Regarding the lightweight flywheel = transmission death (simplistic I know). Would people advise skipping the lightweight flywheel all together? I would happily give up some quick revs (stock is actually pretty good compared to other things like a 240sx) in search of keeping a transmission alive.

I have a 10lb flywheel I haven't put in yet. This was the only thread I saw this mentioned.

 

It is a debated topic. Search flywheel threads, it comes up.

 

https://www.miataturbo.net/suspensio...trength-83376/

Check that thread out. I would advise skipping it if making > 300whp through a 6 speed, for reasons covered in that thread.

 

It seems inconclusive as some try to use calculations (my 1st preference) and compare them indirectly (or I guess directly) to their experiences but not controlled tests.

I think the only way to know for sure would be to do the calculations and then set out with the same car but different flywheels at different times and under the same circumstances in a high HP miata and try to break transmissions. That isn't happening, but I personally might follow suit on the maths involved and part ways with my flywheel I've been holding onto.

 

What seems inconclusive?

 

I read through the thread, albeit a touch quickly, and it seems the theory supports the claim that a heavier flywheel would help protect the trans from abuse from vibrations. But it is followed up with claims of running the complete opposite (10lb and 949 B6 twin disc) for some time without a failure. I see that as inconclusive, but enough maths and background to convince me to continue with my stock flywheel and my FM2. Also, I can recoup a touch from selling it. Win-win

 

Another train of thought is the lightweight flywheel reduces shock loading on shifts because there is less inertia so the rpms match without transferring as much load to the next gear...... It's not a widely accepted believe that light weight flywheels break transmissions, not sure I personally would go selling parts over that thread.

 

Not vibrations, power pulses. Don't worry about it if you aren't making big power.

Doesn't one 300+ horsepower racer here have more broken transmissions in his history than he has fingers on both hands? He's got a very lightweight flywheel to win races and it costs transmissions. It's a trade off.

 

I think you are referring to bbundy

 

Perhaps.

 

He is, and bbundy has broken transmission with every combo of FW and 5/6 speed, as admitted by him. The heavier FW trans didn't last any longer either. What I have said over and over, and posted the background of in that thread, that NO ONE SEEMS TO BE GETTING!!!!! is that until you model the engine and the trans, and determine TRASMISSIBILTY...... any talk or use of damping is a waste of time. If transmissibility is the issue, no reasonable amount of damping will fix it.

posted for like the 18th time for your reading pleasure.

http://www.epi-eng.com/mechanical_en...issibility.htm

Edit: key phrased pulled from the linked page:

"Understand this: No matter how much damping is added, if the engine-PRSU-Propeller system is operating below crossover, the PSRU (thus the gears, shafts and propeller) feels torque pulses greater than what the engine produces."

substitute "engine-trans-diff" for "engine-PSRU-Prop"

 

Please don't go look at the for sale threads. I still want your love...and LS coil brackets.

 

Rad link to a blank page bro.

 

Link fixed.

 

After reading that, it looks like a heavy flywheel could bring initial values lower, but leave the whole thing in a crummy area for most of the rpm range. Where a light flywheel might cross o er much faster.

is that what you guys get out of it.?

 

We can't change the engine-trans-diff resonate frequency, mazda set those when they designed these systems. Nobody here knows what they are. And nobody is going to model all of that crap, and even if they did so, and did it right, and calculated the exact resonate frequency, we still couldn't change anything based on that info, and many would dismiss the data as a theory anyway.

 

Exactly my point. Its all pointless, run the FW you like.

 

never liked lwfw's. waste of money on a street car, for little to no benefit, and quite a few drawbacks

 

It's at least possible that when mazda designed the car, they considered all of this resonate frequency stuff, and put a flywheel on the car that was the correct mass to keep the system in a safe area.

Saying run whatever you want is like saying run whatever engine-PSRU-Prop on a plane and saying it will be fine since you don't have specific knowledge of the system. No, you run what is known to work safe, which would be parts designed to work together. I'm sure the folks designing the engine-PSRU-Prop for a plane took this into consideration, yet we're supposed to pretend mazda did not, and that changing the flywheel is of no consequence?

 

No it isn't, that's quite a stretch Pat. One is an airplane, one is a car. One has a proven track record of actually killing humans due to the exact nature of the issue when these considerations aren't taken into account and are probably required considerations by certain countries and organizations; the other doesn't(that is to say, planes accidents have been investigated and this issue has been verified to be a cause in some, we have 0 proof of any of this in our cars. The only thing we do have is anecdote from bob bolstering my point and disputing yours) and it isn't required.

Also I highly doubt mazda did any of the calculations, at least for the gear box side. I assume(could be wrong) that to be an incredibly difficult thing to model and get any real data out of with todays computational analysis, let alone in 1989 or before. PSRUs are uaully a drive and a driven gear or sprocket with a chain belt or whatever. Not a multi shaft, multi speed gear box. Also, it doesn't matter because we arn't talking about stock engines and drive train combinations that mazda would have modeled. Lol at you(specifically) talking about running parts that are designed to work together.


Again, my point is, that any talk of damping without knowing the transmissibility of the system is an absolute waste of time. We will probably never know that relationship. What little data points/anecdote that exists points tot he fact that is doesn't fuking matter. Im quite surprised that a data driven engineer type such as yourself has no issue throwing this idea around with such certainty, having no data for the specific case of our cars, and having read the article that makes it abundantly clear that you need the data. Even phrased as "understand this".

So, run the FW you like. If that means the stock one because it makes you feel better about your power pulses, then so be it.