Lizard928

I am just curious as to the power it takes to drive a 2.2L autorotor SC, and how much it takes to drive a CS (say the Murf unit). Both being run at 10PSI on an otherwise stock S4.

After a fair amount of google searching I cannot find the information.
So I am asking the experts here.

mark kibort

net power will be a function of air flow and pressure. It would be a guess on my part, but I would think both at 10psi, the murf would be 2x the power consumption. (providing one didnt have an greater efficiencies over the other). Generally, ive heard, that whatever the gain in HP, there is another 15-20% going into losses to drive the supercharger.

mk

Lizard928

MK,

I do understand the physics behind it, and that there is a fair portion of looses that go into the driving of said units. But I am curious as to if anyone has any actual numbers for this on the 928.

Cosmo Kramer

Probably the best way to find out would be to dyno the car stock, then bolt on the supercharger and belt drive but don't attach any of the intake piping etc., just some sort of bleed valve on the output side that keeps it to 10 psi at redline. Go dyno it again and compare the results before completing the conversion.

PorKen

"Just buy a 931."

Lizard928

Porken,

Cosmo, that would not work due the the need to be turning the autorotor to really get air through it.

Cosmo Kramer

Correct, that would only work for a CS. There has to be a way to measure the mechanical resistance. I wonder how do they measure how much HP it takes to drive accessories like A/C alternator etc?

Lizard928

To know the answer we need someone with this type of a SC already installed on their car and a sharktuner to tell us how much air the SC setup uses.
This will then give us a very good idea as to how much it will require.

mark kibort

you can measure the resistance of the belt and pulley, and with the alternator, you can measure the output, and work that back through some of the known efficiencies. the alternator is easy, for an emperical test. do a dyno, cut the belt, do a dyno. If you are not charging a dead battery, and the current draw is low, the drain on HP is pretty insignificant. We did eRAM testing like this, and a current drain of 65amps, had little effect on output, but we didnt cut the belt to see what the belt drain was.

mk



i

mark kibort

that might work, but the air flow through the system would be totally different, in that there is already a moving airstream that you are further compressing, so the compressor losses would not be the same.
much of the loss is really pretty straight forward to calculate, then you just add the belt and pulley losses to it and you get the totals. It all depends on how accurate of a number you are looking for.

Put it this way, in real life, the S2000 we race with with over 20psi boost, was able to bend his crankshaft at the nose. this is not belt tension, it is the force to turn the compressor which adds to the radial load during operation. they are estimating 30hp loss, or load, to gain 250hp on top of a 240rwhp 2.2liter engine.

mk

IcemanG17

Colin
I was looking at Eatons website and they have several graphs that show the amount of HP to run vs boost and efficiency...take a look

http://www.eaton.com/EatonCom/Market...Maps/index.htm

blau928

Classified source, sorry..

"The more efficient the supercharger, the less HP is required to drive it and the less engine HP (parastic loss) is wasted. For example: at 14.5psi and 695 cfm, the Eaton 112 consumes 84HP at 13000rpm. The Autorotor 2.1L Twin Screw uses only 58HP (30% and 26HP less) and typically requires 2 less belt ribs to drive. Belt width (6, 8 or 10 rib) recommendations should be left to the supercharger manufacturer. After 12 psi, an 8 rib belt system is recommended."

Based on my research, and dealings with Autorotor engineers yesrs ago when I started to design my SC application, I was made aware that the Autorotor 2.2L can support more than 600RWHP at 19PSI. This has been documented by many in the Ford Mustang 4.6L Cobra circuit.. Some have gone a good deal above that. The 2.8L can get to more than 700RWHP when done properly...

If tuned and setup properly, a 928S4 motor should be able to have at least 500TQ from 2100 RPM to redline.... It all depends on how it is done...

Hope that helps.....

hans14914

Colin,

What are you thinking out? I am sure you already know this, but the bypass valve (when properly implemented) allows for a complete free-wheeling of the screws/lobes of a positive displacement blower. Most modern units, like the Autorotor, Whipple, Kenne Bell, Techno, TVS.... all have around a 1hp loss or drag on the system under a vacuum condition. I dont know as much about CS type systems, but the general principle of the thing (low rotating mass) would seem to dictate a similar type of minuscule loss under vacuum.

So, why would it matter what the load of the SC actually is? If you use airflow and the efficiency charts provided by the manufacturer, you should be able to get a close number to what the output would be under boost.

Its not a direct answer to the question, but I am not sure I understand what relevance the number has in the real world. Perhaps you can explain the position a bit better. Always up for learning more.

Thanks
Hans

mark kibort

Yes, there are differences in efficiency, but is the below comparison for the same pressure and air flow?

blau928

Hi MK,

The test was done at the same compressor speed..... 13K Rpm (shaft input power required to spin the compressor...) The Autorotor flows more air than the Eaton at the same shaft speed, and uses less input power to do it..

There is a bit more to it than just meets the eye, in that the internal pressure ratio of the compressor will also affect the power required to run the compressor... I believe the internal pressure ratio of the 2.2L Autorotor is 1.2

In any case, maybe Colin should elude to what he wants the information for.. It may already available...