So I've just acquired a slightly used Rx8. I'm not sure of the forums protocol or organization, so this is a cross post of a thread/question I put in the aftermarket parts forum, with one addendum ~ other mfg light weight alternatives.

The dealership tells me, IIRC the numbers correctly, they can supply & will install a MazdaSpeed "light weight" flywheel for @ $620 in parts and something like $750 or so labor. On a motor that seems happiest regularly reving from 3k to almost 9,000 this seems like it might be a good idea, but I'm wondering about some of the details.

A couple or questions. Can anyone point me to the stock flywheel/clutch assembly stock weights?

Is/are there any moment of inertia figures or data available for the stock parts?

How about for the MazdaSpeed flywheel? Weight &/or moment of inertia data?

Last, any end user reports on observed performance benefits? Gas mileage increase? Lower ET?

Thanks
Mike ~ Colorado

 

Mike,

I just swapped out my flywheel for the Racing Beat Flywheel. I think it's a great improvement to make. The car is definitely livelier. If you search the forum you will find a bunch of information on Mazdaspeed and other aftermarket flywheels. The stock flywheel is 17lbs (edited once my scale was recalibrated) and very rim heavy.

If you plan on doing the work yourself definitely make sure you have the right tools, a hydraulic lift, and a friend that has done this type of work before. We did it and it took about 8 hrs. A good mechanic could probably do it in 1/2 the time. Good luck and welcome to the cult!

 

sounds like a ripoff from that dealer.

it won't really make your car much faster, but the engine will change its speed while you're changing gears far quicker. this can be good or bad, depending on your preference.

 

Thanks Shaunv. I just found a serries of Mar'04 posts w/accompanying photos of the MazdaSpeed flywheel by "Cortc" He/she describes the MazdaSpeed parts (plural apparently as there is a separate counterweight that comes with the MazdaSpeed kit) as weighing in at @ 10.5 lbs for the flywheel and 3.5 lbs for the counterweight ~> so (I'm now assuming) something like @ 14 lbs plus misc bolts etc for the MazdaSpeed version vs. @ 21lbs for the stock assembly - but probably, based on the photos, better weight distribution (moment of inertia issues) that would make the 7lbs difference more significant than the raw weight numbers alone would suggest.

Any before vs. after G-Tech accelleration data on the effects of the swap?
The lighter rotating mass should also have a positive effect on gas mileage potential?

I've done this, a light flywheel change, on a couple of UrS4/6 Audi's and found the principal benefits are best noted in the lower gears (faster engine accelleration/spin up.)

 

Here's a thread in which I addressed moment of inertia and flywheels.

https://www.rx8club.com/showthread.p...light=flywheel

 

whether you go with the RB flywheel or not, all of the special tools that you need can be found on their website in the RX-8 flywheel section (flywheel nut wrench, various pullers, etc.)...these tools are applicable to the install no matter which flywheel you go with...

 

[QUOTE=mlx8]

Any before vs. after G-Tech accelleration data on the effects of the swap?
The lighter rotating mass should also have a positive effect on gas mileage potential?
QUOTE]

I haven't noticed any difference in gas mileage. Maybe I'm just driving it harder now since it's more fun? :D

For Gtech results I'm going to sound like every other bogus promise jimbob out there. My Gtech came in at the same time as my flywheel and I only had the weekend at my friend's place to install it so I didn't get a chance to do any base runs. Polak and I are going to get together and do some head to head stuff and I will also get a base run of his car for comparison. We have done this before I made the mod and our cars (and butts) were equal. In the mean time I can post my Gtech run but it's not really useful because I don't have a baseline to compare it to.

 

They sell on the net for about 520.00 and the install should only run about 250-350, and cortc is a he...

 

I'm willing to bet I could throw some calcs together and some CANScan data together and get a pretty good idea of how much power you could free up with one of these things...

so without the counterweights (they are all the same so they can be ignored...) it shouldn't be too hard comming up with at least a ballpark inertia estimate
- MS flywheel is around 11lbs with a vented rim (could estimate as a disk minus the holes)
- RB is around 10lbs with a solid design? (could estimate just as a disk)
- stock is what - 17.5lbs? (another disk estimate)

whats the flywheel radius... anyone know?


