you know --i was wondering if a lighten flywheel was a good mod or not?
I know it is not that simple--but hear my crazy thinking. The rotory engine really doesnt like accelerating and decellerating but its great for constant rpm running ( one reason airplane guys get better life out of it). Now a lighten flywheel magnifies the acceraltion and especially the decel part--right? I do wonder if a lighten flywheel causes more of a particular type of stress on this engine than the oem one?
Mazda went to great lenghts to squeeze out the most power to the wheels from the engine in this platform. I mean --a carbonfiber driveshaft in a production car? If they where that intent--then why did they stick with such a heavy flywheel?
In driving the same model of car-- one with a light flywheel and one that has the oem--i have to admit the oem one is noticeably smoother.
A lighten flywheel does help with rev matching but for anything else--i am not so sure?
When my present clutch goes-- i do believe i will go back to the oem one.


lol Team you hitting that Crown Royal?

 

I think "better" is subjective here.

Depends on your goals in the end I think OD. What those goals are can change which is more ideal.

 

Thats true. Nice to have the options.
Has anyone really proven that a lighter flywheel actually does mean a certain hp increase to the wheels?

 

Soju @ Korean BBQ joint

He was referring to Moment Of Inertia vs. static weight. Discussing the weight of a flywheel without knowing the MOI values is a bit pointless. For all you know your lighter flywheel/clutch combo has the same or higher MOI than the factory setup. The static weight is not that relevant, MOI is what counts for rotating mass ...

 

very true---thanks for the reality check. I do tend to wander sometimes.......
I have no idea where the weight is placed on these flywheels.

 

Hey gang. See this^^^^ Up there ^^^ This is money. Big Money. Huge Money. Want to learn something???? Google the crap out of MOI and read, read, read. You WILL have a paradigm change. Sooooooo many people get this wrong. Sooooo many people ask "what is the weight of XYZ clutch, flywheel, driveshaft, brake rotor, wheel, clutch because I want the lightest one out there" For those of you who enjoy the learning opportunity this forum provides---have fun learning about MOI.

Happy Rotoring,

Eric

BTW, the MOI concepts are not "street" or "race" oriented. Just like the guy in the video doesn't have to be either a college physics professor or an elementary school teacher.

 

Or not.

Since no one here is redesigning the clutch/pressure plate/flywheel/starter ring for the RX-8 and since there is essentially only one practical way to effectively reduce the mass of those components, not only will all available assemblies have roughly the same moment of inertia but knowing that value is almost completely useless since you cannot apply that value to a compensation anywhere else in the system.

When not engaged, the MOI change, as it correlates directly to mass, only ends up amounting to a somewhat trivial change in "feel" and possibly an adjustment to the engine management to compensate for overrun and idle return.

When it is engaged, the effect of the MOI of the total rotating mass of the motor is entirely trivialized by the effects of effective gearing and its synthesis of angular momentum.

 

^^you've been hitting the bottle too, I see ...

 

Most people would see/feel more from a balanced rotating assembly than changing the flywheel. The lighted flywheel will drop rpm faster and rev faster, however the heavier flywheel will retain its momentum during shifts. There is a very delicate balance here you must find/know for your particular set up.

Good read.

 

Paradigm changes only work for people who are open to learning new things.

 

I should have payed more attention in physics class.

 

"Too"? Who else is included in that invite?
Meh. Since I don't really drink much and I'm pretty sure you don't mean nitrous, I'm going to have to just scratch my head on that one.

OK. Edumakate me.

I already know about MOI. A LOT about MOI.
So, what is "new" here?

So far, all you did was point to Team's post and say "hit Google".

So, I hit Google. I looked at all the usual stuff, like the Wikipedia entries on angular momentum, inertia and polar moment of inertia (an article that I contributed to editing, BTW).
I followed the links about flywheels. I read some interesting stuff on the various manufacturer sites. Etc.

So far, I haven't found anything to send me in the right, new and "enlightened" direction.

Since flywheels operate at engine RPM, their effect is direct, so the kinetic energy is what it is. (Part of the reason why the "I gained HP by installing a lightened flywheel!" threads are so entertaining.) Since you can only "lighten" anything one way - by removing mass - you are limited to altering the angular momentum by removing mass in places that it possesses mass that is not structural. On a flywheel, there is only a limited radius where this material exists and the MOI isn't affected much until you remove a fair amount of that material, so the entire radius that can be altered must be altered to have an effect on MOI.
Even the "stupid pet tricks" like an aluminum starter ring or aluminum dowels have a limited effect (even though they exist at the furthest reaches of the "r" in L=r*mv).

So, I most humbly ask again - elucidate us. Google doesn't have your experience in this new and exciting realm, apparently.

 

^2 Questions:

1. Let's pretend someone on these forums wants to make their RX-8 street car faster and asks you to chose which was more important: Weight or Moment of Inertia for measuring the benefits of a higher performing Flywheel and pressure plate/clutch assembly. They want their car to accelerate more quickly. That is their question. You can only chose one. Weight or MOI. What do you tell them?

