More Performing With Efficiency

In Part I of our primer on increasing the fuel efficiency of your Pontiac, we covered the theory of improved mileage. As stated, HPP would then put our hypothesis to the test. Bob Wise from RaceKrafters Automotive Machine originally arranged for the principal of Jones Pontiac-GMC in Lancaster, Pennyslvania, to loan us a late-'60s GTO that he owned. As things would go, though the car was not for sale, someone made him an offer he could not refuse, and our test car was hauled away to a new owner's garage.

Fortunately, RaceKrafters is well entrenched in the Pontiac community, and had no problem lining up another candidate for our exercise. Ed Birchall, also of Lancaster, owns a '69 Ram Air III 400 Trans Am with an automatic transmission. The car is mostly original and in unrestored form except for its engine. Birchall has owned it for more than 20 years, and shortly after taking possession, the R/A-III engine developed a rod/piston noise. Since Pontiac engines were still relatively easy to come by in the early '80s, he slipped a junkyard 400 short-block in the F-body's engine bay and put the original safely in storage. Being a grocery-getter-variety mill with a ton of mileage, it was not as powerful as the factory engine, but it ran well, did not smoke, and sounded excellent. Thus, big power numbers would not be the order of the day.

In 1974, with the implementation of more factory emission controls, the trade organization SEMA, which now stands for Specialty Equipment Market Association (back then it was Manufacturers instead of Market) ran a series of advertisements in hobby magazines such as Hot Rod, Car Craft, and so on. It stated, "A high-performance engine is an efficient engine. An efficient engine is a clean engine." The campaign was meant to erase the bad image hot rodders held in the minds of an ever environmentally aware public. SEMA's statement was prophetic since it can still be employed today, especially when it comes to decreasing the fuel usage of a hot Pontiac.

When we began this journey, we knew our results would be based upon the state of tune of our subject car. Ideally, for demonstration purposes, our sample Pontiac should run well with no driveability issue, but be representative of a typical tune-up a reader would have on their car. If by chance the calibration was perfect on our subject, then there would be no room for improvement.

Since we were unfamiliar with Birchall's '69 T/A, we did not know which category it would fall into. The Trans Am sounded real good and seemed to drive well to the shop, which was only a three-mile ride. Not until we strapped it down on the dyno and started to take some readings would we know if we had a good candidate to extol the virtues of tuning for mpg.

Designing The Simulation
For our results to be credible, a repeatable and accurate test protocol would need to be developed. Actual on-the-road testing would not be an option since there would be too many variables present (wind, traffic, weather changes) and would not allow minor calibration changes to be monitored with accuracy. The use of RaceKrafter's Dynojet chassis dyno would then be the answer, but some modifications to the standard test procedure would be necessary.

The Dynojet is inertia based wherein the drive wheels of the car each turn a drum that weighs approximately 2,000 pounds apiece (a total weight of around 4,000 pounds). In normal practice, the dyno computer uses the rate of acceleration of the fixed mass (the drums) to determine the horsepower and torque at the tires. It is generally accepted that on a rear-drive car the power loss through the drivetrain is approximately 20 percent. Thus, if the drive wheel power is multiplied by 1.20, it will provide a good representation of the flywheel power.