Light flywheels definitely have applications in drag racing as well as other forms of motorsports. Those who think flywheel weight factors into launch quality are thinking too hard and using math to validate an ill-informed opinion. Pro Stock-class racers use flywheels as light as 6 pounds and their engines idle at 1500-1800 rpm's. Pro Stockers also make very little power down low so why would they use such light flywheels? Here's why;

In determining the proper weight of a given engine/flywheel/drivetrain combo engineers certainly use math, but what is the purpose of the numbers they construe? It is to determine a flywheel weight which makes the friction zone of the clutch the most comfortable to manage in the context of a given application. Since drag racers try to have their friction zones/clamping times as close to a zero value as possible, which goes to launch quality, they don't need heavy flywheels. Of course, tire traction is also a consideration but not for this specific point. Flywheel weights are determined for people to use, not for engines to deal with loads. The weight that Mazda chose for the flywheel on the Renesis was more to satisfy the wide-ranging market that they expected to buy and drive the car and not for the more aggressive of us who know how to drive the car in a more performance-oriented context. Remember, this is a four-seater that is expected to be used to carry families and more mature people. Not punks like me. Take the new Carrera for example. It has a super-light flywheel because those who are expected to own or drive the car are comfortable with a more aggressive clutch engagement profile that needs experienced finesse to properly manage. Anybody who pays that much for a car ain't goin' to the grocery store with it. By the same token, road-racers like light flywheels because they allow for easier rev-matching with no loss in low-end power when the clutch is fully engaged. The reason some will experience quicker 60' times with a heavier fly on their RX-8's isn't because there is more torque available on the launch. It is because there is slightly LESS torque available in a car that has traction problems in the first place. With the clutch-lockup time slightly lengthened by using a heavier fly, there is a net effect of slipping the clutch ever so slightly and that results in a more manageable friction zone. Light flys launch hard because there is no extra weight to slow the engine in performing its task of converting fuel to rotational energy.

If anyone would like to drive to Detroit and see, firsthand, how easy it is to drive with a 9.75 lb. flywheel on the RX-8 they are welcome to come to my house and drive my car.

BTW, when I recently compared "driveability" of the RX-8 to an STi he was surprised to find that his launch was no quicker than my own. He was also shocked to find that he only beat me by a car-length and I wasn't using the nitrous. I also was experiencing problems with my MOP volume and currently have top-end issues. With those issues resolved he would have been eating dust.

CRH

 

You know... for once I agree with you :p

I have a racing beat aluminum flywheel on my non-turbo 2nd gen and love it to death. Once you get used to it, took about 1-2 days for me, it's just awesome to drive. I will continue getting lighter flywheels just for the mere fun of it and, for me, better driveability. I love how the car drives more than with the stock flywheel by far on my 2nd gen, and I know it'll be the same on the rx8.

 

That's funny!

 

So, the slight (if it even exists) disadvantage is greatly outweighed by the NET SMILES on your face...interesting...

The stock flywheel, last I heard, was 16lbs...I think going with a 12lbs one would be a fair compromise.

 

That was my thoughts too, so I purchased the RB Flywheel which is 12 lbs.

They sent me the wrong flywheel (got one for an RX-7 turbo -- too small), so ended up using the ACT Prolite 9.75 lb flywheel. Glad I did -- took just a few days of getting used to, but now no driveability issues, and love the launch.

Feel confident to go 'light' in your lightweight flywheel. Racing Beat is currently working on a 'lighter' lightweight flywheel.

 

You guys shoulda seen rxeighter's face after that first trip around the block when we finished his install, too. Talk about a kid on Christmas Day......

CRH

 

It was one of the main mods I was thinking about but I got a little scared about driveablity issues...I know Charles loves them so when the time comes I'll probably go with a lighter one too.

 

I found that the N flash made the task of dealing with the light fly MUCH easier. I can start from a standstill without needing to even touch the gas pedal if I don't want to, and I am still idling at 850-950 rpm's.

One thing I like about light fly is that it is a mod that places no additional stress on the engine or driveline. Unlike nitrous or turbos, the beauty of the light fly is that it makes the driveline more efficient. Of course, the effect of a light fly is nowhere near that of turbos or nitrous but, then again, the light fly also complements those mods just the same.

