garrett376

Came across this in a description for a lightweight flywheel on eBay - sounds great, doesn't it: 10-30hp increase at the wheels?!

Christer

Some of their claims have some foundation in truth or fact:

1. Thats up to you, I love it (well an RS flywheel not a 'Fidanza'), but this is a personal choice.

2. I guess this is largely true....

3. Yes, this is true.(Apart from the 'obsolete' label)

4. Yes, potentially this is true.

5. I have never heard of anyone 'resurfacing' a flywheel in any case, but I guess this could be a benefit....

6. Yes, it does feel more responsive and 'fluid' is a word I would use...not necessarily quicker.

7. Thats horsehit. I think at most you would see 10% of their claims in a 964.

Adrian

Unbelievable. The sad thing is that people believe this stuff, buy them and fit them. Notice it has a steel friction surface. Aluminium with a steel surface plate mounted to it makes for a very nice battery.
Ciao,
Adrian.

David P

Which might make removing the bolts difficult when go back to the orginal...

Indycam

Hiya
All very true in some few cases , just not the whole story , just the "good" side of the story .
They just don't bother with the other details .
If you were to use your car on a super high speed racetrack where it never slows down untill the checkered flag , then the alu fw is a great thing .
Or if you put the drivetrain into a very light weight shell ...

Adrian

Lightweight flywheels do not increase horsepower. They just allow the engine to get into the power band faster. Of course they allow the engine get out of the power band faster as well
Ciao,
Adrian.

Indycam

Hiya Adrian
You are technically , literally correct . But as I'm sure you allready know , it takes hp to spin up the big old flywheel , so switching it out for a tiny flywheel frees up some hp that would have been stored in the rotating mass . Good for a track where you never need to use the flywheel mass to get off the line quick . IE a flying start .

"Figuratively" , if you stomp the pedal down in gear coming out of a corner and you don't have a big fw , your car has more useable hp to accelerate the car . When you go into a corner and need to shed some speed , the brakes don't have to burn off the hp stored in the bigger fw , so the brakes are "stronger " .

With all the "bennies" , I'll be keeping the stock 89 fw .
Don't need or want the alu fw problems .
But if I ever enter my car into the Daytona 500 ,
I'll look into getting one.

Adrian

I guarantee, in real life, that you could not quantify a figure on the differences in transmission loss resulting in changing from a dual mass versus a lightweight flywheel.
The data I have shows no difference in transmission losses between a standard 964 Carrera 2 Coupe and a 964 Carrera RS, both are circa 12%. Oh yes, the 89C4 with its SMF has identical performance figures to its sister with a DMF.
Wheel alignment, wheels and tyres will have a greater impact on the power being transmitted to the ground than the weight differences between flywheels.
Ciao,
Adrian.

Smokin

I thought that if it was on the Internet it was true!?...

Adrian

What you talking about bud. Haven't you been to off topic lately. Everything on the internet must be true, look at the links some people (used loosely) post to support their warped arguments
Ciao,
Adrian.

Bill Wagner

Indycam wrote:

Power is power, period. By definition, it's a measure of the instantaneous rate of change of energy supplied with respect to time (for those of you with engineering backgrounds, is dE/dt, with E being energy). The energy is supplied by the cars engine. A flywheel will NOT alter the amount of energy or power your car can provide because it's not altering the source of power, thus there's no way it can increase power. About the best gain you can expect is with the change you get in the HP to Weight ratio, which will improve performance slightly because the car now weighs a little less. I suppose a tricky marketeer could say that since the HP:Weight ratio is improved, it's equivalent to the car having gained a little power.

Indycam

Hiya Bill Wagner
How much does it take to spin up a 15lb flywheel to 6k rpms and how much does it take to stop that flywheel quickly ?

Hiya Adrian
"I guarantee, in real life, that you could not quantify a figure on the differences in transmission loss resulting in changing from a dual mass versus a lightweight flywheel."
The tests to show the difference between the two weights could be shown , but the difference would be so small , the difference in the over all rotating mass of all rotating parts in the car , minus a few lbs shaved off of the flywheel would be tiny tiny .

"Wheel alignment, wheels and tyres will have a greater impact on the power being transmitted to the ground than the weight differences between flywheels."
I agree with you .

mxbanker

A heavy or light flywheel does not increase power it changes how the power is delivered. a heavy flywheel will make power delivery more tractable down low, a light flywheel will rev faster. So technically speaking at the same rpm (with a heavy or light flywheel) you could gain or lose horsepower at that exact rpm vs the other depending on what rpm tested at.
Bootom line they can make this claim but it is misleading if you dont understand the test results.

Bill Wagner

Indycam wrote:

Interestingly enough, this question sort of points out the falacy of a lighter weight flywheel increasing horsepower. When you ask: "how much does it take to spin up a 15lb flywheel to 6k rpms", I assume that you mean how much time would it take given the same engine as a stock 964, right???

The power of an engine is related to the amount of torque (angular force) it can apply to an object. In this case it's a flywheel. To calculate this stuff properly, you need the moment of inertia of the flywheel. For a simple disk, this is given by (1/2)*M*R^2 (that means 1/2 the quantity of the mass (M) times the Radius (R) squared (I don't think this site supports math symbols so I have to use language symbols similar to those used in the Basic programming language since most people are familiar with them). Additionally, the formula:

Power = torque X angular velocity (P = tw, but normally t is the lower case greek letter tau and w is the small letter for omega). The amount of energy it takes to take your flywheel from rest to a full velocity is W (i ->f) = K(final) - K(initial), and for a rotating mass this comes to:

W(i ->f) = 1/2I(w(final)^w(final) - w(initial)^w(initial))

w(final) is the final angular velocity, which in your case is 6000 rpm,and w(initial) is the initial angular velocity, which in your case is zero.

As you can see, most of these equations relate to the moment of inertial (I) which we don't have, thus I can't give you a realistiic calculation. Additionally, since the 964 has a dual mass flywheel with an angular springing action between two flywheels, this set of equations would become even more complicated.

What you can conclude from all of this is that the moment of inertial is related to the mass of the unit. Obviously, with the lower mass of the lightweight flywheel, means it can spin up and decelerate faster than a heavier dual mass flywheel, and yet the amount of power hasn't changed.

As far as deceleration goes, when your talking about cars, what will decelerate the flywheel isn't a counteracting force from the engine, but rather drag on the entire driveline and engine. There's no way I would know how to calculate that. Also, keep in mind that when accelerating the, case I gave you above is simple and doesn't account for any counteracting forces on the system like friction. Most of these things could be estimated, probably with a fair degree of accuracy for a given car, but you would need some data and someone who knows a hell of a lot more about automotive engineering than me!

JasonAndreas

R = 135mm

M :
DMF = 13.6kg
MWF = 8.6kg
LWF = 5.5kg