Flywheels Who's running what and why?

[Shoaz]

The fact that a lighter flywheel takes less torque to accelerate is a fairly simple math problem, and if you want, I can bore you with all the details. However, in the interest of time and space, it might be better if you just accepted the truth from someone who can do the calculations and actually knows what they are talking about in this case.

You're both right. A flywheel is an energy storage device, and a lighter flywheel can't store as much energy at the same rpm. Power comes from fuel consumption, and how big the flywheel is doesn't make ANY difference in the amount of power produced, because it doesn't affect the production of power in any way.

Getting more "power" from a lighter flywheel is the same as getting more "power" from weight reduction. It's a bit more noticable with a flywheel because it rotates at a pretty good clip, so it can store a lot of energy.

The power "lost" with a big flywheel is just stored, which is what Mark was noticing with respect to a brake bias change.

It looks like less power or less torque on a dyno because some of the energy produced is going into the flywheel. So a bigger flywheel just counts as a bit bigger loss, in addition to all the other losses, and reducing rotating weight always helps reduce losses and energy going into kinetic storage rather than doing the work that you want it to. The weight or mass of the flywheel has zero affect on how much power the engine is actually producing. It really only affects acceleration/deceleration by storing energy and releasing it.

 

[RonPorter]

And, when shifting, you, in effect, have "more" available power from a heavier flywheel......

It's all a trade-off. Small displacement drag cars would usually run heavier flywheels to get more help with the launch.

 

[raceguy1969]

You're both right. A flywheel is an energy storage device, and a lighter flywheel can't store as much energy at the same rpm. Power comes from fuel consumption, and how big the flywheel is doesn't make ANY difference in the amount of power produced, because it doesn't affect the production of power in any way.

Getting more "power" from a lighter flywheel is the same as getting more "power" from weight reduction. It's a bit more noticable with a flywheel because it rotates at a pretty good clip, so it can store a lot of energy.

The power "lost" with a big flywheel is just stored, which is what Mark was noticing with respect to a brake bias change.

It looks like less power or less torque on a dyno because some of the energy produced is going into the flywheel. So a bigger flywheel just counts as a bit bigger loss, in addition to all the other losses, and reducing rotating weight always helps reduce losses and energy going into kinetic storage rather than doing the work that you want it to. The weight or mass of the flywheel has zero affect on how much power the engine is actually producing. It really only affects acceleration/deceleration by storing energy and releasing it.

Props to u! I'm glad u understand y my fuel mileage dropped, it is also because I enjoy it but it also makes me have to dump more fuel in to keep it spinning at the same rpm. anyone want to think about that and try to argue with me? I'm excited for the convention, if any of u want to talk I have the 90 with half ass painted bondo on my right rear wheel well and Hondo slapped next to my license plate . gonna smoke u all on the track!! Ill be the guy going 100%

 

[rubydist]

You guys are confusing "power", "torque", and "energy" and drawing invalid conclusions.

The heavier flywheel will store more energy at a certain rpm than the lighter flywheel (it also depends where the mass of the flywheel is located).

The internal energy generated by the engine does not change if you change the weight of the flywheel.

Because the lighter flywheel requires less energy to accelerate, there is more output torque from the engine with the lighter flywheel. Because there is more output torque, there is correspondingly more output horsepower. This is why putting on a lighter flywheel results in "improved performance" of the vehicle. When Shoaz says "a bigger flywheel just counts as a bit bigger loss" that is another way of saying there is less output torque with the heavier flywheel.

Vehicles with little engines that have low torque output generally have heavy flywheels so that between the engine's torque, and the stored energy in the flywheel, there is enough to launch the car even with a not-very-good driver behind the wheel.

When you quote that the 3.2 SHO motor has 220 hp and 215 lb-ft torque, those numbers were obtained on a dyno. A lighter flywheel increases those numbers, as has been documented.

 

[vortex2450]

As was mentioned earlier in this very thread, the 9lb flywheel made about 5 lb-ft more torque and about 3 more horsepower than stock on the dyno, so you can clearly see the improvement on the dyno. I used to have the graph, but it seems to have gotten lost in one of my computer upgrades...

The fact that a lighter flywheel takes less torque to accelerate is a fairly simple math problem, and if you want, I can bore you with all the details. However, in the interest of time and space, it might be better if you just accepted the truth from someone who can do the calculations and actually knows what they are talking about in this case.

The fact is that "its all a feel thing" is actually measurable.

