So basically it kind of goes both ways...a lot of stops and starts and the heavier flywheel might perform better. For driving around without complete stop n' go driving, the lighter flywheel might be better.

lol an 18 lb flywheel is nothing comapred to the 60 lb ford model A flywheel. engine creates a whopping 24 hp. people get an adverage of 14mpg city and 20-25 highway(or crusing which is 45-50mph). mind you that this si a 78 year old engine design, flathead(essentially 4 lawnmower engines put together) and has a compresssion ratio of about 5:1. but the only way they can achive low rpm's is with that fkywheel. but redline is around 2K rpm ish. so i say while yes a heavy flyuwheel will smooth out the firing at very low rpm's. now weither a computer controlled car will allow this or try to compensate and dump gas in, who knows...

Hmm, the lighter flywheel would probably bump start easier :)

I like the lighter flywheel in my car. Stock was about 18 pounds, new flywheel is 12. 6 pounds makes a noticeable difference in how the car accellerates in lower gears, even at half throttle and low rpm. It hardly makes any difference in top gear. see www.pumaracing.co.uk/flywheel.htm

Yes, it bump starts easier and smoother with less jolt.

It would be fun to see what one could do with a variable dynamically adjustable flywheel where you could move a significant weight in and out radially. For braking, you could move the weight outwards to slow down rpm while storing energy. When accelerating, you would draw weight inwards and gain rpm like a spinning figure skater.
If the device was spring loaded and had an extra clutch towards the engine, it could be used to automatically maintain speed while gliding. Another use would be to accumulate energy from an idling engine instead of just wasting the energy. Without calculating, I guess we would need quite a big and heavy flywheel to make a big difference.

Btw. I read somewhere that one of the Formula 1 teams are going for regenerative flywheel enregy storage now that it will be allowed. However, they used a much more complicated setup with a variable transmission to the flywheel. I guess we will see many interesting regenerative devices now that racing is on board (flywheels, electrical, compressed air etc.).

Dual mass FW do something that (just FYI)... Although, when I asked abut aquiring one - most responses have been that they are typically for heavy duty hauling diesels to isolate vibration and gear chatter...

They use essentially two semi isolated masses. I say semi isolated because they are connected with a spring/damper system. The primary FW is supposed to dampen engine vibration and the secondary (spring/damper connected) FW gives the FW more mass. So there's lag in how the energy goes in, and how the energy goes out.

https://www.lukclutch.com/support/clu...&dir=flywheels

Addressing your variable flywheel (search google for variable moment of inertia flywheel ;) ).... There's critical issues with the simplest form of variable MoI (basically masses on springs that move outward with centripetal forces). The advantage of a FW with a higher mass moment of inertia (typically said: heavier) is that the engine runs smoother, stalls less, launches easier. The advantage of a lighter FW - the engine revs much easier (especially at higher rpm).

So with a variable MoI FW - when launching like a gassaver (not starting at high rpm), you don't have the benefits of a heavier FW. Then, should you ever get up into a higher rev range, your FW is effectively much heavier :thumbdown:

So that means we have to make the FW operate in the opposite direction. At slower speeds, have the masses move outward - and at higher rpm, have the masses move inward. Against centripetal forces... Which makes designing much more complicated - not impossible, just not practical.


Finally, the drawback to both variable MoI and dual mass FW's.... They are tuned systems (especially the dual mass). That is, given a specific torque curve/rpm range - the FW result is specific. Otherwise you could run into vibration issues as the system passes a resonant frequency (making acceleration even harder).

Afaik what you would need for efficiency is a special and super heavy flywheel that operates semi-independently of the ice and uses regenerative breaking to rev itself up while the ice still shaves off rpm's... Technically speaking the ICE ought to shut down at this point while the flywheel absorbs all the rpm's from regen braking.

Then upon acceleration the flywheel transfers rpm's back to the engine and drivetrain, at the very least it could be used to start the ICE back up.

Of course this would also add several hundred pounds to the vehicle... :p