How to lighten a stock cast iron flywheel
 

How to lighten a stock cast iron flywheel



Start with your stock flywheel, In my case, 2.3L Turbo Ford

https://www.miataturbo.net/attachmen...ine=1334940043

Its weighs in at 20.5Lbs

Lets see how much weight can be cut off….



Next is to remove the clutch plate alignment pins….

https://www.miataturbo.net/attachmen...ine=1334940043

A slide hammer works well

https://www.miataturbo.net/attachmen...ine=1334940043

Mount the flywheel upside down, on the flywheel grinder

https://www.miataturbo.net/attachmen...ine=1334940043

Start buy cutting the excess cast iron down to the ring gear..
https://www.miataturbo.net/attachmen...ine=1334940043

Once that was flush, I weighed the flywheel again, that reduced the weight by .75 lbs (12 oz) now 19.75 lbs

Time to thin the fat from behind the ring gear…

https://www.miataturbo.net/attachmen...ine=1334940043

each pass, this machine cuts only .005-.008 off…

https://www.miataturbo.net/attachmen...ine=1334940043


the final weight is now 17.75 Lbs

I removed a total of 2.75lbs…. This should help the engine rev a bit faster, with out giving up too much torque..

Also to get some more off. On the clutch side of the flywheel inwards towards the bolts you can see where the surface is ruffly 1/4 inch farther in than the clutch disc ride, slice that off. You can also bevel the outer lip of the flywheel.

I used to do this on a brake lathe for a few local round track guys.

Boring. I had our russian lathe dude with 30+ years experience lop off the weight ring in the back. Took about 10 minutes total. I swear on our little 1.6 flywheels it's worth something like 4 lbs, but it's been a few years and that might be off by a bit.

Miata 1.8L flywheel has a stupid ridge that's very obviously there just to add inertia. It's about 1.5# IIRC and when I had it removed it made it noticeably pleasantly revvier.

How much weight loss is possible without compromising the integrity of the flywheel, or interfering with clutch operation?

I wouldn't go much farther than OP, myself, and Jason suggested. No point in the risk.

What would be the assumed failure point? Insufficient clutch clamping due to thinning the flywheel? Or are you worrying about actually breaking it?

Get the flywheel too thin, it can crack and shatter.

Also it will not be able to absorb the heat, when that happens the disc will slip, like brake fade on over heated brakes.

hmmm guy at the clutch shop said he could re surface but not remove metal like that.

I'm thinking machinist

Guy at clutch shop is CYA, or CHA i guess.

Get CroMo.

I had a machinist lighten my stock 1.8 flywheel by 4 lbs and resurface/set the clutch up at the same time. Cost me $75. Find one that works on automotive bits and you should be good.