I agree with you. Whether it's at a standstill (idle) or from 4000rpms, a lighter flywheel will not require as much force (torque) to spin as a stock or 17lb flywheel.

IF anyone doubts this please consult newton's 1st law of motion and the concepts of inertia.

Objects in motion tend to stay in motion, objects at rest tend to stay at rest. The more mass an object has then the more force (torque) there is required to accelerate the object.


-josh

 

[RonPorter]

BUT....as I said in my earlier post, you have to shift.....

The heavier flywheel will keep the momentum during gear changes, resulting in less of a power drop between gears.

It's all a trade-off. Personally I would like to see comparable dyno charts with heavy versus a light flywheel, as I don't believe you will see a difference.

For the street, I would stay with something in the 14-17# range.

 

[zach44102]

I think if everyone had solid rotors, heavy flywheels, and 225's on 8" wide wheels we would all I have better cars? Amirite Ron?

 

[Bob Gervais]

I think if everyone had solid rotors, heavy flywheels, and 225's on 8" wide wheels we would all I have better cars? Amirite Ron?

-Drilled/slotted rotors have proven time and again to crack. I've seen it firsthand, a quality Wilwood rotor, on a seasoned SHO guy's car that had logged plenty of track time. Drilling and slotting introduces stress risers. Maybe wanna google that shit...

-Stock flywheels, ultra light flywheels, and everything in between have advantages and disadvantages, which directly fall in line with what the car is used for, and what the owner is willing to give up in driveability.

-You put 205s on 8" wheels duh.

 

[vortex2450]

BUT....as I said in my earlier post, you have to shift.....

The heavier flywheel will keep the momentum during gear changes, resulting in less of a power drop between gears.

It's all a trade-off. Personally I would like to see comparable dyno charts with heavy versus a light flywheel, as I don't believe you will see a difference.

For the street, I would stay with something in the 14-17# range.

If by momentum you are referring the amount of inertia being kept within the flywheel upon the engine being put into a neutral state you are correct.

However, when the output shaft is freely spinning power is being transmitted and a car doesn't accelerate without torque being applied to the wheels. The longer the transmission is in this state between shifts the slower your acceleration given all other variables are the same. A lighter flywheel mean less inertia which mean the engine begin to not only drop speed sooner but also quicker resulting in a much faster shift at speed. This is advantage 1 of a lighter flywheel.

The second thing I would like to hit on is that the flywheel doesn't produce torque, the torque is produced from the motion of the pistons acting upon the crankshaft, the flywheel at this point of basic engine function is a mass at the end of the rotating assembly, the more mass on this assembly the more torque that is required to accelerate the entire rotating assembly and therefore less torque is being transferred to the transmission. This is increasingly important when the engine of discussion will see an rpm of upwards of 7000.

And I guess I could blab amount the smaller amount of energy the clutch friction material will absorb upon re-engagement in matching the mechanical speed of the engine and the transmission but that's probably even more negligible than the gains seen from a light-wheel flywheel over a stocker.

Point being is than from a strictly performance view a lighter flywheel is in my best educated opinion beneficial when used on a car the will regularly spend time under high loads and high speed.

The less weight will also make a daily driven car obviously a chore as the significant loss of mass in a lightweight flywheel results in less inertia and therefore much less time to fully disengage-shift-engage at the right engine speed.

you win some you lose some.

-Josh

 

[rubydist]

I think that how much of "a chore" the vehicle is to drive with the lighter flywheel depends most on 1. the talent of the driver and 2. how sensitive said driver is to flywheel inertia.

In my case, I have no problem at all with the 9lb flywheel in daily driving use, but plenty of others have said they would/did go away from that to stock-ish weight for daily driving.

The time to shift is actually better with the lighter flywheel, imho, because the engine drops to an appropriate rpm quicker (the stock takes too long for me even in "normal" driving), but the "chore" part is in the initial launch - you must either rev the engine a bit more or it will drop down to a lower rpm than you like when starting from a stop, in my experience.

 

[sperold]

The light flywheel is a ton of fun on the street.
You have to get used to the sensation of feeling the pulses generated by the engine during the power-strokes.
You also have to get used to the throttle response... when you are driving along and touch the gas, it responds immediately.
It is easier to stall when backing into a parking space for example, but you quickly adapt and get over that.
It changes the characteristics of the car, with the light wheel and aluminum subframe bushing.... the car is a brute and you feel you are in a race situation. With the standard wheel, the car is smooth and luxurious and totally enjoyable in all situations, and your heart-rate stays low.