lightened flywheel?

[Creation325]

So i was thinking about buying a clutch and flywheel combo for my 325i but after reading around a little bit I have heard that there are many disadvantages to having a light flywheel, such as that it needs to have a certain amount of weight to hold the power between shifts or something like that (im new to this) and that every time you'd let off the gas the car would dramatically decelerate, making for an unpleasant driving experience, etc. or even that removing weight from a stock engine could damage bearings or something. I always thought that removing rotational mass would make a good difference in making the car faster but now i'm confused! does anyone have experience with this? should i just get the clutch and save the money for something else? this is my daily driver not intended for serious racing.

[flyfishvt]

If you had any idea how many people use light weight flywheels you wouldn't be concerned. The only flywheel that causes issues are the single mass flywheels. With those you need to use a spring hub assembly instead of the stock clutch and pressure plate. If you don't use a spring hub then you will get chatter.

forget the rest of what you've heard and get what you wan't. removing rotaional mass is always a good idea. The drop in rpm's between gears is not as dramatic as you are thinking. a common complaint with the e36 is that the rpms don't drop AT ALL when you are changing gears. The light weight flywheel just makes it more like what people are used to with regards to rpm drop.

[Creation325]

Alright that's just what I wanted to hear! seems like some people will always exaggerate some negative aspect about any modification. Well thanks, I just wanted to be more confident before spending the money on this

[orangehatter]

The only flywheel that causes issues are the single mass flywheels. With those you need to use a spring hub assembly instead of the stock clutch and pressure plate. If you don't use a spring hub then you will get chatter.


Which is basically all lightweight flywheels on the market.

Chatter is not a problem, just a commonality. You will still have it regardless of if you have a sprung hub or no-sprung hub. It's just slightly more pronounced with non-sprung hub clutches, but nothing too terrible that would keep you from wanting to daily drive the car.

[sjpgoalie]

A lot of people just repeat what they've heard from other people's hearsay. I have a single mass, 8.5# flywheel from UUC. No chatter, unless I floor it under two grand in gears 3-5 from the torque...and I never drive under 2k rpm in those gears for the most part, regardless. If I am, it's only for a second. Mine does, but only if I come off of full throttle over 4-5k rpms. It's fine for every day driving, I just would advise beating the tar out of it constantly, unless you have deep pockets to replace various bits between the motor and the tires.Single mass flys can unload harshly. Like flyfish said, many E36s that don't even have clutch delay valves, still rev hang a little. When you start getting into the category of flywheels that weigh half as much as a stock one or less, it is the absolute opposite. I find myself giving a throttle blip all the time to kick the revs back up for matching wheel speed, but it's not bothersome. You're not going to gain much out of it. It's great for shifting a little bit faster, but when you stand on the throttle, mash the clutch in, and get back into the next gear...all I hear is BOOM...(less than a second goes by)...followed by another BOOM. It sounds much worse than what's really going on. When you stand on the throttle, then clutch in/back out of the throttle, you better be ready to shift and shift now lol. Depending on how light you go, the rpms are going to drop astronomically quicker. You'll get a little throttle response, but E36s already have that down pretty well. People say you can get synchro grind with them, too. But, I don't experience the slightest bit...and that's with a single mass flywheel which weighs as much as a newborn, a non-organic six puck clutch, and a pressure plate rated for over 600lb/ft of torque. Not the most user friendly setup if you don't know what you're doing, but just making an example that even some of the most extreme setups yield little to no unwanted effects. I don't consider the slightest bit of chatter at 1500rpms, under full throttle anything unwanted. You have a chance of getting chatter with any lighter flywheel, single or dual mass....and you're not going to find many dual masses...especially ones that people have already used extensively. None react the same to used motors and transmissions. In theory, a dual mass shouldn't chatter. In reality, it absolutely happens. Switching over to a single mass is a bit more of an intensive process as flyfish mentioned, though. Sorry for the crappy grammar or typos. I'm tired as hell.

