At the Track
Steve recently changed out the cam in his '70 GTO from a hydraulic flat-tappet to a hydraulic roller, which he advanced 4 degrees. His prior best e.t. was 12.39, and he hoped the new bumpstick would be the guiding force to break him into the 11s. He also wanted to evaluate if his carb jetting was too lean for optimized performance.
For his first pass, he launched at 2,500 rpm, crossed the 60-foot in 1.66 seconds, and laid down a 12.69-second e.t. at 104.83 mph. "The shifter popped into Neutral, which made me lose time," he says.
His second pass produced a more accurate baseline of his GTO's performance. Raising his launch to 3,500 rpm, he clicked by the 60-foot in 1.67 seconds, and tamed the 1,320 in 12.46 seconds at 105.86 mph. "It was a good run, but no better than my old cam," he says.
For his third through fifth passes, he ran with #86/#90 jets in place of his #83/#89s. It brought his time down to 12.43 at 106.68 mph—his best pass of the day.
"The jets helped some, but I was disappointed that I didn't see more from the cam change. I expected it to put me at 11.99 or better," Steve says. "Next year, I'll run the same combo, and I'll experiment with the jets even more, and find the perfect ones for my combo in hot weather. After that, I'm considering building a different combo: a 455 stroked to 496, KRE High-Port heads, and a Holley 1,150-cfm Dominator. I'm hoping that my GTO will skip the 11s entirely and run in the high 10s."
Steve says the Shootout was "lots of fun," and that his GTO "ran good, except for a few tire spins."
Brent also came to make tuning changes to his carb to tackle the day's high temperatures. "I hadn't made any changes to [the carb] in the six years since I first set it up," he says.
After a solid shake-down run that earned him a 12.40/105.33 timeslip, he returned to the track for a baseline, launched at 2,000 rpm, crossed the 60-foot in 1.62 seconds, and tripped the beams in 12.37 seconds at 105.23 mph. "That's exactly what I'm used to the Big-Car running," he says.
Prior to his third pass, he leaned out his carb's primary jets (#79 versus #82). Then, using his same launch technique, he crossed the 60-foot in exactly 1.62 seconds again, and propelled the roaring Cat through the traps in 12.35 seconds at 105.68 mph. "The jet change lowered my e.t. and raised my mph," he says. He retained the leaner jets for the rest of our event.
Brent saved his best performance for the end of the day. Though he launched strong for this fifth time to the starting line, his 60-foot time increased to 1.64, but that only made the determined Catalina pull harder. He made it to the finish line in 12.32 seconds at 106.83 mph—his best e.t. of the day. "I learned that the jets I've used for six years are just too rich for a hot day at the dragstrip, and will use #79s in the future, when needed," he says.
When asked about what he liked about the Shootout, Brent said, "It was nice to tune on the car without the pressures of trying to get it done between normal-round time constraints. He described the track conditions as "pretty good overall, but slightly better before lunch."
This month's Shootout participants came to our event to fine-tune their carbs for hot summer day racing. Though they both already knew the carb-jet changes would effect their e.t.'s, our Shootout gave them the chance to convert that knowledge into real-world numbers.
Like Steve and Brent, you may choose to race on days with high-density altitudes. You may consider adding a full set of alternate-sized jets to your toolbox, just for the occasion. We're sure the cars and combos detailed in this story will give you plenty of ideas for your project.
HPP would like to thank the management and crew at Summit Motorsports Park for their assistance in making this Shootout possible, and John Labuda, Arnie Brewer, and Billy Farrell who helped make the day go much more smoothly.