Sterling

Putting an aluminum flywheel on my 12a stock - Yaw carb/Headers.
Wondering what to expect. Greatly anticipating this. Need to hear good things about how it was'nt a stupid choice to blow $470 on it. (That's right; The price went up!)

So, whaddaya got, and how do ya like it?

Also, if there are any geniouses out here, does anyone know the math involved in the "rotating mass reduction" thingy
associated with lightening the flywheel?

Go ahead and throw out what you "heard", as well. But if someone knows for certain the equasions...well cool!

Will I notice a difference nailing it in 3rd at 60 MPH to pass someone?

JoseReyes

I have the RB light Steel Flywheel.. It takes a little bit of practice to get the car going at first, but once you get use to, it has a much better take off. I don't think you will like very much the all alluminum flywheel. That is intended for racing only, you won't be able to control it very good on the streets, it will require a hell of a lot of attention and reving the engine high for it to to the job... not worth the trouble for street use, now for strip and race that's a different story...

I do like my light steel flywheel.... I also have the RB street/strip presure plate, and the clutch and it does make a difference...

MakoDHardie

For the math part....I can't really type out the equations and send them to you, but the basic theory goes that with less inertia in the flywheel, the engine can get it up to speed quicker, thus producing revs quicker. Its less mass for the engine to accelerated, so it does give you a little bit of a horsepower gain. Just remember that low inertia means that it will not stay in its uniform state of motion as long as a more massive flywheel. That means that you'll be able to get you engine speed up with quick, easy blips, but the speed will fall just about as fast. Your engine will take on more motorcyclic characteristics as far as reving is concerned. It will take a little more attention for street use and throttle blips on downshifts will be a little more difficult, but its quite a matter of opinion.

My best guess on the equations is that you can figure them out by considering the mass of the flywheel directly proportional to the rate at which the engine speed changes. In otherwords, Mass= ForceXAcceleration. A greater mass will require greater force to accelerate it while a lesser mass willl require less force to accelerate it at a given rate. It just takes a little pondering to figure out, but your Force is given by the amount of horsepower at the crankshaft. Mass is simply that of the flywheel. And acceleration is in reference to the speed of the flywheel, or engine rpm's. This is basically calculated while the engine is not in gear and its only work load is the flywheel. An estimate without really doing it on your car would be something like this:

Horsepower= Flywheel Mass X RPM/second squared
(crankshaft) (in metric units) (average time for revs to build)

theNeanderthol

iTrader: (1)

The rotational equivalent of mass is called Moment of inertia. The bigger the Moment of inertia, the more torque it takes to accelerate it. We will call this I. We will call T torque and A rotational acceleration. (Rotational acceleration is usually greek alpha but we can call it A) The proper equation is T = I * A. The tricky part is to find I, rotational inertia. The formula for this differs for the shape of the object you are using, but for a disk, it is I = Mass * Radius ^2. If you work out the equation, when you switch to a flywheel of half the stock weight, you get a reduction of I of about 80%.

mar3

iTrader: (8)

I'm running the RB light steel with a Centerforce Dual-Friction clutch. You do have to get the revs a little higher for engagement without the stumble, but it becomes second nature after a while. I always like to watch other people trying to figure out the virtual "all or none" nature of this set-up. They never believe me when I tell 'em to keep the revs up and play the clutch if they have to, they can't hurt either of them. The faster revving from the light steel was very noticeable after the change was made. It got to 8100 a lot quicker. I toasted the original '79 dizzy by spinning it to 8500 one time after I left a corner in rage. I thought I had killed the engine 'cuz the engine started running real rough after the over-rev. Luckily, Ari and Chris had me on the road in no time after a switch to the present '85 dizzy conversion...that was before I transplanted the whole mess into my current '80...love those guys...

Sterling

MakoDhardie, I think force = mass x velocity(sq).
"Mass = force x acceleration" does'nt quite work out.
But I understand what you're trying to demonstrate.

Neandrathol, You seem to have just the equasion I want, but I can't understand what you're writing at all; particularly your use of " * ", and " ^ ". What do these mean?

I would like to know this formula most particularly if the wieght reduction translates into such a large decrease. I'm then wondering about other spinning things, like wheels, driveshafts, and even engine pulleys.

I had no idea there was so much to be gained. It would be interesting to mathmatically detail the behavior of a car from stock to lightened everything.

MazdaEbrahimi

ok... ^ means to the power of, like 2^3 = 2*2*2
the reduction of the moment of intertia might by 80% if you reduce the weight of the flywheel by 50%, but that 80% reduction is only when considering the flywheel.

For a free reving engine, you need to consider the percent change of inertia for the whole rotating assembly, i.e. rotors, pullies, etc... as well.

