Lightweight flywheels: worth the money?

[Jay 535i]

Now that my transmission swap is looking like a 'go', I'm wondering about, well, all sorts of stuff.

For instance, are any manual-tranny guys out there running lightweight flywheels? What kind of improvement did you notice?

It looks like quality third-party lightweight flywheels for the E34 go for about $4-500. Are they worth it?

The alternative is an E28 flywheel, which will probably still cost $200. So the difference is about $300. Worth it for the performance difference?

[Martin in Bellevue]

E28 flywheels are around for about $100. A machinist cut mine down to 15 lbs. It is nice to have the revs raise & drop quicker, & there is no noisy shutdown. You have a good opportunity with this gearbox swap to get the preferred flywheel.

http://www.bimmer.info/bmw/martin/fly15.jpg

[Jay 535i]

Thanks Martin.

If I got an E28 flywheel, I'd probably do as you did. When I said $200 for the E28 flywheel, I was including the cost of having it worked a bit, as you did.

You said 15 pounds was the result. The "lightweight" items I was referring to are below 9 pounds. I'm really curious as to perceived differences from behind the wheel, both in terms of performance and refinement.

[DanDombrowski]

Jay,

If you get a manual trans and a limited slip from the donor car, you're probably going to be faster than me, so I'm gonna have to encourage you not to do that :)

Seriously, I don't know, but good luck, let us know how it turns out.

[Martin in Bellevue]

The stock e34 m30 flywheel is 32 lbs. The 15 lb flywheel provides noticeably quicker throttle response out of gear. Rev-matching shifts are more enjoyable & easier with a lighter flywheel.
A 9 lb flywheel may be tough on a daily driver. Metric Mechanic has a lightened harmonic balancer that loses 4 lbs, I think. I don't know of anybody with this part.

[Blitzkrieg Bob]

The RPMs moves quicker up & down, but down shifting and hill climbing changes as you go lighter.

You begin to lose the hang on a down shift,and steep/long hills take higher revs to climb.

[Scott H]

your chances of stalling it are higher with a lighter flywheel as you lose the rotational inertia that something with more mass has.


The RPMs moves quicker up & down, but down shifting and hill climbing changes as you go lighter.

You begin to lose the hang on a down shift,and steep/long hills take higher revs to climb.

[Jay 535i]

Thanks everyone. Please keep the input coming.

What's the stock weight of the E28 flywheel, BTW?

[Scott H]

per ETK

sounds about right from the general feel of my E28 stuff

stock dual mass is roughly 33lbs


Thanks everyone. Please keep the input coming.

What's the stock weight of the E28 flywheel, BTW?

[rob101]

The RPMs moves quicker up & down, but down shifting and hill climbing changes as you go lighter.

You begin to lose the hang on a down shift,and steep/long hills take higher revs to climb.
oh so thats why my e28 is more involving to double clutch on the downshift than my e34, well you learn something new everyday

[Brandon J]

I would suggest the e28 flywheel. I had a lightweight aluminum flywheel bolted to my M50tu when it was in my car. It revved up faster and was a good match for the 3.23-stock diff swap to 3.46LS differential. That flywheel was I believe 10lbs. WAY TOO LIGHT for a daily driver. I needed to blip the clutch almost all between any gear as the revs fell fast, it affected lower rpm acceleration as there was less inertia to counter the drive weight, it rattled badly. ex. of lower rpm acceleration: When I wanted to pass a car, I had to down shift 2 gears on the highway b/c the car would bog a little....not enough inertia to keep the engine spinning under load at lower rpms.

The e28 is a better balance, not too light, not too expensive, and the clutch assembly has springs to aid reducing rattle. The e34 M5's flywheel is about 12lbs stock, and its clutch assembly is also made to isolate the rattle. Thus, UUC pairs its lightweight flywheels for the e36 M3 to use the e34 M5 clutch assembly and together it hardly rattles. The dual mass flywheels have springs in them to isolate rattle and so the clutch assemblies don't work like the e28s or the e34 M5 to isolate rattle.

[Jay 535i]

I would suggest the e28 flywheel. I had a lightweight aluminum flywheel bolted to my M50tu when it was in my car. It revved up faster and was a good match for the 3.23-stock diff swap to 3.46LS differential. That flywheel was I believe 10lbs. WAY TOO LIGHT for a daily driver. I needed to blip the clutch almost all between any gear as the revs fell fast, it affected lower rpm acceleration as there was less inertia to counter the drive weight, it rattled badly. ex. of lower rpm acceleration: When I wanted to pass a car, I had to down shift 2 gears on the highway b/c the car would bog a little....not enough inertia to keep the engine spinning under load at lower rpms.

