I've typed three replies to this thread over the last two days and thrown them all away in the interest of avoiding a flame war. Since Larry has softened his position somewhat, I'll jump back in.
My compressor is a 4.5HP rated at 6.2CFM at 90PSI with a 20 gallon tank. I just connected it to the pump, and the pump to an empty gauge set - no car involved. The compressor running continuously was able to keep the input pressure at about 85PSI. The gauge registered 28" of vacuum. I think there must be some disconnect between Robainair's claim of 75PSI input pressure and 29.7" max vacuum. With this result, I'm skeptical about your compressor's ability to keep up. Maybe the CFM rating is more important than the 3HP rating, but regardless it will probably run continuously.
Maybe you should look into renting a vacuum pump and then buy the venturi only if rental efforts are unsuccessful.
82 300D Euro
12 Honda Pilot
14 Tesla Model S
Former MB: 86 190E 2.3, 87 300E, 80 240D
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