Heavier or lighter Flywheel to improve FE?

[abently]

So going on from the other thread, this has crossed my mind since I'm in need of a new clutch soon and changing the flywheel out isn't that much additional work if I already have the box out.

Now I don't turn engine off during coasting, or pulse and glide but I do coast in neutral and idle to a stop light everywhere and anywhere.

So the question is, which flywheel is more suited? Stock, lighter or heavier?

Let the debate begin.

[Angmaar]

A lighter flywheel will improve FE because of the lower rotational mass.

[autoteach]

This has been covered, but I will say what I know, not what I believe. A flywheel has a really important job that cannot be overlooked. If you dont have an engineering degree in ICE design, it may be difficult to choose the best flywheel weight for your engine. A flywheel must carry the momentum of the crankshaft with enough energy left over to compress the intake charge with a minimal drop in RPMs, which would negatively effect the engine as ignition would happen to soon, causing an overload on the crank bearing. What weight is that for your or my engine? I am not an engineer. this is what I do know...

Lightweight= better acceleration after the clutch has been fully engaged, engagement takes longer, as engine torque is decreased due to reasons mentioned above. Idle negatively effected, as well as cold weather starting. Shifting is tougher, causes more wear on trans. difficulty pulling taller gears at lower rpms.

Heavier= accelerates slower, engagement is faster. Shifting is easier, causes less wear on the transmission. Idle is smoother, cold weather starting is easier. Higher top speed achievable.

The info I have given covers stock (heavy) and lightweight (lowest allowable for 3 different vehicles that I have worked on). Is there a happy medium, yes. I am not an engineer, so I have no clue to what weight it should be.

[pounsfos]

i will tellm ya the answer in about 1 month, my 5 speed transmission and 4lb pound lighter flywheel are going in soon, so will tell you my f/e differences, i drive mostly semi town with not to much stop and go so let the measuring begin,

[ConnClark]

Proper fly wheel weight, or more correctly rotational inertia, is as important as a correct harmonic ballancer. Change it to a lighter one and your going to stress your crank, main bearings, rod bearings, wrist pin, pistons, and timing chain/belt. Its your engine do what you want

[Angelus359]

I'd put alloy rims, and lighter pulley set before I'd ever consider changing my flywheel... fly wheel is for engine stability. Pistons pump up and down, up and down, and there has to be some inertia to protect the bearings ncrap.

Do some underbody aeromods, grillcovers, moonwheelcovers, good set of spark plugs (cheap iridiums)... drive well

Given the desire to change it... heavier is good for highway pulse and glide, while lighter is good for city, due to less energy wasted via brakings...

[PaleMelanesian]

The energy wasted via brakings can be fixed with a "nut" tuneup, though.

[dcb]

I think a lightened flywheel is an area a dedicated modder can take good advantage of. The main reason for stock oversized flywheels is driveability and idle smoothness. But many hardcore modders don't hardly idle (because it is a complete waste of energy) and can learn new driving techniques, i.e. launching efficiently with a lighter flywheel. And may already time obstructions and lights to conserve vehicular momentum. As soon as you get off of idle and have the clutch engaged, the big flywheel doesn't offer any advantages and is holding your pistons and your car back.

If you P&G a lot then you are straining your engine against accelerating a heavy flywheel only to throw that energy away at the end of each shift and at the end of each pulse. It should be less strain to bump start a lighter flywheel as well.

I'm going to try a lighter flywheel in the tdi golf once I get around to fixing it rather than synch shifting it everywhere

[gone-ot]

...an analogy:

• LIGHT flywheels are used on drag-racing engines for fastest engine speed rev-up.

• HEAVY flywheels are used on tractors for maximum low-speed pulling torque.

[Fr3AkAzOiD]

From what I have picked up on different conversations is that if you do a lot of steady speed highway travel to keep it stock, if you pull additional loads get a slightly heavier one, if you P&G frequently it could help to get a lighter weight flywheel.

Personaly I'm leaving my flywheel alone as currently there is too much conjecture and not enough evidence as to what is better. I am kind of interested in this lightweight underdrive pulley though.

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