Yes 540's with M1-SC chargers. Why wouldn't you think they made any boost? I've run this set up for years and always pushed out 5 psi at the plenom. They actually dynoed @ 930 @ 5500. I know Procharger doesn't rate them that high but never had an issue until now and all we did was a valve job.

So I ran smaller props over the weekend to get more rpm and spin the Prochargers faster. Got it up to around 4800 rpm and the boost gauges actually show about 5+ inches of vacuum! How's that even possible?

I guess not. I thought they were a 700HP supercharger. Good to know, that opens up options.
Have you borescoped a few cylinders?
Thanks

To me the only way thats possible at all (provided that the boost/vacuum gauges are both accurate) Is that theres something internally wrong with either charger, or theres a boost leak in both systems. If your building the engine RPM which your are you should most definitely be building boost. The weirdest thing about your problem is your having the issue with both motors. What did procharger say when you contacted them? How does your setup work on yours? As in airflow... charger, intercooler then into the plenum? Have you tried pulling one of the connections and verified positive airflow?

https://cimg8.ibsrv.net/gimg/www.off...a6150b5b6a.jpg

Pulled tubing off just before intake and there's definitely positive airflow there.

Have you pulled the pulleys off each charger and inspected the keyway? Long shot but maybe slipping under load/high rpm if keyway is wore/key broke?? Very odd and confusing problem for dam sure, Almost at a loss and makes zero sense as to why it would be pulling a vacuum at high rpm when theres positive airflow at idle

Damn !

https://cimg5.ibsrv.net/gimg/www.off...6544b27cf3.gif

If it we’re mine, I’d swap the chargers, inter coolers and ducting between the 2

See post 37!

5+" of vac at WOT?! Sounds like blower is getting in the way.

Could there be slippage at crank pulley?