how much do lightweight flywheels REALLY help your acceleration?
 

how much do lightweight flywheels really help your acceleration?does anyone really know the answer to this question?

i always read about lightened flywheels "greatly helping your acceleration, but killing your launches"

now i understand how a lighter flywheel will make both of these things happen, and i dont really have any question of the decrease in launches, but how much does it ACTUALLY improve your acceleration?

lets say i went from my stock S5 flywheel on my 91 GXL to a racing beat 9.5 lb flywheel. how much faster is my car?

less weight to speed up.

yeah...

I've heard its quite a bit but have no personal experience. I also read that you just have to get used to launching with one.

I think all the power gain is high up on the rpm range. So once you get it launched, you could recoup any loss through the trips up the gears. Autocrossers love light flywheels according to a thread I started in Race Car Tech. "Makes much better use of the available powerband" one racer posted.

interesting... any more input? (i was thinking about getting a lighter flywheel when i get a new clutch)

Flywheels depend on the type of driving you do. If your drag racing, you want some weight on the flywheel. Autocrossers can get away with less weight.

Jarrett

I had mine changed not so long ago, it's not as good as a couple of extra psi but you'll notice a smoother ride, and more rev's for your squirt :)

Leave it on your "to do" list

A light flywheel will make a very noticable improvement to the way the car drives. It won't necessarily make a huge improvement to 0-60 or 1/4-mile times, but the engine will be much more responsive to changes in rpm, you'll be able to shift quicker (because the revs drop quicker) and overall the car will feel much nicer to pedal fast. This is more important to me than just numbers.

it's not really a power gain, is it...? i thought it was just quicker access to ur power band....

True, good observation. It's kind of a "reduction of rotational mass" type of effect.

i've heard that you actually gain a few whp because you're dropping some of that parasitic rotational drivetrain mass.. so wouldnt that give you back some of your lost wheel horsepower?

does that make sense?

i had one on my n/a and now on my T2 i love them and dont think I would wanna drive without one again.. youll seewhat im talking about when you get one.. It did not hurt my launches.. improved power down low a lot seemed to pick up way more especially around 3-5K.. Started to loose its feel in 4th gear.. I would say get one there great!

if its a daily driver should i do with 9.5lbs or 12lbs?

thanks

Something from the BMW M site:
The stock flywheel mutes abrupt changes in engine rpm. The heavy flywheel adds mass and, therefore, resistance during acceleration. It is like a heavy gyroscope in that it takes lots of energy to get it up to speed and it takes a long time to slow down. This resistance reduces responsiveness. Adding a lightweight flywheel will improve acceleration through the first few gears improving start times. A lightweight flywheel will not add horsepower. The engine rpms are still the same you just get there faster and deliver the energy more directly to the clutch and drive train. Be aware that this will put more strain on the clutch and differential. Any flywheel less than 12lbs is likely to cause idling problems and possibly stall the car. You may have include the purchase of a chip that will increase the idle rpms or have your existing performance chip upgraded by the vendor to accommodate this change.

Flywheel rules if you car is ready to take one, it will definitely put more strain on your drive train but with a good drive train it is definitely worth it, my car hits the red line like no tomorrow and keeps doing it and now the car launches perfectly off the line, it dosnt bogg, and it is the 9.5lbs flywheel, you will get more rwhp cause your loosing less through the flywheel.

I have a (12lb. I think) light steel flywheel on my car, works pretty good for everyday driving, it makes launching on a hill kinda interesting though, especially if there is someone right behind me. I put it on when I got my reman. so I don't know how much it helped acceleration.

ok, the BMW dude is wroooong...I have the RB aluminum (11 lbs I believe with countrweight on and all, all the 9 lb ones out there dont take the counterweight into account ). Aside from the exhaust (full motor back NA system, no cats) the flywheel makes the biggest difference bar none. it took a day or so of driving to get used to the way the clutch grabs again but the motor takes on a different demeanor with the flywheel...it is MUCH more willing to rev and much quicker topping out 1st, 2nd and 3rd...4th is too big to notice the difference and our 5th gears are huge :) basically a light flywheel is equivalent to removing weight from the car proporational to the gear you're in...as ou drive in higher gears the weight reduction is much less dramatic which is why you feel this mod in 1st and 2nd gear most...if you have an Na go buy one :)

They are well worth it. I don't have one, but I will be getting one soon. My friend had one on his car and the difference was great. When I usually end up racing someone on the street or highway, I end up starting from maybe 30-50 so I am usually in second gear. The car will pick up a lot faster from 1-3 like everyone said, but it is a little weird launching. If you are doing mostly drag racing, get the 12 or even a little heavier. If you do just street driving, occasional autocross, drifting, and rolling starts, you might as well get the 9.5. It is definately one of the items I am getting soon.

ok..what are we talking about in cost for those of us that have no experience with them? I have a completely stock 86 GXL and it has 90k on it and is in great shape, so now the mods start!! And I also need to get a clutch done, so now would be a good time

well yeah adding a flywheel will not increase your hp but what it does is allow you engine to rev faster because less rotating mass and in some occations it will release untaped power that engine already has

How would a 9.5lb flywheel feal on an 87 T2? Would it stall while idling, etc? Anyone else have this? I may need a new clutch soon so I may get a lightened flywheel then.

If you are going to spend the money, go with the Aluminum Flywheel. It's worlds different from the stock one... I personally had the Aluminum Flywheel and found It to make a phenominal difference to the way I drive my FC. It was awesome to sit at Idle and touch the Throttle to see thr rpms rev up to 4 grand like It was nothing but the thing I disliked the most was the launches with It. Oh well, a give and take I guess. Don't let anyone tell you they are not streetable and for the money you are paying for It, you are better off going with an Aluminum on over a steel one. D Again, they are plenty streetable!

Well, I'm not quite a RX-7 guy. I'm currently in the works of swapping a 13B-Turbo into my S13 240sx. But I do know a good bit of RX-7 people and work on their cars all the time. The other day my friend let me drive his Turbo-II Convertible (swap) It had a Cosmo engine and the only mods were a 12lb flywheel and short shifter. Well compared to my other friend T-II it was a beast. Both had Cosmo motors, but the one with the 12lb flywheel revved like no tommorw. Not only did it redline 1st gear so fast you'd have to launch in first. But I was driving it on the highway doing about 50, and floored it and was up to 90 in id say less then 10 seconds. With the 12lb there was no probs sitting at idle at a stop light. Only other thing i can think of that was remarkable that night is when I dropped from 5th-->4th floored it, then shifted back up the 5th, floored it again, I nailed the highest boost level that car has seen. Being .98 bar, or about 14.5lbs.
Ryan

It's not really a shear Horse Power gain, but rather a RPM gain. Since the lighter flywheel spins more easily (because it's lighter) the RPMs can drop faster. This is where the "faster" comes on. The faster the RPMs drop, the faster you can shift.