writer: Randall D. Allen
photographer: Randall D. Allen
Hobbyists and pros build race engines to make the most power possible within the constraints of a budget and the design limits of the motor. For all the power that they produce, a keen eye must be kept on efficiency as well. Proper piston-ring seal is paramount to getting the most out of any engine.
Since the factory PCV system is not used on most race engines because it's less effective than on a stocker, positive pressure in the crankcase builds as engine rpm is increased. The result is pressure on the underside of the piston on the intake and power strokes, which reduces efficiency by offering more resistance to the piston's downward movement in the bore. It also places more stress on the piston rings, thereby reducing their seal capabilities and increasing the chance of blow-by. If that weren't enough, high crankcase pressure also forces oil to evacuate through any seal it can breach. On Pontiacs, the rear main seal, valve covers, and oil-dipstick tube are usually the first to seep.
The addition of a vacuum pump to remove the positive pressure in the crankcase and introduce a few inches of negative pressure (vacuum) can increase power production and improve the seal of the piston rings and all those places where oil used to leak.
There are three common vacuum-pump methodologies on the market today; header/collector aspiration vacuum, electric vacuum pumps, and belt-drive vacuum pumps.
Header/collector systems work well on open-headered cars but generally only pull about 1-2 inches of vacuum from a race engine. Mufflers, now mandatory at a great many tracks in the country, can render this system ineffective as even minor backpressure from the exhaust system will drop the pumping efficiencies to almost zero.
After an inventory of the parts, the first order of business is to remove the lower crankshaft pulley from the engine. In this case, the alternator belt is removed and a 1/2-inch socket is used to pull the four crankshaft-pulley bolts. A crankshaft drive mandrel (left) designed to be bolted to the front of the lower pulley drives the pump. The crankshaft drive mandrel is drilled to support either three- or four-bolt harmonic balancers. | 
Set screws are used to secure the pulley to the mandrel, but before using Loctite and a final tightening of the screws with an Allen wrench, it's highly recommended that you first mount the evac pump so the pulley can be slid back and forth, lining it up so that the drivebelt runs true. | 
The supplied 4-inch pulley is attached to the crankshaft mandrel after slipping in the pulley keyway (not shown). |
Electrical vacuum pumps are available and easy to install but can't pump enough volume to produce more than 2-3 inches of vacuum.
From an effectiveness standpoint, a belt-driven vacuum pump provides more vacuum to relieve the crankcase pressure, thus eliminating oil leaks and allowing the piston rings to seal better. Of course, there are downsides. The pump has to be mounted so that it can be driven off of the crankshaft pulley, bringing into consideration packaging constraints that presently will not allow the factory GM air-conditioning units to remain unless custom brackets are fabricated.
According to David Butler of Butler Performance, "For street vehicles that see routine highway miles or spirited weekend-driving duties, owners should definitely retain the factory PCV valve and standpipe with a breather element to reduce the chance of oil leaks if the use of a vacuum pump is not a viable option.
"For aggressive engine builds that feature long strokes, high cylinder pressures, or elevated rpm potential, an Evac Pump Kit is a great way to stop oil leaks and pick up a few extra horsepower. To eliminate oil leaks on a Pontiac, we like to see between 5 and 10 inches of vacuum with a maximum of 14 inches. Some oil mist inside the engine is critical to ensure proper lubrication of the parts that don't have direct oil flow such as the wristpins.
The Butler kit comes with 3 feet of braided hose to attach from the pump to the breather tank, so a suitable location within that length must be found for the tank. Since the '65 GTO test car didn't have inner fenders to provide an easy mounting solution, the owner fabricated a metal bracket for the passenger-side framerail and bolted the Moroso catch-can bracket to it. | 
Pump installation begins by placing the pump's two-bolt aluminum bracket up against the passenger-side cylinder head and threading in the supplied 3/8 x 3 1/4-inch bolts and washers. The bolts are then tightened securely with a 9/16-inch open-end wrench. | 
The 1/4-inch bolt underneath the water pump on the passenger side is removed in order to mount the evac pump's slotted adjustment arm. A spacer is placed behind the arm, and the supplied bolt and washer are slotted through the arm and secured with a 9/16-inch wrench. |
"By designing custom brackets to fit either a modified Ford-style vacuum pump or a Moroso pump, we've created an easy solution to the issues created by too much crankcase pressure. In addition to solving the unsightly oil leaks, by reducing crankshaft pressure the intake manifold charge isn't contaminated with oil, and the additional ring seal consistently produces measurable horsepower gains. On a typical 500-horse engine, the modified Ford-style pump used in our standard kit generally creates 8-12 hp on an engine dyno while the Moroso pump gains 15-25 hp."