Watts Shop Performance |
Belt Drive |
When Pontiac introduced its beltdriven overhead cam six for 1965, the world somehow kept turning. Even though th short lived Pontiac didn't single handedly start a revolution, it was one of a growing number of HOC engine designs that utilized a flexible cog belt to drive the cam. The benefit of a beltdrive over a chain orgeardrive is inherently smooth operation that reduces harmonics while requiring less power to run. Add in a cam pulley that is specially designed to allow instant cam phasing adjustments and you have a drag racer's dream. The phenomenon of the beltdrive camshaft on traditional pushrod V-8 began in the early 1980's in Pro Stock where every last bit of horsepower and tuning convenience must be pursued at any cost. Beltdrives haven't really caught on with street cars due to the fact that many systems are mounted externally and are vulnerable to road debris and the elements. Beyond that, priced from $375 to $850, they are expensive and most hot rodders know there are plenty of other ways to get more power for the same money. Among professional engine builders, there are those who swear by the beltdrive for its ease of cam adjustment and there are those who say they have the potential to do more harm than good. On a typical high performance engine, such concerns are of little consequence. So the cam may (or may not) oscillate a half degree- chances are it wouldn't be noticed even on a dyno. But in the ragged edge world of all out racing motors and gnat's whisker piston to valve clearances, a tiny deviation in the careful orchestration between crank and cam action could spell disaster. |
Pros: Absorbs the least horsepower. Many beltdrives are external, so there's no oily mess when adjusting the cam. Easier to install than a fixed idler geardrive. The belt protects valve springs in extreme applications by absorbing vibrations. By far the easiest way to adjust cam phasing. |
Cons: Poor cost / benefit ratio. Specialized cam cover can interfere with stock water pump in some applications. Controversy surrounds the belt's ability to resist stretch in applications where valve to piston clearance is especially close. Limited availability for less popular engines. External models are vulnerable to road debris. |