Opinions on a lightweight flywheel in a Miata?

Hi everyone. I have been posting quite a lot of questions lately I noticed...just trying to get everything sorted before this clutch and turbo install. I have a FM level 1 clutch sitting in my living room waiting to be installed. I didn't buy the happy meal kit since I didn't want a 10.3lb flywheel at first. After I got thinking, I found the ACT Street Lite flywheel. Now, I'm thinking of either getting my stock flywheel resurfaced and running that, or buying the ACT street lite. The car will be turbo soon, and it is a street driven car (not daily driver though). So what do you guys say? From my search, it seems that there is a lot of debate on whether it is worth it on a Miata or not.

Get the 10.3 lb flywheel, it's awesome.

If you spend all day stuck in stop-and-go traffic or you have a supercharger, keep your stock flywheel.

If you don't, get the lightweight. 

Thanks! I've read on another forum that the lightweight flywheel may be annoying in a turbo car. How much truth is there behind this? If the positives outweigh the negatives, I may just go with one. Just wondering before I drop $300+ on a flywheel.

There's nothing about a turbo that would make a flywheel annoying.

Now, if you have a poorly tuned ECU in the car that has idle droop problems because you can't get the AC compensation working well or because you've vented your BOV to atmosphere with a MAF in the system, that's a different matter.  The flywheel isn't the problem there :)

In reply to Keith Tanner :

What is it about a supercharger that doesn't work with the light flywheel?

I have the FM lightweight flywheel in a turbo car and see no downsides. There are other things about it (like the stripped interior) that make me not drive it often but the flywheel isn't a concern.

I have the FM 10lb flywheel in a supercharged car. Granted, mine is Rotrex supercharged, so standard thinking convention does not apply there

Thanks guys! I think I'll splurge for the ACT Street Lite flywheel then. I appreciate all the input!

I'd go with a lighter one than that. No point spending money for a 13lb flywheel when you could have a 10lb. 

Jesse Ransom said:

In reply to Keith Tanner :

What is it about a supercharger that doesn't work with the light flywheel?

Of course, someone would come and be pedantic already. POSITIVE DISPLACEMENT superchargers. Usually I specify centrifugals because they're so different, but yes. Positive displacement. From this standpoint, a centrifugal is more like a turbo.

Positive displacement supercharger add some drag to the engine at idle, which makes them more prone to droop. They also tend to have greater throttled volume, which also makes them more prone to droop. So a car with a positive displacement supercharger needs that heavier flywheel to compensate.

In reply to Keith Tanner :

Ah! Makes sense. Thanks!

EvanB (Forum Supporter) said:

I'd go with a lighter one than that. No point spending money for a 13lb flywheel when you could have a 10lb. 

My worry is drivetrain noise with something lighter than that. I'd rather not have the drivetrain noise to be honest.

I didn't like the lightweight flywheel in the mumpkin for the drag race portion of the challenge. It is a particularly odd scenario that probably isn't relevant for your decision making.

Japspec said:

EvanB (Forum Supporter) said:

I'd go with a lighter one than that. No point spending money for a 13lb flywheel when you could have a 10lb. 

My worry is drivetrain noise with something lighter than that. I'd rather not have the drivetrain noise to be honest.

If a 10.3 lb is going to make drivetrain noise (ie, the "ringing" on closed throttle decel), a 13 lb will too.

I loved my 9 lb flywheel I had in my 97. There was absolutely no downside in my opinion and the car was so much more fun to drive on a daily basis. 

I have a FM 10lb in the rotrex Exocet and an 8lb in the na6 Miata. I don't mind the 8lb even in heavy stop and go traffic. It seems to suit the Miata well. 

Thanks guys! I'm going to have to think about it again then. Maybe I won't be able to hear the drivetrain noise over the 3" exhaust, who knows. I just know it would end up driving me insane. This is my first time doing any kind of mod like this, so I don't know what it may sound like, but if its anything like the heat shield rattle I had back when I first got my car, I won't be able to stand it!

I have never noticed any kind of noise associated with my lightweight flywheel. 

Turbo 1.6 Miata guy here.  When I replaced the clutch and flywheel a couple months ago I ordered the ACT street lite on the advice of a buddy of mine (fellow racer and mechanic).  The street lite clutch turned out to be unavailable so I had to change my order an get the pro-lite.  

Drivability is fine, it is a touch sensitive to throttle position on launch but that's to be expected in a turbo miata, it drives differently than something setup from the factory to be lazy.  

The happy meal kit is the gold standard for a reason.   I love mine on the street car.

I have the ACT lightweight on my track car since a friend had one new-in-box at the time..  It's closer to stock, and not quite as much fun as the FM one.

I don't think I've noticed any noise with either that I can attribute to the flywheel?

EvanB (Forum Supporter) said:

I have never noticed any kind of noise associated with my lightweight flywheel. 

It's a thing, and it varies from transmission to transmission. Kind of a ringing noise. Doesn't seem to cause any lasting problems that I've seen. It happens on closed throttle decel at around 3000-2000 rpm if memory serves. One of my cars makes the noise very loudly, others don't make any at all.

I can't speak to the Miata, but my friend convinced me to put a lightweight steel flywheel in my RX-7 years ago.  I hated it!!  Sure it revved quicker, but daily driving it became a chore what with the 12A having negative 37 lbft of torque. I couldn't get rid of it quick enough.

Keith Tanner said:

If you spend all day stuck in stop-and-go traffic or you have a supercharger, keep your stock flywheel.

If you don't, get the lightweight. 

My car has a supercharger and a lightweight flywheel.

It's not hard or annoying to drive but it takes practice, and revs definitely fall right off during shifts.  Heel / toe work is of limited usefulness - rev matching was much better in my E46.

[edit]

No ringing in mine.

Revs falling off during shifts is kinda the point :) The real problem manifests itself with idle control. If you've got your car idling at 1100 rpm, it's less of a problem. If you're trying to maintain 850 and you have a positive displacement supercharger, it's very difficult to keep the idle droop at bay especially with the AC on.