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I put one in my Volvo PV544 - lots of you older folks read that without pause, but as a guy turning 40 years old this fall, they are no longer recognized by my peers. Anyway, I had a factory flywheel lightened. I do not to this day know for sure if it is cast or forged, but I know dozens of SCCA ITB cars and at least 2 local IMSA GT3-a-like builds that have used the OE flywheels, drastically lightened and most work. I do recall an ITB guy (Sam Moore, ending up DNF at the nationals, tho). Volvos of that vintage used startlingly good metallurgy. Kevlar blankets exist for the worriers.
Here's what I noticed- 1st and second gear acceleration is remarkably better. This was with ratio (3.13 and 1.99) and a 3.31 rear axle with 24.9" tires, so relatively tall compared to many, so the effect would be even more pronounced with say, a BMW e21 or a later Volvo m46 box, both using 4.03:1 first's, a short axle and shorter tires.

Stalling- only troublesome spot was backing out out of parking stalls- some with a slope might be troublesome or at any time when you are still rolling backwards and want to use the clutch to get first gear engaged and move forward. There is no coverage to stop a slow roll and relaunch the car the other way- you end up revving the cr^p out of it, or stalling.

It was also way easier to do smooth shifts, ie smooth clutch engagements. Up and down.

I think I had it dropped from about 20.5 to about 15.5lbs, but most of that came off the outer diameter, so the before after inertia is changed waaay more than proportional.

It is also worth remembering that there are two main parts to the "easy to drive / hard to get rolling / stalling" issue. Both have been mentioned here, but I don't recall them being specifically identified and separated. Both flywheel weight and clutch design & material play significant rolls.

A lighter flywheel will make it slightly harder to get a car rolling from a stop, but will improve engine acceleration and deceleration. The net effect is that engine will be more free revving and give improved acceleration, but the car will generally require a tiny bit more clutch slipping and throttle to get moving from a stop in either forward or reverse. It is also worth noting that both "stop and go" and "creep and sprint" type traffic may be less pleasant with a lightweight flywheel.

Clutch friction material (and clutch design) primarily define the nature of how the clutch latches onto the transmission when you let the pedal out. A lighter clutch will add some of the effects of a lighter flywheel, but the effect is usually much smaller; it's usually far easier to remove a large amount of weigh from the flywheel than the clutch. Clutch friction material with a higher coefficient of friction, and designs that focus all of the pressure plate's clamping force onto small pucks can significantly alter how the car reacts when the clutch is let out.

Aggressive clutch designs and materials can be much, much harder to slip for smooth starts and tend to be more on/off in how they engage the transmission. This leads to a car that can be very hard to get rolling without stalling, and can be very jerky on up-shifts and downshifts unless the driver is very good at matching revs. In a race car, with a good driver, this usually means the engine spends very little time disengaged with the car coasting between gears. Combine a lightweight flywheel with an aggressive clutch and you have a very good set-up for a race track, but something that can be very unpleasant for parking lot, cruise night or general slow traffic driving.

Alternately, if you combine a lightweight flywheel with a more OE style clutch and pressure plate, you can end up with a fast revving, smooth shifting very streetable combination that takes just a little extra care when getting going from a stop. Where these combinations tend to vary from OE is in multi-plate designs, lighter flywheels and pressure plates with more clamping force. A stronger pressure plate is far easier to modulate than more aggressive friction material or a puck style design.

It is the light flywheel, OE type friction material combination that is used in many aftermarket "tuner" clutch kits. In general they tend to drive well and last almost as long as an OE clutch. Unfortunately many times they get a bad review because the inexperienced driver uses way too much slip and burns off the friction material in a very short time. Frequently these drivers are new to cars with the level of HP they are driving, and have limited clutch experience. I have seen a couple of kids burn up $1,500 multi disk clutch & flywheel kits in under a week, and then blame the kit. More experienced drivers will use (and even track) these same kits for years without problems.

Just thought I'd post an update on this. No this idea hasn't totally fallen into oblivion...Yet.

