Lighter Flywheel for Manual Transmission?

[SVOboy]

I am just going by what I've heard, so it very well may be wrong. I don't have any drivability issues with my very slightly less than stock weight flywheel.

[GasSavers_TomO]

I can personally attest to the CX/VX flywheel being 3lbs lighter as well.

As far as a lightened flywheel helping FE...I took a stock B18A1 flywheel (19lbs stock) and milled it down to 11.25lbs. I had swapped this motor into my 91 CRX Si and it had no ill effect on driveability. It reduced reciprocating mass and allowed for better acceleration. Revs did drop a little bit faster but nothing that an experienced driver couldn't handle. One downfall for FE would be the fact that if you coast in gear the RPMs fall more quickly than with a heavier flywheel. But all-in-all it was a boon to FE on the car. I was able to maintain 42MPG on that car without any real FE orientated driving at all. This did include many runs up to 60MPh on entrance ramps and plenty of auto cross events.

[DRW]

I can vouch for the difficulty in shifting gears with a very light flywheel/rotating assembly. My other car has an 8 pound aluminum flywheel (stock was 19 lbs.), light crank pulley, lighter pistons and rods, and a few other things that let it spin up/down with less force. Altogether there is about 22 pounds removed from the rotating assembly. When I shift slow, like when I'm driving in city traffic, the rpms will fall too quick and the car jerks when the next gear is engaged. If I shift quickly it's smooth.

I could also feel the difference in accelleration; in lower gears it was more pronounced, not so much of a difference in high gears. That link to the Puma Racing website was a nice read, thx.

I'd say that if someone did most of their driving around town with plenty of stop-and-go traffic with pulse and glide, a light flywheel would benefit. In this scenario gas is used to accellerate the car/flywheel, so lighter is better. Since pulse-n-glide does the decel with EOC none of the stored energy in the flywheel is recaptured (like Ted alluded to), so use a flywheel that stores the least energy. The individuals driving technique could also change to suit the cars strengths.

For someone who does mostly freeway commutes (me and my Laser) there might not be much FE gained. There's high gearing and slow rates of accelleration that greatly reduce the benefit of a light flywheel. (is that a circular argument? )

[DRW]

I just finished reading the link to teamswift's discussion and I wanted to add something just in case someone on this forum was looking. On that forum Martinq kept bringing up the point of using a heavy flywheel to smooth out the engines power pulses. This is not needed since the clutch disc does that job already. Here's a pic of a clutch disc, http://www.roadraceengineering.com/p...ksprunghub.gif Notice the six small springs? They are arranged so any torsional pulses, shocks, or bucking will be reduced before it's transmitted down the driveline. It also helps the longevity of the tranny since the gears and bearings aren't being constantly hammered on. HTH

[onegammyleg]

Originally Posted by DRW

Notice the six small springs? They are arranged so any torsional pulses, shocks, or bucking will be reduced before it's transmitted down the driveline.

The flywheel does indeed dampen the firing pulses of the engine.

Those springs on the clutch plate are anti-judder springs and they are for dampening clutch action.

Clutch plates are not even thickness even when new and pressure plates do not provide an equal clamping force across the whole clutch plate.
When being released the pressure plate also does not bear down on the clutch plate perfectly flat.

These combined produce a juddering effect when you release the clutch , caused by a cycling of slipping and releasing.

Road cars (unlike race cars) get a lot of clutch slippage when being driven through the gears.
The anti-judder springs do their job by absorbing the judder.

Apart from that they do no nothing else and they don't absorb engine firing pulses or other road train vibrations as they are fully compressed by engine power in normal driving.

(they may take away a little bump when going on and off the gas pedal rapidly - but this action is not their primary purpose)