Do lightweight flywheels make much difference?

[steffen707]

i have only just started to play with pulse and glide, but certainly having better acceleration is going to be a plus once i swap to crx hf gearing where 60mph is like 1500rpm in 5th.

[steffen707]

is bump starting when you pop it back into gear will doing pulse and gliding? I havn't heard of the term bump starting before. I could totally see where heavier is smoother, but again, MPG is main concern.

[dremd]

Originally Posted by steffen707

i have only just started to play with pulse and glide, but certainly having better acceleration is going to be a plus once i swap to crx hf gearing where 60mph is like 1500rpm in 5th.

flywheel mass will play a VERY small role with acceleration at 1500 RPM's in 5th, at higher rpm's that's a different story.

[autoteach]

Originally Posted by dremd

Hey auto tech, Where did you get info on lighter flywheels + traction? I find it more difficult to launch cars with lightweight flywheels, but that could be a function of what clutch is typically attached (double and triple disc for us Supra guys).

I wish I could remember where, but the function is this: Wheel slip on take off (or in the case of a snowmobile track slip) is = to the excess in flyweight (including all rotational energy of engine parts) energy delivered. Less inertia in, less wheel slip out. If there is really good traction, you can run a heavier flywheel and maximize input energy into the launch.

[dremd]

Originally Posted by steffen707

is bump starting when you pop it back into gear will doing pulse and gliding? I havn't heard of the term bump starting before. I could totally see where heavier is smoother, but again, MPG is main concern.

Yes, put the transmission in gear, and let out the clutch to eliminate starter use.

****** opinion******
If your main concern is fuel efficiency at steady state 70 mph, it makes no difference.

If you are going to pulse and glide around 70 go with the lightweight.

If you are going to be operating at slower speeds where you are limited be "lugging" go with the heavier flywheel.

Since you already own the lightweight, are not concerned with smoothness (NVH) I'd lean toward running the lightweight, but the decision is yours

End Opinion

[steffen707]

Originally Posted by dremd

flywheel mass will play a VERY small role with acceleration at 1500 RPM's in 5th, at higher rpm's that's a different story.

You forgot you can downshift

Also after some online searching i've read multiple times that a stock civic is 18lbs, exedy's stock replacement is 16.6 lbs and the civic vx stock weight is 15lbs.

Hmmm, 16.6% reduction in weight from "non fuel economy" civics.

[dremd]

Originally Posted by steffen707

You forgot you can downshift

I did not, I stated "

acceleration in 5th at 1500 rpm's

", yes the equations change dramatically when rpm's increase "

at higher rpm's that's a different story.

[autoteach]

Originally Posted by steffen707

You forgot you can downshift

Also after some online searching i've read multiple times that a stock civic is 18lbs, exedy's stock replacement is 16.6 lbs and the civic vx stock weight is 15lbs.

Hmmm, 16.6% reduction in weight from "non fuel economy" civics.

16.6% reduction in something that doesn't really matter. Another question, what is the difference between weight and inertia? Maybe we shouldn't be calling them heavy or light flywheels, but high and low inertia flywheels. Is there anything that you can tell about the inertia of the three from there weight?

[dremd]

Well, I believe that inertia is mass* velocity, so unless we define velocity . . .



But I know what you are talking about; moment of inertia/ rotational inertia, and you are correct, that is the important metric.

[autoteach]

well, that mass*velocity is linear inertia. Distance from the center for a rotational object has to be considered. You could produce a flywheel that weighs 20lbs that has the same inertia as ones weigh 18, 15, or 5 lbs.