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turtleman
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PostSubject: Are your s/c rotors too heavy?   Thu Feb 14, 2013 2:18 pm

http://www.stiegemeier.com/lwr.html

Just came across that searching something. whoa!
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PostSubject: Re: Are your s/c rotors too heavy?   Thu Feb 14, 2013 2:42 pm

Well my cat is now out of the bag then. I have a jigg setup for doing this to m62 rotors. and can do other sizes too. Just starting the bore on my test rotors.

Stieg did this awhile ago, and like anything stieg sells, its alot of hype and much monies. As much as he blasts "patent this" and "patent that", he holds no actual patent for it yet which I would suspect is because it’s been done for ages for watercraft supercharged applications. He didn't invent it or come up with it. It’s a proven method of improving performance on blowers. Also they have been avaible in AU for awhile before he made his. So the only thing he can patent is the method he uses to put a hole in the rotors. Everything else has tons of evidence of prior use.

For watersport they don't usually bother capping the ends, and in testing shows a 70 deg drop in outlet temp.(I really couldn't tell you why. open ends has cooling airflow? less mass is less force on the bearings so they don't heat? less heatsoak in hollow rotors?) Also you can spin the rotors faster without rotor flutter since there is less weight overall to start going out of whack. Add the outlet temp drop and better spinning characteristics to the less energy required to spin a lighter mass and the gains are pretty substantial.

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PostSubject: Re: Are your s/c rotors too heavy?   Thu Feb 14, 2013 2:55 pm

This is genius. DUH! who's going to be the first to bore the M90's rotors?!
BORED AS F&CK

" Are your s/c rotors too heavy?"
They are now!
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PostSubject: Re: Are your s/c rotors too heavy?   Thu Feb 14, 2013 9:16 pm

i can donate a test gen V m90 rotor pack if you want to try it out karma?

I'd be down for a lighter rotor pack. Also wonder if leaving the ends hollow effects the sound.

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PostSubject: Re: Are your s/c rotors too heavy?   Thu Feb 14, 2013 10:50 pm

Hmm. Hope it works, but I'm hesitant to do this. I read the Steigmeier page and the benefits aren't so convincing.

"...spin a Eaton Rotor Pack to unheard of levles for higher boost (23#)"

So how does lightening the rotors make the blower that much more efficient? 15 lbs is about the practical limit for roots blowers, but I hadn't realized it was because of rotor mass! My blower is turns SO easily by hand, a 3800 V-6 can get them spinning no problem - it's the boost pressure that causes the engine to work. How does reducing rotor mass help with that? Wonder why Eaton doesn't know about this?

"...also increase the torque."

Engine torque? Has this been measured? How much?

"life of your supercharger will be extended as you will be taking load off the bearings and seals"

Is supercharger life even an issue? My blower has survived 257k miles with only a single coupler replacement. I've even dunked the snout bearings under water, and my blower is still at 100%. These blowers are near indestructible as-is.

The real problem I have is this: what happens to a superheated rotor spinning @ 15-20k RPM? I am thinking quite a bit of stress. Now, what happens when you remove 60% of its mass? Again, why didn't Eaton make the profile thinner to begin with?

Lastly, do they strip off the Teflon coating for free?!! Yikes!

Sorry, I'm gonna sit on the sidelines for this one. Good luck!

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PostSubject: Re: Are your s/c rotors too heavy?   Thu Feb 14, 2013 11:37 pm

..couldnt testify i ever heard of tis one?! looks cool as shit tho!
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PostSubject: Re: Are your s/c rotors too heavy?   Fri Feb 15, 2013 12:45 am

I'm kinda hangin with AA here. Strictly speaking, lighter rotors would be a good thing but I don't see how it would do what these guys are saying and also not have ill affects. Still interested though
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PostSubject: Re: Are your s/c rotors too heavy?   Fri Feb 15, 2013 10:20 am

That’s what I meant about hype. I've noticed that most of anything Steigmeier offers is over hyped. You have to take the claims with a grain of salt.

