TR4/4A Lightening a TR4a flywheel - a couple of questions

[tdskip]

OK - once more with feeling. I found an experienced local speed shop that lightens flywheels on a regular basis. They aren't going to touch mine until I bring them the reference picture below. What is a <span style="text-decoration: underline"><span style="font-weight: bold">safe</span></span> target weight for removal that will make her a bit more snappy in acceleration and gear changes but not compromise her practicality on street use. Is there a weight range that is a good balance?


BTW - here is the image out of David Vizard's reference material

 

[TR3driver]

I believe Joe A. recommends 14# for the street.

My alloy Fidanza is quite a bit lighter than that (under 10 I think), and the car is still very streetable. Takes just a little extra care to keep the rpm up when launching; usually the time it gets me is when I'm just puddling around and not in a hurry. You can't just take your foot off the clutch as with the original flywheel.

 

[TR4nut]

Actually I thought Joe was closer to 17-18#, at least for the TR4.. I bought one from him a couple of years ago. 14# sounds too light offhand but my memory may be flawed.

Edit: thinking about it, we may be talking about the same weight depending on whether the ring gear is taken into account or not. Bottomline, I think the max removed safely on the flywheel is roughly 10 lbs.

 

[tdskip]

So if I have them follow the above diagram and tell them no more than 8 pounds do you think (no guarantees I know) that gives me safe harbor?

Thanks guys - lots to learn here.

 

[TR4nut]

Just my opinion Tom, but yes I think you'd be okay. The FOT archive talks about a 28 lb flywheel going to 24 very easily, and 18 lbs with a little more work.

 

[TR3driver]

I looked back through my notes; Joe was talking about a new, lightweight steel flywheel at 14# for street & autocross, 9-10# for racing. This is the bare wheel, not including ring gear (he also had some lightweight ring gears made) or clutch.

<span style="font-style: italic">I feel there is a market for a STREET VERSION of a TR4A flywheel. I propose the weight to be about 14#s.

Unless you are a 'racer', 9-10#s is a bit light for the street. For street and autocrossing 13-14#s may be better. </span>

A real work of art:

 

[tdskip]

Thanks Randall - that is a thing of beauty.

There is appear to be some concern over the safety of lightening a 30+ year old flywheel. Not knowing any better are there any risks here that folks considering this need to be aware of?

 

[TR3driver]

Well, of course the major risk is that the remaining metal will not be strong enough to withstand the forces involved. The centripetal force trying to tear the flywheel apart goes up with the square of rpm. Explosions, while rare, do happen, but mostly at rpm well over the factory redline.

But you should be OK at 8# removed, as long as you don't go too wild on rpm.