my first bench

[misc.motorsports]

Hello I am new to the forum and in mid process of building my bench. I was just wondering can you use basically any supercharger for the blower on a bench and also do the superchargers really suck hard enough to get good flow out of them? I have a couple factory vw superchargers that I used to run 20psi out of laying around, would one of those work maybe?

[Thomas Vaught]

Probably the easiest Blower to use for a flow bench is a small roots type
blower. That is what GM used in their flow labs for years. a 6-71 GMC
blower. Course they had access to a lot of electrical power and also
GMC blowers from Detroit Diesel. Lots bigger blowers out there today
on the Top Fuel rails.

Because the Roots blower is a Positive Displacement Blower it is easy to
calculate volume per revolution. Some info below:

All Roots blowers basically moved 27.2 cubic inches of volume each revolution PER inch of rotor.

a 6-71 blower has rotors 15" long so 15 X 27.2 = 408 cubic inches

a 8-71 blower has rotors 15" long so 16 X 27.2 = 435 cubic inches

a 10-71 blower has rotors 17" long so 17 X 27.2 = 462 cubic inches

a 12-71 blower has rotors 18" long so 18 X 27.2 = 489 cubic inches

a 14-71 blower has rotors 19" long so 19 X 27.2 = 516 cubic inches

A cubic foot of air = 12" x12" x12" or 1728 cubic inches.

1728 divided by 435 cubic inches = 3.97 so it takes about 4 revolutions
to equal one cfm. 516" would be about 3.3 revolutions.

So if you want to move 500 cubic ft of air in a minute 500 x 4 = 2000
blower rpm. Sounds pretty good until you figure out that the HP to
drive the thing might be 40 hp!

A centrifugal blower will move the same 500 cfm very easily at less hp

Considering that a SF1200 bench will draw about 87 amps per leg of
current you can use some pretty serious SINGLE 220 volt electric motors
to spin the centrifugal blower too.

JMO

Tom V.

[jason pohlman1]

hey guys. got an update on my bench.i found out pretty quick that i did not have enough electric in my garage to support this bench.5hp motor was not enough,so i used a 7.5 hp motor along w/ the 5hp for a total of 12.5hp. it still wouldn't do it.found a good deal on a 25hp 3phase motor but had to keep the bench at a buddies place who had 3phase electric.well that was a pain, having to go for a drive every time i needed to test.so it's back home and i want to use the surplus motors and build a box.i have 100 amp service to the garage and ended up with a 70 amp circuit to power the bench with the 12.5 hp motors.my question is how many surplus motors will 70 amps support?the specs say they use 10-12 amps but i believe i saw a post by bruce where he used 4 of them and they only pulled 20 amps total?i plan on wiring them in gangs so the start up amps can be staged.will 70 amps support 10 of these?by the way if anyone is interested in the 25hp motor are the pro-charger it is for sale.

[thomasvaught-1]

I would think that 8 of the surplus motors would be equivalent to or less than the SF600 bench with 115923 ametek motors.

On the distribution bench (when running) I say 10.5 amps at start-up and 7.5 amps when running open in the air per motor wires at a 110 circuit.

Could be 30 amps per leg x 2 legs or 60 amps draw. The SF bench is wired as 220 and will pull 38 amps. Not a big savings as all of their motors are on all the time even with the speed control.

Say you need 6 motors to do most of the flow curve at 28" so that would be 45 amps total. Only 7 amps difference and less motor wear.

Tom Vaught


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