Would the type of dyno you run it on make a difference in showing the HP/TQ difference between a stock or a lightweight flywheel? Thus eliminating all the non-sense to find out if initially "does a lightweight flywheel increase power?"

Wheel dyno vs crank dyno?

 

I'm assuming that you are referring to where the dyno is measuring(wheel or crankshaft). You actually have to look at how the dyno works. Most dynos measure how fast an engine can rev while turning a large rotating mass. This method is flawed because changing the rotating mass(adding a light pulley, flywheel or lighter wheel/tire) will cause the reading to be inaccurate. An eddy current dyno uses a different principal. It can accuratly vary the torque that it absorbs so as to keep the engine at a steady rpm. It then use the torque it's exerting, the rpm of the engine, and the speed of the wheel to calculate hp and torque in the engine's steady state. A flywheel would not change this measurement.

 

Since nobody cares about how much power the car makes except when it's accelerating, it will suffice to say that the lightened flywheel will "add power..." as long as you are unable to wrap your mind around F=ma.

I did some back-of-the-napkin math. In first gear, the stock FW is 7% of the total inertia of the car (because it spins very fast, 15 times the speed of the wheels, in first). If you go from a 17lb to 9 lb FW, you reduce the flywheel's inertia by about 60%, and the car's total inertia by about 4%. Thus in first gear add 4% to the wheel horsepower, or about 5hp.

In the higher gears, the difference is much less because the flywheel spins at a lower speed compared to the wheels. The horsepower "gains" for each gear are below:

1st: ~5.6hp
2nd: ~1.5hp
3rd: ~.75hp
4th: ~.4hp
5th: ~.2hp

I accounted for the inertia of the car (3100lb w/ driver) and the wheels (I guessed 34lbs and 24in OD) but none of the spinning engine internals other than the FW, so the actual gains will be a bit lower than the above numbers.

Engine pulleys, I'd probably guess about one-tenth of the above gains.

My estimate: $350 (fidanza price) for 5.6hp isn't a terribly bad deal, but you only get to use it in one gear.

 

This thread makes Steven Hawking a proud little vegetable.

 

That sounds about right. After waking up before dawn for exams i sorta didn't want to do any more math. What did you model the wheels as to calculate their moment of inertia?

 

34lb, 24"OD, solid disk. Conservative guess.

 

At first I was thinking hollow cylinder but if you also count the brakes solid disc makes more sense. I over think things.

 

Maybe this is one for the Mythbusters...

 

Import tuner

The physics are true.. even if import tuner decided to disagree with newton and the others

Vlad is dead on, as have been MANY more on this subject.

A heavier flywheel INCREASES THE INERTIA of your whole drivetrain.. thus it is HARDER to slow down an engine with a heavier flywheel. Thus, you can launch harder at a lower rpm with more mass.

A lightened unit reduces the engines inertia but also allows it to rev easier. It has ZERO effect at steady state, which is where power is truly measured. Some people just cant grasp the point that even if something makes the car quicker to 60 by some amount, it does not necessarilly gain or free up power to do it. The import tuner guys have learned enough to read a dyno chart, but not nearly enough to know WHY it is telling them what it is. Their description you quoted is even seriously flawed.

A flywheel of any sort does not carry parasitic loads in the way they describe. A flywheel stores energy. It only releases or absorbs energy when you speed it up or slow it down. At a constant rpm, it is as if it does not exist at all as far as the engine is concerned. That is the same for any momentum related topic. If you ignore changes in rolling friction (which is relatively small) a car that weighs 2000lb will get the same fuel economy as the same car loaded with 1000 extra lbs if you drive at a constant speed. That mass is mostly affecting inertia, so it only has an effect when you speed up or slow down. Same principle applies to rotational inertia.

So, when you lighten a rotating part, you dont "store" as much of your energy under acceleration, hence you dont have that energy when you let off the gas.. in turn netting a zero hp gain, even if the car is a bit quicker.

 

This is all great stuff, really, but honestly, while everyone is showing off there vast knowledge of physics the only thing i (and most people) really care about is tangible proof of our cars 0-60, 1/4 mile time decreasing, wheel horsepower/torque on a dyno increasing and the feel of my tC pulling a little harder. And i have been granted all 3 by installing a lightweight flywheel. Its as simple as that.

 

No one said you could not make a car quicker to 60 with a lighter flywheel ... what you dont seem to understand is that doesnt mean you free up or make any more power.

And we are hardly showing off a "vast" knowledge of physics.. as this is pretty much 101 level

 

Well so far we have tangible proof that a flywheel can make a dyno look stupid. This thread is completely missing the point of getting a flywheel and that is to make the engine change rpm faster when you shift. While your tC will pull a little faster in 1st and you might see an improvement on the drag strip but in actual driving and or racing(autox and track) there will be no improvement other than the aforementioned shifting benefits.

I believe i learned this in high school and physics 123(analytical physics 1A).

 

man after reading all this i really should of stayed up in my high school physics class

 

Its been 7 years since my last college physics course and i havent used the **** since. I must say that i consider this thread a good refresher.

 

Nah man i understand that. U already gave me that lecture. To put what i said in a different way; the dyno is tricked so higher numbers show up on paper and thats all i care about.