Come on guys, it's plain physics: T=L x F, while F=M x g. Decrease M, you decrease F, you decrease T, which simply means you need less power to spin the lighter flywheel (smart, heh ? ).

In theory and in practice, by installing a lighter flywheel you don't increase the crank HP, but you certainly increase the percentage of this HP/torque that reach the wheels, i.e. you increase WHP.

So, a lighter flywheel does not increase crank HP, but certainly increases WHP And of course allows the engine to spin up faster, since its reduced mass proves less of an obstacle (less inertia)

 

It is plain physics but you're confusing energy with power. A flywheel is an energy storage device, it doesn't create, absorb or provide power. If you had NO flywheel, the horsepower delivered by the engine to the rear wheels at a given RPM would be the same (minus the frictional losses in the drivetrain and assuming you could keep the engine running). The improvement comes from allowing the engine to spin up quicker (which the lighter flywheel allows) which translates to HP being available earlier. In the end, the maximum horsepower (heavy flywheel, light flywheel or no flywheel) remains the same.

Reducing flywheel weight just re-shuffles the existing horsepower throughout the RPM range. If you really think that reducing flywheel weight increases RWP, then you should concentrate on reducing the weight of the wheels, tires, brakes and other rotating machinery in the driveline. Those items weigh an order of magnitude more than a flywheel.

 

We agree on your second paragraph, but I don't quite agree with your first comments. Of course I am not confusing energy with power. The flywheel is -in broad terms- a disc with a certain mass. In order to spin it, you need to transfer energy to it, which means applying a certain force. This force comes of course from the engine. So, reducing the flywheel's mass, you reduce the amount of force needed to spin the flywheel, assuming the other variables remain constant.

I'm not discussing whether the flywheel moves the powerband up or down, or relocates the point of maximum output. I am merely pointing out that reducing the mass of the flywheel increases the net amount of force with goes "through" the flywheel and finally spins the wheels (which is measured as WHP).

I had done a very generic calculation as to how much power is "freed up" by reducing the mass of a flywheel by a certain percentage, but it was done in Greek and cannot translate right now. I did this because I didn't want to take the assumptions of ACT or MazdaSpeed as granted. The result (my result) was that for every Kg of mass shaved off, about 0,5% of WHP is gained (actually it was 0,5% of wheel torque that is gained).

 

A flywheel is an energy storage device - storing rotational inertial energy. This energy is dependant on the inertial moment of the flywheel, and its rotational speed.

The flywheel is connected to the engine - which varies in speed.


When the flywheel varies in speed, its stored energy changes. The change in energy over time is POWER.


When the engine spins up, the flywheel spins up increasing its energy, and the power that it takes to increase the flywheel energy is power that could be going to the rear wheels but is not. The faster the flywheel changes speed the more power it consumes - therefore the most gains from a lighter flywheel will be in first gear, and diminishing in every gear after that.

 

I think that you are the one confusing energy and power.

After reading the previous posts I'm beginning to see where you're coming from.

You think of the flywheel solely as a storage medium for potential energy.

Basically in your world you think that the engine can spin up the flywheel, energy goes completey into the flywheel and then can be transfered completely into the driveshaft upon engagement of the clutch.

It does store energy for the engine, it's sole purpose is to make it easier for humans to shift gears by keeping the momentum of the engine constant. But it saps energy doing it!

To put it simply, having mass at any distance from the center of any rotating object is going to need energy to spin.

Remember the good old days of the merry-go-round?

Now it was easy to spin the merry-go-round with no-one on it, you could make it go around really fast(giving it 100% of your energy), but it stopped spinning rather quickly.

-Because you had enough energy to perform the work required, factor in the amount of time it took you to get it spinning and we can calculate your horsepower!

Now when all your friends were on it, it was so hard to get spinning(giving it 100% of your energy) that you needed a grown-up to help you and even then it wouldn't spin that fast, but once it got spinning it seemed to go on forever.

-Because it was too hard/impossible for you to spin the merry-go-round you did not have the energy to perform the work required!

Now look at the speeds! the light merry-go-round went fast for the same amount of energy as the heavy merry-go-round needed just to get it started.

This is exactly what a flywheel is, its purpose IS to store energy, but what you neglect completely is the quantity of Impulse. Impulse is the amount of energy required to change the inertia of something.

Yes, changing the inertia of something does require energy! This is why it was harder to spin the merry-go-round with people on it!

Com'on dude I was a physics tutor.

 

Just for argument's sake.... Don't you think that Mazda, who is DESPERATE to rate this engine's horsepower higher than it is, wouldn't have put in a lighter flywheel from the factory just to get the higher horsepower rating? They don't because they know flywheel weight doesn't make any difference in HP.

Don't get me wrong, there are plenty of good reasons for a lighter flywheel from an engine response standpoint. You can deliver what HP you've got faster and earlier. Because of that you can end up with improved quarter-mile or lap times. But, in the end, you've still got the same HP you started with - just delivered differently.

 

Translation for Marines: Light flywheel, car go faster. Ooo rah!

 

lightweight flywheel costs more for mazda to make and they dont care about any mods that only increase whp bc they advertise bhp. 238 bhp sounds better than an estimated 210 whp with a lightweight flywheel

 

are you still in mi????

i will drive you and your car to tampa... you pay for gas...

yes i can fly to detroit for free.... we need you here..


beers

 

Absolutely! I have the aluminum SR flywheel for my RX-7. Very noticable gain in acceleration. That's only possible if more power actually gets to the ground.

On the 13B nonturbo engines, you could get very large gains from a new exhaust. They were gains not possible with the Renesis. We're talking on order of 30+ hp from an exhaust alone. The 2 largest gains you could do to a nonturbo RX-7 was the exhaust and a flywheel. Everything else was less important. The acceleration gains were on par with that of streetporting the engine. That's right, a good flywheel could add the acceleration capabilities of a ported engine with the stock flywheel! I laugh at those that say a flywheel makes no difference in power to the ground. They need to actually drive one instead of speculate as to how something works that they have no experience with.

 

The flywheel is there to begine with the smooth out the engine vibrations between power strokes (actually, to keep it running) and increase driveability in a manual transmission car by making it harder to stall. Many people are willing to sacrifice a bit in both categories for more performance - many others are not.

Judgeing by the amount of people complaining of squealing brake pads on this forum from the braking system that produces the shortest distance of any japanese car, they were probably right in using a big ol driver friendly flywheel.

 

Others can correct me if I'm wrong, but I think this is the lightest flywheel they've ever used on a production rotary.
Paul.

 

^Don't you know? Can't you just go into the back room and weigh them all??? You're slipping Paul!