However, I've found that for the most part their tricks are based at least on a grain of truth. It’s just in how you interpret it. For example, they say that one of their ported blowers will make more boost than someone else's using the same pulley size. Boost is great, but the grain of salt comes when you figure out that they replace the rotor gears with a set of 4 that basically overdrives the rotors just like a pulley drop would. It just does it right inside the snout. So it’s not a lie that it would out boost a similar SC with the same pulley, but the portrayal is a bit of a misdirection. And the grain of truth is that turning the rotors faster in ratio to the engine makes more boost.

For lightweight rotors, I'd disregard their claims. Since they claim the highest hype on every product they sell, you need to take the whole lightweight rotor thing in context with how they hype their other products. So to see if they are worth it, info needs to be taken from other sources. Those sources can be hard to find since its Steigmeier who shouts loudest about it. Most of what I've found though does indicate a fairly substantial benefit. Mostly taken second hand from the Australian sites where they tried it ages ago, and from the racing boat scene.

Quote :

"...spin a Eaton Rotor Pack to unheard of levels for higher boost (23#)"

So how does lightening the rotors make the blower that much more efficient? 15 lbs is about the practical limit for roots blowers, but I hadn't realized it was because of rotor mass! My blower is turns SO easily by hand, a 3800 V-6 can get them spinning no problem - it's the boost pressure that causes the engine to work. How does reducing rotor mass help with that? Wonder why Eaton doesn't know about this?

Don't over think this. Under the hype, the grain of truth is that lighter rotors CAN be spun to a higher RPM before starting to flutter. Which technically could mean more boost. BUT your mind went to efficiency, as it should. The reality is that you will still be limited by the heat maps of your particular blower. It can only move so much air, with so much heat. The above is just a general claim with a slight truth and your mind sticks it to something. That’s marketing in action.

Quote :

"...also increase the torque."

Engine torque? Has this been measured? How much?

I'm not sure about this one. My guess is that a light rotor gives the perception of torque in that it starts spinning more readily. It will also take less torque from the engine to maintain speed at boost levels. Sort of like the extra torque found with the m62. The rotors are much lighter and it belches out boost with less draw on the engine(at low levels, this tradeoff goes right out the window once boost pressure increases.) I also suspect their "torque" gains showed up on their "blower dyno" which runs on a giant DC motor at around 90-110HP IIRC. Especially with their geared overdrive snout, that dyno's results would be squewed in favor of the change for ANY rotational weight loss. The bottom line is it can't be really that significant.

Quote :

"life of your supercharger will be extended as you will be taking load off the bearings and seals"

Is supercharger life even an issue? My blower has survived 257k miles with only a single coupler replacement. I've even dunked the snout bearings under water, and my blower is still at 100%. These blowers are near indestructible as-is.

Again a slight grain of truth. Technically less mass to get out of wack will be better for the blower. But, as you say it really doesn't matter. I could drop a heatsink on top of my blower and claim its better. Technically it would be right, but it’s a raindrop in an ocean.

Quote :

The real problem I have is this: what happens to a superheated rotor spinning @ 15-20k RPM? I am thinking quite a bit of stress. Now, what happens when you remove 60% of its mass? Again, why didn't Eaton make the profile thinner to begin with?

This is the one that can really only be decided through real world testing. My experience and gut says that even a 1/16" is plenty around the bore since the forces are rotational and the air pressure along the face really wouldn't put that much pressure on it. Anything we do for "extra" performance can be argued to cause stress and lower the life of parts. From what I've read the boat racing guys do this as standard on their blowers. Is it going to be safe to run for 15+ years on a daily driven car? I doubt it. Is it just as safe from failure as the bunch of other things we do to our cars? I rather think so.

And Eaton not doing it in the first place... Well, comes down to manufacturing. Trying to bore out a rotor that has a 60 degree helical twist in it so that the same material is taken out evenly by each lobe is crazy hard. I'm using a pretty advanced milling machine that can do the calculations as well as using a dividing head. Eaton wants something decently easy to produce that will last the lifespan of the car. Our mission goals are a little bit different in what we want out of it.

Quote :

Lastly, do they strip off the Teflon coating for free?!! Yikes!

They do that to most of their rotors. Yeah. I have a set of uncoated rotors for my test because I've been messing with alternative rotor coating as well.


