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Discussion Starter #1 (Edited)
Learned a bit today, have some "new" thoughts (long post)

I have LOTS of thoughts in here and I'm not sure how to organize them so bear with me.

(note, I made a mistake and used engine rpm as 6700, it was changed to 6200)

I spoke to a tech at Magnuson today and got a little insight on the M62. I asked what the maximum rotor speed for the M62 was and the response was that 14,000 was the reccomended limit for this unit and this number was based primarily on efficency. He said additionally that he has spoken to people that have turned the unit into the 20,000 rpm range but this was done with less than stelar results (blower went boom in one case). Aditionaly he said that turning the rotors beyond 14,000 isnt just a issue with charge air temps, the bearings apparently are suseptible to failure due to extreeme heat in the blower body. One thing he did point out that was interesting is that the blower will eventually "tip over on its self" exceeding what the throttle body and inlet side of the supercharger will flow. Kind of left me thinking just how much was left in the M62.

I know Psi-Fi have been working with pulley upgrades and it will be interesting to see what they come up with. It was mentioned in a previous post that the pulley ratio was believed to be 1.85 to 1. This would mean that the rotors are spining at 11,470 rpm @ 6200 rpm for engine speed. Just for reference the M62 moves 1 liter of air per revoloution so it is displacing:

*11,470 liters of air per min @ 6200 rpm and
*409 cubic feet of air per min @ 6200 rpm

Just for refference there is 28 liters per cubic foot.

Looking into this further using the pulley ratio of 1.85 to 1, I came up with some interesting math. If the motor is opperating at 12 psi of boost at 6200 rpm from the factory (supposidly ECM limmited) then there should be more in the motor. Here's my thoughts:

First off lets figure naturally aspirated flow; cid x rpm x 0.5 x Ev / 1728

Our engines displacement is 122 cid, figuring Ev (volumetric efficency) of an assumed .90, you come up with 196 cfm @ 6200 rpm.

Now figure the pressure ratio; 14.7 + Boost / 14.7

The pressure ratio here using 12 psi of boost is 1.82

Multiplying the pressure ratio and the n/a cfm @ 6200 rpm i came up with 356 cfm. Now upping the boost to 15 psi in there with a p.r. of 2.02 the number jumps to 395 cfm.

Ok, this means the pulley ratio mentioned above is wrong (I think). The correct pulley ratio should be 1.61 to 1 to get to 356 cfm @ 6200 rpm or if indeed out motors are set up for 15 psi and regulated to 12 the pulley ratio should be 1.78 to 1 to get 15 psi flowing 395 cfm.

Now assuming that the pulley ratio is 1.78 to 1 the rotor speed @ 6200 rpm is only 11,036 rpm, far below the 14,000 rpm eaton says is max safe range. 14,000 rpm would be achieved using a pulley ratio of 2.25 to 1 moving 500 cfm of air.

Now, using the above math the max speed of 14,000 rpm should be able to make 23 psi flowing aproximately 500 cfm.

All of the math I used is from maximum boost, granted it is geared tward turbos but the basic math is for forced induction. If somone in the field could please take a look at this to see if it is accurate or if I'm just way off the ball I would certinly appresiate it.

If it is right and we do have a ratio of 1.78 to 1 with the rotor speed at 11,036 @ 6200 rpm engine speed there is a lot of room for improve ment.

Who knows, mabyee I am just dumb and thinking about this all the wrong way.
 

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This REALLY should be looked at if I knew the math I would do it but I'm not sure. However if this is possible this would be AWESOME!!! GOOD LOOKING MotorMouth.
 

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Discussion Starter #5 (Edited)
Sp00ner said:
and dont you think that a volumetric efficiency of 90% in a N/A version of out motor is a bit much?
You might be right, but....

If I drop the Ev down to 0.80 (80%) and re-figure the math using the engine redline of 6450 the pulley ratio drops even more.

Using .80, n/a engine flow drops to 182 cfm, using the assumed 15 spi boost level (again regulated down to 12 spi by the ECM) with a p.r. of 2.02 the flow should be 367 cfm.

This would lower the pulley ratio quite a bit. From 1.78:1 down to 1.60:1. Using the 1.60 to 1 the rotor speed would now be only 10,320 moving 368 cfm.

This also means the pulley ratio would be able to be raised all the way to 2.18:1 to acchieve a 14,000 rpm rotor speed but still capable of flowing 500 cfm. This would be 2.75 times the n/a flow of the engine.

Also, even using a pulley ratio of 1:1 (the same rotor speed as engine speed), the M62 is still out flowing the engines n/a flow using an Ev of .80. The 1:1 flow of the supercharger is 230 cfm compared to the engines 182 cfm naturally aspirated. Even with the Ev of .90 @ a 1:1 pulley ratio it out flows the motor.

