How do I model a supercharger rotor?

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aonemarine

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Gail, you give me too much credit.... Im still learning, just like many following this thread :) Thank you for your time helping us out.
 

MachinableWax

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I thought they were screw type compressors?? Maybe i need to take a better look at them.
I have heard them referred as roots blowers over the years, but I looked it up, and this is wrong. They are twin screw. My mistake.
 

aonemarine

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I have heard them referred as roots blowers over the years, but I looked it up, and this is wrong. They are twin screw. My mistake.
Im still trying to figure that one out, they are high helix rotors designed to pull air from the back of the case and push the air forward a bit before dumping it out the bottom, but there are also 8-71 blowers that are 3 lobe high helix rotors that are draw thru type. Question is would the eaton rotors work as a draw thru supercharger if the case was altered? Ive been trying to look up the twist on the 8-71 high helix rotors but havent found it yet....still searching...
 

aonemarine

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NEW ENFORCER SUPERCHARGERS
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Maybe?? I would love to see a breakdown of the case to make sure they arent doing anything strange with the flow path...
 

MachinableWax

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When you say back of the housing, do you mean the area of the s/c housing that is closest to the distributor when mounted?

I would think that the air flow would go straight down, and into the LIM.
 

aonemarine

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Pulley side = front.
Basically, they made a custom case but kept the admission point at the rotors the same as the eaton.
You can really see it in the link i posted above.
 

stevehuckss396

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Tring to figure out how to model the hypocycloidal and epicycloidal curves of a supercharger rotor in alibre cad. This is really making me pull my hair out!
Steve H, have you managed this with your model blower??
Im trying to design a 3 lobe rotor for a blower with a 71ish cid displacement...
I seem to be a little late to the party. I didn't use any fancy math, just trial and error. The radii on the lobes needs to be smaller than the radii in the valleys. The difference in radii depends on the clearance you want. I made by rotors with a .005 clearance so the outside diameter was .010 smaller than the bore and the radius on the nose was .005 smaller than the radius in the valley. The perfect fit is so no rotating parts touch so the pair get installed and geared together. Then they get blued and checked for wear spots. Alot of hand work to get them tight but not touching.

I basically took two bores on a known center (for gear mesh) and designed a rotor to fit. Sorry I cant help more than that.


Machining the lobes
[ame]https://www.youtube.com/watch?v=wF3fiEoAVKA[/ame]


Machining the valleys
[ame]https://www.youtube.com/watch?v=jhOgIGKxnC0[/ame]






 

aonemarine

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If you look at pictures 6, 8, and 9 in the gallery of this link http://www.superchevy.com/how-to/0610ch-magnuson-superchargers/parts-cost.html it looks like the only function of the back side of the housing is for the boost bypass valve. It looks to me that the air flow goes straight down, from what I can see in those pics.
From thier description of the housing...

Inside the housing, the air travels from the carburetor to the rear of the housing, then into the inner cleaves of the rotors and out the bottom; this is described as an axial flow.

I think it may be possible to cast a housing that will work (they did). Ill be putting more thought into canabilizing one of the eatons. i can pick one up off e bay for $150.00 shipped. but right now I have a yoda to attend too ;)
 

MachineTom

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Beautiful work on the rotors. Having been inside the blowers of Detroit Diesel engines. The 53 series used a 2 lobe design and the 71 series used a 3 lobe helix design. Both rotors had 3 lands at the top of the lobe, similar to the way a drill is relieved at the lands.these had a close clearance of about .003"to the matching root. if I recall, When fitted to automotive engines blowers had the lands replaced with teflon strips, so to run near zero clearance.

I had an Eaton blower on my Honda motorcycle, That was a two lobe design. That was a Beast.
 

mattb.351

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Ive been trying to look up the twist on the 8-71 high helix rotors but havent found it yet....still searching...
This site reckons the angle for a 6-71 is 30 degrees. I guess the 8-71 would be similar.

http://victorylibrary.com/mopar/blower/blower-GMC2.htm

I guess the limiting factor on the upper helix angle would be that that the back edge of the rotor has sealed against the housing before the front edge opens into the plenum. As you are probably aware, they did the twist to lessen the pulsing effect that supposedly happens with the straight rotors.

How would you machine the helix on a manual mill? Or will you be doing straight rotors? You could design the housing to allow the trailing edge (near the back) of the rotor to be closed last and the leading edge of the rotor to be opened first (triangular shaped opening) if pulsing was an issue. I suppose there'd be some tradeoff for volume pumped, but you could just design it a little larger to compensate.
 

Badhippie

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Maybe this is something I can help you with I have personally rebuilt hundreds of blowers in my time and btw Machine Tom is correct in his statements. I would think this is where a rotary table would maybe help. But if you think about it wouldn’t you be better off by casting the part first then machining it from a casting. Since you are wanting to do this without A CNC. Also instead of using the old style 2 or 3 lobe rotors. Would it be easier to machine twin screws they are way more efficient then the old style 2 or 3 lobe design in every aspect. If you are wanting the rate of twist for the lobes I probably have that information written down somewhere in my notes.
Just throwing in my opinion which won’t even buy you a cup of coffee
 

propclock

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Just my thoughts. My friend Dwight Giles has a 1/3 scale blown v8
Black Widow. It started to smoke and he allowed me to overhaul it.
On rebuild all internals were perfect , some small scoring on the cylinders. I thought just no air cleaner and many years of running at shows. But a close look at the blower lobes shows they were making
occasional contact, and guess where that aluminum/
aluminum oxide goes. So the gears have to be perfect the machining has to be perfect and then no problem. Otherwise !!!
and another note seal the main shaft, Dwight's had a vacuum leak
and prevented a low idol I used a sealed bearing backed up with a Teflon home made seal.
I think rotors made out of Delrin would be a better choice.
Untested & untried but ??? Whos 2 know.
Just my 1.414 cents worth
 

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