PTS Flowbench Forum

Hello. I started collecting parts for a flow bench to test 50yr old 750-1172cc 4cyl 2V racing motorcycle cylinder heads. Expected range of intake flow at max lift is:

75cfm @ 10” to 110cfm @ 10”
125cfm @ 28” to 184cfm @ 28”
142cfm @ 36” to 208cfm @ 36”
164cfm @ 48” to 241cfm @ 48”

I’ve acquired 4 Ametek 114787 vacuum motors for the project.

My intent has been to be able to test at multiple test pressures. I had a bunch of notes set aside detailing the presumed depression capacity of the bench given the details above, but I managed to lose track of it in the move(and it’s been a while).

Would someone mind taking pity on me and give me a idea as to what I should be able to accomplish with this equipment given my desires and motor selection? Or guide me to the related formulas to figure it out myself again.

FWIW, a have a dedicated 200amp shop panel so power supply is not an issue. Plan was to run 3 of the motors with tight sealing scupper valve FWIW.

Thank you.

George

Hi George, welcome to the Forum.

The total pressure that the motor(s) need to work against will be the test pressure, plus the 16 extra inches developed across the measurement orifice at full rated orifice flow.

So at 28 inches test pressure the motor sees 28 + 16 = 44 inches.
The Amtek chart says 68 cfm at that pressure differential for one motor.
Four motors will produce slightly less than four times that, the reason being that the motors fight between each other for air on the intake side, and tend to rob each other slightly of air. It depends on how close the motors are together, so its not possible to nail down an exact figure for that effect.
Anyhow, expect very slightly less than 272 CFM flow at 28 inches with four motors running.
That 44 inches also hits right at the peak of the efficiency curve, so its an ideal motor for a "normal" flow bench.
Maximum air for the fewest possible amps at that point.

Going up to a test pressure of 36 inches, we need 36 + 16 = 52 inches from the motors.
Amtek say 54 CFM, so expect a bit less than 216 CFM from four motors.

At 48 inches test pressure, its 48 + 16 = 64 inches.
The motors are really going to suffer against that high a test pressure, and efficiency will be quite low. Difficult to say, maybe 30 CFM per motor.
So a tad less than 120 CFM maybe ?
Not a snowballs chance in Hell of reaching 164 CFM with only four motors. Even six of those motors may struggle and still fail to get there.

Also, be aware of the massive extra structural stresses on the flow bench at higher test pressures.
If you work out the force in pounds per square foot of panel area, it all starts to become pretty frightening for a bit of glue and a few wood screws, especially in blow mode.