Hey Guys,

I've been thinking about putting my flywheel on a diet to improve throttle response in the old hunk of iron. It is currently 24 lbs and I'd like to get it down to at least 20 lbs. Short of going to an aluminum unit or someone makng a billet steel unit (does anyone make a steel flywheel for a B21 (my internals are B21)).

Thoughts?

There are people who feel that lightening a stock flywheel is dangerous, but for the life of me I can't see why. Lightening a stock DISHED flywheel might be because you're potentially weakening the heavy ring that holds the pressure plate and flywheel together, but lightening a flat one seems like child's play, and can only help.

It's the plan on the 780, anyway.

I don't think taking 4 lbs off a flywheel will make much of a difference. You probably would need to take off around twice that to make a difference that would be worth the time/expense to lighten your flywheel. Some of the more "expert" members may not share this opinion, however. I'm sure some of them will be more than happy to weigh in on this and offer their opinion.

They do make a Cromoly flywheel for an 8 bolt B20 crank. I don't know if that would work for you or not. They weigh about 14 lbs I think. I have one sitting in my garage. I got it on eBay a couple years ago.

Are you wanting to part with the flywheel? I'm thinking 20 tops and 16 would be even better. The plan (after spending some time with it this afternoon) is to take off some on the front side, outside edge and remove more mass off the backside near the edge as well.

Where you shave it is as important as how much. If you shave a few lbs off of outside where the pressure plate bolts up, it really makes a large difference in rotational inertia.

Some people carve it out of the back side and you can carve a fair bit without it being dangerous, but the rotational inertia loss isn't as pronounced as when the weight is shaved all off of the outside edge.

There are about 20 cars here in town with as much as 10lbs carved off the stock flywheel on the outer edge mostly and a touch on the back with no problems whatever. A friend's car had an 11lb flywheel that was hammered upon in a 275 wheel torque 242T flathood...no issues with it that I could see when I looked at the flywheel 60K miles later.

With the stock 240T clutch, 15lbs is something you can daily drive (5lbs off the outer edge) without much fuss, and it makes the car very nice to drive if the gearbox shifts nice. 6-bolt or 8-bolt?

Outside was the thought, there is also some weight to be saved on the inside. I'm going to get my machinist (if I can talk him into it) to re radius the inside cone, then cut a little off the back (basically skim it) then hog out the ouside edge on the backside. On the front, the plan is to cut it down to the clutch mount. I'd be happy with that.

It's an 8-bolt crank.

My machinist will have it done by Friday - no questions, he figured 15 pounds is realistic. I love Lethbridge machining - the guys down here are very good with all my strange projects. I think the like the variety.

How much was the machining? Think I'll have this done when I do my T5 swap...

- R

I'll let you know on Friday - it's a straight time sort of job.

The total was $80 - I haven't put it on a scale just yet (it's at the machine shop awaiiting balancing). I'm guessing it's about 15 lbs.