The success level of a vacuum pump is all relative to the design of the ring package, health of the engine, application and how well the engine is sealed(to the outside world ie... gaskets/seals)
The big gains will be if you take advantage of the vacuum pumps ability by utilizing a very low tension ring package. In this case, the 30-40 horsepower claims out there, may be based on the fact that the ring package used, is just not capable of working well without a vacuum pump. They dyno it no pump, it's a sloppy mess in terms of ring seal, and then they stick the pump on it and it picks up 40 horsepower becuase now the rings are sealed. That's probably a more realistic viewpoint for the big hp claim folks.
But there is some hp in it regardless of the ring package, and with a nitrous engine it really improves oil control.
But that is a double edged sword. Now you have a condition where oil is being pulled from the cylinder, and that includes the pins. If you have a vacuum pump I always tell my guys to keep it unhooked unless you're making a pass... let the oil get up into the pins, let it soak the cylinders good... this has improved the pin bore wear DRAMATICALLY upon teardown, versus just leaving it connected all the time.
If this is a street deal, then put a regulator on it and keep the vacuum at just around a couple inchs.... that will be alright for street duty, and then when you get to the track crank the vacuum up to where you prefer to have it.
So to answer the question, do I recommend one? Always, but keep in mind what I'm suggesting for both a track car and street car.
Chris