I still have no idea if what I am thinking is correct or not, it dose sound promising if it is correct though. :D
 

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Discussion Starter #7
Sp00ner said:
My grasp on your math is strained at best. I see what you're getting at though.
Even my grasp is strained on my math. I have taken automotive math from a couple textbooks and put it all together. I sent Anthony from Psi-Fi an e-mail to see if he or Mark could take a look at it to see if I am even close to being on the right track.
 

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Discussion Starter #9
I would have when I started my brain smoking math but I don't have my car right now. It's being "serviced".

Let me know what you find.
 

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Discussion Starter #10
I went out today and measured the crank pulley and the supercharger pulley and here is what I came up with:

Crank Pulley= 6.51"
Supercharger Pulley=3.60"

Pulley Ratio=1.80:1

I am hoping this is acurate becuase it is good news. This means the pulley ratio only puts the supercharger at 11,610 rpm @ the engines 6450 rpm red line. This also means the supercharger is moving 11,610 lpm or 414 cfm @ 6450 rpm. As noted above the M62 displaces 1 liter per revoloution.
I still haven't heard back from anyone at Psi-Fi, I had sent Adam an e-mail to take a look at this to see how acurate it is. Hopefully they can chime in.

I really hope my math and measuring method are right, if it is this means that the pulley ratio could be increased all the way to 2.10:1. This create a rotor speed of 13,545 rpm @ the engines 6,450 red line. Nearly 500 rpm below Eatons maximum "safe" rpm. The pulley in this case would be 3.10", taking 1/2 an inch off of the size of the current pulley. This is of course if the fuel system could handle it. If not alky is always an option.

Seems there may be some promise of performance in the stock supercharger yet.
 

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MotorMouth said:
I went out today and measured the crank pulley and the supercharger pulley and here is what I came up with:

Crank Pulley= 6.51"
Supercharger Pulley=3.60"

Pulley Ratio=1.80:1

I am hoping this is acurate becuase it is good news. This means the pulley ratio only puts the supercharger at 11,610 rpm @ the engines 6450 rpm red line. This also means the supercharger is moving 11,610 lpm or 414 cfm @ 6450 rpm. As noted above the M62 displaces 1 liter per revoloution.
I still haven't heard back from anyone at Psi-Fi, I had sent Adam an e-mail to take a look at this to see how acurate it is. Hopefully they can chime in.

I really hope my math and measuring method are right, if it is this means that the pulley ratio could be increased all the way to 2.10:1. This create a rotor speed of 13,545 rpm @ the engines 6,450 red line. Nearly 500 rpm below Eatons maximum "safe" rpm. The pulley in this case would be 3.10", taking 1/2 an inch off of the size of the current pulley. This is of course if the fuel system could handle it. If not alky is always an option.

Seems there may be some promise of performance in the stock supercharger yet.

Why do we have to do all the work and calculations?
 

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Discussion Starter #12
loumoll said:
Why do we have to do all the work and calculations?
What do ya mean?
 

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Sp00ner said:
Perhaps you could just ask Eaton what the pully size and the current rpms are.
GM could have adjusted it, and not let eaton know, i wouldn't count it out even though it's unlikely
 

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Sp00ner said:
I was thinking if he had the pully size, then they would know for certain what the RPM of the blower is. I'll give it a shot.

can't hurt, let us know what you find out!
 

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MotorMouth said:
What do ya mean?
That was great effort on your part. It just seems the aftermarket guys should be all over this.
 

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What worries me is the possibility that they already have. In fact, I know this discussion has occured at some point already. I'm just not sure if people had looked up what speed the supercharger spins at, or if they trusted what they were told and were told wrong. To their defense, they are having a hell of a time with this header shipping and all that crapola. Maybe they just want one product at a time, I know that's all I would take. I'm also re-interested because I found a few sites that are selling pulleys for the Cobalt SS. I'm also smart enough to know that a company will sell you tha part that you want, even if it dosen't help ya out. Look at all those $1 Ebay 'chips' and the Tornado!



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Sp00ner said:
Just found some stats on the '04 SC Ecotec. Says the pulley ratio is 1.85:1

Article is a little bit old though.

That puts the rpms of the charger at around 11,933. Sounds pretty low still huh?
wouldn't quite say that, as lowering the pulley size wil drastically increase RPMs. i'd say it's near max at redline, as i've said before, but there is still room for improvement.

also, the max RPMs is shown on eatons website, but it never technically states that 14000 is the max RPMs, that's just where the graph tops out at, and there's only what, 50 degrees of an increase in charge temp between the 12xxx we're at and the max on the chart of 14000
 
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