Re: lightened flywheels

[Simon Favre <favres@engmail.ulinear.com>]

I wrote:

>"Steel flywheels can be lightened to improve engine "revviness" without
>compromising street driving.  Aluminum flywheels can make a car almost
>undriveable on the street."

Mike Bendickson replied:

>hmmm.  Never really given flywheels much thought but....  Why does the
>aluminium flywheel become undriveable on the street?  Does the inertia
>of the heavier version help the transition from a stop?  I'm guessing
>that the undriveable characteristic is a large stumble?  The only car
>I've ever driven with one was a friend's 5l Mustang and it seemed fine.
>However, I suppose the rest of the weight of heavy moving bits in a Ford
>engine results in less relative inertia loss from a lightened flywheel
>and the extra couple hundred hp probably helps as well?  just curious,
>my car is not coming apart to replace a perfectly good flywheel.

The flywheel stores rotational energy because i's a (*gasp*) flywheel.
The more inertia, the more energy it stores up.  When you leave the
intersection when the light turns green, you drain some of that energy
out.  You burn gas to put energy back in.  Having a low-torque motor
like an Alfa 4 with a 5 or 7 pound flywheel makes it awfully tough to
get started without killing the motor.  Us racers do it by revving the
motor, slipping the clutch a lot, and praying the motor doesn't die.
;=) I drive a Formula Junior with an Aluminum flywheel, a close ratio
transaxle and a curb weight of only 1100 pounds, and I still manage to
kill the motor once an event.  Often the car is rolling, but the motor
dies anyway.  All I do is pop the clutch and it starts again.

Your friend's 5L Mustang comes with a factory feature called "Torque All
Day Long" that makes it more driveable even with the Aluminum flywheel.
I bet that flywheel still weighs more than one you would put in an Alfa.
It may even weigh more than the stock Alfa flywheel.