So I feel that reading between the lines there is something here. But IMO it’s not worth paying someone to do. I'm trying it because I can. I have the facilities. And for some reason I can't seem to leave the damn m62 alone. As far as doing a set of m90 rotors, I might, but the coating would be the thing. I would be hard pressed to bore them and not be wary of the coating stripping away starting at the holes. If I did it to an m90 I would need to find alternative coating, and in the case of the Gen V I don't think anything I could source would be as good as the stock coating.


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PostSubject: Re: Are your s/c rotors too heavy?   Fri Feb 15, 2013 11:17 am

All good points. Thanks for clarifying. More questions:

What exactly is flutter, and how does lightening the rotors relieve it?

On the torque issue, one might assume a heavier rotor would help more than hurt because of inertia - the same way a heavier flywheel results in better engine torque. Just saying...

Regarding durability, they say they re-balance the rotors after boring. What if they don't get that right? This would be a durability compromise that didn't exist before, since Eaton balances them correctly from the factory.

Also - and this is my biggest peeve with this mod - who decided that removing 60% of the rotor mass was acceptable, and how did they arrive at this conclusion? I'd like to see the R&D on this because my guess is somebody picked up a cutter and said, "this will work."

Where is the FE analysis that shows a hollowed out rotor is just as strong and immune to deflection and/or fragmentation spinning at 20k+ RPM? What happens to someone's blower housing, intercooler or engine if such an event were to occur? Does Steigmeier assume responsibility? I don't see any guarantees on their page. All I can find are examples of poor sentence structure and grammar errors that lead me to believe these guys aren't the sharpest tacks in the box.

But I hope it works. I may have mine done of it proves safe - I won't be the guinea pig though!

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'98 SC Riviera • 268k miles • 298 HP/370 TQ • 0-60: 5.79s • ET: 13.97 @ 99.28 • 4087 lb • 20.1 avg MPG • Nelson Ledges Lap: 1:30
3.4" pulley • AL104 plugs • 180Ί t-stat • FWI w/K&N • 1.9:1 rockers • OR pushrods • LS6 valve springs • SLP headers • ZZP fuel rails
KYB GR2 struts • MaxAir shocks • Addco sway bars • UMI bushings • GM STB • Enkei 18" EV5s w/ Dunlop DZ101s • F-body calipers
EBC bluestuff/Hawk HP plus • SS lines • Brembo slotted discs • DHP tuned • Aeroforce • Hidden Hitch


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PostSubject: Re: Are your s/c rotors too heavy?   Fri Feb 15, 2013 11:21 am

i dont think our S/Cs will ever experience "flutter" they just dont put out enough power. maybe if the engine went thru a $10 thousand dollar rebuild, maybe.
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PostSubject: Re: Are your s/c rotors too heavy?   Fri Feb 15, 2013 11:56 am

AA wrote:

On the torque issue, one might assume a heavier rotor would help more than hurt because of inertia - the same way a heavier flywheel results in better engine torque. Just saying...
This is what I was considering. Definitely an interesting subject! Someone be a scientist and conduct experiments!!!
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PostSubject: Re: Are your s/c rotors too heavy?   Fri Feb 15, 2013 12:06 pm

Reducing rotating mass does not create more power, but it will very slightly reduce 'accessory drag'. Theoretically it will allow you to increase revs quicker. Unfortunately, this does nothing except maybe make a dyno curve look a little higher. It has a negligible effect when it comes to moving 4000 lb down the track any faster.

If you are making a full drag race motor and every ounce counts, you can consider it. But you'll be breaking other parts long before the .6 oz of material removed from the SC rotors is going to make any difference. Besides, that's less weight over the front wheels for the slicks to connect with, and we all know what effect 60' times have on the ET.

