[tikiklubracing]

I see, at the race track, all ways to mount evac sys. The "cleanest" I've seen is to drill and mount them to front of valve cover and not to the top. Use 90 degree Russell, Earls or equal bulkhead fitting and run the pass. hose down and under timming cover. No welding with this method, but seal it good. It's really clean man!

BIGGERISBETTER-15 yrs in NHRA tech ret.

[Tom Vaught]

Quote:

"The device in the passenger valvecover, is that the relief valve you can buy through Jeg's? What kind are you using, Moroso's? So are you saying to NOT use the mandrel drive and use a larger pulley to make more vacuum (12-14") and let the relief valve bleed off excess pressure? Where did you get your valvecovers, IA?"

Most Vacuum pump systems work the same way as flow
benches. If you have a big hole on the inlet side the pump(s) will create very little vacuum. On a
flow bench you close off the air bleed circuit and the test pressure (vacuum) goes up. With the Vacuum system Bruce has a calibrated spring would keep the bleed almost shut during idle conditions (so high vacuum with minimal pump speed). As the pump speed increases, the valve opens farther and will maintain the same 12-14" of vacuum throughout the speed range of the engine. It is actually a negative pressure in the system with the valve controlling how much negative pressure is in the crankcase. Because the pump is belt driven and the bleed and pump are matched to each other, it is fairly easy to calibrate. An electric pump system will have high vacuum at low speeds but will quickly run out of volume at high rpm. You may need two pumps to pull proper vacuum at high speed with the second pump triggered off rpm of the engine. Tom V.