patsmx5

iTrader: (16)

It seems the forums believe the the failed gear teeth from people's transmissions that failed under high HP builds all seem to have sheared the teeth of, and that the gears teeth failed due to fatigue.

A heavy flywheel will reduce this. So will the springs on the disk.

The question is, how much? My guess is it's significant, but I haven't done the calcs. I did find a machine design book that goes over how to calculate the fluctuations in torque of an engine vs flywheel weight/ mass moment of inertia, but that book is $$$. I should go look at my old machine design book and see if it goes over it.

Someone could calculate the loading a peak torque with 2 different flywheels and find out "how much" difference if makes. But more flywheel weight WILL bring the peaks down, that is a fact, and that will reduce fatigue loading on the gears. So if gears are failing due to fatigue, heavier flywheel = longer life.

Joe Perez

iTrader: (8)

Quoting Schaeffler Automotive, a manufacturer of bearings, clutches, and other drivetrain parts:

Posit: Of those who have installed a lightweight flywheel and then blamed it for the subsequent gearbox rattle, how many of these cases were accompanied by the installation of an aftermarket clutch disc which has either no sprung damper, or a less-effective damper than the stock or stock-equivalent disc?







And less noise, and easier shifting, and on and on. There are really no negatives to retaining the stock flywheel, insofar as I am aware.

patsmx5

iTrader: (16)

I ran an ACT extreme with the organic sprung disk it came with, on a stock flywheel for 5 years, it was silent. Went to a 10lb and same clutch, it's very noisy now. No idea how the springs in that disk compare to the stock ones though, but they were quiet with a stock flywheel.

patsmx5

iTrader: (16)

Only negatives I know of are that the car will weigh 8lbs more, and won't rev as quickly, and the second part isn't that bad, some wouldn't care at all, some would prefer it not to rev/drop as fast as you say, easier shifting.

hi_im_sean

iTrader: (3)

without knowing the resonant frequencies of each component (engine and tranny, or probably more importantly the combination of the 2 in a given gear), and from that, being able to demonstrate if there is or isnt a crossover point where transmissibility increases exponentially within the useful rpm range, any talk of damping is a waste of time.


as far as sprung hub/vs non sprung, my anecdotal data point/s:
when i went from the stock 1.6 FW to the 9lb F1, i retained the sprung clutch hub and noticed exactly 0 increase in noise or rattle. my subi on the other hand, that im 90% sure has a solid hub, ceramic clutch installed by the PO, has a decent idle rattle only when the clutch pedal is pushed in.

y8s

iTrader: (8)

My disks were most definitely solid flat pieces of metal between the splined hub and friction material. no cushioning beyond the internal flexion of the steel material itself.

The last clutch I had on the car was the FM happy meal. Hub is sprung, flywheel is light. I don't recall the buzzy buzzersons.

Savington

iTrader: (31)

Yes, but lower power = longer life too. Increasing the flywheel weight reduces the performance potential of the car, so you're throwing the baby out with the bathwater. Perhaps that tradeoff is worthwhile for you, but that's a case-by-case decision.

We took a Fidanza out of a customer's car a few years ago after he complained of decel noise. IIRC that was a sprung clutch disc.

If you shift quickly, lighter flywheels will improve shift speed and reduce synchro wear in the tranny. They should also improve acceleration in lower gears, although the exact improvements might be tough to accurately measure.

patsmx5

iTrader: (16)

If a heavy flywheel means my transmission won't break, sign me up!

As for lower power, how? The motor is going to make the same power no matter what flywheel I run. All the flywheel is doing is taking that graph I posted at the top of this thread, and reducing the height of the peaks. It's not changing the power up or down, just dampening it. The closest thing to "power" that it's going to change is how fast the motor revs, we all know that!

Joe Perez

iTrader: (8)

How is that, exactly?

At the moment that you are moving the shifter, the flywheel and pressure plate are decoupled from the transmission. Only the clutch disc itself is effectively a part of the rotating mass of the transmission input shaft, and therefore contributing to the force applied to the synchro rings during a fast shift.