The e28 is a better balance, not too light, not too expensive, and the clutch assembly has springs to aid reducing rattle. The e34 M5's flywheel is about 12lbs stock, and its clutch assembly is also made to isolate the rattle. Thus, UUC pairs its lightweight flywheels for the e36 M3 to use the e34 M5 clutch assembly and together it hardly rattles. The dual mass flywheels have springs in them to isolate rattle and so the clutch assemblies don't work like the e28s or the e34 M5 to isolate rattle.

Thanks very much for that.

So it sounds like a lightened E28 flywheel (down to ~15lbs) and matching clutch is the way to go. I want to keep my car driveable and refined.

Any more thoughts?

[Scott H]

and keep your cash in your wallet.

Martin's 535 is a hotrod so it gets different treatment :p


Thanks very much for that.

So it sounds like a lightened E28 flywheel (down to ~15lbs) and matching clutch is the way to go. I want to keep my car driveable and refined.

Any more thoughts?

[Jay 535i]

and keep your cash in your wallet.

Martin's 535 is a hotrod so it gets different treatment :p

If the difference between the stock 22lbs and the lightened 15lbs is really noticeable, then I'll go for it. Otherwise, not.

Obviously this is really subjective, but do you think there's a substantial difference between 22lbs and 15lbs, as perceived from the driver's seat (I don't give two hoots about lap times or anything like that).

[Scott H]

I think the substantial difference is that the 22lb flywheel will make the car easier to drive on a daily basis while the 15lb flywheel will cause you to work a little more


If the difference between the stock 22lbs and the lightened 15lbs is really noticeable, then I'll go for it. Otherwise, not.

Obviously this is really subjective, but do you think there's a substantial difference between 22lbs and 15lbs, as perceived from the driver's seat (I don't give two hoots about lap times or anything like that).

[Brandon J]

If the difference between the stock 22lbs and the lightened 15lbs is really noticeable, then I'll go for it. Otherwise, not.

Obviously this is really subjective, but do you think there's a substantial difference between 22lbs and 15lbs, as perceived from the driver's seat (I don't give two hoots about lap times or anything like that).

That difference in weight is substantial as you have to take into account rotational forces and how that makes those 7lbs feel much more. you will feel the difference as the engine will spin faster and you will be able to match revs much easier.

[Jay 535i]

I think the substantial difference is that the 22lb flywheel will make the car easier to drive on a daily basis while the 15lb flywheel will cause you to work a little more

Hmm, I know it's tough to explain, what I really wonder what "working a little more" means. My driving style already includes matching revs on every shift and heel-and-toeing around every corner, so maybe I'm there already in terms of "work"?

I know this is a tough one and the best thing would be to try both, but that's not practical. I want to get as much performance as possible, and I'm not a crappy driver, but at the same time I want to maintain the car's easy-going nature.

I appreciate all the input.

[Scott H]

nicer for the track, but not for the street as revs drop much faster as well...


That difference in weight is substantial as you have to take into account rotational forces and how that makes those 7lbs feel much more. you will feel the difference as the engine will spin faster and you will be able to match revs much easier.

[Scott H]

possibly forcing you to blip on the upshifts as well.....

I have the E28 stuff and have had to do that ever since I installed it. Making it any lighter and causing me to do any more work would make the car more frustrating on a daily driving basis



Hmm, I know it's tough to explain, what I really wonder what "working a little more" means. My driving style already includes matching revs on every shift and heel-and-toeing around every corner, so maybe I'm there already in terms of "work"?

I know this is a tough one and the best thing would be to try both, but that's not practical. I want to get as much performance as possible, and I'm not a crappy driver, but at the same time I want to maintain the car's easy-going nature.

I appreciate all the input.

[Jay 535i]

possibly forcing you to blip on the upshifts as well.....

Ah, I see. That is more work. I'd like to avoid that.

Stock E28 flywheel, then? Or lightened, but only slightly?

If I use an E28 flywheel and matching clutch, I'm not going to get a lot of new noises and vibrations, am I?

[Scott H]

and associated short bolts and clutch.

Use the saved cash on a new rear main seal, pilot bearing, throw out bearing, and all tranny seals.


Ah, I see. That is more work. I'd like to avoid that.

