Lightweight flywheels For NA: Pros and Cons

[diabolical1]

Originally Posted by infernosg

... I guess this is something unique to the rotary?

not really. from what i understand, Porsche 911s (at least the 964s and 993s) do the same thing when you use a light flywheel. however, i also understand that some people solve the problem by tuning or fooling the computer into thinking the A/C is on all the time. i guess that roughly equates to raising the idle, like you said.

[jtbshaw]

You guys must be coming from more of a mechanical engineering side talking about your inertia/"moment". I've always taken a more mathmatical/physics approach is why I mentioned torque. We are talking the same thing here.

All the lightweight FWs that I have used have always made improvements. Drivablility did change a bit, but nothing difficult at all. You do gain acceleration by going lighter. As B/TTT mentioned, I would do it again if I had anything with a stock FW.

[infernosg]

^^^ Aerospace Engineering, but isn't engineering just the application of mathematics/physics?

Moment = torque. Inertia is something entirely different, but I'm sure you know that. The only reason you have to give it more gas to get the car going is because it takes a certain amount of energy to get a 2900 lb car moving. Mass and rotational speed are independent, directly proportional variables of that energy so if you decrease one, you have to increase the other.

[jtbshaw]

Again, we are talking the same thing. Didn't mean to turn this into a physics/engineering discussion Phoenix.

[TitaniumTT]

Originally Posted by infernosg

What happens to the idle? I never noticed anything on my other car so I guess this is something unique to the rotary? Are we talking "car will randomly stall" idle effect or something like "idle is more erratic"? I suppose nothing bumping up the idle 100 RPM or so wouldn't fix?

Stock FW is what, 27 lbs? The stock ECU, I should mention that this only really relates to a stock edu'ed car, thinks you still have a 27lb flywheel and is thus tuned to rotate that mass. By removing mass you free up a little torque, so now it's taking less power to move that 9.5lb flywheel and the idle hunts around a bit, becomes irradic etc etc.

With a standalone, it's possible to get a perfectly smooth idle, it just takes time. Idle is the most difficult thing to tune. It's such a delicate balance between fuel, timing and BAC duty.

Originally Posted by jtbshaw

I love that pic

Originally Posted by jtbshaw

Again, we are talking the same thing. Didn't mean to turn this into a physics/engineering discussion Phoenix.

Well, don't ever tell an engineer that a lightweight FW adds torque because they'll jump down your throat and say you didn't add anything, you free'd it up. THen you can say, alright motherfucker, here's a stock FW dyno, heres the same car after a lighweight FW. It added torque and hp to the dyno sheets didn't it? Then they say, you dumbass, you free'd it up...... and it goes back and forth all depending on how you interprete it.

[Rotary#10]

Originally Posted by TitaniumTT

Stock FW is what, 27 lbs? The stock ECU, I should mention that this only really relates to a stock edu'ed car, thinks you still have a 27lb flywheel and is thus tuned to rotate that mass. By removing mass you free up a little torque, so now it's taking less power to move that 9.5lb flywheel and the idle hunts around a bit, becomes irradic etc etc.

With a standalone, it's possible to get a perfectly smooth idle, it just takes time. Idle is the most difficult thing to tune. It's such a delicate balance between fuel, timing and BAC duty.



I love that pic



Well, don't ever tell an engineer that a lightweight FW adds torque because they'll jump down your throat and say you didn't add anything, you free'd it up. THen you can say, alright motherfucker, here's a stock FW dyno, heres the same car after a lighweight FW. It added torque and hp to the dyno sheets didn't it? Then they say, you dumbass, you free'd it up...... and it goes back and forth all depending on how you interprete it.

