BrianCunningham

Is there a graph that shows how much HP & Torque it takes turn turn a blower at various RPM and BOOST #'s

Looks for S-trim and T-trim to be specific

I know I can get fan curves from suppliers, looking for the same for superchargers

thanks.

bogor

Well, I dont have a graph but more than 10 years ago the company Autorotor (they are the orginal manufacturer of the Whipple screwcharger) tested my vortech V2 s-trim in their blower dyno. My notes are not very clear but it looks like the blower required 67kW with a blower rpm of 13000 at 1.6 bar absolute pressure (1.6 Bar absolute equals 23psi relative to vacuum and about 8.5 psi relative to atmospheric pressure).
According to my notes, at 11000 rpms and absolute pressure also at 1.6 bar the blower flowed 656cfm and consumed 33kW (and the air temp increased from +20'C to +90'C).

This means that the blower require in the area of 100 horsepower at max blower rpm (14000), kind of impressive that it can be transferred by a tiny 6-rib belt.

BrianCunningham

Thanks

And, yes, that is pretty impressive!

dizwiz24

Im confused on something (thank you for the translation from metric to english units - the USA still uses english units)....

You mention 14000 rpm blower rpm. Thats slow.

You sure you have that number right?

My procharger p600b spins up to 55000 rpm or so (I dont have my spreadsheet handy, so I might be off a little). It has a max-rated blower RPM of 60000 rpm - I just checked that in its owners and manual.

BrianCunningham

I believe that's the drive speed not the impeller

bogor

Correct, this is the speed of the input shaft. The internal gear ratio of the V2 is 3.6 so 14000x3.6=50400 rpm on the impeller (max rpm according to Vortech is 50000).

BlowerWorks

CFM1/CFM2 = RPM1/RPM2 = (SP1/SP2)1/2 = (BHP1/BHP2)1/3

NOTE: the 1/2 and the 1/3 are raised - I do not know how to do. 1/2 = raised to the 1/2

bogor

Maybe I'm slow but what does SP and BHP stand for ?

BlowerWorks

The formula I posted is for centrifugal fans.
SP = static pressure, i.e., boost in psig. BHP = brake horsepower.
Simply put and the advantage to a centrifugal blower over a positive displacement blower is the power to operate. A centrifugal requires almost no power unless moving a lot of air. Hence no matter the RPM the power to drive is nill for no flow (light throttle). However once you open the throttle the power climbs as a cube relative to flow (CFM). So say you are cruising at 100 MPH (i.e. light throttle) maybe the blower sucks off a HP or 2. Then you stomp on it and go to max accel - well the centrifugal blower jumps to 50 then 100 then to 150 HP sucked off the crank !!!!!!!!!!!!! If you cover/close the discharge on a centrifugal blower at max RPM (i.e., close the throttle) the power to spin drops to zero (well almost) !!!
On a positive displacement blower under the same conditions the power to spin would max out and thus the need for a by-pass valve.
Each style blower has its' advantages and disadvantages. Your choice depends upon your application - like track vs. street vs whatever ?
greg

Tom400CFI

This part, I don't "get". If you have your throttle plate ahead of the blower, and you close that, inlet pressure drops (you have a vacuum). How is there a load, when the blower lobes are rotating in a near vacuum?

BrianCunningham

This is making me want to stick a pressure gauge before the throttle

Of course the only time the blower will be spinning fast with the throttle closed will be under braking.

humm... that explains my belt wear issues!

BlowerWorks

Good question - I don't know ! All I do know is that a positive displacement blower needs a true by-pass (usually a valve between the blower discharge and inlet.)

Tom400CFI

Thanks for being honest. I much prefer that to a made-up answer.

BrianCunningham

The pump is working to pull a vacuum

There's also mechanical losses from the gears

BTW you take the belt off a Roots blower it will freewheel and it will still run

The belts currently off my Vortech, and the car drives fine, the power is just down.