I'm thinking I could put the inertias together with rpm logs i have at WOT for 2nd and 3rd gears and do some energy equations and get a hp number...

 

There is a thread out there on a flywheel swap where someone measured the stock flywheel at 21lbs and the counterweight is machined into it. RB is 9.5lbs. Counterweight is 3.5lbs. RB quotes a reduction in inertia of 55% over the stock flywheel if that helps. I measured my stock flywheel and it's 12.5" from tooth tip to tooth tip.

 

here's what my feable mind came up with... (i choose to not include the counterweight since they all pretty much have a similar 3.5lb counter weight)

stock inertia - .073714 lbm ft^2
RB inertia - .040016 lbm ft^2 (hey, it actually came out to 55% of stock without cheating :p )
MS inertia - .042702 lbm ft^2 (don't hold me to that exact number... its close though)


I ran it through some rpms's I had logged of a WOT 2nd gear run, converted the I's into kinetic energy, then differentiated to get horsepower.


So when it all comes down to it you probably get about 4-5hp in 2nd gear, 2-3 hp in 3rd gear. The placebo effect it probably greater then the actual effect... but sometimes thats all that matters <shrug >

 

The stock flywheels mass in concentrated near the edge...

 

Why is that cortc? Why not have c[g] at the center line?

 

Just a guess, but because that will have more inertia than it would at the center, which makes for easier drivability because the revs don't change so quickly.

 

i really don't understand that...

if you want to say it has less mass near the edge because it has holes drilled out there - OK, i agree and I made an effort to account for this.


if your saying its a lightweight flywheel that has its mass concentrated on the edge thus eliminating the whole reason for a lightweight flywheel... then i'm not agreeing with that

 

I dont get why people keep brining this up... If your chaning out ur flywheel to go faster than ur a dingus. Most people change there flywheels to rev faster. For us drivers who down shift Heel 2 Toe, we would appreciate the lighter flywheel. For those who don't... go buy nos.

 

Can you post a graph of rpms vs. time? I'd love to see that.

 

using a lighter flywheel will free-up horsepower from the engine to go to the wheels - I have no idea how much. You can also think of it as a reduction in the mass of the vehicle but the apparent reduction changes depending on which gear you are in. Someone on a different thread found some numbers that suggested the effects were similar to reducing the mass of the vehicle by about 200 lbs. in first gear - roughly equivalent to an extra passenger. I don't know about you, but I can definitely tell the difference in acceleration performance when I have a passenger in the car versus me by myself!

I've asked for documented performance numbers before and after a flywheel install but no one seems to have any. Plenty of butt-dyno results, though! :p SO, I have a G-Tech Pro Competition and a MS flywheel both en route. I PROMISE that before I get the flywheel installed I WILL do multiple runs to get a baseline. Then I'll do multiple runs with the lightened flywheel to get a valid statistical comparison and post the results! The flywheel should be here middle of next week (sept. 14) so stay tuned. Hopefully, my experiment will finally give us some concrete numbers to talk about! (incedentally, I'm also going to look at the effects of light rims - which should be significantly less than the effects of the flywheel on acceleration)

 

[QUOTE=MadDog]using a lighter flywheel will free-up horsepower from the engine to go to the wheels - I have no idea how much. You can also think of it as a reduction in the mass of the vehicle but the apparent reduction changes depending on which gear you are in. QUOTE]

the second idea is what's actually happening... "freeing up horsepower to the wheels" as i've said in another thread is just an illusion created by the dyno.

 

Hmmm....not sure what you mean by that... can you point me to the thread you are referencing? I'd like to understand your point. I don't know how you can fool a dyno into measuring HP that's not really there...

