Lighter flywheel. Effects.

[simple101]

I have an e30 318 IS which i believe has a duel mass flywheel. If i put a 325 one on (which i will call single mass for sake of argument) or even a light weight alluminium(sp) one, what will the effects be?

My main concern is fuel economy if im honest but being poor i must consider these things.

i know about rough idle but i can live with that, as long as it isnt too bad. My guess is it would feel the same at idle as a 325? or is there something im missing.

[SkinnyBoy]

I have a lightweight Fidanza one on my car, and to be honest its a pain as a daily driver. Sure pick up is quick but you have to keep on the boil a lot more and in stop start traffic it gets boring.

[christer]

simple101 said:

My main concern is fuel economy if im honest but being poor i must consider these things.

The difference between a heavier and lighter flywheel is really only the energy stored in the rotating mass. A heavier flywheel is used to smooth out any real-time fluctuations in that energy applied in order to make the car more refined. Yes, it does take mor energy to move a heavier flywheel, but once going it has more energy stored so I would think the difference in fuel economy is minimal - almost a zero sum - but only almost due to friction.

The lightflywheel in a Porsche 964 for example, weighs about 8lbs less than the DMF (dual mass flywheel) so let us assume it is the same in your case. Lets also assume that your car weighs 1250kgs and that you save approx. 3.8 kgs by installing the light flywheel in outright weight. This would equate to such a miniscule gain in fuel economy that even if you only spent £100 installing the light flywheel, it would probably take you in excess of 20 years to make the difference back in fuel (at current fuel prices).

Let us know how you get on.

[Nick M]

simple101 said:

I have an e30 318 IS which i believe has a duel mass flywheel. If i put a 325 one on (which i will call single mass for sake of argument) or even a light weight alluminium(sp) one, what will the effects be?

My main concern is fuel economy if im honest but being poor i must consider these things.

i know about rough idle but i can live with that, as long as it isnt too bad. My guess is it would feel the same at idle as a 325? or is there something im missing.

Have to say, my gut reaction is that because of the way the car will drive you could end up using more fuel.

If you need to keep the revs up in traffic to avoid stalling when pulling away then you'll use more fuel. Similarly you'll have more engine braking (less rotating mass) so you'll have to get back on the throttle to maintain the same speed, whereas with a nice big flywheel you'll have a smoother drive with less on / off throttle moments.

If you're worried about fuel economy then doing all the dull stuff to make sure the engine is running as smoothly as possible, that tyre pressures are correct, being smooth when driving, etc., are likely to all pay off more than replacing the flywheel which, in and of itself, is likely to be an expensive exercise relative to what you might hope to save.

[simple101]

It inst so much a fuel saving modification. rather one for increased acceleration and i wanted to know the effects. All considered, im probably going to keep my stock one. I just cant see the point for daily use and after reading the replies about revving higher to prevent stalling it seems even more pointless.

ill save the monet for something worthwhile.

thanks alot people

[RatBoy M3CS]

Unless its a race car that spends its life between 6.5-8k rpm... forget it..

The engine does spin up quicker yes.. but its not as smooth, a heavier mass flywheel acts as a damper, ironing out the power curve before it gets to the gearbox.. it affects the torque delivery too..

Not generally recommended for road cars.. you will be constantly stalling it too with superlightweight ones..

Edited by RatBoy M3CS on Tuesday 7th July 20:08

[bazking69]

Save your money...