mlx8

"... So MS "light weight flywheel only weighs 1.54lbs less then Stock? That seems as if it is hardly worth $620.00? ...."

I'd agree as a gross number, 1.5# lbs doesn't seem like much. But then again it's the redistribution of the remaining mass that's also important. It would be nice if some one else gets a chance to try to pull off a set of "before" and "after" dyno runs for somekind of comparison.

Total cost for my LWF install, including the parts, came to @ $750. That's what the dealership was quoting for labor alone to put the MS unit in.

I see from your thread at https://www.rx8club.com/series-i-aftermarket-performance-modifications-23/light-weight-flywheels-points-interest-40514/, you recently bought a RacingBeat flywheel. I'll be interested hear what your SOP (seat of the pants) assessment of it is after you have a chance to drive it.

For me, at altitude (i.e. for instance 187 "SAE" bhp actually works out to about 145 real, actual, unadjsuted ponies at the wheels at 5,280 ft), every little bit helps... IMO.

shaunv74

hey MLX8. I just wanted to say nice post. Well put together with good supporting data.

GeorgeH

iTrader: (2)

Yes, distribution of mass is critical, and that's why the simple "flat disc" calculations that I and others have engaged in are flawed.

9 ft-lbs in second, and a nicely offset torque curve everywhere in the rev range - that seems pretty good to me. I'd be surprised if there is any other $620 mod out there that would have an equivalent effect.

Also interesting that you got more peak HP in hiugher gears. I wonder if that is a dyno effect or a result of the different ECU maps in different gears.

Thanks for the psot, MLX8.

mlx8

GeorgH Questions "Also interesting that you got more peak HP in hiugher gears. I wonder if that is a dyno effect or a result of the different ECU maps in different gears...."

The dyno folks don't often (if ever) regularly do pulls in 2nd gear. They too remarked on the difference. Their innitial speculation was that it may have to do with possible losses as a result of the gearing selected. If that were the case, I would then guess/conclude that if one were to do a pull in 1st gear, one might expect a porportionately greater drive line loss? I guess I'll have to ask them if they want to voulunteer a dyno session with a 1st, 2nd and 3rd gear runs to test that hypothesis out.

Of additional concern to me, an the reason I added two 4th gear dyno charts, is the "ragged" nature of the power & torque curves that start to show up as the gear ratio moves higher. I don't know if this is something that is engine related, or the dyno induced. Certainly in the higher gears the dyno is spiniing a whole lot faster, than with 2nd or 3rd gear pulls. I didn't include or post the bhp curves on the charts just to keep them clean, simple and easy to read, but, for example, the "jaggies" in 4th gear actually have the car making slightly less "peak" bhp with the LWF (178.76 SAE bhp at @ 8,263 rpm with "smoothing" set to 0 vs. 175.77 bhp with smoothing set a t 5), than with the stock flywheel (176.85 at @ 8,455rpm with smoothing set to max, 5 ~ 179.81 @ 8,445 with 0 smoothing applied)

GeorgeH

iTrader: (2)

Yes, the curves get more ragged in the higher gears. One possible explanation is the sampling frequency on the dynos. In second gear, the rollers are accelerating very quickly, and, depending on the sampling frequency, the dyno may not catch all the local dips & peaks. On the other hand, in fourth gear, the rollers are not accelerating as quickly – the pull takes more time – so the dyno sensors pick up all the minutia of the torque curve.

Just a theory. I wonder what the sampling frequency of the dyno is?

MrWigggles

mlx8,

Thanks for the data. I think the data clear shows that the effects of the RB flywheel are more pronounced in the lower gears. A 9 ft-lb increase in 2nd gear seems a little high but reasonable.

Jaguar,

It is not the weight that is important. It is the the moment of intertia that is important. The moment is determined by where the weight (or more accurately mass) is located.

The Mazdaspeed flywheel acts as basically the stock flywheel with holes drilled along the outer rim. Doesn't sound like much but it is. To show how important this concept is:

On a 12 inch flywheel (6 inch radius), removing 1 lb along the outer rim where the radius is 6 inches is equal removing 4 lbs from the wheel where the radius is 3 inches. Also no amount of weight reduction near the center of the wheel would ever equal 1 lb of reduction on the outside. (for this reason the weight of the counterweight is essentially meaningless, it will have almost no effect on interia.)

So while the Mazda speed flywheel which is about 13 lbs is only 4.5 lbs lighter than stock, most of that weight loss is along the outer edge. The effective drop in moment is probably close to half and that is the only thing that matters.

Also the amount of interia also has this square phenomena. At 9000 RPM the interia in the flywheel is 4 times that compared to when it is at 4500 RPM.

My guess is that since the transmission of the RX-8 was barrowed/modified from the Miata, the flywheel was borrowed as well (just a guess). I don't know what redline on the Miata is, but if were say 7000RPM, then the interia of the heavy stock flywheel would only be 60% of that compared to the RX-8 at 9000RPM (i.e. (7000*7000/(9000*9000) = .604 )

-Mr. Wigggles

Ps. They really need to sell "lightweight flywheels" as "low-interia flywheels". Weight is very much secondary.

Pps. I think this is the last time I try to explain this topic. My fingers are getting tired.

r0tor

iTrader: (1)

hmm... looks like the laws of physics still work pretty well


On another note, the reason for the increase of hp with higher gears is the same reason that the flywheel free's up more hp in lower gears - most drivetrain related losses are effected by the rate of angular acceleration... aka you rev much quicker from 3-9k rpms in 2nd gear then 3-9k rpms in 4th gear, therefore any inertial losses in the drivetrain will be bigger in 2nd gear then 4th gear. PLus gear frictional losses are slightly lower when there is less of a gear ratio.

Actually, the best dyno results of all should be in 5th gear because not only do you lower inertial drivetrain losses, but I believe 5th gear in our tranny is a straight through design which eliminates the frictional losses of transferring power to different shafts. Thats why most dyno's are (and should) always done in the 1:1 ratio gear, but some people get nervous when their car is doing 140mph sitting still.

army_rx8

hey MrWigggles I was listening....learned a lot of flywheel and benifts 9real tha tis) tha tcan be had from them....thanks fo rthe informative post. I think i'm going to settle on the Mazdaspeed flywheel. Thanks for all your effort.

Swedishmax

I just got my ACT prolite flywheel and clutch installed. first impressions are not impressive. The revs are a little quicker but no noticable horse power increase. the clutch grabs sooner and harder...which will be good when i get supercharged. here are the weight measurments:
stock flywheel: 17.4 lbs
ACT prolite : 13.1 lbs

grinn253

Either you got the 'streelite' or are quoting the Prolite with the 3.x lb counter weight.

Laters!
Edgardo