Flywheel mass has no effect whatsoever on the speed at which one can move the shifter from one gear to another, or the wear imposed on the synchros in this process, presupposing that you are in the habit of depressing the clutch while shifting.



This is the usual justification I hear in favor of installing lighter-than-stock flywheels.

Intuitively, I find it difficult to believe that such a tiny reduction in mass (as compared to the weight of the vehicle) can result in any significant improvement in acceleration. That said, I prefer to rely upon solid data rather than gut instinct in cases such as this.

Except that I can't find a single shred of solid data one way or another.

This isn't the first time I've gone a-Googlin' in search of some sort of data which compares back to back runs of a vehicle with a stock flywheel and a lightened flywheel. I literally cannot find a single reputable source offering concrete numbers which either prove or disprove the theory.

patsmx5

iTrader: (16)

I don't have concrete data. I did go from a heavy 18lb stock flywheel to a lighter, much less MMOI 10lb flywheel and yes it reved quicker in nuetral. If I floored it, by the time my motor would normally hit 5K, it would now hit 7K. So a noticeable difference. In theory, this would help with accel in say, 1st gear, but I'm traction limited in lower gears anyway so no idea/doesn't matter.

I think we all know how much it "helps" could be calculated, but it's almost nothing.

The real purpose of this thread was to see ask if running a stock flywheel will, at least in theory, improve transmission life as compared to running a lighter flywheel. I think that part is true, and as Sean pointed out with his links on post 2, not having a torsionally rigid connection also helps!

I have read about how many transmissions some of the high HP guys have broken (BBundy for example) and from what I've read, BBundy is running a 1.6 lightweight flywheel and unsprung clutch. If true, that's interesting as he's broken a lot of transmissions, I'm curious if he's always run this setup or if some he broke had a stock 1.8 flywheel/sprung disk clutch? Or for that matter, anyone's who's broken a transmission, what flywheel/clutch disk were you running?

hi_im_sean

iTrader: (3)

i would also add that it make the peaks slightly wider in addition to lowering the amplitude.

patsmx5

iTrader: (16)

Of course, but that's a good thing.

hi_im_sean

iTrader: (3)

its all about area under the curve

patsmx5

iTrader: (16)

If I can find the box my old machine design book is in, I'll see if it has the maths to do the calcs to answer "how much" the stockflywheel helps reduce those peaks vs a lighter aftermarket flywheel. The book I found online that has these calcs was over 400!

hi_im_sean

iTrader: (3)

i have one at hand, ill see what i can find

hi_im_sean

iTrader: (3)

im told, from the internet, so take it fwiw: the flywheel and PP never completely, 100%, disengage. there is residual drag and friction putting a moment, however small, onto the momentarily decoupled(which also has it small residual frictions with the rest of the gear box) input shaft. less(smaller) moments fighting each other equals happier syncros, etc.

Savington

iTrader: (31)

Lower power was an example of another thing you can do to cure transmission failure, not a consequence of increased flywheel weight.

In theory, yes, but in reality, the drag on the clutch as the engine decelerates more quickly will drag the input shaft speed down as well. It's the same reason you can depress the clutch on the highway in 5th gear, let the motor idle, and it won't toggle 4th gear (or anything else), but if you blip the throttle with the clutch still depressed, you'll be able to get 4th.. In a perfect world, the clutch fully decouples the box, but in reality there's always a bit of drag.

guttedmiata

It's not just the mass. It's also the moment arm. Two flywheels with different diameters but the same mass will not accelerate or decelerate the same.

Speaking of which, deceleration under load is a factor as well.

guttedmiata

I'm guessing Bob can break a stock transmission with any flywheel clutch combo.

codrus

IIRC, one of the reasons FM went with a slightly heavier flywheel when they revised it a few years ago was to reduce buzziness. (well, that and steel cheaper than aluminum).

I have the old FM happy meal (aluminum flywheel, ACT clutch which is a sprung hub) and it definitely buzzes on decel/idle with clutch pedal pushed in.

--Ian