If I were to suggest only a few mods to those on a limited budget I would say that the light fly is one to be made a priority.

CRH

 

Charles,

Do your comments on the lightweight flywheels apply to piston based engines, or primarily just rotary based ones? Since there is significantly less rotating mass in a rotary, I'd imagine its effect would be slightly different on the whole rpm dropping extravaganza then a piston based engine. If you get a chance, I'd appreciate any thoughts.

Car in question is a 6s with a 25 lb stock flywheel . Two aftermarket sources exist, a 15 lb lightened flywheel, and a 8-9 lb fidanza alumnium flywheel.

 

Rather than looking at the rotary engine and its design, think of it in terms of its general dyno curves and as a device that provides rotational energy used to move a car. Sometimes we get all hung up on sophistacated technology and disallow ourselves the sheer joy of going fast or quick, whichever your particular thrill may be. As an engineering point, the rule of thumb is that for each pound of rotational mass removed from the flywheel you will typically see the effect of a 2.7 h.p. gain. In your particular example, to go from a 25 lb. flywheel to a 15 lb. would net in the neighborhood of 27 h.p. and even moreso with the 8-9 lb. wheel. I tend to be curious as to whether that original number of 25 lbs. on the factory wheel is accurate. Remember the difficulty we had in pinning down the RX-8 flywheel weight until we actually tore the trannys apart and measured the various parts? I am assuming that the 6s is a heavier car than the RX-8 and, if that is the case then, the 8-9 lb. flywheel will require a bit more finesse in the 6s than it would in the RX-8. The matter of which flywheel weight would be best for you really depends on your particular goals or tolerance levels when dealing with the clutch's friction zone. To go with a lighter flywheel will most definitely enhance the performance of any vehicle but the question is at what expense of driveability. The conversation regarding the 6s will probably follow the same path that the RX-8's discussion has with differences being only in the details.

To sum it up: a flywheel's purpose is to allow the driver to most easily start the car from a dead stop and once full clutch engagement has been reached the flywheel is just along for the ride. Heavier flywheels allow more variance for driver error. In other words, little old ladies do better with heavier wheels and young dudes enjoy the light wheels. A better explanation involves more details but not of the mathematical variety.

If your question is really which wheel best suits your use in the 6s my response is first to make sure that your number of 25 lbs. is accurate and what that all includes. We need to see just how dramatic a weight reduction the 15 or 9 or 8 lb. wheels will provide. THEN we will have a more predictable scenario. The next consideration is the real-world use in which the car will be driven. As far as my own specific experience, I am able to drive my RX-8 with a 9.75 lb. flywheel every bit as smooth as I was able to do with the factory wheel.

CRH

 

here is a pretty slick calculator to show the 'effective' gains a car will have, by gear, by using a lighter flywheel. Enter in RX8-specific parameters; it's set for Miatas.

http://www.imagehostingsite.com/user...calculator.xls

works regardless of engine layout.

 

That is a cool calculator but, unfortunately, most people have a difficult time relating to numbers and it is easier to describe for them the effect rather than quantify it. I think that has been the root of most of the discussions surrounding the light flywheel matter.

Thanks, dmp.

CRH

 

Thanks for the comments charles. Basically the flywheel was weighed on a scale after it was removed.




Stock on the left. Lightened on the right (shot-peened and heat treated). A 6s MTX bare bones weighs around 3247 lbs. (With a full tank). Mine weighs roughly 3185 lbs. Still a fat pig, but slightly less piggy . Hoping to eventually have it around 3050. (Stock exhaust is rediculously heavy)

 

It looks like there are no other external balancers needed like on the RX-8 that would skew the comparison. In that case, the next question is: How aggressive ya wanna go? If it were me, I would go as light as is offered without fear of driveability. It seems that the 6s and RX-8 fully loaded really aren't that far off from one another in terms of overall weight. Mine weighs about 3,269 with my bulk behing the wheel.

