It would be much easier to make than your flywheel, because the flange could be cut by laser or water-jet and the hub would be much simpler to machine than an entire flywheel.

[This message has been edited by Will (edited 04-22-2011).]

quote Originally posted by Will: (from a guy who hasn't measured a dam thing related to this task) Instead of making an entirely new flywheel, is it possible to make an assembly to stack on top of the flexplate? The assembly would consist of: - a hub that would stack on the OE flexplate. The crank flange bolts would go through the hub and the flexplate. - a flange that would bolt to the hub. The bolts would come through from the engine side and thread into the flange. The side of the flange opposite the engine would be the clutch friction surface. The flange would be 5/16-3/8" thick steel. The OD would be large enough to bolt the pressure plate to it and the ID would be large enough to for the sprung hub of a clutch disk to slip inside. I bet the whole assembly could fit inside 15 lbs. It would be much easier to make than your flywheel, because the flange could be cut by laser or water-jet and the hub would be much simpler to machine than an entire flywheel.

That could work as well.

You could use the flex plate, two .417" LS1 crankshaft spacers (off the shelf items) stacked on top of each other, topped with a turned down LS1 flywheel (just needs the pressure plate pattern). This would push the clutch surface to about 1.75" and within the acceptable range to use a fiero style 9 1/8" clutch. The hardest part with this setup would be finding the proper length bolts... M11x1.5 around 45mm long, but some of the imports use this diameter and thread pitch for head bolts.

Before the custom flywheel, I had a stacked the Flexplate/LS1 crankshaft spacer/LT1 aluminum flywheel setup. This setup would not work for the 9 7/8" clutch I was trying to use (pressure plate clearance to the transmission), nor would it work with my current 9 7/8" clutch setup, but it would still work with a 9 1/8" size clutch/pressure plate.

You could turn down a stock LS1 flywheel to accept the 142 tooth ring gear and drill the flywheel for Archie's F40 spacer/clutch setup.

Lots of different ways, but almost all of them will require some level of custom machining or outlay of cash.

quote Originally posted by fieroguru: Probably the best/lowest cost solution is for someone to manufacture blank flywheels for the F40. The 2.5, 2.8, 3.1, 3.4, 3.4TDC, 3400, 3500, 3900, 3800, 4.9, N*, and LS4 could all use the same basic flwheel design, just with the proper center bore, crank pattern and imbalance for those that need it.

I wonder if LSC would be up to the task.
They're already used to dealing with us, and their prices are quite reasonable.

quote Originally posted by fieroguru: That could work as well. You could use the flex plate, two .417" LS1 crankshaft spacers (off the shelf items) stacked on top of each other, topped with a turned down LS1 flywheel (just needs the pressure plate pattern). This would push the clutch surface to about 1.75" and within the acceptable range to use a fiero style 9 1/8" clutch. The hardest part with this setup would be finding the proper length bolts... M11x1.5 around 45mm long, but some of the imports use this diameter and thread pitch for head bolts. Before the custom flywheel, I had a stacked the Flexplate/LS1 crankshaft spacer/LT1 aluminum flywheel setup. This setup would not work for the 9 7/8" clutch I was trying to use (pressure plate clearance to the transmission), nor would it work with my current 9 7/8" clutch setup, but it would still work with a 9 1/8" size clutch/pressure plate. You could turn down a stock LS1 flywheel to accept the 142 tooth ring gear and drill the flywheel for Archie's F40 spacer/clutch setup. Lots of different ways, but almost all of them will require some level of custom machining or outlay of cash.

I'm talking about something that can be produced in runs and bolted together... You're talking about hot rodding it every time.

For example, the hub in my design could be counterbored to use stock LS1 flywheel bolts. No need to play with machining a flywheel for a ring gear if you start with a flex plate.

quote Originally posted by Will: I'm talking about something that can be produced in runs and bolted together... You're talking about hot rodding it every time. For example, the hub in my design could be counterbored to use stock LS1 flywheel bolts. No need to play with machining a flywheel for a ring gear if you start with a flex plate.

Agreed, but until a vendor comes forward and wants to spend the upfront costs to get a production run together, we all will be left with doing them one at a time. I was merely sharing some possibilities to do them one at a time with some relatively minor machine work (excluding the custom flywheel).