"super" light flywheel?!?

[e30rapidic]

I plan on running my old M20 single mass flywheel/clutch set up between my S50 and zf trans. After a quick search tonight, I realized that the M20 flywheel is already 10 pounds lighter than the stock S50 stuff. Kicker is that I just sent the M20 flywheel out to be lightened this week!


According to Turner, the stock S50 flywheel weight is about 24.5 pounds where the M20 single mass is 18.0 pounds. So is it going to be too light now to drive around town without issues?? I sent an e-mail to TRM to see their thoughts on it as I will probably use their chip.


Hopefully I won't have a lightweight M20 flywheel for sale...

[blackhawkimpact]

Lightweight is more like 8-13lbs. You can take the m20 one and have it lighten more.

[Wh33lhop]

You can take the M20 fly down to 12lbs or so without issue, the aluminum S5x flywheels are around 8lbs. My M20 flywheel is down to 12lbs mated to an M50, it's fine.

[e30rapidic]

ok thanks. Told the machinist just to take the mass off the frontside so its all flush..if that makes sense.

So I'm good to go...thanks.

[328ijunkie]

What do you mean front side? motor or trans side? You take too much off the clutch surface and youll have trouble

[e30rapidic]

What do you mean front side? motor or trans side? You take too much off the clutch surface and youll have trouble

side facing the back of the motor, told him to just skim the clutch surface side.

[328ijunkie]

okay yeah thats fine

[e30rapidic]

okay yeah thats fine

cool....thanks!

[Beej '86 325es]

I have a single mass machined down to 12 lbs. from Metric Mechanic that I've run for years. It's light, but not so light that I get excessive clutch chatter.

[Adrian_Visser]

8.5lbs is the lightest flywheel that you can buy, if you go lighter harmonic vibrations become an issue I believe. I have an 11lb JB racing fly and love it.

On the subject of lightweight flywheels is it normal for your engine to sometimes die on return to idle from high rpms when cold?

I mean if I let off the throttle to shift at say 3k and let the revs drop off it will sometimes die when the engine is cold.

I'm not sure if I should be tracking a vacuum leak down here or if it's just a quirk of having such a light flywheel.

[Van Westervelt]

I would think you have another issue. I had an alum fly and machined down right to 8 lbs, schricks in an s50, and I never died when I took the foot off the gas.

Also, shouldnt be driving it too hard while cold still. 3k isnt bad, just saying in general.

[Adrian_Visser]

Yeah I hear ya 3k is the highest I shift at when cold and I try to never push it hard until she warms up.

So this is definitely a problem then, grrr I hate vacuum leaks! I'm getting a MAF code on WOT too I bet they're related.

[imwhyteyo]

my lightweight jb m20 flywheel will occasionally cause me to stall out too.. bu if im rolling popping it in 3rd gets her fired up again

[Chris916]

8.5 lb UUC

[e30s50dan]

15lb lighten m20 fly Cost me$90 and had it resurfaced. Not bad! And oh yea luv it :)