Pinch may have been a poor choice of words.
Restriction on the intake is better description.

Also, my criticism of buying a variac might have come off harsh.
You won't be sorry owning it. It's one of my most versatile test tools.
It just seems not suited for use in the final design.

I wholeheartedly agree! And no, I did not think you harsh in your input. I'm here to learn and possibly be a part of this active community.

Variac is a fine piece of equipment, alas, I have no current use for it!

I simply came at my problem from the wrong angle.


Curses, foiled again.

 

There is no relationship between ultimate air flow and start voltage because there is no air flow during start. The motor will start as hard as it can just because the rotor isn't turning. You're also missing the basic fan laws.
CFM2/CFM1 = RPM2/RPM1
Static pressure2/static pressure1 = (RPM2/RPM1)squared
HP2/HP1 = (RPM2/RPM1) cubed!

My Blower Fan: http://www.grainger.com/product/DAYTON-Blower-1XJX8?s_pp=false

I'm figuring current Static Pressure of the system @ .81 W.G.

With a square footage of 5 square feet at the intake surface of the filter, I need an output of ~100 CFM for my application.

Which is 500 CFM at the face of the HEPA filter. I add 20% to that for the increasing Airflow resistance to allow for long term use.

Does that add up?

 

Words not making sense. 100 CFM/5 square feet = 20 CFM/square foot. Maybe you meant, "1000 CFM"?

I picked up, "600 CFM" from an earlier post, so, 600 CFM/5 square feet = 120 CFM per square foot.

Even if I'm paddling in the wrong pond, you can see how the math works.

Trying to choke this fan down to 600 CFM is going to require a properly made intake gate. Trying to run it at 1000 CFM is within its specifications (which makes me a lot more comfortable).

ps, you could build a zero voltage switching control to turn your Variac on by using an opto-isolator, maybe part # APT1231