Changing the gearing, now that's a different story. Useless, IMO, when you can change pulley sizes to the same effect. I suppose if you reach the level where an 8-rib pulley with a wrap kit is still slipping, then you might consider a gear overdrive. But then you'll be adding rotational load from the additional gears.
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PostSubject: Re: Are your s/c rotors too heavy?   Fri Feb 15, 2013 1:04 pm

Rotor flutter is when the rotors begin or try to flutter away from each other in the bore. We have forces acting on the outside of the lobes against the SC casing from the air that gets shoveled around the outside and out to the outlet. As boost increases we start to see the PSI of boost pushing back from the plenum against the flat faces of the rotors. Some of this force gets offset by the air trying to push back up between two rotors with their rotation. But you still have a high pressure zone under the rotors trying to force itself up. Since the sides are still actively driving air down the result is the center wants to lift and split the rotors away from each other. Most susceptible to this is the needle bearing end, since there isn't the room for larger bearing at that end. Hence why the most replaced bearings are the needle ones.

The idea of a lighter rotor being better is because there is ALWAYS a tiny bit of flutter going on. Since there are 3 lobes sending the air in pulses the air pressure and forces on the two rotor lobes will also pulse which causes the minute flutter. (More of a vibration really.) A heavier rotor means the peak RPM you can spin the rotor at before issues is a bit lower. A light rotor can reach a higher RPM before seeing the same vibration and eventually rotor flutter. Picture a pager vibrator motor with a heavy weight vs a light one of the same size and shape. We know one shakes more. Its not intuitive, but an eaton blower rotor isn't a spinning flywheel. The forces acting across it makes it to always want to shake(and slide backwards in the bore, but that’s another issue altogether.)


The torque, I was really just wondering aloud. I agree there probably isn't any. That’s why I offered that it is the illusion of more torque by seeing the rotors begin to move faster, and an illusion by way of how they test SC's on their "blower dyno"


Rebalancing the rotors... yeah. I don't believe for a second they do anything of the such. What would you balance? You can't take anything off the outside and there is no reliable way to remove material in small bits from one fin at a time like balancing a car tire. The RPMs are way too high to do something like that. I call shenanigans on the claim of "rebalancing" them. Checking how they spin.. sure, but rebalancing.. no.


And yeah. I wouldn't make any of the bold claims they are or even sell such a thing without more backing it up by way of real world time proving it safe and more numbers. But that’s why I just mess around in my own shop with my own things to break. smile


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PostSubject: Re: Are your s/c rotors too heavy?   Fri Feb 15, 2013 2:34 pm

Agreed, there will always be slight vibrations as the spinning rotors deal with pressure zones building and falling, plus balance issues at higher RPMs. Although lighter vs heavier rotors may move the RPM at which the vibrations become harmonic/in sync/creating flutter to a different RPM, it would take a physics lab to find the exact RPMs. To say lighter = higher RPM is not really verifiable either. The harmonic/structural integrity of the rotors will change, that's for sure, but how much and at what RPM is nearly impossible to predict without some very advanced modeling software or a very advanced lab to test in.

How can you prove that your rotors are fluttering?
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PostSubject: Re: Are your s/c rotors too heavy?   Fri Feb 15, 2013 3:06 pm

Our rotors do flutter in stock state. Though is it from failing needle bearings? You can see the evidence of it in the scores on the bores and on the tips of the rotors. They also load backwards in the pack due to their angle and the manifold pressure. Again, worn blowers show this in the scoring that occurs when they have been REALLY over spun. Every blower I’ve pulled apart exhibits some wear that would indicate the rotors are trying to flutter. I suspect Eaton also knows this and that was just another thing to add their list of reasons for increasing the twist in their TVS design. That and the extra 4th lobe both work to remove that.


Fortunately we are all just armchair scientists here. Not like we have a business or anything that wants to sell something like this. smile

I'll do up a set of rotors for the m62 and spin the crap out of them. I'm already way outside the rated RPM range of the blower, so if bored m62 rotors survive at its "hyper" rpm the m90 should be pretty safe. Maybe I'll try a set of m90 ones too. That blower at least lends itself easily to popping in and out a stock to modified pack without too much trouble.


Everything aside we come back to rotor coating. If you bore rotors they need re-coating or it will all flake off. Even at best case scenario, the gains will never offset the loss of rotor coating. (Unless the powerboat guys are right about a 70 deg drop in outlet temps of bored vs not. But I only have that second hand, have to run temp measurements to validate it.)

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