How to Choose Cams for a Superchargerby Richard Rowe
There is something of a tendency among supercharger aficionados to place all of their focus on increasing boost. While increasing pressure in the intake manifold can shove more air into the cylinder, that air may well go to waste if the engine itself is not set up to accommodate the blower. After all, pressure does not make power; burning air and fuel does. Picking the right cam for use with a supercharger or turbo comes down to ensuring that the waste gases can get out of the motor as efficiently as the pressurized air goes into the motor.
Determine where you want your power-band to be. Positive-displacement or "Roots-type" superchargers tend to produce massive power at low rpm and taper off higher in the rpm range; centrifugal superchargers (which are really just belt-driven turbos) work only in the rpm range.
Acquire a cam with more exhaust lift and duration. This is quite possibly the most crucial element of supercharger camshaft selection, since the supercharger cannot push more air in if there is already exhaust gases in the cylinder. Most performance cams use more lift and duration on the intake side to pull more air in; you will want to utilize a cam with exhaust lift and duration at least ten percent higher than the intake.
Specify your cam with the wide lobe separation angle to ensure the lowest possible overlap. Overlap is the amount of time in degrees that the intake and exhaust valves are open at the same time, and excess amounts of it can work against your supercharger by allowing exhaust backpressure to negate supercharger pressure while the valves are open. Avoid any cam with more than 30-degrees of overlap.
Purchase a cam designed for use with roller-lifters. This is not a strict necessity; you could go with an old-school flat-tappet camshaft, but you are losing out on horsepower, torque and quite possibly fuel efficiency. A roller-tappet camshaft allows the valves to open and close quicker, which allows you to run a bit less lobe separation while keeping overlap to a minimum. A slightly lower (about one-degree) lobe-separation angle will increase cylinder pressure and low-rpm torque without adversely affecting the engine's octane tolerance or idle quality.
- "Turbo: Real World High-Performance Turbocharger Systems"; Jay K. Miller; 2008
- Comp Cams: Effects Of Changes In Cam Timing And Lobe Separation Angle
- Vortech: Supercharger Support