Lightend Flywheel

[JSE]

I'm upgrading my clutch to an Exedy. Just wondering if a lightweight billet flywheel would be worth putting in as well? Pros/cons? Also keep in mind I will be turbocharging in the very near future. Any comments or help would be appreciated.

Thanks in advance to all you crazy knowledgable mx5 gurus,

Joel

[trader]

JSE, I have installed a lightened flywheel (6.64 kgs) with standard clutch.
Have found it more responsive on takeoff and very little difference in driving. Climbs as good as ever. Could not justify it though unless the clutch was also being replaced.

[adamjp]

I had my flywheel lightened to just under 6kg when i had the engine rebuilt.

Excellent thing to do and I would recommend it to anyone.

For the best results you may want to consider the billet steel one sold by MAnia, but at 5 times the price of getting a machine shop to do your stock one, it is a bit pricey. Much stronger though.

I am unsure about the aluminium ones, I have never dríven one and the sub-4kg weight does make me wonder if it is too light. However many modern cars have very light flywheels from the factory, so perhaps it is just a matter of getting used to it.

[CT]

Do not lighten a factory cast flywheel - I know people do it but you shouldn't - no questions. MX5 Racing had one fail a couple of weeks ago during a race which was lightened poorly in japan. Cro-moly ones are the strongest and should be the only choice for replacements. Much better than ally.

[adamjp]

CT is correct in that for certainty of safety you should go for a purpose built lighter flywheel.

There are two ways to lighten a piece of metal. Make it thinner or drill holes in it.

The art of skimming down the outer ridge of a stock flywheel has been a constant activity in the motor trade for a very long time. Refacing the wheel and machining the ridge just inside the circumference of the ring gear is less risky and is done every day by clutch and brake shops in this country. My understanding is that it is either done in a similar way to machining brake disks or by placing the flywheel on a lathe. Either way little stress is generated in the cast metal, but it is possible to thin it so much that it loses structural integrity. This is classed as BAD.

IMHO drilling holes in a cast flywheel is just asking for trouble. This is classed as DUMB. Cast metal just does not have the consistent structure needed for this kind of machine work. Holes create stress concentrators in the disc and cast metal simply cannot be stress relieved. Eventually it will come apart, and the rotational speeds of an engine means it will be spectacular and happening around the lower half of your legs.

I have never seen a flywheel come apart, but the fact is that they do, and it can cause serious injury. Old school V8 and rotaries got lightened flywheels because they were machined, and they had shields placed in the transmission tunnel to protect against flywheel disintegration. Just like driveshaft loops are mandatory on drag cars.

You need to make sure you understand the risks and benefits before you commission this kind of change. Some workshops won't do it, some specialise in it.

[JSE]

I would never machine a standard flywheel - thats asking for trouble. I would buy a quality product from someone like Mania. Thanks for the info so far - i guess what Im trying to ask is would it be worth getting if Im going to turbocharge my car and will it be stronger then the standard one?

[Curly]

I fitted the lightweight mania one to my car, and to be honest, it didn't make a dramatic difference.

I wouldn't say there's less power in the lower part of the rev range - you've got less inertia to overcome, so you'll accelerate faster at all rpms.

The supposed downside is that you may lose speed in hills easier, but it's rare to find a hill that you don't have the power to maintain your speed up.

Supposedly it's easier to stall and may idle a bit rougher, but I didn't find either of those things.

[Curly]

i have found the revability on my 1.6 was greatly increased after i fitted a fidenza alloy , with a little better acceleration , but no more pwr.

I'm not following you - how can you have more acceleration but no more power?

[adamjp]

how can you have more acceleration but no more power?

Easy, because you made it lighter.

Acceleration is the rate of change of speed. The engine does accelerate/decelerate quicker because it is not having to change the speed of quite so much metal. Same power, less weight, faster acceleration.

Not sure it makes much difference to the acceleration of the car though.