Originally Posted by Billman250

The issue with aluminum flywheels is the holes in the friction surface used to bolt the steel to the aluminum. During heat cycles, the edges of the holes get hotter quicker than the rest of the surface. Just as if you hold a torch on the edge of a one inch piece steel, the edge will turn red right away. Yet if you hold it in the center, it takes a while to concentrate that heat.

It is during this heat cycle that the edges of the holes raise up like a volcano. not to that extent of course And in turn, shave the disc like a file. I have found disc life to be horrible on the S2000 with an aluminum flywheel. I believe this is the reason.

Nothing beats function, reliability, or clutch life like a one piece steel flywheel.

As far as SOS I am not familiar with their product but if its a one piece steel I'm sure it's a nice piece.

Originally Posted by slipstream444

It confounds you because you don't know what you're talking about. Ductility and elasticity are two very different material properties. Elasticity is a materials ability to deform and return undamaged to its original form (hence the name "elastic") Ductility is a measure a materials ability to PLASTICALLY deform and not fracture. ANY plastic deformation is permanent damage. This permanent damage increases with subsequent cycles until the material ultimately fails. Go grab a wire hanger and bend it back and forth until this soaks in.

I have to say this from time to time to remind folks of this important fact: this is a technical forum - not an opinion forum. You stated your opinion, which was obviously based in nothing more than a loose thought that ran through your head. The fact is your opinion is wrong.

I have in fact read more than one article specifically about aluminum flywheel failures (more than one of us on this site have) - especially in race situations and at high RPMs. This is NOT a good thing.

Here's my philosophy: Safety first - and billet aluminum sucks as a flywheel material (as well as applications such as brake rotor hats in two-piece rotors). A forged aluminum flywheel would be better, but it's still not nearly as strong or durable as Chromoly steel.

Here's the quick and dirty data to back my points regarding elastic deformation - I'll keep it easy for your and stick to Young's modulus for this example which measures one function of the modulus of elasticity:

Aluminum (billet - typical):
E-modulus of around 11.5 million psi from around -400F reducing to around 8 million psi at slightly below 400F. There is no elastic modulus above this temp - the material becomes extremely weak and fails.

Chromoly Steel:
E-modulus of around 33 million psi at -400 reducing to approximately 19 million psi at 1400F (that's a 1000F higher temp than aluminum, if you didn't catch that number). Chromoly steel's E-modulus is around 27 million psi at 400F... the point where aluminum fails. You do the math.

Here's the rub: Aluminum is a reasonably strong and light material if you keep things cool. However, it's greatest weakness is the fact it will suffer micro-fractures every time it is cycled and it becomes very weak at relatively low temperatures. Every time you cycle that clutch, you are cycling the material, and if it can't handle that in an elastic manner - it will eventually fail. Hence my point.

I fly planes for a living - and guess what, every plane I've flown was mostly built out of aluminum. It's an inexpensive, lightweight and relatively strong material that makes aircraft design and construction affordable. However, the material will fail over time due to micro-fractures in the aluminum. Airplanes have a structural lifespan that's based on cycle loads. The structure begins to fail if you exceed these cycle times based on design loads. You can extend the life of the aircraft if you reduce the design loads over time. However, the airframe will only get weaker and will eventually fail. You don't want to be in the aircraft when this happens.
I recently put a plane in the bone yard out a Davis-Mothan AFB, and the place is littered with over 4,000 airframes that have exceeded their cycle time in one way or another.

You stated (somehow) that you don't think a flywheel gets that hot. This may be the case in your average street car. This is not the case in aggressive street driving, and certainly not on the track. To give you an idea about friction based components (especially if they're used frequently) - brakes (street) can easily see 400F+ on a warm day. Track use can easily drive the temps to 800-1100F.
While my car doesn't have a flywheel temp gauge (I'm assuming yours does - or was the 200F temp you threw out a professional swag), I can tell you with reasonable certainty that my flywheel sees temps above 200F on a warm summer day when I'm driving the car aggressively or on the track. The closer you get to that 400F mark with an aluminum flywheel (especially with a modified car)... the closer you are to setting off a grenade.

