Some hobbyists believe that different camshafts were used in the '78 and '79 T/A 6.6 engin
Analyzing The ResultsAlthough we regularly use our simulator to predict the effects of different variables or components, we don't always assume the peak horsepower and torque numbers are accurate. However, in this instance, where the program assumes ideal running-conditions with the carburetor and distributor optimized and an open exhaust system, the 260hp rating it generates mirrors the NHRA rating for the '77 T/A 6.6 engine. So we're confident its predictions are accurate.
Upon reviewing the results, we quickly noticed that since the '77 camshafts share the same duration and lift, the two generated similar numbers. But we clearly see the effects ICL and LSA have on dynamic compression and idle vacuum. This might suggest that Pontiac engineers were willing to trade a slight amount of manual-transmission engine idle-quality for more dynamic compression and mid-range torque.
The most surprising result came from the No. 402 camshaft. Factory literature suggests it should fall somewhere between the two '77 grinds. Contrarily, we found its intake duration was extended a few degrees, and approximately 0.030 inch was added to its gross valve lift. The simulator projected an increase of 10 hp without a significant reduction of dynamic compression or idle vacuum. And from this it becomes very apparent that the factory-rated 20hp increase from 200 in '77 to 220 in '78 may not have been from the exhaust enhancements alone.
Additional CommentsWanting to learn a little more about camshaft fundamentals and how they specifically apply to Pontiac engines, we approached retired Pontiac engineer Malcolm "Mac" McKellar and asked for his input. Since McKellar was a driving force behind Pontiac camshaft design, with a few performance cams even carrying his name, any comments he was willing to share on the subject were welcome.
After hearing the specifications, McKellar immediately recognized the retarded ICL positions. He said that generally, a retarded intake lobe tends to shift the power to a higher rpm while increasing dynamic compression and producing a smoother idle. The end result is improved engine efficiency without sacrificing low-end power. We also asked McKellar why the lower advertised exhaust duration of the No. 402 cam did not agree with our 0.050-inch measurement. He noted that Pontiac's advertised duration was an approximate value based on ramp action, and that only original camshaft blueprints contained the answer. He added, however, that our 0.050-inch numbers would accurately indicate any potential performance difference.
Next, we contacted Pontiac performance legend Nunzi Romano of Nunzi's Automotive in Brooklyn, New York. Not only was Romano involved in a number of vintage-magazine road tests and projects featuring T/A 6.6-powered cars, he has likely tuned more T/A 6.6 engines than anyone over the years. Romano says the T/A 6.6 cams were tough to beat when used in original applications, but because of the short valve lift, the T/A 6.6 engines respond favorably to higher ratio rocker arms.
When asked about operational differences between the original applications, Romano said the '77 manual-transmission cam's idle was more aggressive than the '77 automatic-transmission cam. He strongly agreed with our thought that the camshaft was a contributing factor to the 20hp increase for the '78 model year. He went on to say that the '78-'79 cam was definitely more aggressive than either '77 unit, and he felt the later engines seemed to run a little better.
ConclusionSome readers may wonder why the interest in these smog-era camshafts. But only after 30 years in obscurity have many of the unknown details finally surfaced. Only now do we know of the various markings on the T/A 6.6 camshafts, as well as the 0.050-inch duration and valve lift of each. And after hearing comments from two individuals who know Pontiac engines as well as anyone, we're confident that our dyno simulation results provide an accurate idea of how these camshafts stack up.
While the T/A 6.6 engine is considered Pontiac's first attempt at emissions-conscious performance, we also know that it was the company's last attempt at big bore traditional V-8 power. We only hope our recent findings have made this story a little more complete.
The camshafts from the '78 and '79 engines also shared the same identification stamps (left). The only difference we could find was the color code (right). We've found No. 402 cams with both white code and orange color codes. However, because they contain the same valve timing and identification stamps, we're confident the two camshafts are identical.
Special thanks to Dave Hall, Jim Hand, Mac McKellar, Nunzi Romano, and John Witzke for their contributions.
|Predicted Operating Characteristics of the T/A 6.6 Camshafts|
| ||549112-'77 Automatic||549431-'77 Manual||10003402 '78-'79 All|
|Peak Horsepower||260 hp @ 4,100 rpm||261 hp @ 4,100 rpm||272 hp @ 4,300 rpm|
|Peak Torque||360 lb-ft @ 3,100 rpm||364 lb-ft @ 3,100 rpm||362 lb-ft @ 3,200 rpm|
|Idle Vacuum||22.3 inches||21.0 inches||20.5 inches|