When we built our Trans Am’s...
When we built our Trans Am’s 467ci in the early 2000s, we used an aftermarket single-plane intake manifold, square-bore carburetor, and a long-duration hydraulic flat-tappet camshaft. We recently decided to change directions, and installed a factory dual-plane intake manifold and Quadrajet to improve street manners. While these components had a noticeable effect, a cam swap gave it the largest attitude adjustment. So how much did the cam affect engine output? Read on to find out!
A camshaft's primary task is to open and close the intake and exhaust valves at specific points of crankshaft rotation, and small specification differences can have drastic effects on an engine's attitude. A cam designed to allow for 6,000-rpm performance will usually idle rough and make a typical vehicle laborious to drive in normal situations. While low-speed street manners may be less important if going fast is the goal, the best cam for a street-driven application is usually a subjective compromise of strong performance and tolerable street manners.
Our Pontiac engine rebuilds generally feature such factory-issued components as cast-iron cylinder heads, a dual-plane manifold, and a hydraulic flat-tappet camshaft with specifications similar to one of Pontiac's performance grinds. The approach rewards us with excellent reliability, driveability, and performance, while maintaining original appearance. And because of their reasonable cost and ease of installation, we can try another flat-tappet cam if the initial selection doesn't live up to our performance or drivability expectations.
To measure the cam swap’s...
To measure the cam swap’s effects on engine performance, we took our Trans Am to C&S Dyno Shop in Omaha, Nebraska. After a complete tuning session, it peaked at 355 rwhp and 402 rwtq on the company’s Mustang chassis dyno with the No. 2043NHL camshaft, cast-aluminum 455 H.O. intake manifold, and modified Quadrajet. When factoring the driveline loss, the engine was producing about 450 hp and 500 lb-ft at the crank.
We deviated from our usual plan when building the 467ci for our '76 Trans Am. The engine was fitted with an aftermarket single-plane intake manifold and carburetor, and a long-duration camshaft to improve its high-rpm potential. We were willing to tolerate its boisterous low-speed attitude to achieve the desired performance level, but after
several years in this configuration, we decided to tame the 467ci slightly. The easiest and most cost-effective way to change its demeanor is to replace its aggressive flat-tappet camshaft. Follow along as we document that process and measure the results.
Assembling the Combo
When assembling the drivetrain combination for our '76 Trans Am several years ago, we wanted a high-performance engine that produced around 500 hp, and ran and drove as well as it could. A '74 code-YY 455, which had been bored 0.030-inch, was the foundation of our buildup, and Chuck Willard of Willard Auto Machine (WAM) in Omaha, Nebraska, resized the nodular-iron crankshaft's rod journals to 2.2 inches and lengthened its stroke to 4.25. Total displacement measures 467 ci.
We selected a Nunzi’s Automotive...
We selected a Nunzi’s Automotive No. 2042NHL camshaft for its 232/243 degrees of 0.050-inch duration, 0.490/0.500-inch valve lift with 1.6-ratio rocker arms, and 113 degrees of lobe separation. It’s designed to produce strong full-throttle performance, while offering excellent low-speed street manners when using stock-type components. It retails for about $250 and is available directly from Nunzi’s Automotive.
A pair of round-port No. 197 455 H.O. cylinder heads were shipped to Nunzi's Automotive in Brooklyn, New York, where owner Nunzi Romano modified them to improve airflow. Knowing that our Trans Am would be primarily street driven and the already high-flow intake port would provide strong top-end charge, Nunzi maximized low-lift airflow to promote strong throttle response and low-speed performance.
To complement available airflow and help us reach our performance goal, Nunzi recommended his No. 2043NHL hydraulic flat-tappet camshaft, featuring 244/252 degrees of 0.050-inch duration and 0.500-inch valve lift, an Edelbrock Torker II intake manifold, and a Holley 950 HP-series four-barrel carburetor. Based on similar combinations he's built for other customers, he estimated that our 467 was capable of generating 475-500 hp and 500-plus lb-ft of torque with proper tuning. We also added a five-speed manual transmission and 3.73 gears to maximize engine acceleration.
A camshaft swap is a fairly...
A camshaft swap is a fairly involved process that requires partial engine disassembly. After draining the coolant system and removing the engine accessories, intake manifold, and timing cover, we were able to extract the existing camshaft and install the new unit. The replacement was inserted into the block, and its valve events were verified using a camshaft-degree kit from Comp Cams. Since we already featured a step-by-step cam swap in a previous issue of HPP, we decided not to repeat it here. For that story, log onto the HPP website at www.highperformance pontiac.com/tech/hppp_0709_pontiac_comp_cams_camshaft_swap/index.html.
On the street, the Trans Am's lumpy idle let everyone within earshot know that a far-from-ordinary 455 was under its hood. We spent a great deal of time maximizing idle quality and low-speed street manners by adjusting the Holley carburetor and HEI distributor. Even with the long-duration cam, the car drove exceptionally well and its docility was impressive. Matting the accelerator, however, unleashed a near-500hp beast that happily pulled to 6,000 rpm without a hint of submission.
Back To Basics
After nearly 10 years and several thousand miles, the Trans Am's lumpy idle and deep rear-axle gearing began taking its toll on the driving experience. It just wasn't as much fun to drive on the street as it had once been, and it wasn't safe or practical to wind the engine out to 6,000 rpm in each gear. Driving in traffic meant continually shifting gears to keep the large-cube engine in its happy range, and that roused its healthy appetite for 91-octane fuel. We began searching for reasonable ways to shift engine power downward into a range that was more practical for normal street speeds.