Originally posted by DennyW
Yes, you have to match the power valve to the intake vacuum, plus, you have to make sure you have a hole that goes to the vacuum source from way up there.

Ok, but I'm still not understanding.

You source the vacuum from the intake under the blower, right?

And then you have to drill the Holley carb so you can set up vacuum to the power valve?

It sounds reasonable and a little tough to do.

Seems too that just plopping the Holley on the adapter plate on top of the blower would work ok.
That would be under a vacuum at low speeds and once the engine/blower were spun up, the vacuum at the adapter plate would drop close to zero and would allow the power valve to open.

The advantage I can see with an intake sourced vacuum to the carb would be that the power valve would probably come in quicker when the intake vacuum rolls over to pressure when rpm's come up.