M90 Rotor mod

Slysc

Registered User
I'm thinking of gettting a set of M90 rotors drilled down through the center at their thickest section from one end to the other. The hole would be about an inch in diameter or the biggest diameter hole that would leave 3/16-1/4" wall thickness. I think that it would reduce the weight of the rotors by about 1/3 and therefore take less HP from the engine to turn them. I spoke with a shop who said that it is feasible and they gave me a price to do a set of rotors.
I also have an idea about how to check the balance of the rotors after they are drilled to make sure that the drilling hasn't taken them out of balance.

Does anyone think this is a good idea or is it crazy talk?
 
You know what I think on the matter. If the rotor shafts were dimpled with a drill in a lathe it would make rebalancing them a lot easier.

Jeff
 
would doing that reduce or increase sc exit air temps? i would think it may reduce it some because the rotors would not radiate as much heat.

no one has ever tried this- i say go for it. you might find the next breakthru since the mag 3.

but then again the rotors might warp themselves from not having enough metal solidity to withstand internal case heat.

just something to consider- i still say try it, those m90's are a dime a dozen.
 
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Dan,

Reducing rotating mass is always good when accelerating an object, but I would be very concerned about rotor deflection at high speed with high boost/load. From what I've read the existing rotors can get as much as .002 delfection and thats the reason for the .004 clearance from rotor tips to the case.

Making them hollow would most likely reduce the rotor rigidity and cause additional deflection. I also question wether reducing the rotor weight will result in any power gains. From what I've read, the unloaded blower only requires 1/2 HP to turn it and when under max load around 65 HP. So, It's not like they are free to spin faster if they were lighter, the main HP draw is from moving the air against a restriction (the motor).

David
 
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I don't think you could drill through the entire lobe from front to rear. Wouldn't the incoming air charge be drawn inside the lobes and then seep through the other end where they mount to the gear pack/plate? Unless you are talking about drilling the lobe from the gear pack toward the back of the blower, but not breaking through the other side of the rotor. But this might make the rear of the rotors heavier to where the bearings fail quicker?

I'm sure you are onto something if you wanted free HP. So i say go for it. However, it sounds like the cost in durability might not be one that I would be willing to trade.

Micah
 
I think that the rotors would be less likely to deflect because they would be under much less stress. The centrifucal force of the mass of the solid rotors must be huge. Lighter rotors would not have as much stress at high rpms. If the deflection is from the force of the air, then your right, they would flex more. The screw type compressors have hollow rotors.

I may just have to be the guinea pig and see if my blower desinigrates if I want an answer to this question. Unless anyone else wants to be the test pilot??

I wonder if the 1/2 HP spec that you read was the amount of energy that it takes to keep spinning the rotors once they are at speed. It would make sense because they have inertia and it wouldn't take much energy to keep them spinning without load. But accelerating them may be a different situation. The stock pulleys turn the blower about 2.9 times per engine revolution so taking car through the gears, you are accelerating the blower 3 or 4 times in the 1/4 mile and you are accelerating the blower from 7200 rpm to 15600 rpms each time. In my case, I am spinning the blower 4 times for each engine RPM and I shift at around 6200 and go through the traps in 4th. So I would be accelerating the rotors from 12000 to 25000 rpm 4 times in 12 seconds.
 
You drill them, and I'll be the guinea pig :D

Seriously, I am awaiting the new engine, and will be bolting all my boltons to the old engine in ordrer to get the tune close, and to figure out how to tune with the wideband and eec-tuner. SO if I break something oh well....

I am in the middle of porting my blower case, and using some aluminum filled epoxy to buildup the center and outter areas.... So that blower is already being experimented with....

My quesiton, is how will you accurately drill that far while maintaining balance???

What does your shop want to do this???

Wouldn't this be expensve, as an accurate jig would have to be made???
 
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Dan,

I bought the ESM titianium input shaft for the same reasons, and according to the dyno and my times on the track, the considerably lighter shaft didn't do squat.

David
 
Micah brings up a good point. I was planning to drill from the back of the rotors where they are exposed through as close to the front as possible without drilling into the front plate that they are attached to. I wonder how the air would respond at the inlet to the rotors with holes in them.