With those facts established, let's look at my other point regarding the purpose of flywheels and their respective weights. Compare the markets that the RX-8 and 6s are expected to satisfy and compare the factory flywheel weights. It seems that the 6s has a wheel that is about 7-8 pounds heavier than the RX-8. However, the aftermarket offers weights that are comparable to one another. How much ya wanna bet that if you were to put the same weight wheels in both the RX-8 and 6s you might find similar driving/acceleration mannerisms?

To further the conversation, I have discovered that each 5 h.p. we can raise to our wheels will result in a .1s reduction in 1/4 mile e.t. Of course, the quicker we go the more power it takes for each tenth but at these levels that is a good rule of thumb to start with.

Here's something I was thinking about last night with regard to describing the feel of certain gains; to me a simple tenth of a second is not noticeable. A three tenths gain can be felt a bit. Half a second will get my attention and raise my eyebrows. 1 full second is quite exciting and with my nitrous I tend to high-five myself when all goes well. A 1.5 second gain is downright shocking and to suddenly cut 2 seconds off of your e.t. is flat-out scary as Hell.

CRH

 

BTW, have you seen the Nitrous Express project Mazda 6?

CRH

 

Charles,

The 6 has major issues with dry shots. So far every 6 thats sprayed has ended up on the route to engine replacement. =/ Even venom blew a 6 to pieces while setting up a kit. It seems there isn't equal distribution of air between the front and rear bank (partially due to an extremely abnormally long EGR valve blocking the front bank...see photo). This of course causes the rear bank to go lean, and blows out the rings something fierce (40-50% compression on the rear bank). Also if you get too much detonation, you go the route of spun rod bearings and damaged rods.

Here's a shot of what happens when you spray a 90 dry shot in the 6.





EGR Photo (Left is front bank, right is rear bank, photo after Throttle body)



Someone is trying to run a more conservative 55 wet shot now, with a cut EGR, and will be providing data on its effectiveness. (If you cut the egr, it drops the LFT's to a much closer 1.5% off. (vs 6-7%). )

Right now the fastest 6's are in the low-mid 14's (A/F tuning, Headers/Exhaust). Hopefully with some more tuning we'll hit the upper 13's, or at least consistently low 14's.

I completely agree with you in regards to the wheel selection. I'm currently running SSR comp's in 17x8 with some Toyo T1-S rubber, total weight is about 34 lbs vs the stock wheel/tire of 48. Quite a savings in unsprung weight, and a totally different vehicle in terms of responsiveness, braking, and acceleration. I'm greatly anticipating the Toyo T1-R's which I'm going to throw on after June in 245/40/17's.

Thanks again for your feedback and thoughts!

 

^ GOOD GOD! What is that ugly thing laying on top in the first picture? :p Children, avert your eyes! :D

 

Crossbow, when I used the term "wheel" in the previous posts it was intended as an abbreviated version of "flywheel" as I grew tired of typing the entire word. So, I have yet to be able to take credit for any conversation regarding wheel/tire selection. You do have a nice set of wheels and tires, though.

If the volume of air between the front and rear banks on the 6s is different, couldn't you install a direct-port nitrous shot and tailor each nozzle to the particular needs of that intake port?

CRH

 

Ya charles...we could. But at what point does it become rediculous to try to throw tons of power and money into a FWD open differential family sedan .

At least your car is RWD with an LSD!

 

Cross, how can you go from talking about trying to hit high 13's in one post and then ask me to define the threshhold of ridiculousness when upgrading the 6s? If you don't think there is much potential with that particular vehicle, why are you contemplating a flywheel swap? BTW, the Neon didn't seem to have much going for it until Mopar put a Quaife and a turbo in it. :p

CRH

 

Ah. Well the flywheel thing comes up because mazda is replacing clutches in the first 12,000 miles due to a shutter issue.

So while the clutch is out, there is a chance to replace the flywheel. So I figure its in my best interest to gather information and research .

I'm sure someone will go for a direct port soon...but then of course the turbo kits are starting to pop up now. Now if we could only get an LSD at a semi-affordable price .

 

That's one thing about nitrous and turbos; the matter of power production is no longer the engineering mystery it used to be. Instead, the matter of durability and control are the issues these days.

CRH