is lightened flywheel worth it

[Tut]

I have an '87 that I take to several DEs each year. Suspension is now a rolling advertisement for Elephant Racing. Time to move on to drivetrain and brakes. Engine is stock. I'm going to install a Steve Wong chip for 93 octane, as well as a cat bypass. Have been looking a lightened flywheel/clutch packages at Patrick Motorsports. Would that make a noticeable difference in terms of low end acceleration?

[mreid]

I have one of the PMS lightened flywheels in my 74 with a 3.6. I love it!

[will hung]

I also have a PMS lightened flywheel along with an aluminum pressure plate. I was afraid that it would be too light, but it's perfect. The engine revs so freely all the way to the redline, but it isn't exhausting in stop and go traffic.

The only problem I have with the parts is that you can't see them. I sat and admired the flywheel for longer than I'd like to admit, it was so awesome looking.

[bkreigsr]

Yes
Ignore the nay-sayers - you will be able to adapt to what some consider 'drivability' issues once you get a few hundred miles under your belt.
Bill K

[Quicksilver]

The flywheel on an 87 is already light. The weight is in the pressure plate.

I put in a Kennedy Engineering lightweight pressure plate about 14 years ago. It makes a noticeable improvement is how fast the engine will rev-match plus if you measure acceleration with a stopwatch it makes a real improvement in 1st and 2nd gear. It took me a couple weeks to get used to the reduced mass so for a couple weeks I had a tendency to stall the motor when backing into the garage. That hasn't been an issue since.
It does have a slightly higher pedal effort so you should be prepared for that. Plus if there are any issues with the release system it will make them more noticeable.

Was it worth it? I wouldn't settle for the stock setup ever again.

[Bill Verburg]

Originally Posted by Quicksilver

The flywheel on an 87 is already light. The weight is in the pressure plate.

...

and in the rubber center clutch disk which is worth getting rid of even if you wouldn't lose any weight.

[wildcat077]

I second all of the above ... i have a Patrick Motorsports lightweight flywheel and a KEP lightweight pressure plate in my 89 with a 3.6 conversion and i also have a Lindsey Racing lightweight flywheel and pressure plate in my 944 race car !

Cheers
Phil

[DRACO A5OG]

Originally Posted by bkreigsr

Yes
Ignore the nay-sayers - you will be able to adapt to what some consider 'drivability' issues once you get a few hundred miles under your belt.
Bill K

Brother Bill,

So, do you have both "LITE" Fly Wheel and Pressure Plate set up on your 915? I assume you also have LSD. Any other mods to the Clutch, Gear Box to Axels of note? I just don't want to leave a weak link if I go this route and do not mind at all to re-learn how to clutch play.

Is OEM Sachs clutch adequate. I am picturing a faster spinning clutch will wear sooner, no???

Jim

[911pcars]

Originally Posted by DRACO A5OG

Brother Bill,

So, do you have both "LITE" Fly Wheel and Pressure Plate set up on your 915? I assume you also have LSD. Any other mods to the Clutch, Gear Box to Axels of note? I just don't want to leave a weak link if I go this route and do not mind at all to re-learn how to clutch play.

Is OEM Sachs clutch adequate. I am picturing a faster spinning clutch will wear sooner, no???

Jim

Jim,
The flywheel just has less mass, thus will rev to speed in less time. Max. rpm isn't affected - that's determined by the reciprocating mass inside the engine. Clutch rotational speed is as before, but speed differential w/flywheel can exacerbate wear, but minimized by skillful rev-matching. Smooth clutch engagement from a standing start can potentially accelerate clutch disk wear. YMMV.

Sherwood

[DRACO A5OG]

Thank you Dr Sherwood.

Yeap, I am a dork on the clutch on my OEM set up. As my buddy keeps yelling at me to stop worrying about stalling clutch and properly without riding it.

I will most likely than not wear out the clutch faster than I do now.

I have a new pressue plate to put in since mine has lost it tensil strength and did not know there was a LITE pressure plate option besides the NLA OEM aluminum pressure plate.

Hmmmmm???

Jim

[trond]

I did not like it all. Had the (beautiful) Patrick Motorsports light flywheel and light Sachs clutch but went back to stock for in town driveability. Depends on use I guess

[DRACO A5OG]

Has anyone just do the pressure plate?

[irobertson]

I have a stock flywheel and a Kennedy Engineering pressure plate and spring centred clutch in my '88 and I really like it. There is a little gear rattle at idle in neutral, but the engine revs nice and free. It requires a little more finesse off the line, but the shifting is nicer once you get rolling.

[911pcars]

Originally Posted by DRACO A5OG

Has anyone just do the pressure plate?

Jim,
Yes (al. cover PP), but I'd be hard pressed to tell the difference. I have/had no reference point.

S

[TimT]

The flywheel on an 87 is already light.

Love me some maths

The PP is the elephant in the room as it were... get a lightweight pressure plate

[Driven97]

Having just replaced an oem flywheel, I can't believe there is all that much weight to be lost there. Porsche made it really light.

As stated above, a steel pressure plate is pretty heavy. The aluminum option pp is a bigger deal than the flywheel. That said, it's only money.

[chris_seven]

It seems that this post was not wanted

[Driven97]

^Are those values actual measured inertia or calculated inertia assuming constant mass density? Because if it's the latter, all those calculations are only slightly better than useless.

Tape a C battery to the end of a yardstick, and try to rotate it. Flip it around so that the battery is on the same end as your hand, and try again. Same overall mass, totally different rotational inertia. A flywheel, a rotor, or a wheel are not constant density. The weight is only part of the story, it's more important where the weight is.

For a reduction in inertia, you want mass removed in priority from the largest radius position. Unfortunately, manufacturers just give us weight measurements to go by. That gives you a vague idea, but not necessarily an accurate measure of "better."

[Flieger]

Originally Posted by Driven97

^Are those values actual measured inertia or calculated inertia assuming constant mass density? Because if it's the latter, all those calculations are only slightly better than useless.

Tape a C battery to the end of a yardstick, and try to rotate it. Flip it around so that the battery is on the same end as your hand, and try again. Same overall mass, totally different rotational inertia. A flywheel, a rotor, or a wheel are not constant density. The weight is only part of the story, it's more important where the weight is.

For a reduction in inertia, you want mass removed in priority from the largest radius position. Unfortunately, manufacturers just give us weight measurements to go by. That gives you a vague idea, but not necessarily an accurate measure of "better."

We aren't talking about composites here, so I'm sure he's using "constant mass density" for the material. He already stated that he has the inertia for the various shapes of lightened flywheels (RSR scallops). What he's done is factor in the gear ratios (and then done some complicated maths with energy being stored and released in the flywheel between shifts) to give the effective linear inertia of the flywheel. You do know that gear ratios change the effective inertia, right?

[Driven97]

That's kind of what I'm saying. Looks like whoever did it knew or calculated the actual rotational inertia of the flywheels in question, so those numbers may have merit.

Porsche scalloped the edges of the rsr flywheel because that's where it counts. More effective than "shaving" the equivalent mass out of the entire cross section of the flywheel.

But then they say "simple spreadsheet" and mention wheels. It's not that simple. For example, an 18lb 15" Fuchs is going to have way less rotational inertia than a high dollar 18lb 18" wheel. That's because most of the mass of a wheel is in the barrel. Even though the wheels are the same total mass, the 18" has most of its mass 1.5" further out from the center.

Therefore, an 18lb wheel is not necessarily equivalent to an 18lb wheel. And by extension, a 20lb flywheel may actually have less inertia than a 17lb flywheel depending on how it's lightened.