Stock E28 flywheel, then? Or lightened, but only slightly?

If I use an E28 flywheel and matching clutch, I'm not going to get a lot of new noises and vibrations, am I?

[Brandon J]

Ah, I see. That is more work. I'd like to avoid that.

Stock E28 flywheel, then? Or lightened, but only slightly?

If I use an E28 flywheel and matching clutch, I'm not going to get a lot of new noises and vibrations, am I?

You should not get more noise with the e28, or at least not noticeable. It is great to see all the good and bad points provided in this thread. Good luck with your decision whether you decide on this upgrade or a different one. I do see that you are trying to do a 5spd swap. It just might be cheaper to go with the e28 flywheel/clutch. Also, you don't exactly want to find a used M30 e34 flywheel, so a new one is more expensive.

[Scott H]

noise on shutoffs is virtually gone and no other noise is noticeable.


You should not get more noise with the e28, or at least not noticeable. It is great to see all the good and bad points provided in this thread. Good luck with your decision whether you decide on this upgrade or a different one. I do see that you are trying to do a 5spd swap. It just might be cheaper to go with the e28 flywheel/clutch. Also, you don't exactly want to find a used M30 e34 flywheel, so a new one is more expensive.

[Jay 535i]

I do see that you are trying to do a 5spd swap. It just might be cheaper to go with the e28 flywheel/clutch.

It's looking like that's the way to go.

Thanks everyone

[DanDombrowski]

Brandon is right, its about the intertia.

Basically, your engine is putting out so much energy/time (power). You put less of that energy into making a big disc spin (and more into making the car go forward). However, when you downshift, you don't have any stored energy to bring the RPMs in your engine up quickly, and therefore must take that energy from the speed of your moving vehicle. Get it?

For a spinning disc like a flywheel, there is energy in translation (22lbs vs 15lbs) and energy in rotation (some funky formula. Last I checked, its 5pm, and I don't do engineering after 5pm :) )

[Kalevera]

EDIT: the thlot pickens. I'll have to measure this sucker to determine if it will work -- I think it's 228mm. schwaaaa.

Fritz has an E30 M3 flywheel waiting to go in. 7.85kg, best of both worlds.


best, whit

[Qube]

Hmmm... *listening intently*

I may have to investigate this as well. Good reading.

[Jay 535i]

However, when you downshift, you don't have any stored energy to bring the RPMs in your engine up quickly, and therefore must take that energy from the speed of your moving vehicle.

Wouldn't a well-timed throttle blip also give the engine the revs it needs to downshift without stealing energy from the moving car? I blip on every downshift already, so that wouldn't involve a learning curve for me.

I do own a manual car, but it's not my BMW -- yet :D.

[Brandon J]

It's great to get the pros and cons of this subject. Good luck with your decision. You may just find that MAF is the way to go for more power without giving up driveability. Since you have an auto already, depending on what gear you have, 3.91? that helps with the acceleration. So, clearly there are other performance choices. However, if you are starting from scratch to swap in a 5spd, an e28 flywheel is cheaper than an e34 flywheel.

[Turbo Ready]

Jay, are you using a gearbox from an e34 or e28? I am rebuilding an m30 from an e34 and will be bolting up an e28 260-6 gearbox with the e28 flywheel to it.
I was doing some research on the flywheels as well and was advised to go with the e28 flywheel and gearbox.

All the information here really reinforces the advice I was given.

[Jay 535i]

Jay, are you using a gearbox from an e34 or e28? I am rebuilding an m30 from an e34 and will be bolting up an e28 260-6 gearbox with the e28 flywheel to it.
I was doing some research on the flywheels as well and was advised to go with the e28 flywheel and gearbox.

All the information here really reinforces the advice I was given.

The gearbox is from an E34. I'll use an E28 flywheel.

[Kalevera]

Jay, are you using a gearbox from an e34 or e28? I am rebuilding an m30 from an e34 and will be bolting up an e28 260-6 gearbox with the e28 flywheel to it.
I was doing some research on the flywheels as well and was advised to go with the e28 flywheel and gearbox.

All the information here really reinforces the advice I was given.
You're actually going through the trouble of using an E28 gearbox and you're not using a 265?

[Jay 535i]

Whit, can you tell me a bit about the differences between the 260 and the 265?

I've been told the 265 is superior, but fate dealt me a 260. I hope to eventually turbo the car up to ~320rwhp. Will the 260 take it?

Thanks!

[Kalevera]

Whit, can you tell me a bit about the differences between the 260 and the 265?

