How many motors for a given cfm/ depression?

[Tony]

Yes, welcome Aldowin.

[John Doney]

So I've been starting to look at vacuum motors and am wondering if I am evaluating them correctly. Recently I have been using the air watt number to gage efficiency and then look at the cfm rating around 44" of water. Is this a good method or should I use a different method? Are there other variables that could affect reliability that should be taken into account? I have seen motor life ratings of around 500 hours, and I could be picky, but this doesn't seem like a very long life ( 20 days of use).

I'm kind of having a hard time differentiating between "good" motors and "average" motors. I'm seeing for the most part, very little price variation. Most of the vacuum motor seem to be around $100-$150 a piece, then jump up to about $200 something.

[Tony]

The CFM rating at 44 inches is the one to judge motor capacity, or how many motors you may need.
The other and probably more important efficiency figure is CFM per Amp at 44 inches.
For 110 volt motors, 4CFM to 8CFM per amp covers the efficiency range to be expected.
For 230 volt motors, expect to see between 8CFM to 16CFM per amp.
And of course cost !

Vacuum motors are typical consumer "made down to a price" pieces of crap, definitely not military/aerospace quality.
But in a flow bench with electronic speed control they will rarely if ever be run absolutely flat out, and that greatly extends the prospective life.

[Malvin]

John Doney Wrote

I'm new here and was wondering if there is a loose relationship between the number of motors put into a bench, and how many cfm can be moved at a given depression. I'm looking to build a bench that can test a big block chevy head of around 400 cfm at 28" of water. I don't see myself needing much more than that.

Any thoughts?

So your real Question here is how many vacuum motors do I need to flow a BBC head @ 28" depression with around 400 cfm ? Right

What type of flow bench do you plan on building ? In my thoughts this does matter.

I can say how many motors it takes to flow this BBC head with my flow bench @ 28" depression @ 0.875" of int valve lift this is a spread port BBC

[John Doney]

I'm building the flowbench per the design instructions included in the pts plans. I just don't know much about these vacuum motors or how to evaluate them overall. Bruce gave me some great advice on how to determine the approximate number of vacuum motors needed, but I'm admittedly a little ocd. And since you guys have been down this road before, I figured I would pick your brains. So I have been seeing airwatt numbers, life expectancies etc. and can't help but want to use all this information to make the best choice I can for my bench.

[Malvin]

The air watts I must say I never looked at that I have found vacuum motor that can pull 23" of H20 with 244 CFM at 47"136 CFM

9" fan http://www.centralvacuummotor.com/Produ ... 892-00.pdf

[John Doney]

Well, I ordered up six of the lighthouse lh2093-240 vacuums. I think this should do the trick for me.

[Brucepts]

Well, I ordered up six of the lighthouse lh2093-240 vacuums. I think this should do the trick for me.

Those motors sit to high for the 8 motor PTS build, Ward has a note specifically stating they work for the larger flowbench design.

They will fit but they are really really close to the front of the motor chamber

[John Doney]

Thanks for the heads up! Yeah I guess I lied a little tiny bit when I said I was doing the build per the plans. I make adjustments here and there as I go. This will be one of those areas I guess . I have to say I'm having a lot of fun building this bench.

[Brucepts]

Thanks for the heads up! Yeah I guess I lied a little tiny bit when I said I was doing the build per the plans. I make adjustments here and there as I go. This will be one of those areas I guess . I have to say I'm having a lot of fun building this bench.

I understand, just didn't want you to have to try and fit those motors in the 600 cfm cabinet. They are spec'd for the 12 motor bench but I don't think you gain much with them. I've never tried them as I do not have a 12 motor bench built in my shop and that design is not for the average user.