m20 singlemass flywheel machining

[StereoInstaller1]

Here's another link with mathemagics 'n' stuff to explain the benefits of light flywheels:
http://www.pumaracing.co.uk/FLYWHEEL.htm

Yeah, wow, never thought of using math to figure out that a bone stock E30 isn't gonna change shit when going to a lightweight flywheel.

All of the bullshit about "quicker rev-match" is just that...bullshit.

Guys, it is all in your head. Yeah, it goes vroom faster. No, you aren't shifting better. Yes, the 25 fucking pound flywheel (mistake) that BMW dumped on the poor little M42 is a turd, but that was BMW trying to make a buzzy little motor feel like it has some torque...did it gain torque? NO, it just made it FEEL like it had more torque.

Same thing with the lightened flywheel guys, just makes if FEEL like it spins faster.

[e30e]

lulz to some of these comments:
Conventional wisdom is that for every 100 pounds you remove from your ride, you shave 1/10th of a second off your ¼ mile E.T.

so do you think removing 8 lbs is really going to do anything?

[Aptyp]

taking weight off the drivetrain is different from taking rear seats out...

[Sean]

I'm running a stock clutch (SACHS OEM) with a metric mechanic 12-13lb flywheel (Can't remember the exact weight).

My transmission rattles in neutral.

[nando]

the "getrag rattle" isn't from running a LTW flywheel. that's inherrent to the transmission itself - the input shaft and layshaft bearings go "bad" (they'll keep working forever, just noisily). Lightening the flywheel just makes it more apparent.

and yeah, 8lbs by itself won't make a big difference. But name several 100lb things you can remove from your car to make it lighter, without being a douchebag with a totally gutted street car?

and reducing rotational mass *is* a big deal. Go from your heavy chrome 17" wheels to some light 14" wheels on race tires. It's an enourmous difference, because it affects everything (braking, acceleration, turning). A LTW flywheel does the same thing, on a smaller scale - but add a lighter crank, rods, pistons, etc, and it adds up. If it didn't matter, why not run the heaviest flywheel possible?

[gearheadE30]

lulz to some of these comments:
Conventional wisdom is that for every 100 pounds you remove from your ride, you shave 1/10th of a second off your ¼ mile E.T.

so do you think removing 8 lbs is really going to do anything?

Removing rotational mass is far and away a different thing than removing static mass. Although maybe the reason that mine feels better is because the M42 has a 28lb flywheel from the factory, and now I have a 15 lb one. Stock is 19, so I could see the difference being very negligible on an M20, stock for stock.

[Dyno4mance]

So no one actually read the article posted by puma race engines in the UK then?
Just something that stuck out to me was;

So in first and second gear this is a pretty important effect - I built an engine recently and managed to remove nearly 3 Kg from the outside of the standard flywheel - so that would be equivalent to lightening the car by over 100 Kg in 1st gear - not to be sneezed at in terms of acceleration from rest.
And for the dumbasses amongst us who can't convert kg to lbs I will sumarize;
removing 6.6lb from the outside of a flywheel with a 5" radius is equivalent to lightening the car by over 220lb in 1st gear not to be sneezed at in terms of acceleration from rest.

And with that I will rest my case....looks like "no tech 550 the super engineer over on bimmerforums needs to return to the physics books and kendogg needs to stop swinging off his nuts and go and figure something out himself for a change.

[4bangerfury]

Getting rid of the dual mass flywheel on the m42 felt great. Even got to lighten it myself on the lathe at school.





Had an actual engine machine shop resurface it and then balance it with the clutch and pressure plate for me. There hasn't been any noticeable difference in noise or vibration.

[KenC]

Should have taken it down to 12 :).

[e30e]

So once again how much time does this lightweight take off your 1/4 miles times.......oh yea and those light weight pistons and crank that suddenly is now being brought up.

Dual mass flywheels are used to make the luxury cars you own (they were luxury cars in the 80's) smooth and not feel like a rattling fwd econo shit box 4 cylinder car. BMW engineers knew that if they kept the car feeling like the 6 cylinder brothers in terms of shifting and drivetrain they knew the cheap asses who bought this car would brag about how great it was.

The argument of "every bit" helps, is dumb .03 faster is something your going to notice its all in your head.

[F34R]

So once again how much time does this lightweight take off your 1/4 miles times.......oh yea and those light weight pistons and crank that suddenly is now being brought up.

Dual mass flywheels are used to make the luxury cars you own (they were luxury cars in the 80's) smooth and not feel like a rattling fwd econo shit box 4 cylinder car. BMW engineers knew that if they kept the car feeling like the 6 cylinder brothers in terms of shifting and drivetrain they knew the cheap asses who bought this car would brag about how great it was.

The argument of "every bit" helps, is dumb .03 faster is something your going to notice its all in your head.

Rev matching is fun, and I don't mind a lighter flywheel at all.

[KennyT]

Cliffs:
Lighter Flywheels allow engine to change RPM faster.
Makes Getrag rattle more apparent.
Lower inertia makes engine easier to stall (only affects inexperienced drivers).
Great for speed shifting, annoying for granny shifting.


For DD cars, if your normal shifting tends to 'beat' the engine into the next gear, you should lighten your flywheel. By 'beat' I mean the flywheel rpm is higher than transmission when clutch is released. If the transmission 'beats' you into the next gear you should not lighten your flywheel.

Race cars: You will almost always 'beat' the engine to the next shift, thus lightened flywheels are a good idea. Also, r3v matching will be easier and less likely to break the rear end loose when de-clutching under high lateral load with a poor r3v match.

[F34R]

I was wondering if the ZF has a rattle when you use the m20 fly? I am using the ZF with the m50 and a m20 fly and pressure plate. The splines are 100% the same and with the duel mass and plate it is the same height as the m20 single and pressure plate. So there should be no issues with the clutch setup.

Just wondering if there is any rattle like in the 260?

[4bangerfury]

So once again how much time does this lightweight take off your 1/4 miles times.......

Don't know. My 318 isn't a drag car, so I'm not gonna waste my time at a drag strip.

[kendogg]

I was wondering if the ZF has a rattle when you use the m20 fly? I am using the ZF with the m50 and a m20 fly and pressure plate. The splines are 100% the same and with the duel mass and plate it is the same height as the m20 single and pressure plate. So there should be no issues with the clutch setup.

Just wondering if there is any rattle like in the 260?

I'm not sure where you guys got the idea that only Getrags do it. ALL transmissions do it, some moreso than others. Even UUC wrote an article about it, and recommended using a hodgepodge of fluids to raise the overall viscosity to help eliminate the issue, and those guys don't know squat.