Since a Pontiac V-8 is a pushrod engine (instead of being an overhead cam design), it afforded us the opportunity to explore a different rocker-arm ratio and determine its impact on power. As built, the Mule enjoyed Comp Cams full roller rocker arms with a ratio of 1.65:1. The stock ratio is 1.5:1 on Pontiac V-8 engines except for the Ram Air IV, V, and SD-421 engines, which used 1.65:1.
With the more aggressive rocker arms, the engine made just under 492 hp—stunning results for a mill that is able to produce that output on 88-octane Rocket Brand gasoline. It did not even require premium, let alone race gas. But being the hotrodders that we are, we are never satisfied—we always want more.
To this cause, we decided to see how the Mule would like a little less rocker arm (a lower numerical ratio). This might fly in contrast to conventional wisdom where bigger is usually better, but we had some bench racing theories that we wanted to test. More on that logic later.
As an aside to this, when the rocker-arm ratio is altered, it’s usually done on a production-style cylinder head such as our 6X castings by moving the pushrod cup closer to the pivot point of the rocker. If you were to measure accurately from the pivot center point outward to the pushrod cup, and then measure from the pivot to the end where the valve stem rides, you will see the difference. A rocker that is 1:1 would be equal in length from the pushrod cup to the centerline of the pivot, and from there to the valve stem contact area.
 The Comp Cams full roller rockers in 1.5:1-ratio are the same color red as the 1.65:1
The other area we wanted to explore was the phase of the Comp Cams bumpstick. According to the cam card, the intake centerline was 106 degrees of crankshaft rotation, and Comp instructions specified installing the cam at 106 degrees, the straight-up position. A quick review of cam logic establishes that as the number goes numerically lower from the intake centerline, the cam position is advanced. In contrast, as the value goes numerically higher than the centerline, the cam is retarded. During the build of the Mule, Craig Wise from RaceKrafters Automotive Machine installed the cam exactly at the desired position of 106 degrees. This was confirmed with a degree wheel.
Thus our plan was as follows: Install Comp Cams 1.5:1-ratio full roller rockers (the same model rocker, just a different ratio), at first on the exhaust valves only, and test; then we would fit the 1.5:1 rocker arms to the intake valves too. This meant that both valves would have the 1.5:1-ratio rockers in lieu of the previously tested 1.65:1-ratio. Depending on the results, we would keep the rockers that made the most power and then alter the cam phase.
 Here is a 1.65 on the intake with a 1.5 on the exhaust.
With the timing chain the Mule had, there were four positions to advance and retard the cam timing manufactured into the crankshaft gear of the cam drive. The cam can either be straight up (at the intake centerline), or advanced and retarded in 2-degree increments for a total of 8 degrees in each direction. This allowed a total range of 16 degrees—8 degrees advanced and the same amount retarded.
Cam phase or position usually follows a steadfast rule: Advancing the cam will improve bottom-end power at the sacrifice of high-rpm output. In contrast, retarded cam timing softens the bottom-end and increases the output at the upper rpm range. Some engine-builders like to advance the cam from the ideal position when the engine is new, since wear in the timing chain will cause the phase to retard, the logic being that the engine will self-compensate for wear by slowly retarding the cam timing to a straight-up position. As with any theory, you can chose to accept it or reject it, but there is validity in that concept if the engine is going to stay together for many years and be used in a street/strip car.