Driving daily my gtus now with a RB 12lb FW and a ACT Street/ Strip clutch. Plus I do have vert wheels. Its fun to drive now, even more so with the flywheel on. I haven't really noticed my idle being erattic.
But thats what I've tell folks it just makes it easier to move what power you already have. For example you jog a block or two with two 40lbs bags of sand on your shoulders. Take the bags off the next block and jog. How do you feel? Lighter of course. Less effort for your engine to spin.
IDK about the gains in actual HP at the FW and at RWHP. That doesn't really concern me right now. I've read a few articles in theory it does. But Dnyo sheets are the evidence and facts of the matter if HP made it to the rear wheels.

[Kentetsu]

It was my understanding that the idle can become a bit rough because you don't have quite so much rotational mass to smooth it out. The idle, after all, is just a bunch of small controlled explosions, so it will have a natural lumpiness to it.

Picture trying to keep a merry-go-round spinning when empty. It might visibly slow between each shove you gave it, but it would be easier to move.

Now picture it loaded up with a bunch of fat harley dudes. It won't slow down much between pushes, but it would take a lot more to get it going.

[Rotary#10]

Originally Posted by Kentetsu

It was my understanding that the idle can become a bit rough because you don't have quite so much rotational mass to smooth it out. The idle, after all, is just a bunch of small controlled explosions, so it will have a natural lumpiness to it.

Picture trying to keep a merry-go-round spinning when empty. It might visibly slow between each shove you gave it, but it would be easier to move.

Now picture it loaded up with a bunch of fat harley dudes. It won't slow down much between pushes, but it would take a lot more to get it going.

LOL!

[NoDOHC]

Originally Posted by kentetsu

It was my understanding that the idle can become a bit rough because you don't have quite so much rotational mass to smooth it out. The idle, after all, is just a bunch of small controlled explosions, so it will have a natural lumpiness to it.

Picture trying to keep a merry-go-round spinning when empty. It might visibly slow between each shove you gave it, but it would be easier to move.

Now picture it loaded up with a bunch of fat harley dudes. It won't slow down much between pushes, but it would take a lot more to get it going.

This is actually an excellent description.

Now imagine how much easier it is to accelerate the merry-go-round without the Harley dudes on it and you have the lightweight flywheel benefit.

[Phoenix7]

I just picked up a FEED 12lb. flywheel....now looking for an Auto-transmission counter-weight (http://www.rotaryresurrection.com/2n...vs_aftfly.html I Miss Landers

Thanks for the good feedback on this...

2 questions:

1. How the HELL do you torque the flywheel to 500 lb/ft of torque? I can remove a flywheel by myself but I don't know if I can torque it ON...

2. I noticed Landers said there are 205mm and 225mm flywheels...are you SURE I can use a TII flywheel (225mm) on the NA (stock 205mm) ??

[Sharingan 19]

no you cannot, and you should sell me your flywheel

[Phoenix7]

I have a turbo FC also so it will end up being used either way...

but I just need to confirm that it'll work on the NA.

[infernosg]

There are different sized flywheels for the different clutch diameters. The 225 mm flywheel goes with the newer N/A transmissions and clutches, and I'm pretty sure they will not work with a turbo transmission, which uses a larger flywheel as mentioned below, and vice versa. Mazdatrix has a pretty good transmission narrative.

[Phoenix7]

I'm looking at mazdatrix right now...

Originally Posted by mazdatrix

NOTE: Excluding the TURBO, all the different flywheels and clutches, from 74 through 92, are basically divided by 215mm clutch (74-82), and 225mm (83-92), then by rear counterweight needed for the engine. We mix and match these all the time. This means if you want to put the larger diameter clutch assembly on a pre-83 application, just let us know - it is no problem. You just need to remember what diameter you have when you next purchase clutch parts.

[TitaniumTT]

Negative -

- Like I said before, you match the counterweight to the engine.... or the series rotors you have.

The flywheel MUST be matched to the TRANNY. If you have an N/A tranny, you need an N/A flywheel, if you have a TII, FD, RX8 tranny, you need the TII flywheel. The diameters are different and the starters will not engage.

This is why it's so easy to swap and mix and match trannies between cars.