[pchamaa]

I just replaced my clutch on my 97 M3. I went with a single mass steel flywheel that weighs 14 lbs. It's not super light, yet it is 10 lbs less than the dual-mass stock unit.
The difference is noticeable but not annoying for a daily driver, even for my wife. The grab is a bit more sensitive due to a lower rotational mass, but the downshifts are smoother with less rev-matching sensitivity. There is a low but noticeable gear noise that did not exist before.
However, if I had chosen a super-light aluminum unit it may not have been as forgiving. I have driven some of those cars and they are fun. But they can get annoying for a daily driver. Light-weight flywheels eat up clutch plates faster because they need to be slipped more.

[Joshh]

You get used to them pretty quickly. I've never had issues with lightweight fly wheels.

[flyfishvt]

All I can tell you is after seeing thousands of threads over the last three years...Ive never heard anyone complain about one or even hint at replacing it with a dual mass unless it was for budget issues.

[Pierre3400]

Im in the process of building a stroked engine, and had a few concerns about the flywheel.

Persoanlly due to the increase in power not being to much, and the fact the my current flywheel is siezed, im going with M52 flywheel that will be milled witha lathe to take off about 1kgs which is only about 2.2lbs. My reason for not taking off more, it mainly because i want to keep my torque levels at higher speed, even though i am building a torque engine.

I was offered a single mass M20 flywheel, which is what alot of tuners like to use, due to the fact that it can handle huge amounts of torque.

If you ask me, it all about personal choice. I milled my friends flywheel for a small 1,3l jap tuning project, took of about 1.2kgs, the car rockets from 0-120km/h, but after that its slow going due to the engine having no highend talk due to missing mass on the flywheel.

So its a balance on what you want from you car.

[e363161996]

think ill just go from dual mass to single mass, not a lighter single mass one. seems power wise ill probably loose my power if i go too light? with my new engine going to spit out 150-180hp

[orangehatter]

think ill just go from dual mass to single mass, not a lighter single mass one. seems power wise ill probably loose my power if i go too light? with my new engine going to spit out 150-180hp

You aren't losing power. With a lightweight flywheel you are putting more power and torque to the wheels because you eliminated extra weight from the rotating mass of the drivetrain. The less weight being turned by the crankshaft, the greater the output.

[pchamaa]

Stock flywheels are dual mass and cannot be milled. While some people do, it is not a recommended practice even on a new one.
Single mass flywheels are always going to be lighter than the dual-mass. The steel single-mass are heavier than the aluminum but they are all lighter than the dual-mass.
Single mass flywheel are generally cheaper than the dual-mass unless you go with a siperlight aluminum. I bought my kit for $500 delivered including the flywheel, clutch plate, pressure plate and T-O bearing.
Flywheel weight does not increase or decrease power. A heavy flywheel is in fact storing energy and that's why, the take-up is smoother and less throttle application is required from a standing start. The main advantage of a lightened flywheel is the ability for the engine to rev quickly WITH NO LOAD which makes downshifting and rev-matching quicker. It does lower the overall weight of the car but that only applies to racecars where minor weigh loss is a concern.
Happy new year and happy motoring E36 style.

[orangehatter]

It does lower the overall weight of the car but that only applies to racecars where minor weigh loss is a concern.
Happy new year and happy motoring E36 style.

It's not about overall weight so much as it is weight in the drivetrain. A car with heavier wheels and tires will make less hp and torque at the wheels than a car with lighter wheels. Cars with larger differentials make less hp and torque at the wheels than the same car with a smaller differential. All of this applies to flywheels too. So the lighter the flywheel, the smaller the differential, and the lighter the wheels and tires, the more hp and torque the car will put out at the ground.

[sjpgoalie]

lol this thread took a dump. Everything orangehatter is saying is correct. It's not about saving weight. 10-15lb detraction? I'll buy lighter shoes, suit, and helmet lol. If we were focusing on weight of the car, it would probably be best to leave the original one in, honestly. You'd have a lower center of gravity in theory. Like he said though, it's about reducing rotational mass between the crank and the tires hitting the ground. The more the better and flywheels are the first (and one of the most important) parts of the equation.

