I'm not a complete expert on this, but don't be fooled by the weights of the flywheels. The weight is not the most important factor, rather the flywheels moment of inertia. The placement of the weight is more important than the amount. If the weight is closer to the center than it will have a lower moment of inertia, this is a good thing, but you also want to consider structural integrity. You wouldn't want a company to compromise build quality for a slightly lower moment of inertia. I think I'm right, but someone will correct me if I fudged something up.

 

I wouldn't get a flywheel until your ready to replace the clutch also, thats an expensive install, might as well do everything at once.

 

The "moment of inertia" point has been made elsewhere, ad nauseum, but it is still a valid point in a way. I don't think that the RX's flywheel diameter is such that weight location will have as much impact as total weight. Brillo's point about doing a clutch/wheel combo is also good advice. If someone only had a couple thousand miles on their car and wanted a flywheel swapped I would say to do it now would mean they might only need the pressure plate and input shaft bearing and seal because the Exedy discs that come stock are pretty much what SR Motorsports provides with their kits.

Charles

 

This xls spreadsheet was made for a miata - however, if you factor in the numbers for a RX8, it'll still show how the relative gains associated with a lighter flywheel reduce as you go up thru the gears.


http://www.d-mphotos.com/movies/flywheelcalculator.xls

 

Charles, I noticed you have a ACT clutch, I went to their site but its not listed, could you explain how you got it? Is it a prototype?

 

now i want a flywheel too...... Aside from the RB front bumper i really like the kit.

 

The spreadsheet shows what the final results will be but there is no engineering explanation as to why this is.

My clutch kit was purchased at SR Motorsports. It contains the ACT Extrmeme Duty pressure plate(MZ-010-X), Exedy disc(which looks very stock), Mazda counterweight, and the associated bearings and seals which were genuine Mazda parts. I can't remember how much I paid as it was part of a litany of things I ordered all at once. From things I have read since then, it looks like the RX-8 clutch is the same as the FD set up. Perhaps only the counterweight is different but there are better people than myself who know about that.

Charles

 

according to that spreadsheet, I gain the most hp by using a 100 lbs flywheel....


also, i'm strongly considering a lightweight flywheel, but with so many people having transmissions replaced, engines replaced, etc. How do you guys justify voiding your power train and engine warrantees? From what I've read, the MS flywheel is 10 lbs and since it has holes around the edges, should perform close to the RB flywheel, while being made out of a stronger chromly (sp) material.

 

How come I can't understand that spreadsheet???
Is it me? Can anyone read it?

 

If I were an engineer I could tell you, since I'm not, I'll quote from the guy who made the xls spreadsheet:

 

Well I R one and I have no trouble with the theory it's that speadsheet that makes no sense.

 

what clutches are you guys buying when you replace your flywheel? and what did they cost?

my car just hit 8,000 miles. Wouldn't the stock clutch last 100k+ miles?

 

If the spreadsheet engineer were thinking of things in terms of percentages, then I see exactly where he is coming from. The problem is, what constitutes a "10% improvement in acceleration"? I could see one saying that he cut 10% off of his acceleration time by going from a 5 s 0-60 to a 4.5 s, but the problem is that evaluating acceleration by using percenatges is not very useful. To see a .5s reduction in the 0-60 time would be more easily analyzed by using the popular weight-to-power ratio models alongside the rules of thumb offered out there. In my case, I have read the formula to be 2.7 h.p. per pound off the drivetrain weight. I realize that is a rather vague way to go about it, but my car is responding in at least the fashion (if not better) than those models have indicated. Besides, my handy slide rule from Moroso, which is over 20 years old, has been right on the money since I started modding my car. The only caveat with the slide rule is that it assumes 100% traction. The cool thing is that the G-Tech is showing similar results, which is why I am fairly confident that my readings are accurate.

Charles

p.s. I have an ACT Extreme Duty(#MZ-010-X) pressure plate with a stock-looking Exedy disc and Mazda counterweight, bearings and seal.

 

Keep kickin' *** Charles. By the way, you still working on that header design? Thanks

 

The spredsheet doesn't show percentage of acceleration improvement - it shows the 'net effective gain' - as if the car would accelerate as if it had "x" many HP, for each gear. That's the point of the spredsheet.

In first gear, the car will accelerate as if it has 10 more HP (Than it had w/ a heavier Flywheel)...and so on.

 

OK, so Charles you can't read it as I can't. I just went back and looked again with what you said and what dmp said in mind. I still can't understand it. Remember when you were in elementry school you had to turn in your worksheet with your math to show you really know the equations. That would help here.

Someone tell the guy to turn in his worksheet.

 

simon i see you already made your decision but i thought i'd throw my .02 in anyway.IMHO if your going to do the flywheel you might as well save up the money and have a new clutch installed at the same time. no sense in doing the flywheel only to open her up a second time to do the clutch. waste of Labor dollars.

 

oh well upon furthur reading i see brillo and Charles already made that point. so carry on

 

I would make a clear distinction regarding the flywheel alone vs. the package approach, and it is this- if one is not too likely to go for major boosts in output like FI or nitrous and the vehicle has only a few thousand miles on it, then do a flywheel-only deal and save some money. The factory disc is an Exedy disc that looks very much like the one that can with my kit from SR Motorsports and the rest of the kit is also full of OEM Mazda parts . In addition, I have spoken with a friend who dyno's Indy and now NASCAR engines and he told me in the past that the Indy cars use factory Honda discs because the cars are so light and the factory piece works great.

Charles

BTW, Aoshi, the header, Ti PPF, and Ti rear links are all coming up very soon. I will be storing my car in the next week, or so, and that's when the prototyping begins.