Whether it be a late-model GTO or an early-model Firebird, I don't know of any hobbyist who doesn't want his or her Pontiac running at its best. While significant power increases may require the addition of such components as a long-stroke aftermarket crankshaft, high-flow cylinder heads, and/or a high-rise intake manifold, many times additional performance can be extracted from an existing combination by simply improving its current state of tune.
The carburetor and distributor found on a typical Pontiac V-8 are responsible for feeding the engine a combustible cocktail of fuel and air, and igniting the compressed mixture. Too much or too little fuel and/or inopportune spark timing can result in significant performance degradation. While small changes followed by a thorough road test can sometimes get one close, oftentimes the minute changes required to attain maximum performance must be measured on a dragstrip or dynamometer.
In '72, the Trans Am's standard...
In '72, the Trans Am's standard 455 H.O. mill carried a net rating of 300 hp at 4,000 rpm and 415 lb-ft at 3,200 rpm from the factory. The new net rating system more closely represented actual engine output when installed into a vehicle. Our Trans Am's engine is mildly modified, and its actual output was measured using the Mustang Dyno MD-1750 chassis dynamometer at C&S Dyno Shop in Omaha, Nebraska.
Over the years, we've painstakingly tuned our street-driven '72 Trans Am for maximum seat-of-the-pants performance. While it certainly performs up to our expectations, we suspected that a few more ponies were hidden within-and a controlled testing session was the only way to find them. Since dragstrip testing wasn't a practical choice for us at this time, we opted for a complete chassis-dyno tuning session, which would provide the same result in a fraction of the time. Follow along as our Firebird hits the rollers and is tuned to perform better than ever before.
The Vehicle
Our '72 Trans Am is powered by its original code-YE 455 H.O. engine. Several years ago it was rebuilt to stock specifications by a previous owner. Since then we've made some subtle modifications to improve performance without grossly affecting originality or appearance, including an aftermarket hydraulic flat-tappet camshaft from Nunzi's Automotive in Brooklyn, New York, that features slightly more duration and lift than the original No. 068, reproduction round-port exhaust manifolds with oversized outlets from Ram Air Restoration Enterprises (R.A.R.E.), and a 2.5-inch exhaust system with a reproduction crossflow muffler from Waldron Exhaust.
With continual carburetor and distributor tuning, we arrived at what we felt offered the best part-throttle street manners and full-throttle performance on the street. The Firebird ran and drove extremely well, and while we were confident that we were fairly close to the optimal tune, to date we hadn't ever measured its performance in a controlled testing session, which would tell us just how close we really were.
Shop owner Tom VanVugt loads...
Shop owner Tom VanVugt loads the Firebird's information into the dyno computer. The computer then applies resistance that's equal to vehicle weight on the dyno's roller drum, which represents the load the engine has as it accelerates the car down the road. This feature allows the tuner to provide the ideal amount of fuel and spark a particular engine requires for maximum performance in the real world.
There's no doubt that the dragstrip passes would be great fun, but it's not totally practical since the nearest track is approximately one hour away and the first several passes would be spent establishing a repeatable baseline. In addition to general wear and tear on the drivetrain, we'd likely run out of time before we could find the best settings on a particular day, and that may require one or more subsequent trips. We ultimately decided that a chassis-dyno session was best for us.
The Chassis Dyno
A chassis dynamometer is used to measure the amount of rear-wheel horsepower (RWHP) and torque (RWTQ) that a vehicle transfers to the road surface. Output is measured by placing the vehicle's drive wheels on a roller drum, and it's calculated using several factors, such as vehicle speed and the drum's acceleration rate.
Tom VanVugt of C&S Dyno Shop in Omaha, Nebraska, has been using his company's Mustang Dynamometer MD-1750 chassis dynamometer to tune various cars in and around the Omaha area for the past four years. In his opinion, his inertia-based Mustang Dyno unit is among the most accurate on the market. While the roller drum of some is a simple fixed weight, the Mustang Dyno unit incorporates a 2,500-pound roller drum that uses a power-absorption feature (eddy current brake) to apply a variable amount of resistance on the roller drum that equals the vehicle weight.