Now I don't know about you, but I wouldn't be so fast in putting your good name behind a type of product in a technical forum that has the genuine possibility of hurting or killing someone - especially when you have absolutely no clue what you're talking about. Go back to the chat room.

Originally Posted by LeonV

Sure, I agree that CrMo Steel is "stronger" but that in no way automatically discounts Al as good material as well. By your logic then, Beryllium is a better material than the rest. Why take your chances, when you can have a Beryllium flywheel? The point here is this, and I'll rephrase once again, while one material may be stronger than the other, it does not rule-out the use of other materials. Aluminum has proven to work great in these applications, and besides the point, the OP asked for a recommendation on a street-use flywheel. I have no problem at all with recommending Aluminum, and in fact I'd do it myself in a heartbeat if I were looking for a lighter flywheel.

This is not about stroking egos, but rather having at least a modicum of professional courtesy when involved in a discussion within a technical forum.

Originally Posted by slipstream444

Courtesy is important. However, it is a two-way street, and you should probably re-read your first post.

Material properties are measured in several ways: elasticity, ductility, strength, toughness, resilience, shear modulus... etc. This forum doesn't need to get into the weeds to understand the underlying principles. However, your innacurate approach required a little adjustment to get the "technical" aspect back on track. Here's some useful reading:

http://www.ndt-ed.org/EducationResou...al/Tensile.htm
This is a good primer on basic material properties. The stress/stain curve is the most illustrative.

http://www.optics.arizona.edu/optome...PTI_222_W4.pdf
This is a little more in-depth - page 21 really breaks down the difference between steel and aluminum. Mild steel is the subject steel - but represents a number of steel alloys very well. Chromoly steel is significantly stronger than mild steel.

Ultimately, it's the combination of these properties that make a material ideal for a given application. I keyed on elasticity for several reasons, but mainly to highlight the fact that aluminum spends very little time in the uniform elastic region, and ultimately spends most of its cycle life past its yield strength and in the ductile region (a point you unwittingly made). Chromoly steel remains elastic long after aluminum has deformed and failed.
When you add heat to this problem, forget about aluminum - it's not the right material.
The shear modulus of aluminum is another problem, especially since your flywheel experiences strong shear forces every time you work the clutch. Ask anyone foolish enough to have run cheap aftermarket two-piece rotors with aluminum hats - on the track. There have been several cases where the bolts holding the two pieces together shear right through the aluminum hat as the aluminum fails. Not good.

Ultimately, the single property that typically trumps all others is material cost. You can't afford a Beryllium flywheel - and it doesn't matter how 'strong' or elastic the material is (about 50% more elastic than mild steel) - it's just too expensive, and a major health hazard if not alloyed (with copper or aluminum, for example).
A chromoly steel flywheel is typically more expensive than an aluminum flywheel by about 10-30%. However, the benefits of using a Chromoly flywheel greatly exceed the bump in cost over aluminum. The piece of mind alone is more than worth the cost difference.

Originally Posted by LeonV

I saw this coming from a mile away, hence why I'm trying to keep the discussion practical. I can respond to your post and keep this going forever, but cleary it would be a waste of my, and your, time.

Instead, I'll skip that, and once again ask for any evidence that backs up your point. So far, I have a data point which backs up my statements as well as billman's possible explanation as to why he doesn't recommend Aluminum flywheels on S2000s. All I've read has been engineering conjecture. There has been not a drop of hard, real evidence from your side.

We can get down to the atomic level as to why something is better than something else, but ultimately, the only thing that matters is real world performance. A good engineer understands this.

Originally Posted by slipstream444

Cheers - I saw your blinders and ego from even further.

Okay - how is this for practical: a 5-year service life for a flywheel sucks. Is that simple enough? A flywheel that chews through clutch discs because it's made of an inferior material and warps - that sucks too. Perhaps you haven't pulled this transmission and gone through the headache of changing out the clutch and flywheel. It's not fun. Having to re-do the process because the flywheel is screwed? Double not fun.

Beyond all the water I've put in front of you - the pain I just mentioned would be enough for most people with even a borderline intellect.