The engine can only do so much work per unit time (HP). It has to do work to impart both rotational energy to the drive train, and translational energy to the entire vehicle. If you lessen the amount of energy stored in the flywheel (by reducing its moment of inertia), then that energy can go elsewhere in the system, i.e. translating the vehicle. The engine doesn't change its ability to do work - its still got the same power. By using the flywheel with a lower moment of inertia, you just redistribute where the energy goes. The same effect could be had be reducing the energy stored in the vehicle for a given speed by reducing its mass. The magnitude of the flywheel's effect varies with the vehicle's speed because the ratio of the flywheel's stored energy to the energy of the entire system goes down with the square of the vehicle's speed.

But I am pretty sure that the effect of increased HP to the wheels is real. Help me see your point, Wakeech.

THX
-MD

 

here's the plain data... i'm too lazy to make the graph and turn it into a picture and upload it :o

time (sec) RPM

1.171 2435.75
2.143 2504.5
3.164 3301.75
4.146 4124.5
5.157 5025.5
6.179 5965.75
7.16 6855.5
8.182 7713
9.153 8419.75
10.174 8945.25

 

Well, I haven't decided on a flywheel swap just yet, but as far as "rotating" masses are concerned, FWIW I've just recieved a set of SSR Comp 18x8.5 wheels with (opps) 255/35 (probably should have used 40's) x 18 Dunlop Super Sport Race UTQG 60 AAA to replace the stock 255/45x18 Bridgestone's RE040 (UTQG 140 AAA) for use at driver ed/track day events.

FWIW, my digital Hammacher Schlemer bathroom scale, claimed by H&S as accurate to 1/2 lb., indicates "gross" rotating mass/weights of:

41.0 lbs for the SSR Comp + new, no wear Dunlop 255/35-18's; vs.
45.0 lbs for the stock tires, which are probably now at @ half their original tread depth ~ so I'd guess @ 47lbs fresh (? anyone got a fresh, new, unworn OEM tire + wheel weight handy?)

HTH
mike

 

I just changed out my flywheel for the SR motorsports lightweight fly. It weighed in at 11.5lbs with counterweight and bolts. My stock flywheel only weighed 17.5lbs. Mazda must have a problem with producing these flywheels to have that much of a difference in the stock weights.

 

philodox, what are your impressions of the flywheel?

 

Well, I have only had it for about 32 hours now but, I can say that the engine is much more 'free revving' from 0-4000 RPM, after that it's not much more noticible because it's already spinning pretty darn fast. This isn't scientific, but I had my friend of mine with a stock RX-8 take a stopwatch and measure the time it took from idle to redline on his car and mine. The difference is only about 6 tenths of a second in neutral, not sure what it is when the tranny is under load. But I would assume that you would be able to go through the powerband in each gear a little bit quicker, not really giving you more horsepower, but freeing up the power that was originally wasted turning a heavier flywheel. Check out the other threads on here about inertia. Just do a search on it.

I also notice that it is a little bit quicker coming off the line, mainly because you can go through the power band faster. I also found that it is much easier to downshift and you don't feel the car wind/slow down as much when downshifting. But that is going to be true with any other lightweight flywheel you decide to put on your car.

I like the SR fly compared to the MS fly because it's about $200 cheaper and that it has a replacable friction plate if you're even so inclined to replace it. Like I said in an earlier post, I measured the SR Motorsports fly/counter weight/bolts on a scale and it weighed in at 11.5lbs compared to my stock fly which weighed in at 17.5lbs. Just make sure that you buy one from a reputable company that will stand by their product. Make sure that it's not made out of 100% aluminum as aluminum teeth won't last very long. So make sure the teeth on the fly are made out of steel. A good lightweight fly 'should' last the life of your car as long as you don't pop the clutch every day... but that could be said of any flywheel.

Hope that this little review helps you or anyone else that wanted some first hand news about the SR Motorsports fly. Regardless of whatever lightweight flywheel you decide to get, it is a very good mod and I would recommend it for everyone as a must have mod. Enjoy!