I've collected a stock replacement ranger flywheel and a couple of stock replacement ranger clutches to measure, and be able to analyze in relation to the dimensions on my Duratec 2.0L and Ranger trans. I have also been in contact with a handfull of people regarding dimensions on other flywheels and clutches to compare them against. So hopefully I'll be finding out more about possible alternatives in the next few weeks.

I picked up both a self-adjusting clutch made by Luk and a non-adjusting clutch made by Sachs. I have to admit that the Luk does appear to be somewhat better constructed than the Sachs, but I will be keeping with the Sachs as still being a quality clutch that I can run which also saved me a bit over the Luk non-adjusting unit I could have ordered. Ironically enough, the non-adjusting Luk is actually more expensive than the Luk self-adjusting clutch as well.

My main reason for getting one of each type, only to end up returning one, was mostly to satisfy my own curiosity regarding just how equivalent they are dimensionally. The most interesting part, which I hadn't really considered to possibly be that significant previously, is that when weighed with the ~19.5lb flywheel the total weight of the self-adjusting setup was 36.0lb and the total weight of the non-adjusting setup was just under 32.0lb. That's a weight savings of a little over 4.0lb (10%+) just from going with the right type of stock replacement clutch.

While previous information shows the Focus setup to be a bit taller than the Ranger setup, I have now received measurements showing that the Miata setup is substantially shorter. This confirmation doesn't make the lightweight flywheel endeavor any easier, although it's not totally unexpected either. With the relative stock configurations all cleared up now, it helps pare down the potential paths that this idea can follow.

i have noticed that with my 2.3 duratec, at high revs the engine has too much stored energy in the rotating mass to make fast shifts, you can't bang it through the gears.

this resulted in using excessive force on my shifter causing me to break the the thing off at the neck!

if i just back off the throttle and reverse the torque a bit it shifts quicker.

good case for lightening the flywheel?

Don't see how you can expect the synchronizers to change flywheel speed. They are doing good to change the speed of the clutch disc. Maybe a lightweight clutch?

Oh yes. You are using the clutch, aren't you?

Bill

if you didn't have a clutch you would have to get the road speed and the engine speed matching for the gear you wish to engage, have you never driven a car with no syncromesh? pehaps something from the early fifties like an m.g. td or even a vw beetle try an old truck like a 40's mack.

if the engine doesn't slow down fast enough on up shifts you have to wait for them to syncronize before the next gear will engage, on the down shift, you have to put revs into the engine to do the same.

try driving a car without using the clutch, engine and road speed matching is everything.

cars didn't always have syncromesh gearboxes, this was introduced to help the many people who didn't have the abillity to change gear smoothly, do you know what "bouble declutching" is?

you young boys, pampered at every turn, or shift.

Excuse this liberal arts grad's questions for the engineers here...

1. Wouldn't rotating mass at the edge of the clutch be more important than the rotating mass towards the center of the crank? So, if you're gonna cut down, you'd wanna cut towards the outside edge if at all possible?

2. And I was looking through some old materials, and noticing the number of "clutch explosions" in the past. I would assume that most sanctioning bodies require a shield at some point even today, correct? So, if I'm lightening up a clutch assembly, am I flirting with disaster, given that the clutch in this car will be an inch or two from my right foot?

Yes the Ranger flywheel has substantially more energy at high revs than ideal for these cars, but honestly I'm no quite sure how that could cause the failure in question on the shifter. Once you disengage the clutch the synchros should theoretically only be changing the speed of the friction disc, input shaft, and some of the transmission internals on the input side and matching them to the speed of the output side. Only after the shift is completed and the gears are fully engaged should the transmission be loaded through matching the speed of the flywhee/engine to to the transmission via engaging the clutch again. While I do think a lightweight flywheel would be great for our use of these components, I'm not sure that it would solve the problem you describe.



Good questions...For a liberal arts grad.

1.) Technically speaking you are correct. However there are a number of factors that limit the minimum thickness (weight) of a material used in any given area of both the clutch and the flywheel.

