Wide-open throttle seems to get all the attention when it comes to carbs. Whether on the dyno or on the strip, carb tuning will usually come down to the wide-open mixture-a jet change here or there, the big squirters and pumps, and once it's pulling as hard as it can, it's time to put away the wrenches. While it would be wrong to neglect a carb's calibration while running all four butterflies on end, it is just as wrong to believe the job is done at that point. Consider the big Holley 750 HP fitted to our solid-roller 408 small-block in Project Talladega. There was no denying the sharp tune found when the linkage yanked the carb to full noise-our dyno and dragstrip calibration sessions ensured that fact. No, the problems here were much more subtle, the kinds of things you could easily neglect with a shrug.
To really dial in the fine...
To really dial in the fine points on Project Talladega's Holley 750 HP, we brought the carb to The Carb Shop and let them work their magic. Technician OJ Bretzing began with a careful teardown, inspection, and cleaning.
Getting to the specifics in the case of our Laguna, it was only when the car was not straight ahead and wide open that the carb's performance inadequacies made themselves known. Starting with its behavior right at idle, the stroker small-block was not quite happy. The idle seemed unstable, with excessive rpm pull down in gear, and the feeling that a two-foot driving style was required to keep the engine lit at a stop. Sure, this might be put down to the big .600-inch lift, 242/242-at-.050 COMP roller cam, but we had to think there was room for improvement in idle quality, even with the big cam.
From the jagged idle the engine would snap to attention if the throttle was stomped, boiling the hides at will. But at more meager inputs the results were far from satisfying, with a rough tip-in and light throttle transition to pedal inputs. On the jammed Southern California freeways, the poor light-throttle response was tormenting. Finally, when pressed hard around corners, the seamless straight-line performance just seemed to fall apart, with the engine coughing and sputtering against the g-force. Under hard extreme braking, the engine would just want to stall. When you are serious enough about cornering performance to run R-compound tires on the street, this is nothing but bitterly disappointing. On the autocross course, the let down was especially apparent. While such a set of circumstances would be enough to make an enthusiast seriously consider a change to fuel injection, we had to think that some massaging to the carburetor combination could yield very satisfactory results without breaking the bank.
The Fix Is In
We needed better fuel control...
We needed better fuel control during hard cornering, and the solution was custom angle-cut Nitrophyl floats. This puts the center of buoyancy near the centerline of the bowl, making it less sensitive to fuel sloshing to either side during cornering. The floats are sealed with epoxy where modified to prevent fuel absorption and to add stabilizing mass.
Rather than just accept the shortcomings of our carburetor setup as par for the course when running a radical carbureted small-block on the street, we figured with some expert tweaks, the all-around performance could be dramatically improved. To prove that point, we headed to one of the country's premier carburetor specialists, The Carb Shop in Ontario, California, and took notes as they worked their magic. On the job was technician OJ Bretzing, who disassembled our fuel mixer and then went through the unit with a fine-toothed comb, making minor modifications to achieve specific results. Nothing done to the carb could be considered a major reworking. Rather, the modifications centered upon intelligent changes that specifically addressed some of the problems with solutions that come from knowing the intricacies of how the carb functions. To begin, Bretzing disassembled the carb, carefully cataloging all of the parts, and then treated the mixer to a bath in a sonic cleaning machine to start with impeccably cleaned parts. The carb was then reassembled, making the required changes as the build progressed.