Vacuum Pumps: Why use them & what do they do?

By Gregory P. Zucco, Owner GZ Motorsports LLC

These are some of the most common questions we receive here at GZ Motorsports from our customers wishing to learn more about Vacuum Pumps and how they can help make more power and make engines live longer. Please remember you can also call us at (270) 856-8890 or email if you have any questions.

When does a Vacuum Pump benefit an engine?

A vacuum pump, in general, is an added benefit to any engine that is high performance enough to create a significant amount of blow-by. A vacuum pump will, in general, add some horse power, increase engine life, keep oil cleaner for longer.

How do Vacuum Pumps work?

A vacuum pump has the inlet hooked up to one or both valve covers, sometimes the valley pan. It SUCKS the air from the engine, thus reducing the air pressure build up created by blow due to combustion gases going past the piston rings into the pan. Vacuum pumps vary in the amount of air volume (CFM) they can suck so the potential VACUUM a pump can create is LIMITED by the amount of air it can flow (CFM). The exhaust from the vacuum pump is sent to a BREATHER tank with a filter on the top, which is intended to retain any fluids (moisture, unspent fuel, air born oil) sucked from the engine. Exhaust air goes to the atmosphere thru the air filter.

So what actually happens at high RPM during the combustion process, and how does a Vacuum Pump change that?

As RPM increases the rings start to get pushed upward on the outer ring edge due to the pressure behind them due to the blow-by build up in the pan, this causes a reduction in ring seal to the cylinder walls, this causes more blow-by. It also causes the rings to "flutter" which further increases blow-by.

The increased pressure in the pan (due to the fact that in a higher performance engine you cannot get all the excess air pressure out of the engine with just breathers (much less engines with PVC systems that are sealed) then PUSHES oil entrained in the air past the rings on the intakes stroke when the engine is SUCKING in air. During the intake stroke oil is also SUCKED past the valve guides. The net result is oil contamination of the fuel (the same way a PCV system contaminate the fuel by sucking oil into the intake), which effectively reduces the octane rating of the fuel. This reduces HORSEPOWER, and on a nitrous or power adder engine can actually burn a hole in the pistons from the increased heat in the chamber due to the faster flame front.

The vacuum pump can reverse every one of these problems by reducing, eliminating or even putting a negative pressure on the engine. The net result is better ring seal, less or no oil contamination, less oil leaks, cleaner oil, longer engine life and MORE HORSEPOWER. An added advantage is your engine builder can use lower friction ring packages because the resulting blow-by is mitigated by the Vacuum pump.

What about the oil pressure loss we are told about?

There are lower gauge pressures typically with vacuum pumps, there are lots of explanations. However, we have information from tests indicating that oil flow is not reduced and that lower oil pressure is a result of the fact that a pressure gauge shows zero at atmospheric pressure, hence unless the gauge is located inside the engine (gauge thinks that is the ambient atmospheric pressure) it will read lower pressure since the air pressure reduction in the pan begins at atmospheric pressure and reduces from that.

There are other reasons, however, one is poor oil returns to the pan are not capable of returning oil as quickly with a vacuum being created starting in the valve covers, causing oil starvation. Also a higher vacuum in the valve covers than in the pan will cause the oil to be SUCKED up through the rocker arms, hence less resistance to oil flow and lower pressure. We suggest installing an AIR BALANCE TUBE between the pan area and a valve cover to help balance air pressure in the pan and allow the oil to easily flow back.

Why are GZ Motorsports LLC Vacuum pumps one of the best on the market

That is easy, compared to other manufacturers, they generally have higher maximum air flow (CFM) resulting in higher potential vacuum, they require much less maintenance and have a much longer life between rebuilds. For these reasons, they perform very well on street driven vehicles, road race cars and boats as well as race only vehicles.

Want to learn more? Read our Complete Vacuum Pump Guide for even more in depth discussion.