Opinions on a lightweight flywheel in a Miata?

Keith Tanner said:

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.

I didn't mean to be pedantic. I did acknowledge that the Rotrex bucks the normal convention of most superchargers 

Keith Tanner said:

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.

Agreed on both counts.  And yes, it idles at 950-1000, and droops a little sometimes.  AC is long gone.

In reply to Mazdax605 :

I wonder if that has to do with the nature of the rotary? I've had two 8lbs flywheels on 2 separate 1.6 miatas that were driven with some frequency in awful traffic (in the bay area and through nashville rushhour with frequency). The first one the ONLY time you'd notice it is reversing: it was really touchy - but I have a theory that it wasn't broken in well? My current car with an 8lb flywheel feels identical to the stock unit that came off of it, but I changed to a stainless straight line and did the slave cylinder at the same time - so not exactly apples to apples. 

OP If you do the clutch/flywheel you might consider doing those two things at the same time, if nothing else the stainless straight clutch lines clean up the clutter! 

In reply to NickD :

Your comment didn't sound pedantic to me. You literally said "Granted, mine is Rotrex supercharged, so standard thinking convention does not apply there"

PS: I really love my rotrex! Same setup on it, FM 10lb happymeal. 

It's my mistake for thinking "I should specify positive displacement...nah, it'll be okay, I don't need to split that hair right now". Immediately, hair gets split.

It's just impossible to win. Every time we post any sort of tech information on our site or in a video it's like a race to find the edge case or the exception or the weird-ass problem.

In reply to Keith Tanner :

I think everyone knew what you meant. I have a dream! To own a turbo miata, a rotrex miata, and an N/A miata simultaneously! Though I guess rotrex exocet isn't quite a miata. I plan on trying my hand at turbo on my "spare" NB with all the extra random parts I have laying around. 

I also mentioned Rotrexes just because I was curious if they fell under that statement to see if I had screwed up (again.) I have a habit of doing something to my car and feeling good and then after the fact reading Keith tell someone "Don't do that." Case in point: I found someone selling a polyurethane suspension bushing kit for a Miata, got it for a song, got it all installed and then within a month read in a thread where Keith said "Don't put poly bushing in a Miata." Whoops.

In reply to NickD :

If you counted up the "don't do that" 's from the internet on my cars you'd think they'd all explode before I left my driveway much less get to the track and harrass expensive cars.

accordionfolder said:

If you counted up the "don't do that" 's from the internet on my cars you'd think they'd all explode before I left my driveway much less get to the track and harrass expensive cars.

That's true. But, when Keith says you shouldn't do something, there is always sound logic behind it. I just don't always do it. Like 4 years later I still have the poly bushings in the car.

Just add bronze bearings and all your poly bushing problems will be solved.

I'm about to put a 9 pound flywheel in my Miata as well, since I have a rear main leak and I'm not about to put a used clutch/flywheel back in if I pull the transmission. Things have a way of...snowballing. Hopefully I don't hate it.

I once did a 1.8 swap and a complete rewire because I had a leaky front main seal on the 1.6, so you definitely don't want to listen to me all the time.

Bronze bushings on poly bushings. Interesting.

cmcgregor (Forum Supporter) said:

Just add bronze bearings and all your poly bushing problems will be solved.

Mine came with bronze sleeves inside the bushings. Are those the jam? (Whoof, we are really getting off-topic here) I was supposed to be getting some slick Delrin rear upper control arm bushings with a rod-joint insert that reduced camber gain from lowering and eliminated toe changes through travel but the dude kept dodging me.

NickD said:

accordionfolder said:

If you counted up the "don't do that" 's from the internet on my cars you'd think they'd all explode before I left my driveway much less get to the track and harrass expensive cars.

That's true. But, when Keith says you shouldn't do something, there is always sound logic behind it. I just don't always do it. Like 4 years later I still have the poly bushings in the car.

No argument there, I try to do what the experts say and Keith in particular has given this ungrateful mongrel more advice than I deserve. I'm just saying sometimes I've done, done it, before I've found the experts or I've done it "good enough" for me (and my budget). There's a lot of gray between here and there.

Back on topic, get a light flywheel! Miata's love them. Treat yourself! Replace that annoying to bleed clutch line while you're there! Or don't! The world is your oyster and you're polishing a 30 year old turd at this point. 

Thanks guys! I guess I will give the ACT flywheel a try. I already have a stainless line installed from 2 years ago, so I'm good to go there! The slave is also about 2 years old. @Keith, is the "ringing" noise pretty annoying, or is it easy to live with? I'm hoping that I don't get it too bad so that I can live with it.

NickD said:

cmcgregor (Forum Supporter) said:

Just add bronze bearings and all your poly bushing problems will be solved.

Mine came with bronze sleeves inside the bushings. Are those the jam? (Whoof, we are really getting off-topic here) I was supposed to be getting some slick Delrin rear upper control arm bushings with a rod-joint insert that reduced camber gain from lowering and eliminated toe changes through travel but the dude kept dodging me.

Not to continue derailing this further, but.....

Not the ones that came with the kit. TheCarPassionChannel did a video on them, check it out here https://www.thecarpassionchannel.com/poly-bushings

Keith Tanner said:

It's my mistake for thinking "I should specify positive displacement...nah, it'll be okay, I don't need to split that hair right now". Immediately, hair gets split.

It's just impossible to win. Every time we post any sort of tech information on our site or in a video it's like a race to find the edge case or the exception or the weird-ass problem.

I had a college roommate like that once. After a while I wanted to beat him over the head with his own bong. Only the smell of spilled bong water prevented me. 
 

Don't lightweight flywheels increase wear on the synchros since you have to shift faster to match the revs?

I have one on my 1990 300ZX NA and it's kind of annoying for street duty IMO.