And, after the clutch is engaged, then it's the rotating interia of all rotating drivetrain components

so, don't expect an 80% difference in inertia...

REVHED

I'm running a light steel flywheel and sprung button clutch. Great setup.

I agree with mar3... it's funny watching other people drive my car.

It's great seeing the look on their faces when they go to take off the first time and they stall the engine without fail. It's a good chance to give em **** about their driving skills.

theNeanderthol

iTrader: (1)

yeah ^ means to the power of and * is a multiplication sign. I have a million equations in my brain 'cause I'm a physics student. If you have any more questions about the equations needed this kind of stuff I'll be happy to cough some more up for you.

Sterling

Heh heh...They did'nt have computers in school when I took my math courses. That's why " ^ " was unfmiliar.
Guess I really am getting old!

The whole equasion makes sense now. At first, I thought you were trying to represent pi, which was'nt working out too well for me!

So yeah, I do understand that I have to take into concideration the overall rotational wieght, and look at the flywheel reduction in the proper perspective. But still, that is an impressive relationship between disc mass and 'Moment of Inertia'.


If we can so noticeably feel a difference with a 12 lbs reduction, then my guess it to find the next largest diameter rotating wieght (the wheels), and work on that.
Then comes brakes?

See? I'm learning here all the time. I thought all this wheel weight reduction crap was just a way to sell wheels!

All I needed was the formula.
Now why don't wheel makers just put that damn formula on their ads?

The RB light steel deal says they concentrate the meat of the wheel closer to the center (Not on purpose; just that they show a side view, and it works out that way.).
This would then have to be two seperate equasions (of the same) with the mass at one diameter, and the remaining mass at the other diameter, combined afterwards, right?
As the aluminum wheel has the heaviest part (ring gear) on the outer edge, I assume then that just one equasion is needed.

My point here is that by design, and because of the 'radius squared' factor, there may be very little difference in the light steel wheel compared to the aluminum.

Any of you driven both?

theNeanderthol

iTrader: (1)

sorry about the long post, my brain is exploding with physics today
Well once the density throughout the flywheel is not constant, the formulas start to get tough to derive. If the change in thickness of the flywheel was very abrupt, then you could use two equations to approximate very closely the actual moment of inertia. You will need to break it into 2 parts. the inner thin part of the flywheel, to be treated as a disc. ( Use I = M * R^2) But if we treat the inside as a disc, we outside part must be treated as a ring. The equation for the Moment of intertia of a ring is a little different. Here goes.

r = inner radius measured from central axis

R = outer radius " " " "

I = (1/2)*(M) * {(r^2) + (R ^ 2)}


Moment of inertia equals (1/2) mass times (inner radius squared plus outer radius squared)

Now just add this result to the one you got for the thin, inner part of the flywheel

This will work if there is and abrupt change in thinkness of the flywheel. You will get a very close aproximation. If the flywheels change in density across the radius is way different, then you will have to derive a special equation for it.

There is a simple way to find out the moment of inertia. You could roll the flywheel down an incline, ( on a surface that wont scratch it) write down the angle of the incline, and the mass of the flywheel, the outside radius of the flywheel, the length of the incline, and the linear velocity of the wheel after it reaches the bottom if the incline, and give the data to me. I will analyze and give you the moment of inertia of the wheel with about +-10% error. Although i think the equations should work okay if the flywheel isnt too oddly shaped. Good luck !

genrex

I agree with Jose Reyes.. I also have the 16-lb RB steel flywheel, and it's perfect for street driving, and fast acceleration.. it really puts a smile on your face! I also use it to decelerate, and it's very handy when going downhill.. don't need the brakes as much. And problems when starting from a stop?.. vastly over-stated.. it's not a problem.

I think you'll be unhappy with a lighter aluminum flywheel (which is illegal at drag strips without a scatter-shield, by the way), because maintaining a constant highway speed will be a total pain in the ***. Going too light on a flywheel will require you to make constant little gas-pedal adjustments, just to maintain a steady highway speed.. and that would become very irritating.

twister

Have any of you come across a chrome-moly flywheel, I use one on my Gen 1 racer car with great success. Weight is 10.1 lbs. This is here in OZ.

MIKE-P-28

iTrader: (1)

Yeah everything good comes from Australia... We get robbed on stuff here...

By the way my 17# RB flywheel should be here soon...

Hopefully it aint messed up like setzep's was... Id hate to be at Racing Beat today

Siraniko

iTrader: (13)

Im using a 215 aluminum flywheel with kevlar clutch in my 13b monster streetport. My only complaint is that I cant launch at low RPM at the track and a PITA in a stop and go traffic. Have to downshift once the RPM falls appx 1500. Otherwise, it’s a good flywheel.