What I got out of churning that speedtalk thread is that the port velocity during testing is very important and should be matched with what it is in an actual running engine. Of course it takes high depression/high pressure to get the velocity that high on a flow bench. It's pretty obvious that flow bench test depression/pressure needs to be much higher than I previously thought to get the port velocity even somewhat close to the levels it is in running engines.

If the exhaust port average flow is only 6% of the peak flow (from a book Panic is reading) it would take a tremndous amount of test pressure to get the flow bench port velocity close to what it is in a running engine. You would have to start measuring test pressure in HG or psi.

No wonder some head porters say they are barely scratching the surface.

What are you going to use for a blower in your new bench?

Have you thought about computerizing your new bench?

That would eliminate the 120" manometer - you would need a tall shop for that thing.

What is the suction limit of centrifugal blowers anyway?

We have some "exhausters" where I work that will pull 26" hg, and lots of CFM. These are a centrifugal design not a roots type blower, they would be very smooth.

I wonder how a big diesel turbocharger would work if you spun it with an electric motor? Probably fine for pressure but how good for vacuum?