Does anyone use them? How much do they help? How pronounced are their downsides (easier stalling, etc)?

Lightweight flywheels and spur gears have their ups and downs, it really depends on the terrain you are running on.
The up to a lightweight, is that you will be able to spin up to full speed much quicker than normal, since there is not as much weight for the motor to push.
Yet at the same time, there is also going to be a reduction in torque.
Now granted I do not have the expierence with this in RC cars, but the above stands true for real cars. I would assume that logically the same would stand for nitro RC as well.
I think it would really just depend on the application.

I use them on a couple of my engines. Quicker to peak rpm and quicker back to idle.

Yeah I understand their benefits on real cars, though I know a drop in torque production at the wheels doesn't make sense. I know that with real cars (specifically manual transmission'd ones), a lighter flywheel means it is more likely to stall during takeoff. In that same light, I just wondered if the reduction in rotational inertia would make it die much easier when it would otherwise already be close to dying (when starting up, if the engine loads up).

But, I think I might try it out! At the very least Ill lighten a stock flywheel.

on my Pro.15 i have one of those vented/lightened MIP flywheels
and on my .28 i have just a normal OFNA flywheel
(Big engine difference i know)
And i personally like how the MIP flywheel idles down and how fast i revs up
(you engine WILL have to idle a bit faster due to reduced weight keeping the engine rotating)
And yes it does make a noticeable decrease in torque, Cuz even with my smallest CB i cant do wheelies anymore

Un-related the Buggy with the .28 with the OFNA Flywheel WILL do wheelies.....

Hmm. I wonder why that is? I know on full-sized cars the whole point of a lighter flywheel is so less of the engine's torque is needed to accelerate the flywheel, and thus more of it is used to accelerate the vehicle. Now that I think of it it probably has something to do with clutch engagement. Maybe when you floor it, at the point the clutch engages there is less inertia transmitted to the drivetrain, and thus less off-the-line punch. However, overall acceleration should improve. Id imagine that one would have to use lighter clutch shoes or stiffer springs to get the same low-end punch as with a heavier flywheel.

yea thats what i was think with the stiffer springs
(since i have a worn clutch to that my have something to do with it, but i also have the 360pipe which is for low-mid power)

Here is what i found on the 1:1 stuff


"Torque is simply force with a rotational component. For simplicity's sake let's ignore the rotational component for the moment. Force = Mass(M) * Acceleration(A). So if you decrease M and leave A constant then you would lose torque. But a lightened flywheel will accelerate faster than the stock unit so if you should see the same amount of torque maybe a little more.

Where people are coming from when they say you lose torque with a lightened flywheel is a lightened flywheel has less momentum than the stock unit so it can "transfer" less torque to the drive train in the moment when the clutch engages the flywheel. So you have to give an engine with a lightened flywheel more gas to prevent it from bogging as you let the clutch out than you would an engine with a stock flywheel."

And thats why with our little engine we have to idle them up quite a bit with the lightened flywheels

In my rc experience the flywheel weight can be an advantage or a handicap, the most obvious thing is that your engine will stall more easily if your clutch isn't in proper working order and your tune is not spot on, in my experience stalling once during a main will largely undermine the fractions you may gain with a lighter flywheel, not to mention that a heavier flywheel gets better fuel mileage and produces a smoother more tractable power wich is much appreciated when traction is low.

At least a lightened fly wheel on an RC won't cut off your toes when it goes bang