I hope nobody taught you that in school. Are you sure you know what acceleration is? Change in speed over time. If you move something you are accelerating it. You are ACCELERATING the roller on the dyno!

The final answer is, and has been reached like 20x on H-T, and always was, that a lighter flywheel takes less energy to rotate in general and more energy can to go the wheels. The "loss of torque" when launching is merely PERCEIVED. It means there is less stored angular kinetic energy in the flywheel itself, so to accelerate in the same manner more throttle input is required. There is no loss in torque, the torque just comes from somewhere else. But I assure you, the "massive" stored KE in your super-heavy flywheel is not all that massive. So once you want to /actually/ move the car it becomes a burden rather than a contributor.

So we do not need any more "this guy said this" and "I don't care what you say I'm right" type posts because this is the answer.

Dustin

 

This question is for dustin..

I currently run 13.0-13.1-13.2 et's in my 1994 Turbo gsr. (Times are on nitto drag radials) I purchased a Fidanza Flywheel 9lb and a Cusco Differentail.

I am currently using a Clutchmasters Stage 4 Clutch. Will the effect Of the flywheel and Diff be enough to put me in the 12.80-12.90 region. I have a stock diff and stock flywheel right now. I launch around 3000 rpm now with full boost engaging at 4000 rpm. First gear feels almost nonexistent and the beginning of second is similar. I am hoping distributing the power to each wheel versus lowering the rotational mass my car might spool quicker and accelerate quicker.

Any insight on the subject would be greatly appreciated. Thanks

 

I'm pretty sure I know what power and acceleration is. I'm also pretty sure that when a McLaren is going 230mph it will be using every one of it's 620+ horsepower, and yet it won't be accelerating beyond 230mph. There will be no "change in speed over time." You don't have to have acceleration where you have power.

Acceleration will only happen when the power being put into the object exceeds the power that's trying to slow it down (friction).

If this is not the case, I'll be the first to say that the last five years of my life have been a waste.

Anyway, I guess I don't know how a dyno works. I thought they floor the car and attempt to keep the engine from accelerating (changing rpms) by putting a load on it. From that load, the horsepower can be figured out. In that case, I don't see how a heavy flywheel would make a difference. Apparently that's not the case.

I'm not arguing that it wouldn't make a difference, by the way. I just don't see how it would. None of the explanations given helped me out any.

However, I can see how it would make a huge difference on the street, where the engine changes rpm's all the time.


[Modified by Lsos, 11:16 PM 1/20/2002]

 

a lighter flywheel is easier to spin... which is less load on the motor... so the motor can use the power elsewhere instead of trying to spin the flywheel... hence more hp...

and when a mclaren is going 230 is is NOT using all its hp... its uses it to get up there... not to stay at that speed... it doesnt need 2...

thinkabout it this way... if u are pushing a car... u need a lot of ur power to get it going to lets say 5mph... once u get it to 5mph... are u still using all ur strength? no... ur not... it gets a lot easier... same thing goes for a car... once u get to a steady speed u arent using that much power

 

Where else does the motor use power? To spin the muffler bearings?

 

 

to turn the wheels!

 

does that mean u agree or disagree

 

VIA the FLYWHEEL?

 

Now lets sing this along to the tune of the hip bone is connected to the leg bone...

The engine is connected to the... flywheel!

The flywheel is connected to the... clutch disk!

The clutch disk is connected to the... tranny!

The tranny is connected to the... axles!

And the axle is connected to the... wheels!

 

Yep you're right, I had a brain fart there. However, I will not comment on the dyno because I have not read up on how a dyno works.

As for why it can show up on the dyno, think a heavier flywheel like heavier wheels. The engine rotates both the wheels and the flywheel, and we all know that heavier wheels with their greater mass and thus greater moment of interia are harder to accelerate.


[Modified by Ein, 5:22 PM 1/20/2002]

 

exactly... did i mess up my in my explanation or "1"... are u just messing with me?

 

Tom are you referring to the English 1 or the German 1? You stated something about the engine using power elsewhere besides turning the flywheel. I was wondering where else you think the engine distributes power to.



[Modified by 1, 5:54 PM 1/20/2002]

 

I think you misunderstood what Tom was trying to say. Every component in the drivetrain by simply having mass is going gain energy from being rotated by the transmission. So with a lighter flywheel the freed up energy does go somewhere, which is ultimately the wheels.

 

This makes perfect sense to me
My whole dyno explanation was assuming that it measures power at steady state. I think I threw that term in there about five times.

If they don't measure power at steady state, which seems to be the case, then I could definately see how something that is heavier is harder to accelerate.

I just don't see how something that is heavier is harder to keep spinning at a steady speed (except for friction). Steady state dyno testing was my assumption. It was wrong. In this case, I'll say that a lighter flywheel will definately affect dyno numbers.