2. Why?

 

Weight

Because they wont have an f-ing clue what I'm on about if I say "MOI".

And, more importantly, weight and MOI are directly and inextricably tied in this particular part on this particular application, so you aren't imparting any useful information when you try to impress them with your brandishing of an engineering term like "MOI".

 

You're not fooling anyone

Are you saying that all the different flywheels have more or less the same momentum? I think that I misunderstand you, english is not my mother language, but just wanna check. Cause from a theoretical view, as mine is, you're gonna store less energy in a wheel that has the same shape, but is made from a lighter material. And of course you will have the same effect if you remove mass from the original wheel.

What leads me to say that you're gonna increase whp because you're "filling" less energy into the flywheel when increasing RPM, and instead puts it out to the back wheels.

Or have I forgot something?

@eric:
When you say that lighter isn't always better, you're point is that two axles with same mass and diameter, but where one is hollow and the other massive, the massive will have less MOI than the hollow since the hollow necessarily have more mass further away from rotation center? Pew! - that was a long sentence...

 

MM, you are making the mistake of thinking that everyone doesn't understand because it's the easy answer. While some won't, you may be surprised at the number that do. Then there will be the others, without a " f-ing clue" that are curious enough to look it up.

 

The location of the weight it what is important.
Lets say there were two fly wheel and clutch/pressure plate assemblies of the same or similar weight.
Assembly A has a higher concentration of mass towards the center of the plate.
Assembly B has slightly less weight near the center but more closer to the edge.

Even though the weights of the assemblies are the same Assembly B would have a higher MOI because its extra weight is being applied at a large distance from the center.

 

That's true but what happens when the friction disc is just slightly smaller than the flywheel itself? The radial weight you can remove is not much at that point thus frustrating the end result.
That's part of the reason why race cars have 4.5 or 5.5" flywheels and clutch combos
MOI is an interesting subject but real world results may be disappointing for the aforementioned reason. Now swap for a smaller diameter flywheel\clutch combo and that argument becomes relevant again

 

being a pragmatic man i will follow the results.
Results being subjective, i probably need to better define my meaning.
Street driven performance? This includes longetivity as most street driven cars are in for the long haul. The way I understand this is the MOI will only be of any measureable benefit in 1st and 2nd gears. All street driven drag racers will tell you this and show you their 60ft times to prove it. They also have to balance the driveability of the car on the street with performance.
It is impractical to go with a flywheel that would interfere with idling with the a/c on and difficulty to start off on a hill for example. So with the amount of total practical weight reduction limited it can be very important to get the MOI of the wheel as good as you can.

Road Track monsters? 1st and 2nd gears are usually not used? But also the overall diameter/weight of the clutch/pressureplate is not as critical. The weight of the flywheel is also not as critical. So road guys go with a smaller in diameter pp/clutch with a much lower moi than the larger ones like oem. They then mate it to the lightest flywheel with the best MOI that they can get. The combo of the smaller in diameter PP/clutch with the decreased moi flywheel is what keeps most of the weight in the same area of the total assembley. The overall significant reduction of weight from the smaller in diameter pp/clutch plus its decreased moi plus a lighten flywheel with its decreased moi is what helps with the overall race cars performance? Tracks change the leverage/weight and the moi?
Am I in the ballpark? If not I will just shut up and eat my ball park frank.

 

You are such a wonderful optimist.

Unfortunately, the day-to-day reality is quite the opposite.

I realize that there are people that will take the initiative. However, they usually aren't the individuals asking the questions.
One of the traits of autodidactism is "saving" of questions for the time in which they are most valuable.

No. I am saying that different RX-8 flywheels of the same net weight have more or less the same MOI because of the way they must be assembled and that fractional differences in mass distribution over the range where milling can be done have little or no effect of MOI because the effective "r" is the same.

 

What MM is saying is that all flywheels need to be the same size for our car and minor manufacturing difference such as weight distribution have miniscule effects on Moment of Inertia.... realistically meaning static weight has the greatest effect on MOI (because all of the flywheels must have relatively the same dimensions for the same application) and the lighter the flywheel the less MOI the flywheel will have meaning faster RPM change and less HP needed by the engine to spin the flywheel

 

What is being left out of this discussion is the importance of the flywheel as part of the entire rotating assembly of the motor. The net MOI affects the balance of the entire rotating assembly.

 

I have to agree that it is the entire assembly instead of one part. I should have stated my sentence better earlier in the thread.

 

In any event, I would love someone to help me assemble some Socratic-method questions to pose Eric with so that we might led down his path to discovery.

 

I think the problem we run into with that, is, "Do we actually have all of the factors identified?"

I think that plenty of the people that aren't scared of learning that are on the boards have no problem with this method at all, but when we only have part of the possible factors identified, then it can mean an incorrect conclusion.

Perhaps we should start with a basic question, then identify every single possible factor, and then we can apply this method.


Of course, the niggling thought that it wouldn't matter crosses my mind. Since we can get all the way to a 'confirmed' solution to this, and all it takes is someone coming along and saying "talking about it doesn't prove anything. Take it to the race track and see if you win"