The shop want's $300 to drill out a set of rotors. They would jig them and assure accuracey of the hole. They said "I can drill the hole exactly how you want it but if the thing blows up when you try it out, we're not responsible." :D
 
Hey, ... I just noticed that I have a green dot next to my ID and Micah has a blue one. What does that mean?
 
The Ti driveshaft from ESM is a waste IMO, because it’s not very heavy to began with. If it was teamed up with lowering the rotor weight then it might be worth it. The rotors on the other hand weigh exactly 4# each. Here are some numbers I came up with based on the numbers stated here and what I remember. As I recall the rotors are 6” long. Although the amount of metal removed would be longer than 6” because of the 60* helix in the rotors (as far as I can tell).


Steel drive shaft .75 X 10 = 1.25#

Titanium drive shaft .75 X 10= .7204#

1.25-.7204= .5296 weight loss from going to a Ti shaft from a steel shaft.

Aluminum 6061 1” X 6”= .4626

Aluminum 7075 1” X 6”= .4768

.4626per lobe X 6 lobes = 2.75 total weight loss

I don’t know what grade Al the rotors are so it could be higher or lower.

The Rotors being open at the inlet end might be an issue, but they might not be an issue because of the speed the rotors turn. Not sure on that one.
 

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I think RPM falloff would be enhanced.

Less inertia due to lighter rotors would help to quicken decelleration. That would be a bonus for the 5spd guys, wouldn't hurt the auto drivers feelins either!

'bird

ps: Jeffro mah livin' breathin' everluvin' mentor...looky what I done did for a Saleener >>>>
 

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J57ltr said:
Flipped the fill plug and cut back on some of the support or is that a negative?

Jeff
Yep, flipped the filler because it's inverted on the Saleen but didn't mess with the support ribs if that's what you're askin'. It was for a S231 setup with a 94/95 style Super Coupe blower. Had rubber gaskets between the inlet plenum/blower inlet, also between the blower outlet/adapter plate. They were a joke, squished out into the airstream like crazy so I deleted the inlet gasket and trimmed the one on the outlet. Bearing plate didn't have gear shrouds either, maybe the rotor pack was a GM item? Ported the snot out've it too, betcha he likes it!

Hey, wanna drive LOLA to the Shootout?

'bird

PS>>>>> Slysc, sorry about the momentary hijack!
 
At a minimum the holes being drilled like you describe Dan, might make a god aweful howl. But maybe that would be cool. Or maybe the pressure building inside the rotors would cause fatigue. Or maybe it would equalize pressure on both sides and reduce deflection. I dunno...there's only so much you can do by just thinking about it. But I at least like to think of almost every possible scenario so that you are surprised as little as possible when things turn out different.

How the heck do you drill with that helix though? That's gotta be tough.

Micah
 
Drilled rotors

Sly Ive told you a thousand times already


Just go for it
Stop second guessing yourself
You have alot of good ideas its about time you start trying them out



Just my 2 cents
 
I've never looked at the internals of a blower so I dont have a good visual. But if I am understanding corectly couldnt you fill the whole up or insert a rod of a light weight composite? I guess this would take away slightly from the weight advantage but help keep rigidity and take care of the airflow concern. Might even make it easier to balance them by allowing you to add or take away the filler material. Could someone post a pic to show more of what you are proposing?
 
Micahdogg said:
At a minimum the holes being drilled like you describe Dan, might make a god aweful howl. But maybe that would be cool. Or maybe the pressure building inside the rotors would cause fatigue. Or maybe it would equalize pressure on both sides and reduce deflection. I dunno...there's only so much you can do by just thinking about it. But I at least like to think of almost every possible scenario so that you are surprised as little as possible when things turn out different.

How the heck do you drill with that helix though? That's gotta be tough.

Micah

The rotors are set so that they are drilled straight through. It will have to to be drilled at an anlge so that you are not drilling through the face of the lboes. Hardest part is holding them and making sure the drill doesn't walk as the hole is being bored. I really doubt that they can be drilled without rebalancing them. But you won't find out unless you try.

Jeff
 
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