I've had my chromoly flywheel on since mid 2004. I believe I had it installed with 18,000 miles on the car. My car has over 72,000 hard driven miles on it at this point - and the clutch and flywheel have operated flawlessly. 8 years and almost 55,000 miles. I wouldn't even think of changing flywheels. In fact, I'll be having my transmission replaced with a custom built one by Puddy Mod racing this spring. There's nothing wrong with the clutch, but I'll change it out because the trans is out. I'll take pictures of the flywheel and have the machine shop measure if there's any runout - I'll let you know how that works out.
As smooth as my clutch engagement is - I seriously doubt the machine shop will have to do anything but clean the friction surface with one very light pass - just to make it clean for the new clutch.

I believe Billman and I have the exact same setup: Comptech chromoly FW, ACT HD PP, OEM disc - and many more miles on the setup. And I can assure you: His car gets driven!
Ask him how he likes it.

Originally Posted by LeonV

Fantastic, I'm so glad that your setup works works for you.

I think you're having trouble seeing the forest through all those pesky trees. This is hilarious, I'm not the one with the blinders here...

If you would've just said that you don't like Aluminum flywheels because of a possible issue with service life, that would've been more acceptable. But no, you stood up on your soapbox touting how an Aluminum flywheel is going to explode into pieces as soon as you start the car. Don't switch up your argument half-way through just because you've realized that what you've been saying all along is pure dogmatic conjecture. Thanks for your input on this matter, I think we're done here.

Originally Posted by slipstream444

Wow - you're not so good at the basic communication thing. You first ask to avoid the whole engineering "masturbation" thing... while smugly asking for an engineering explanation. Then you ask for a "practical" explanation (as if engineering isn't practical enough), and I revisit the very evidence that CONTRIBUTING members and guests have provided... and you then say I'm changing my story. And FTR - I never stated that an aluminum flywheel was going to "explode"... only that I have read articles that have discussed catastrophic failures of aluminum flywheels - and is therefore a genuine possibility. Possibility does NOT = certainty. It's science... look it up.

Here's the problem - you opened your mouth and were served your foot. You obviously didn't and still don't know what you're talking about, and you are now all sad because you have egg on your face. Stop bitching and instead try to learn something. You defend your position like a liberal - it's annoying and it shows. Try this thing called facts next time and you won't get your feelers all hurt.

I have never changed my "story" - I've only laid out (neatly I might add) the information so simple that even the lowest common denominator should go: "gee, that makes sense". The only explanation is you don't want to find reason - you want fairy dust and rainbows. Not going to happen here bub. This is what we call a "technical" forum. You need to go to the "fairy dust and rainbow" section of S2ki.com.

Originally Posted by LeonV

Funny, this is exactly how I feel about your replies... I'm compelled to keep going.

To the contrary, you've provided absolutely no evidence. It's still conjecture. Facts? I've given you the facts, as in empirical evidence. Not "it's true because I say so." Great, you regurgitated a bit of engineering theory. That doesn't get you any closer to proving anything without hard evidence. You kept harping on how Aluminum is prone to failure, "the material will fail over time due to micro-fractures in the aluminum". Where have you proved this, beyond belligerently demanding that you're right? Jeebus, I admitted that I used the wrong term, it was a long day. Get your mind off of ductility, or elasticity, or Young's Modulus, and understand what the end-goal of this is.

Here's the problem, what you've laid out doesn't make sense. Sure, it's something to bench-race about but it's not helping you beyond that.

At this point all that's going on is this thread is cluttering it up with garbage. "Let's see who can pee farther." Clearly, you plan to keep thinking you're right and drag this on ad nauseum, instead of actually processing what I'm saying. If you have a problem, then send me a PM. This is not helping anybody.

FYI, you're breaking S2ki rules.

may not post content which is political in nature or express political ideogy or beliefs. This is not the place to post your own Mein Kampf. This includes religious theology and beliefs.

Originally Posted by slipstream444

Actually, I have provided plenty of evidence - that you refuse to recognize, to include scientific references from respectable sources - that's academic.
I have provided anecdotal evidence from more than one respectable member in this very post string - that you refuse to recognize. Those are first-hand reviews worth listening to.

And since you have flatly failed to provide any information worthy of merit to this discussion - you default to the "that isn't fair" argument - further proving my previous "political" point, and the fact you should have left this discussion a long time ago. Please do.