mlx8

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

shaunv74

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!

wakeech

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.

mlx8

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.)

shelleys_man_06

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

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

ScudRunner

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...

shaunv74

[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.

cortc

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

r0tor

iTrader: (1)

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...

shaunv74

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.

r0tor

iTrader: (1)

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 >

cortc

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

shelleys_man_06

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

robertdot

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.

r0tor

iTrader: (1)

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