Anyone increase the speed of their moroso original style 4 vane vacuum pump? Max engine rpm 7500.

currently running a 2.5" on the mandrel and 5" on the pump. That puts the pump at 3750rpm

Moroso has conflicting instructions that say max rpm of 6000 and 6500 rpm

Only other pulley moroso sells is a 4" That would put the pump at 6000rpm

Fighting weak vacuum. recently rebuilt, cleaned, engine smoked checked. Been this way since new

This message has been edited. Last edited by: Nitrous1,

run the engine with the suction unconected from engine,look for pulses from connector

My 4 vane, enhanced version acted same way with 2.5 pulley, would only pull 5-6". Put a 4" on it and would go to 15". I have been running it that way for 4 years, and have had 0 issues whatsoever.

Same here.. "Enhanced" 4 vein. 4" on the bottom no problem... 14.5" Seen it too many times wrong lower and the pump will collect more junk quicker.

More to it than just the pump speed that everybody neglects.
Manifold bolts that are through into the valley, they leak like a sieve. Teflon thread sealer
Poor silicone job on the manifold to china rails.
Poor sealing valvecovers.
Distributor seal leaking.
Poor hone job/ rings not seating. (leakdown)

80% of engine