turbo flywheel and diff q for an m20

[Northern]

There are other load related parts as in drive shafts etc that might be lighter on the more modern cars making a different net effect.

Maybe some parts have gotten lighter over the years, but from just switching from a 5speed G260/ZF320 to a modern 6-speed, I would assume there would be more rotating mass.

I also think the turbo e9x run a larger diff, whether it's a 210mm ring or something else, its components are likely heavier, if anything.

[Wanganstyle]

Maybe some parts have gotten lighter over the years, but from just switching from a 5speed G260/ZF320 to a modern 6-speed, I would assume there would be more rotating mass.

I also think the turbo e9x run a larger diff, whether it's a 210mm ring or something else, its components are likely heavier, if anything.

heavier driveline items are nice for loading turbochargers.

rotating mass for Gearboxes is not the same as gearbox weight; the ZF 6 speed in the e46 and e92 are MORE EFFICIENT than a G260 or zf 5 speed; the bearing design and rotating mass is more efficient - less loss between flywheel and output flange. Imput flange diameter is not changed between a e30's G260 and e92 335i's ZF 6 speed; the splines went to a high efficiency involuted 22 spline design.

A e30 with a ZF 6 speed will put down more power to the ground and get better fuel economy than a e30 with G260; I had both mated to the same engine.

Both have ~0.83 top gear overdrive so the 6th gear does not have any numerical advantage

135 and 335 manual use a 215K kompact differential; its style of bearing is lower drag than the older e30/36 styles; the ring and pinion size is bigger and would be heavier than a classic 188mm unit.

135 and 335 auto use a 188k kompact differential; these are very lightweight and use low drag bearings with races mounted on diff instead of bearings mounted on diff; these are less rotating mass than a 188mm classic unit.

[The Dark Side of Will]

Try it for yourself:

2006 subaru sti
Stock flywheel gets up San Francisco hills happy

Light flywheel not so much.

I think cars were designed to be driven on public streets; flywheel weight reflects this.

This is correct. OE's size flywheels and choose gear ratios--among many other factors--based on how easy the car is to get rolling from a dead stop, up a standard hill, etc.
The flywheel is an energy storage device that give you access to a little more horsepower for a start from a dead stop than you'd otherwise have access to.

There are even *LIMITED* circumstances in which a slightly heavier flywheel can help a drag race... basically it comes down to whether the car hooks well enough, and the engine is cammed up enough that the heavy flywheel helps the holeshot more than it hurts acceleration after the holeshot.

The flywheel in my subaru wagon non turbo was about 10 lbs lighter than the sti turbo flywheel. Subaru ej22 non turbo and ej257 turbo are physically almost identical besides for the turbocharger setup

That's for smoothing power pulses, just like the turbo vs. non-turbo on the BMW app you mentioned above.

Here's a some info on flywheels from David Vizard:

http://www.popularhotrodding.com/features/0602phr_engine_drivetrain_rear_wheels_power_increase/viewall.html

[The Dark Side of Will]

Maybe some parts have gotten lighter over the years, but from just switching from a 5speed G260/ZF320 to a modern 6-speed, I would assume there would be more rotating mass.

I also think the turbo e9x run a larger diff, whether it's a 210mm ring or something else, its components are likely heavier, if anything.

Moment of inertia is proportional to the square of the radius at which a mass is located from the axis of rotation. That means that the diameter of the rotating part is the most important factor in its moment of inertia (MOI). A typical Chevy flexplate at under 10 lbs has a moment of inertia comparable to an entire Chevy crankshaft at over 40 lbs because the flexplate has a much larger diameter.

Because of it's small diameter (and lower RPM than the engine), the driveshaft has almost no effect on the overall MOI of the driveline.
Even though the diff carrier and ring gear are heavier and have a larger diameter, they turn even more slowly than the driveshaft and also have a very low contribution to driveline MOI.

The biggest chunks of angular momentum in the driveline are the flywheel and the wheels and tires. The flywheel (and clutch assembly) are typically fairly heavy (>~30# together and can be over 60 in some cases), turn at engine speed and are the largest diameter parts that turn at engine speed.
The second biggest chunk are the wheels and tires. They turn slowly compared to engine speed components, but they have the largest diameter of anything in the driveline and are heaviest components in the driveline other than the crankshaft.

[GunMetalGrey]

I love the science behind it but I am just going to post what I have experienced in my own build.
I am running an m50 turbo with an HX35, e36 m3 ZF, 11lb AASCO aluminum flywheel (240mm) , standard weight clutch/PP, 2.93 LSD, and 3" exhaust.
I get 6psi before 3100rpm without full throttle, 6psi is my current spring pressure, but I cannot imagine I will be able to spool much faster.
The extra rotating mass does make sense for more load to spool the turbo faster, but I am quite satisfied with my current setup, lightweight flywheel makes rev matching a breeze.