I've been told the 265 is superior, but fate dealt me a 260. I hope to eventually turbo the car up to ~320rwhp. Will the 260 take it?

Thanks!


Jaybaby, that depends more on how the car is driven than anything else. The 265 has larger and better bearings and fatter shafts. They're better because fewer tend to need a rebuild.

The Getrag 280 used in the M5s, even with the extra gearing, are known to need rebuilds. And that's with less hp at the wheels on a 3.6l US M5. So, the transmission might need to be rebuilt at some point. If you're doing the turbo setup for reliability (pistons, 5 angle valve grind, new engine consumables, good quality FI parts), the money spent on that work will pale in comparison to the 2 grand it will cost to buy one of blanton's correctly rebuilt 260s, should it ever be needed.

The more immediate concern for an FI setup is pressure plate clamping force, the requirement for which I assume is calculated based on drivetrain drag and engine output. There are differences that I'm not sure will translate to a performance issue, but are always worth knowing about. Either way, the clutch kit for a 260 (or 265, for that matter) from an E28 would include a pressure plate rated for less than 200hp. Which means that there'd be some, if not a lot, of slipping on any kind of decent acceleration with 320 rwhp.

An E28 M5/M6 (single mass) flywheel might merit a look. All of the UUC flywheels seem to use uprated clutch components (E36 M3 -> E34 M5, anything V12 -> E31 850CSi) and work fine.

best, whit

[Jay 535i]

Either way, the clutch kit for a 260 (or 265, for that matter) from an E28 would include a pressure plate rated for less than 200hp. Which means that there'd be some, if not a lot, of slipping on any kind of decent acceleration with 320 rwhp.

Thanks.

I can always get a higher performance clutch. My concern is lunching the transmission.

I take it the 260 with the stock clutch will handle power figures in the mid 200s?

[Turbo Ready]

You're actually going through the trouble of using an E28 gearbox and you're not using a 265?

This is a project for my 87 e30 325is. I got a half decent deal on an 87 e28 535i with only 150,000 Km on it. I would have preferred a 265 but they are difficult to locate here. I know where a 265 is (taken out of a US e30 M3) but the guy wants to sell it with a huge package.

I needed the gearbox, flywheel, driveshaft (for the flange) and most importantly the 3.25 limited slip diff as well. The 3.25 will allow me to pull first gear longer, and since being a taller gear along with the LSD, will reduce wheel slip. Since my car will be FI, it should be really helpful on launch.

There are a few guys I know running FI e28 m30 engines with the 260 gearbox, putting down in excess of 320 RWHP and almost the same torque with no gearbox failures so far, so I am keeping fingers crossed that my 260 holds up for a bit.

Jay, there is a guy I know in TO with an FI e34 535i and was quite successful with it. He is looking for more power and is in the processed in building a whole new separate engine for the same purpose. He has ordered JE pistons made to his compression ratio specs and has done lots of other mods as well.

I might use a Sachs 6 puck clutch kit for my car.

[Jay 535i]

Sounds like a great plan, man. :)

[Turbo Ready]

Sounds like a great plan, man. :)

Jay one of my friends drove your car last Summer and really liked the way it felt. He has a 5 speed 535i.

I called up a guy who had some e28 stuff for sale hoping to get you a flywheel but he decided to keep his stuff. He will let me know if he changes his mind.

[Jay 535i]

Jay one of my friends drove your car last Summer and really liked the way it felt. He has a 5 speed 535i.

I called up a guy who had some e28 stuff for sale hoping to get you a flywheel but he decided to keep his stuff. He will let me know if he changes his mind.

Ah, that'd be Greg -- I remember that. I'll soon have a 5-speeder too :D Thanks for making that effort to locate the flywheel.

The car's even better now that it's got Bruno's subframe inserts and the intake returned to stock (the previous K&N filter was just sucking hot air).

She's comin' along :)

[Turbo Ready]

Ah, that'd be Greg -- I remember that. I'll soon have a 5-speeder too :D

The car's even better now that it's got Bruno's subframe inserts and the intake returned to stock (the previous K&N filter was just sucking hot air).

She's comin' along :)

Yup, that's right.

We have to install his subframe inserts as well. With Mark D's chip, his car pulls really well. I used my G-Tech pro to do some HP runs with it but gave all the files to him. Hoping to get him on the dyno soon.

The stock filter seems to breathe really well so no need for the K&N.

Good luck with the swap, you will enjoy it.