alluminum flywheel?

[Hib Halverson]

It's not the aluminum flywheels that rattle.

It's the transmission. The correct nomenclature is "gear rattle". It happens at idle and at very low engine speeds under light load. It occurs because, at idle and low engine speeds and only four firing impulses per revolution, engine speed actually fluctuates enough at a low frequency that the main drive gear and the counter gear start "rattling" because of the clearance between the teeth.

In the manual transmission nomenclature, "center distance" is the distance between the centerline of the drive gears and the centerline of the countershaft. The greater the center distance, the more pronounced the gear rattle will be. During early development of the S6-40, it was quickly obvious that gear-rattle was a problem.

The dual-mass flywheel designed for the first LT5?one of the first applications of that technology in a light vehicle?was a partial solution to gear rattle. The flywheel had a spring damped secondary mass the purpose of which was to "smooth out" the torque fluctuations caused by firing impulses at idle RPM.

Install an aluminum flywheel, which is a standard or "single mass" wheel, and you eliminate the gear rattle mitigating the function of the dual mass wheel. With an early-style, 610-Nm transmission, the increase in rattle is very noticeable. With a late-style, 540-Nm transmission, the increase is noticeable but not so bad.

As I was not a drag racer and liked the quicker engine acceleration which comes with an aluminum flywheel, I installed a McLeod aluminum wheel in Barney, my dear-departed '95 SN 140. There was an increase in rattle, but I cut that about in half by installing higher output ignition coils, then opening up the plug gaps by .010 or so and going to Red Line Lightweight Shockproof Gear Oil which used a calcium-based EP additive package that has a cushioning effect between gear teeth.

Those solutions would still be valid, today.

[Karl]

Thanks for the tips Hib. I have a spec aluminum flywheel and it weights ~18 lbs. Gear rattle is minimal compared to the fidanza. I also use the redline oil.

What high output ignition coils were you using?

[EvanZR1]

I have Pete's 391 and stage 2 cams with stock clutch & flywheel and the trans rattles a good amount, would hate to see what it's like with an aluminum flywheel. Doesn't really bug me much as the car is already loud and obnoxious. If I was running a car with stock cams, I don't know if I could bring myself to run an aluminum flywheel because the rattle would stand out more.

[efnfast]

I have a light weight, single mass flywheel. Not a big fan of the rattle, but just couldn't leave that additional hp laying around. ( I know, it's really not hp.)

[Hib Halverson]

Originally Posted by Karl

Thanks for the tips Hib. I have a spec aluminum flywheel and it weights ~18 lbs. Gear rattle is minimal compared to the fidanza. I also use the redline oil.

What high output ignition coils were you using?

At different times I had either Performance Distributors or MSD coils on my engine. I ran Denso IT22s with the gaps opened up about .010 more than the stock gap. The idea there was a bigger gap exposed more of the air/fuel charge to the spark. In some cases that would light a lean air/fuel charge which otherwise would not ignite making for a misfire.

The gear rattle is always worse if there is a misfire at idle. My strategies were to 1) reduce misfire at idle with hot coils and 2) bigger plug gap.

The "cushioning" effect of the calcium-based EP additive package in all Red Line Shockproof Gear Lubricants, mitigated the gear rattle problem.

I was never able to get rid of all the gear rattle increase from the use of an aluminum wheel, but I did reduce it such that it was less annoying.

[Karl]

Originally Posted by Hib Halverson

At different times I had either Performance Distributors

Do you have a part number or source for the Performance Distributors ignition coil?

[BigJohn]

Now you have me Confused again!

[Karl]

I believe this is the part

https://www.summitracing.com/parts/dui-31727

https://www.summitracing.com/parts/dui-31733

"Screamin' Demon Coils"

*edit will these fit under the plenum without any issues?

[Paul Workman]

Here is my LT5 with the 13# Fidanza FW. The idle was bumped to 900 AND, per Marc Haibeck and Hib's suggestion, I switched to the Redline Heavy Shockproof gear oil. Oh, also, the temp was ~ 25?F (in the video), but in fact the rattle (or LACK thereof) is also still true of summer temperatures - FWIW. The coils are stock GM AC/Delco and the plugs are good ol' copper core AC Delco 41-602s gapped @ .042" per Pete Polatsidis'

In contrast, Ami's Z has Pete's cams and AL flywheel, and it idles with a righteous sound thru the B&B catback, but it rattles in neutral like a box of rocks(!). (I doubt a ▲ of gear oil (to Redline or whatever) would make much difference tho...)

https://www.youtube.com/watch?v=y1YFa8ruh8A

[Flyman 27]

When I purchased my ZR-1 it had a Fidanza aluminum flywheel in it. I absolutely hated it. It rattled loudly and I really got tired of explaining to everyone that the engine was not going to blow, it was just trans gears rattling. I am running a Haibeck 500 pkg.
Mark swapped a dual mass flywheel & clutch asm and I could not be happier with it. It is quieter, shifts smoother and no more rattles!
That's my 2 cents.