2.) Lightening of stock flywheels, and to a lesser degree the clutch assembly, can be done, but has its dangers. While it's common to remove the extra "non-structural" ridge of material towards the outer edge on the engine side of many stock flywheels, removing anything that ultimately turns out to be structural to the flywheel can result in failure during high rpm use. In general stock type cast iron flywheels are not ideally suited to high rpm use, which is why SFI will not certify one for use in race cars. The safest way to remove a substantial amount of weight in this area, espeically for frequent use at higher rpm, is always going to be having dedicated parts engineered from steel and/or aluminum. Being able to do this correctly is how you can get a ligitimate Duratec race flywheel that weighs less than 6 pounds.

so what you ar saying is that the clutch disc is storing the energy because if i limit the revs by about 1000 and shift at 5000 instead of 6000 the shift is much smoother and faster?

A syncro is a pretty small thing to change the speed of a clutch disk by 1000 RPM in a fraction of a second.

I suppose dog boxes must depend on close ratios to be able to work as well as they do..

Well remember that since the ratios are a percentage, then shifts will be more difficult as rpm increase and in lower gears. For instance, the 1-2 shift will drop the input side by 2043rpm from 500rpm, and by 2451rpm from 6000rpm. So the synchros have more than an extra 400rpm worth of synchronizing to do. Thus faster the engine is spinning the more work the synchros have to perform, and thus shifting issues will generally be more prevalent at higher rpm.

That being said, 6000rpm sounds a bit low to be encountering inherent shifting problems.

So it sounds like there are a few possibilities, or some combination there of, as to what is causing the shift quality issue:
1.) My logic is neglecting some other factor related to engine rotational inertia that is actually causing your problem.
2.) Your specific transmission is not performing as it should and may be in need of some type of maintenance/repair.
3.) The M5OD-R1 does not tolerate being abusive shifting at higher rpm.

Now that I think about it, I suppose that there could be enough friction between the pilot bearing and any light disc contact with the flywheel or pressure plate, even with the clutch fully disengaged, to influence the speed of the input shaft by a sufficient amount so as to make it that much more difficult for the synchros to do their job during shifts. In which case a lighweight flywheel might help. Since I've never really thought about this specific issue before or tried shifting into gear with the engine already revving significantly beyond idle, I couldn't tell you how much of an effect this does or does not actually have. This also would make sense as to part of why powershifting is so hard on synchros too.

Unfortunately I do not have enough experience on the finer points of transmissions to be able to form a strong opinion on the root cause of your specific problem.

I have driven vehicles with no synchromesh. The whole idea of double clutching is to get the input shaft (not the engine/flywheel) running at the same speed as the gear for the next speed. The clutch is depressed during the actual gear selection.

Yes, I have driven a car while not using the clutch. In fact, I taught my boys how to do that, along with starting the car while in gear. It comes in pretty handy when a clutch linkage or throwout bearing packs it up.

This young boy is 69 years young.

Do you realize the clutch disc spins free of the flywheel, dependant only upon the speed of the input shaft, when the clutch pedal is depressed?

Bill

I learned to drive a non-syncro transmission when I learned to drive a 1964 International Harvester-based fire truck.

Trying to double clutch a transmission when you've got fire boots on, while your heart is racing and the sirens are wailing, is something of a skill it turns out.

Of course, our professional truck drivers on the fire dept (we were a volunteer fire shop) didn't seem to need a clutch...

yes i do know, thats why you come off the clutch half way through, so that the input shaft gets momentarily reconnected to the engine and takes up engine speed.

maybe my problem is that the transmission is just draging it's feet as it were and i can move the shifter faster than the transmission can sort it's self out, i'm already using atf in there so don't want to go lighter with the oil.

i guess i'll get the hang of it eventually, more seat time needed.

parts for my diff will be here next week and i can put the beast back together, i have gone from 3.92-1 to 3.34-1 so i may not have to rev the thing so high and my speedo will be back in the realm of reality.

Bill, thats not old, and i should have realized by the fact that you are somewhat knowledgeable.