 

Holy you need to take a physics class. Power has nothing to do with force. Something accelerates when the net force on it is not zero! Power is the ability to provide force over time (thus torque over time). Horsepower means nothing in the real world. For example, when your McLaren is at its top speed, the torque output force of the motor through gearing and the drivetrain is equal to friction force (arial drag, rolling resistance, internal friction). Horsepower is a measure of how useful a given torque is (torque relative to rpm). Obviously the faster something can spin the more useful it is .. since it can be geared down for more effective torque. Horsepower is a figure to describe motors, not to describe the acceleration of a vehicle (which is better described through torque). And in case you did not know, Power and Horsepower are synonymous.

If they kept the engine from accelerating on the dyno, what would be the point? You do not want to discern torque output at a fixed RPM and then stall the motor, you want to see torque output at ALL RPMs. The dyno basically records engine RPM over a length of time and then integrates to calculate effective torque given the weight and momentum of the dyno roller. The dyno returns torque. It is then mathematically converted to horsepower.

Heavy flywheels require more force to accelerate. F=ma. That is just how it works. If the flywheel was held at a constant rpm (engine RPM the same, car not accelerating) then in general the weight of the flywheel would be of no consequence (the only difference would be additional friction because of more weight force due to gravity pulling the flywheel towards the earth than the lighter flywheel). Weight (and thus mass) affects acceleration.... in a perfect world holding something at a constant velocity requires no force input (thus the lack of V in the equation F=ma).

Either way, lighter flywheels are better... as long as they are strong enough to handle clutch engagement. Heavy flywheels are included in stock passenger cars to ensure smooth idle and to make the car harder to stall with light throttle input... they are not there for performance.

This is how it works.

Dustin

 

I don't understand why you are arguing with me. You are ultimately saying the same thing I was saying, except in a different way.

You also contradict yourself a little, though.

I don't know, man. Seems we have a miunderstanding, because I'm reading what you wrote, and I'm kind of like....yeah, that's exactly what I was saying....Maybe there's losses due to communicating over the keyboard.

Anyways, I suggest you reread what I wrote and compare it to what you wrote. If that doesn't work, get a third party. If that doesn't work....I don't know what to tell you.

F = ma
Power = F x distance / time (or power = torque x rpm, or power = IV.......it's ultimately all the same)

Hence, if you want to accelerate faster you increase the power. With the aid of a gearbox you can either get more "distance / time" or "F" (or rpm, or torque) at the wheels. More F at the wheels = more a.



[Modified by Lsos, 9:10 PM 1/21/2002]

 

You were getting the concepts of force(torque) and horsepower confused. They are not synonymous; they are indirectly related. You need RPM to calculate horsepower.

I understand what you are saying, and it is wrong.

Horsepower = (Torque * RPM) / 5252

If you want to accelerate faster, you increase torque. If the RPM is held constant, horsepower will also increase. HOWEVER, You can also increase horsepower by holding torque constant but increasing RPM. This does /NOT/ make you accelerate faster through a given gear. It simply moves where the torque is made. The only reason horsepower is useful is because of /GEARING/. This is why peak horsepower numbers are absolutely worthless. Higher redlines allow you to accelerate LONGER, thus why it is in fact useful to have a high redline. This does not make your motor accelerate faster. You will burn through the rev range at the same /rate/ which is linear to torque!

We are not saying the same thing. Either way, lighter flywheels are better. That is the point of this discussion anyways.

Dustin

 

Lighter flywheels are better.

And the Toyota Prius has an electric motor rated at 258 ft-lbs. I doubt anyone will say that that car is fast, feels fast, pushes you in the seat, accelerates fast but for a short time, or anything of that nature. It is slow. It has very little power.

Power is also a measure of how fast you put energy into something. A moving object has kinetic energy. To accelerate an object quickly, you need to put kinetic energy into it, quickly : power. Torque itself will not do.

I myself can give you a 1000000 ft-lb of torque with a long enough lever, but I will not be able to acelerate a car quickly.


[Modified by Lsos, 10:01 PM 1/21/2002]

 

Yay.

 

I agree with dustin.. the physics just work out. Problem is, why do reputable companies such as South Florida Performance do NOT recommend aluminum light-weight flywheels on turbocharged vehicles? I called them and their argument was the loss of rotating mass.. less torque. :/

 

Correct me if I am wrong. Too much torque would just spin the wheels, right? Wouldn't it be better for drag racing if the torque was a bit lower because of the lighter flywheel allowing the horsepower to be greater when you need it (in motion)?
I also believe that a lighter flywheel would be better in any racing application.

 

Ok, I'll correct you

Horsepower is higher when torque is higher at a given RPM. A car will accelerate entirely linear to its torque curve. The solution to "too much torque" is not to simply have less turning force! By this theory we would all be turning the boost down to gain traction... Flywheel or not, it still requires the same amount of torque at the wheels to launch the car.

Dustin

 

Actually there are boost controllers that can vary boost for each gear. Lower boost in lower gears to make launching easier and higher boost for the higher gears.

 

I know I have the AVC-R. But the real way to solve the problem is just to get bigger slicks... lowering the torque output doesn't make your car faster than just getting the traction the right way Maybe it was a bad example.

Dustin