As an engineer who works with pumps and also the owner of an 68 Firebird with a 455 prone to overheating, I was amazed to read that the vane to plate clearance was as high as 0.25"! My God, how did that pump pump anything! A typical clearance for this style of pump would be 0.030" and that is for a much larger pump. I think clearance should be tighter than even 0.1", but I guess if it works.........
This variation in clearance maybe explains what has always puzzled me - Pontiac designed these cooling systems to cope with Death Valley ambient temps, fully loaded vehicles, towing, etc., but now they cannot handle gentle cruising about town! Maybe this summer I will be able to wait in the drive-thru lineup without watching the damn temp gauge.
By the way, pump flow goes up directly as RPM and demanded pump power goes up as RPM *cubed*, so pump power demanded at 5000 RPM is theoretically eight times the power demanded at 2500 RPM. But it is not that simple in an engine cooling system because as RPM (and flow) increases, the temp rise of the water decreases, so T/S closes down and throttles the flow, which reduces power demand of pump. The power demanded by the pump goes up as RPM rises but not as rapidly as RPM cubed. So a T/S will reduce pump power demand across the board but especially at higher RPM. The worst situation for power loss seems to be running with no T/S at high RPM, i.e. pump is pumping full bore through an unrestricted cooling system. This may be why some of the dyno tests show water pumps consuming 10-15 HP at max RPM.
Pump suction pressure is 15 psi or whatever rad cap is set at, but I have no idea what pressure rise across pump is. Pressure increases as RPM squared so it probably gets pretty high at 5000 RPM, as I experienced when my heater core exploded while overtaking somebody. Say pump discharge pressure gets up to 50 psi. At a flow of 48 GPM (what the SBC was originally designed for at 4400 RPM), the power demand calculates to be about 2 HP. So I don't think a pump run with a T/S (especially a 195 T/S) takes much power.
To get demand of 10 HP requires 100 psi discharge pressure and 100 GPM flow. Maybe that is what these high performance pumps are putting out.
Sorry for the long post, but this subject combines two of my favorite topics!
Malcolm
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