It never fails. A guy will spend months or even years dreaming about his ideal engine, and when it comes time to order parts for the induction, the index finger slides to the bottom of the page for that big kahuna camshaft. Or maybe he’s a high-tech guy, and he opts for a pair of huge hair dryers, or a monster blower. In a politically correct world, we’d have to say that most high-performance engines are “vacuum challenged.” Before you know it, you’ve got a dangerous fire-breathing hot rod that just can’t stop.
Craig Chaffers of Classic Performance Products (CPP) explains: “There’s a diaphragm that holds vacuum, and whenever you step on the brake, the diaphragm cavity gets small and it pushes on the brake pedal rod. If it’s an engine that doesn’t produce enough vacuum, the booster doesn’t fill up fast enough and doesn’t apply enough pressure.” The end result is a brake pedal that feels hard, but doesn’t stop the car. If you’ve ever turned the key off and pushed the brake pedal and the brakes don’t work—this is the same thing, only worse, because you’re moving a lot faster. For power-assisted brakes to work properly, they safely need 15 inches of vacuum, and quite often, powerful engines are lacking in this area. “When you have an engine like this,” Chaffers says, “you’re going to have brakes that don’t work very well when they’re booster equipped.”
The performance experts at CPP have seen this scenario a lot, and have developed a vacuum boost kit that is a simple add-on to cars that already have working power-assisted master cylinders. The kit (PN VP612, $389) includes a billet aluminum pump with integral 12V motor and Hobbs pressure switch, hose, fasteners, and an electrical harness. Our 1968 Chevy Nova project car was a top candidate for the CPP vacuum boost kit, since its 400ci small-block was only able to muster 4 inches of vacuum at 900 rpm. That’s nowhere near enough to operate our new CPP four-wheel disc brakes (or any other disc brakes for that matter), so we made the vacuum boost kit our next priority.
Our ’68 Nova is equipped with...
Our ’68 Nova is equipped with a new CPP master cylinder/booster kit (PN 6874BB4-11, $299) designed to work with their Big Brake kit, but it wasn’t able to work any vacuum miracles: For it to work properly, we needed more than the 4 inches of vacuum that our 523hp small-block could deliver at the idle speed of 900 rpm. Check out the cool factory-appearing electronic tach from Shiftworks (PN S517-G, $134.50, www.Shiftworks.com).
Of course, there are other options—like converting to manual brakes or even a pricier hydro boost system—but in the end the cost effectiveness and functionality of the vacuum boost kit won us over. “The next step would be to go to a hydro boost,” Chaffers says, “but there’s a lot more money involved. On a hydro boost you’re looking at $700 without the master cylinder. If you’ve got a good master cylinder and you go with the vacuum pump kit, you’re going to save over $300. Plus, with a hydro boost you’ve got to make a line kit to the power steering box and the power steering pump, so the vacuum pump is simpler too.”
We’re now one step closer to getting Project Nova on the road. Stay tuned to this same Nova channel—next month we’ll be bringing you a really cool story on the Switch Pitch variable-stall Turbo 400 converter from Phoenix Transmission Products.