|Watts Shop Performance
| 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.