M20 Flywheel-how much power/noise?

[brads2002]

I am going to be pulling my JB as it is just too loud for daily use and now that i have turbo power i really don't need something this light.

Am I correct to assume a stock M20 will hold around 200hp or so? I am running 9LBS of boost.

Going this route might save me from having to buy a HD clutch for my stock M42 flywheel.

How is the noise with this setup?

Thanks in advance

[TobyB]

The M20 seems to be good for 200 ft/lbs, give or take. If you get a more aggressive
disc, I suspect it could hold quite a bit more.

dunno about noise on an M42 (rattle) but it's pretty heavy...

t

[bmwman91]

I didn't have too much tranny rattle with a stock 19lb M20 flywheel and some RedLine MT-90 tranny fluid. Now, the 11.5lb M20 flywheel that I have in there now makes for a damn noisy tranny!

[e30slidewayz]

I'm running an 8lb flywheel on my M20 with a stage 2 clutchmasters Kevlar clutch. It revs sooooo quick and rev matching is easy as hell. Car dynoed at 198hp and it handles it fine. The rattle is ridiculous, 8lb flywheel amplifies the bajeezus out of the getrag. I know it's bad, but I hold my clutch down when there's people around so my awesome e30 doesn't sound like complete shit lol.

[brads2002]

its funny, my 8lb doesn't really rattle at idle but off the gas at 3-4K it sounds like the car is going to fall apart. Its nuts loud but agreed, also very fun. Can anyone comment on the 323i flywheel with 325i clutch? Being a stock setup I would think its a lot better.

[pantelones]

I am pretty sure that the flywheel itself has nothing to do with your power goals. Someone correct that if I am wrong...

The strength of your clutch is what determines whether or not it will be sufficient for the amount of torque you are producing. As long as you balance the flywheel and pressure plate together you should be fine. Some of the more professional high-end racing shops require you to balance the entire rotating assembly on a 4cyl motor if the flywheel is replaced. It's not entirely necessary, but it makes for a safer motor as well as improving the longevity. You can machine the stock m20 single mass down to about 12lbs, and from what I have read it's not going to be terribly noisy or un-streetable. I machined my eta single mass down to 16lbs and loved it.

[jwal]

I am interested in this topic as I'm looking at flywheel options for my m42

[brads2002]

I am pretty sure that the flywheel itself has nothing to do with your power goals. Someone correct that if I am wrong...

The strength of your clutch is what determines whether or not it will be sufficient for the amount of torque you are producing. As long as you balance the flywheel and pressure plate together you should be fine. Some of the more professional high-end racing shops require you to balance the entire rotating assembly on a 4cyl motor if the flywheel is replaced. It's not entirely necessary, but it makes for a safer motor as well as improving the longevity. You can machine the stock m20 single mass down to about 12lbs, and from what I have read it's not going to be terribly noisy or un-streetable. I machined my eta single mass down to 16lbs and loved it.

Well the M20 has a bigger clutch disk and surface area so it should be able to handle more power then m42 clutch. Stock those motors were mid 170's.

I had my 8LB match balanced with the new pressure plate. It didn't really change anything.

The 323i flywheels appear to be around 13 lbs are are pretty cheap at 250 from the dealer. I am worried that it won't due much for my noise problems but others say they are not noisy. If anyone has direct experience please chime in.

[bmwman91]

I say keep the mega light flywheel and use a different tranny. From what Metric Mechanic told me, the 318ti driveline can be swapped in without too much trouble and the G250 is a stronger tranny. The 205bhp NA M42 I have is going to blow up my G240 pretty soon.

[jntar]

I have a lightened m20 flywheel. The one I bought was the heavier version so it's probably around 12-14lbs after shaving the back off. I get a small amount of rattle at lower rpm when the car is warm. Whatever you do, don't buy the damn stage 3 f1 racing clutch/fw combo. Pedal from the Sachs hd pp is stiff as fack and the clutch is either on or off, barely any slip. Even with the sprung clutch it's rather jarring in traffic.


Bmwman91, what makes you feel your g240 isn't going to hold? I know several people running them behind an s50/52 and several turbo cars. Both making more torque than yourself. Mine seems to be holding up great behind 12psi ~200whp. Going for final dyno tuning to get torque numbers soon.

[brads2002]

Thanks good to know. Do you mostly get rattle off the gas under deceleration? Sounds like its tolerable? I am going to try the 323i flywheel with a stock clutch. I think the clutch should hold since i am running light boost and don't intend to add to it. It can't be all that much more then a lightly modded M20.

I really don't want to replace the transmission unless its necessary. Are the 260's quieter for some reason?

[bmwman91]

Metric Mechanic told me that the G240 does not hold up well with higher power. It sounds like some people on here have the opposite experience though.

The G250 from the 318ti is supposed to be a stronger unit while being just as light as the G240. No idea if it is quieter though, but I kind of doubt it. "Getrag rattle" is called that for a reason!

[brads2002]

So i just wrapped up the swap. I ended up using the 323i flywheel, spacer removed from the original flywheel, 28mm bolts, late 325 starter, stock 325 clutch, 325 TO bearing. It all went together well. It holds fine at 9.5LBS of boost and the rattle is much less. There is still some noise but it is acceptable. Idle is a little improved but it does not spin up nearly as fast as the JB. I know there is come controversy with the 323/325 to bearing. 325 seems to work fine. There is maybe 1/4 petal travel before it engages but hardly noticeable. All in all i am very happy. Car feels right!