http://forums.pelicanparts.com/showthread....threadid=293701

worth any additional HP??

This is worth "0" HP.

What it will do; it will let your engine rev up and down faster, which can increase your time to accelerate/decelerate the car - that and quick throttle response.

Ask him if it's still available.

brando owns it...

It will be hard on synchros as your engine will rev down quicker between shifts.

John Williamson (Otto) says he doesn't use a lightened flywheel in his super fast 914 racer. He feels keeping mass movement works out better. Kind of like why slow down if your trying to go fast. I have a lightened flywheel.

And it'll definately let you rev faster which means you've gotta be quicker with the heel and toe. in the end it'll save you time.

You'll also stall the car easier.......

Has anyone ever calculated the "theoretical benefit" as far as acceleration goes? It's an inertial effect, so it should be possible to roughly calculate an equivalent weight loss of non rotating mass. I.E. every 1 pound of mass removed from the flywheel is equivalent to lightening the body by x pounds. I'm guessing it would be something like 1.03.

This wouldn't takie into account the possible ability to shift faster, but you have to be pretty darn good to take advantage of that anyways.

Well, the old drag racer's moto is that every pound of rotating mass you can take off the car is the equivalent of 10 lbs of unsprung weight...

-Josh2

No need for calc....it takes less hp from the engine to spin it up...reduction in rotating mass, just like lightening the crankshaft.......to me specifically for racing...ya know the drag race between corners.

As far as it's weight vs vehicle weight and translation to HP, we would be talking a fractional amount, but in racing every 1/4 HP can be the difference between 1st place and 1st loser.

It wouldn't help you in shifting faster, just sooner as the engine spins up faster.

For a street car, I would stick with a stock or slightly lightened flywheel. The rotating mass seems to help the engines idle smoother and transition from a stop sign easier.

Be carefull if you get a lightened aluminumumnumnum flywheel. I had one on a customers car with a high torque starter to boot. The timing was off just a little, kicked back on a start up and sheered some of the teeth down. Good for race cars, but not street cars.

I completely forgot about this thread - thanks guys - jim

The math is here if anyone is interested

http://www.uucmotorwerks.com/flywheel/how_...wheel_works.htm

and here

http://www.uucmotorwerks.com/flywheel/flyw..._mass_calcs.pdf

i've driven my car as a daily driver (think bay area parking lot, err, i mean commute) with a light flywheel and racing clutch ...

BIG PAIN IN THE ASS

for a street driven car, i wouldn't do it again. you'll hate it ...
Andy

Those numbers look impressive, but they're based on removing 17.5 lbs from a flywheel (for the 3 series ayways), which you'd be hard pressed to do by drilling holes. If you're removing say, 5 lbs, dividing those numbers by 3 will give you a better idea. We also have smaller flywheels, which would further reduce those numbers.

Right, but they're also talking about cars that weigh considerably more than 1000 lbs over the weight of our 914's. We don't need as much of a change to give us a pretty good bump in acceleration.

-Josh2

There is some interesting numbers in THIS THREAD

I found this quote from the thread interesting
"The lighter the rotating components the less energy needed to change their
rotational speed. The shape and radius also are important in this regard. lw
components let the drivtrain rev quicker(and shed revs quicker) and makes
clutch control more critical during street starts.

the biggest factor in the energy requirement equations is the angular velocity
which is a squared quantity it is analagous to v in the more familiar mv2
formulation

this means that the faster something rotates the more significant the loss of a
small quantity of mass is. Losing 2# from the clutch flywheel is far more
significant than losing 2# at the wheels.

I made a ss once that calculated compared the relative energy requirements
of the various components, both rotational and translational, during
acceleration. I'll have to see if I can dig it up, but from memory ~1# at the
flywheel is roughly comparable to ~10# at the wheels which is roughly 3hp"

Just ignore the butt-dyno comments because they are worthless without a proper scientific procedure behind them.

A lightened flywheel in a daily driver isn't as much fun, especially if you live in an area where there are hills you have to shift on. BTDT. Besides, the 914 revs pretty quickly as it is

Ok... butt dyno's asside...

I found it fascinating that at redline, a wheel is only doing 400rpm where as a flywheel is doing 5,000 rpm.

Thus the comment about 2#'s savings on a wheel being insignificant to the motors ability to accelerate and use energy when compaired to a similar savings of 2#'s on a flywheel (that has to rotate 13 times more often...)

holy-moly.. wow....

brant

On my first 914, it had a hotrod 2056 and a lightened flywheel. Lots of fun, driveability was pretty good around town. I don't think it was superlight though.

That engine died on me (because I didn't know how to take care of it) and the mechanic I took it to built at 2056 with stock 1.8 heads and stock cam, and stock flywheel. What a pig.

Correct.. I went through the calcs from UCC a few years ago substituting appropriate numbers for a 1970 911. I dont have the results handy anymore, but they were similarly impressive...

One assumption thats NOT made is that effective "R" changes when you lighten a flywheel.

In the MOI equation its MR^2. Most flywheel lightening is done on the perimeter, unless of course its an aftermarket alu flywheel.

If you take mass away from the perimeter, at some point you could make an assumption that the effective radius changes.... which will make your efforts ,in lightening more worth while.

Which of course changes all the results..

The UCC calcs are for a uniform disc. With a few more iterations and substitutions you could have more specific results.

Lighter=Faster always

It may not be a good thing for street use though

I have a lightened fly on mine, driving around town is something you get used to.

My playground is canyon roads, what I enjoy is the quick accel and decel for

cornering. Great inprovement over the stock fly.

I run a lightened flywheel in my SIX.

I don't know what it would be like with a stock one, but I like it the way it is. Street or track.


KT