Let's talk lightened flywheels...

[maytag]

I'm looking to add a lightened flywheel while I;ve got the car torn down. there are several options out there, with as much difference in weight as there is in price.
A quick search of the customary vendors' sites nets the following:

$400 gets you the "ultralight". ~7.1 lbs. But not for me because it uses an expensive Tilton clutch.
$375 gets you a beautiful (machine-porn-worthy) Aluminum unit. ~9.5 lbs. But right now Jason says he's 4-6 weeks out.
$189 for a lightened stock unit. <13lbs
$60 is a lightened stock unit. ~14lbs

So for those of you who have them (or have had them)....
Which one did you go with, and why. And do you wish you had gone lighter / heavier?

I would really like to get the Aluminum one, but I'm not sure I want to wait that long.... plus another $375 into the already over-budget project. Should I wait?

waddy'all think?

[azruss]

you definitely have a trade off here. Lighter means less rotational inertia, thus quicker revs up and down. It also means less strength, so the question is, how often do you want to be doing clutch work. Aluminum has issues in the fact that it is much softer than steel and doesnt dissapate heat as well. A lot depends on what they do with the aluminum (hard anodizing, 7075 t6511, etc) that will determine its wear resistance and strength. Mr. Miller could probably enlighten you on these details. I havent done either, so this is just my thoughts.

[maytag]

you definitely have a trade off here. Lighter means less rotational inertia, thus quicker revs up and down. It also means less strength, so the question is, how often do you want to be doing clutch work.

I'm not following. "Less strength", in what way? It looks like you are suggesting that a lighter flywheel will wear a clutch faster?

Aluminum has issues in the fact that it is much softer than steel and doesnt dissapate heat as well. A lot depends on what they do with the aluminum (hard anodizing, 7075 t6511, etc) that will determine its wear resistance and strength. Mr. Miller could probably enlighten you on these details. I havent done either, so this is just my thoughts.

You do realize that the aluminum flywheel still has a steel friction surface, right?

[johndemar]

My guess is that it's the durability and life expectancy of the flywheel itself. Of course I could be completely wrong on this but it is something I would address with Jason if I was going to do this.

[131]

My guess is that it's the durability and life expectancy of the flywheel itself. Of course I could be completely wrong on this but it is something I would address with Jason if I was going to do this.

Jason's aluminium flywheel has a standard ring gear and replaceable steel insert for the clutch friction surface. No reason for life expectancy concerns unless it's abused and subjected to a squillion revs, then fatigue may be an issue. I was going to buy one from him, but ended up getting a standard flywheel machined locally. I like it and even lighter would be nice. But too light can be a dog in traffic, especially if the motor is a bit cammy and temperamental at low revs.

[vandor]

Whichever way you go, be sure they balance it.

[BEEK]

i have both, a lightened steel unit which weighs 11.8lbs and a aluminum one. both are good, i never have had an issue with breaking one, and have raced both.

[maytag]

i have both, a lightened steel unit which weighs 11.8lbs and a aluminum one. both are good, i never have had an issue with breaking one, and have raced both.

So for a street motor, is it worth waiting for the aluminum one? Or is your lightened steel one plenty good?

[Daniel]

if you lighten the stock flywheel that is plenty good shouldn't run more the 75 for lighting and balance
I've had many done .

[spiderrey]

Maytag, I had a stock flywheel lightened. I run the crap out of that car when I drive it with no issues. Dont know the end weight, I would have to look it up in crofts book. The bottom end of my 2 liter was built to Crofts fast road specs. The crank was balanced with the flywheel and clutch. Ive had no issues at the bottom end because the car has a ton of torque at the bottom end. the overall setup works great. This is not saying that the aluminum flywheel setup wont give an improvement on this somewhere.

[mdrburchette]

I have a custom clutch/flywheel setup on my built 1608. Both the engine and clutch/flywheel were made for high rpms. I like the fact that it is quick off the line and rev happy. The only shortfall is the car doesn't coast like my stock 1608 in my 71 so when I'm driving down the highway, I have to keep my foot on the accelerator. That's not been an issue with me.

[pastaroni34]

A couple of things:

1. Yes, our aluminum flywheels are weaker than their steel counterparts. They are, however, plenty strong for this application. In fact, they are more suited to a higher revving motor than the OE cast flywheels. There is no way I would trust a cast flywheel above 7000rpm. Cast parts tend to be susceptible to cracking and fracture. While aluminum is weaker, it is not brittle, and has a good amount of "give" it will stretch and bend a long way before it cracks, these flywheels are plenty happy at 10000rpm, if you're approaching these speeds, worry about your clutch.

2. Aluminum dissipates heat better than steel. It does, however, have a lower "heat capacity" than a steel counterpart. This is really only a significant factor when you slip the clutch (which is normal behavior on the street). You have to slip the clutch ALOT to overheat things, again, I am sure your clutch pressure plate will overheat before the flywheel.

Don't forget, weight means very little. The important factor is moment of inertia (MOI). I don't know anyone else who can give you MOI numbers but me, reason being is that my parts are engineered, not just haphazardly machined.

I am of the opinion the lower MOI the better. At the very worst, you just have to rev the engine more, which I have never heard anyone complain about.

In the past I would also say there was not a significant gain in HP with a lighter flywheel. This is true in the steady-state. Racing engines rarely live in the steady state though, they're always accelerating. Accelerating or "spinning up" takes a significant amount of energy, to the point that through some extreme lightening I can expect a gain (or rather not loss) of 16hp. I can find even more power by removing accessory drives, pumps, etc.

On a street engine, this is probably not realistic. With an aluminum flywheel, you will see about 3.5hp, lightened stock, about 2hp. Is this significant?

I think the real question is, how quickly can you pull the transmission and swap a flywheel?

[maytag]

A couple of things:
I think the real question is, how quickly can you pull the transmission and swap a flywheel?

The answer is: "Pretty-damned..." (fast, I mean)

But I think what you are really suggesting is that I don't wait for the aluminum one, but rather go ahead and get it all done.... get it assembled, get it in the car, etc etc, and then swap it out with the aluminum one when it arrives?

What about balancing? I think I read that your alu flywheel is zero-balanced, or neutral. But is that the case with the factory flywheel? Or can I have my machinist balance without the flywheel? (I'm swapping pistons, so I figure I'll lighten & balance/match the rods and then get the whole assembly balanced)

[Daniel]

the factory flywheel will need to be balanced after lighting which should be done at the same machinist .

[maytag]

No, I understand that part.
What I'm wondering is if the flywheel is "neutral" (and when balancing is performed after lightening a factory unit, it is merely to bring it back to neutral) or if the flywheel adds dynamic balancing to the rotating assembly.

in other words: can I install a (correctly balanced) flywheel now, and then 6 weeks down the road, remove it and install an aluminum flywheel from Jason? Or must I then re-balance the assembly because the flywheel is providing that counter-balance to the rotating assembly?

This all has to do with whether the motor is inherently balanced (because it is a 180d crank)? Which I think the TC motor is....

am I right?