Ok, im trying to pick a flywheel and im having a hard time. some people have said get the lightest FW i can (and that it will make no difference in drivability), others have said the exact opposite. i have only experienced the stock FW so i wanted to ask around first. anyway, im basically trying to decide between the racing beat light steel, and the aluminum.

the rx7store.net site has some conflicting information regarding the weight of the lightweight steel one. on the flywheel selection page it is listed as 12lbs.... but in the description (and on racing beats site) it is listed as a 17lb wheel. just wanted to clear that up....

anyway, do people using the aluminum wheel have any drivability problems? is lighter just flat out better when it comes to FW's? thanks, heath

(PS this is for a 20b.... but the car will be a street car)

 

Rb makes a steel 17lb flywheel and a aluminum 11-12lb flywheel.

I wouldn't go 11-12lb aluminum with a 20b but I'm sure some people have. The heavier flywheel will make a smoother idle.

 

So Jeff, are you saying a heavier FW is better for higher HP applications, and that you wouldnt see as many gains as a stock motor? am i missing the point? basically my logic was that since i have an extra rotor spinning (and therefore more rotating mass) that i should try to cut down on weight (moreso than with a 13b).

maybe i should be asking my questions differently... what are the pros and cons of heavier VS lighter flywheels? but im even more interested in how increasing or decreasing the internal rotating mass of an engine would skew the previous answers.

 

No what he is saying is a heavier flywheel will give you a smoother idle while a light weight flywheel will be a bit more of a rough idle. Light weight will really make engine breaking harder almost to where it does nothing because it gets rid of that rotating mass that usually helped in slowing down the car. Light weight your gonna have faster revs and you'll free up some HP while your at it. This wont give you HP just free it up but you probably already knew that. Hope what I put helps you out some what.

 

Well I think you'll have better throttle response due to the higher cubes of the 20b. I don't think you'll have any problems with 1st or 2nd gear acceleration.

Cons for light fw would be rougher idle, more clutch slippage for launching and maybe heat buildup in the small steel insert of the aluminum flywheel.

Clutch slippage for launching might not be as much of an issue with a 20b, rougher idle vs a 13b, I dunno, I doubt it. Heat buildup may be an issue.

Flywheels are used to keep the engine turning at a more constant rpm, they damp out the power pulses. I think a 1 cyl 4 stroke engine would need the biggest flywheel.

Flywheels are also used to help get a vehicle moving from a start by storing some energy. I heard a "rule of thumb", usually you have 1lb of flywheel for ever 100lbs of vehicle. Of course this all depends on application, engine type, etc. The FD has 21lb flywheel for a 2800lb car. The TII (S4) has a 28lb for a 2800lb car.

All that said, the cons might contradict what I said in the first post. I'd call Mazdatrix, Pettit, etc, they have a 20b car and see what they have to say. Without their opinion I'd probably go with the 17lb steel unit.

 

With a lightweight flywheel you slow down faster than with a heavier flywheel...it has less rotating mass so the inertia is less which causes it to slow faster than a stock, or heavier flywheel which has a large rotating mass and the inertia is alot more which makes it continue to spin.

 

so if it slows down faster, would this not INCREASE engine braking?

 

It slows down faster, therefor it does increase engine braking.

 

revs go up and down WAY faster. some people who are slow shifters will be quite a bit more jerky when tooling around town

 

Yeah my fault, I thought about it afterwards and I got confused and said the opposite. Sorry everyone I'm wrong here.

 

Its ok, we still love you. lol

 

I love my RB 12 lb flywheel. 1st gear acceleration would be sick if I could get traction. 2nd gear is damn fast as well. I dont notice any drivability issues at all, and neither does my friend with his 9lb flywheel. it might make it a bit harder to launch as said above, but once you figure it out, the acceleration gains in the lower gears makes up for it

 

While technically I agree that the light flywheel will result in slightly more engine braking (in the "just let off the gas" sense), that effect is very minor and probably isn't very important or noticable.

The light flywheel will significantly reduce the amount of "engine braking" you get if you downshift and then let the clutch out with your foot off the gas. You normally get a bunch of "engine braking" there as the heavy flywheel is accelerated up to some higher RPM. But it takes a bunch less energy to accelerate a light flywheel, so the car does not slow down nearly as much as it does with a heavy flywheel. This is a good thing for the track, since you are less likely to upset the balance of the car if you fail to rev-match appropriately (too high or too low) while approaching a turn. Here are two graphic scenarios of bad rev matching to illustrate my point:

HEAVY FLYWHEEL: downshift as you approach corner, fail to match revs, let clutch out, rear tires lock, OH ****!, spin out

LIGHT FLYWHEEL: downshift as you approach corner, fail to match revs, let clutch out, rear tires chirp, oh crap!, recover

I found the RB aluminum flywheel to be very streetable. It makes the car a bit jerky while cruising in parking lots, and idle smoothness suffers a bit, but I did not find it difficult to launch the car or otherwise drive it in a normal manner. I really like the way the light flywheel "wakes the car up" versus the heavier stock flywheel.

-Max

 

The light flywheel in my car helped acceleration, and made shifting easier and smoother. The idle was not quite as smooth. Overall, I have been very happy with it.

BTW, I got the SR motorsports 12 lb unit (counterweight weight included)

 

Rx7store lists the flywheels without the counterweight. Racingbeats site is with the counterweight.

Jason

 

Get the 9.5 lb (w/o counterweight added in) if you want to double clutch and do clutchless upshift.

 

beautifully said.... exactly what i wanted to know. thank you max