FAST on the STREET: The Stage 1 Story

1970 GSX Prototype at the Burbank Training Center. Provided by Dennis Manner whose handwritten notes are on the margin.

Last month we traveled to Michigan and had the opportunity to meet with some very important players in the story of the Buick Gran Sport. We spent an afternoon with Dennis Manner, Powertrain Engineer and father of the big block 400 and 455, as well as the 455 Stage 1 and Stage 2 engines. Dennis gave such a thorough and excellent explanation of the theory and execution of the Stage 1 engine that we decided the only way to do it justice is to print it verbatim. Here, in Denny's own words, is the story of the Stage 1:

"The objective, as we developed the Buick Stage 1 400/455-CID engines, was simply to provide maximum street performance in a vehicle sold from the showroom floor. We allowed no compromise of Buick features- if you wanted air conditioning, power steering, power brakes, power windows or seats, etc, they were available. This was no trick lightweight or stripped-down model, nor were any tinkering changes necessary once you bought it. There were no ifs, ands or buts about it- we optimized the Stage 1 package to move on the street.

Furthermore, we did not compromise the car's street performance so that it would be quicker at the drag strip. For example, a wilder camshaft would have provided more power when running without mufflers at the strip, but it would have reduced power on the street with an exhaust system.

The Buick 455-CID engine was designed to produce high torque durability and power relatively heavy cars, including the Gran Sports, which weigh in excess of 3600 pounds in typical street trim. The Stage 1 was an extension of that philisophy, to enhance the high torque characteristics of the engine, and focus on the automatic transmission for the majority of sales.

Heavy duty cooling and suspension, G-60 tires and Positraction rear axle combinations quickly became part of the package. We retrained the GS cold air induction air cleaner and developed a low-restriction dual exhaust to improve power and provide a pleasant sound while conforming to legal noise restrictions. The power development engine on the dynamometer was equipped with an exhaust system and air cleaner to ensure that our camshaft, carburetor, spark timing, compression ratio and valve sizes were focused toward developing real power on the street. Significant work was done to the camshaft, including the fitment of special valve springs and push rods to ensure clean valve train behavior at 6000 rpm. A higher pressure oil pressure spring was used to ensure adequate flow to the rod bearings at higher rpms.

We selected a 3.42 rear axle ratio on for air conditioning (3.64 for non-air cars) to maximize performance and driving enjoyment with the high-torque engine and G-60 tires. To further enhance street performance, the automatic transmission option was calibrated to allow downshift on demand, all the way back to first gear at speeds below 35 mph. This feature provided exciting acceleration in a rolling situation.

Larger valves with specially machined combustion chambers were developed for the 455-CID Stage 1 engine to improve the air flow characteristics of the larger bore size.

All of this special engineering was targeted toward the basic goal of maximizing total street performance. The axle ratios, camshaft timing, transmission calibration, valve size, exhaust system, fuel and spark all played their part.

It is rewarding to see a classy legend live on! "

-Denny Manner