The dude machining dual mass flys...don't. It would no longer be dual mass and you now have a flywheel that is out of balance. What's the point of ditching 2.2lbs? You're never going to notice it and it will chatter. The little flywheel for your friend might not chatter, but yours will and the whole car will vibrate like a bastard because the fly will still be heavy, just out of balance by roughly two pounds on one side. Your friend's little motor isn't dying up top due to the flywheel. The motor itself doesn't produce enough torque. The faster you're going, the more drag on the car from a lot of things (ambient AND internal forces) and little motors don't like drag at all. The motor is just rev'ing through the gears. It doesn't retain momentum or anything... Any moment is lost as soon as you shift. I figure once he hits 3rd or 4th gear it falls flat on it's face, as soon as he lays back into the throttle in said gear...am I right?

[dieselbro]

Refer to UUC's website for a wealth of great info.

http://www.uucmotorwerks.com/flywheel/how_a_lightweight_flywheel_works.htm

http://www.uucmotorwerks.com/flywheel/there_is_no_torque_loss.htm

[Pierre3400]

lol this thread took a dump. Everything orangehatter is saying is correct. It's not about saving weight. 10-15lb detraction? I'll buy lighter shoes, suit, and helmet lol. If we were focusing on weight of the car, it would probably be best to leave the original one in, honestly. You'd have a lower center of gravity in theory. Like he said though, it's about reducing rotational mass between the crank and the tires hitting the ground. The more the better and flywheels are the first (and one of the most important) parts of the equation.

The dude machining dual mass flys...don't. It would no longer be dual mass and you now have a flywheel that is out of balance. What's the point of ditching 2.2lbs? You're never going to notice it and it will chatter. The little flywheel for your friend might not chatter, but yours will and the whole car will vibrate like a bastard because the fly will still be heavy, just out of balance by roughly two pounds on one side. Your friend's little motor isn't dying up top due to the flywheel. The motor itself doesn't produce enough torque. The faster you're going, the more drag on the car from a lot of things (ambient AND internal forces) and little motors don't like drag at all. The motor is just rev'ing through the gears. It doesn't retain momentum or anything... Any moment is lost as soon as you shift. I figure once he hits 3rd or 4th gear it falls flat on it's face, as soon as he lays back into the throttle in said gear...am I right?

So where in my text do i write in removing weight from one side? Honestly only an idiot with do that. The concept of a Lathe comes into play here.

[pchamaa]

A dual mass flywheel is a two piece unit attached to each other by rubber.
The main reason a dual mass should not be machined is that the weight of the two parts are critical to each other. Resurfacing the friction surface makes one of two components lighter and that throws off the weight relationship between the two parts.
Dual mass flywheels are not designed to be resurfaced, just like BMW brake rotors are not designed to be turned. People do it anyway but turned brake rotors warp. Luckily, replacing rotors is not a big deal. Replacing flywheels? A little more involved.
Most machine shops won't resurface a dual-mass. Because of the rubber mounting, it is very difficult to get it perfectly straight on the lathe and have it stay that way during the machining process. Rubber moves. If you don't get that surface perfectly straight, the clutch will give you all kinds of trouble.
One more thing. Rubber ages. The rubber in the dual-mass flywheel is subjected to tremendous loads during it's life, not to mention thousands of heat cycles. It is designed to survive and sustain abuse for the life of one clutch plate, not two. Rubber eventually deteriorates, cracks and fails. So even if you dual-mass looks good, reusing it, even without resurfacing is not recommended.
One last thing. The whole talk about "lighter is better" and the whole relationship between flywheel weight and horsepower is being oversimplified. Go tell that to the engineers in Munich. This thread has not taken a dump. It's good discussion. Yes, there are are some questionable statements being made by some but that is the purpose of this board. Flywheel weight is a complicated subject. Flywheels do not rob horsepower. They vary in the way power is delivered. Rotational mass does store energy. Google "flywheel energy storage."

[ChuckDizzle]

the chatter sounds similar to the chatter you get from modern diesel motor, like a TDI volkswagen but not as loud. It doesn't take long to adjust your driving style for it either and sometimes people don't notice the difference. Whether its better than stock is relative to you.
The benefit for me is during auto-x sessions and track days.

[Spyke]

flywheels do not rob horsepower. They vary in the way power is delivered. Rotational mass does store energy. Google "flywheel energy storage."


ThAnK YoU!!!!!!!