When we left our overachiever 4.8L-powered Chevelle last month, we had managed to nitrous shock our 3,650-pound Chevelle into some amazing 12-flat quarter-mile times. The Chevelle ran this number despite a hideous 1.95 60-foot time, because the only way to not spin the tires was to launch the car soft and wait until the 60-foot mark to smack the nitrous. This was a ready-made situation for the Lingenfelter Performance Engineering (LPE) nitrous control computer, which promised to launch the Chevelle much more efficiently.
To recap last month’s adventure, we started with a 100,000-mile 4.8L truck engine we swapped into our Orange Peel ’66 Chevelle. All we added was a mild 219 degrees at 0.050 Comp hydraulic roller cam, new springs, an Edelbrock dual-plane intake, a vacuum secondary 750-cfm Holley carburetor, and an MSD ignition box. We swapped the tiny LS motor in the car with help from a Champ oil pan, and because the motor was so undersized, we didn’t bother with headers, opting instead for a budget set of Hooker cast-iron manifolds. On engine power alone, the 4.8L revealed why few car crafters would think to mess with this engine. Our best normally aspirated pass was an eighth-mile 8.47 at 85-mph run that is equivalent to 13.29 at 105 mph in the quarter. We thought that a 150hp shot of nitrous would get us in the mid-12s and that would be cool. Surprisingly, even with our sundial-slow 60-foot, we were knockin’ on the 11-second door. That 4.8 was just a short skirt teasing us—we had to go quicker.
The key to entering the 11s would be the LPE nitrous control computer NCC-002*. The NCC unit is designed to pulse-width modulate the nitrous and fuel solenoids, and that allows us to use a single stage of nitrous yet launch with a softer hit. Our first full 150hp shot on the starting line created nothing but tire spin. Rather than work on the suspension, we anticipated quicker results by modulating the nitrous. The computer was originally designed to be used with EFI cars, but it’s just as happy with a carburetor. If you’re not afraid of laptops, you can modify the configuration digitally. Or it’s just as easy to change parameters with buttons and the direct readout screen.
The NCC Nitrous 1 position offered a simple setup that allowed us to set the initial percentage of nitrous, followed by a gradual increase in volume. The NCC box does this by pulse-width modulation of the solenoid. This works just like a duty cycle. We initially configured the box so the solenoids begin at a 20 percent duty cycle, gradually ramping up to 100 percent duty cycle after 2 seconds. A separate NCC feature allows you to delay the nitrous solenoid (we chose 0.10-second after the fuel solenoid) so the fuel can get a head start into the manifold and prevent a lean air/fuel-ratio spike. This is accomplished because the NCC controls the nitrous and fuel solenoids with separate relays. We also wired the NCC to send a 12-volt signal to the MSD to retard the timing at the exact moment the nitrous engages.
The NCC box offers several other control functions that can be very useful. An optional fuel-pressure sensor (0–15 psi in our case, 0–150 psi for EFI) allows the NCC to monitor fuel pressure and act as a safety shut-off should the pressure drop below a configurable minimum pressure. There’s also an optional nitrous pressure sensor that can be set to monitor bottle pressure and control an electric bottle heater. We also took advantage of a simple function that allows you to command a given percent of nitrous engagement when the throttle is reapplied should you have to lift. We chose to reapply the nitrous at 50 percent rather than 100 percent, as would be the case with a simple on/off switch.
LPE recommends that when modulating nitrous solenoids to use a Hella electronic relay (for
Before we hit Irwindale again, we had a chance to run the Chevelle with the nitrous tune-up by driving up into the high desert north of Los Angeles to Willow Springs Raceway, where they were holding a Saturday night 1,000-foot drags. The most important thing we learned was that we could hit the tires harder at 30 percent on the starting line and be more aggressive with the nitrous earlier in the run. While we did that, our bottle heater failed, so our nitrous pressure was low. The worst part, however, was that we were at 3,500 feet of altitude, which means thin air. The best the Chevelle ran that night was a 1,000-foot time of 10.52 at 105.9 mph. Our best estimate is that this equates to a 12.77 quarter-mile time—way short of our 11.90 goal. We repaired the bottle-heater wiring, added a fresh NOS 10-pound bottle, and waited for Irwindale’s Test ’n’ Tune night.
We also added a blow-down tube to our nitrous bottle to fit NHRA rules. We check nitrous p
Irwindale is usually very crowded, so we chose to jump right into our nitrous test. We also brought along a newer pair of Mickey Thompson E.T. Street tires when we discovered our original tires were 11 years old. Our new NCC tune consisted of hitting the nitrous at 2,800 rpm with 30 percent and ramping quickly to 100 percent in 1.8 seconds. This produced an odd situation when the car left really soft with a slow 1.945 60-foot and only ran a 7.91 at 93.38. This was much slower than we expected, and it was clear the nitrous was not engaging right on the starting line. After much head-scratching, we realized that new carpet underneath the throttle pedal was preventing the last 10 percent of throttle opening, so the linkage was engaging the nitrous only after the car was well into the run. We adjusted the linkage to lift the pedal off the floor slightly, and we were ready to try again. Now that the nitrous was really hitting, the Chevelle shot off the starting line with a 1.678 60-foot (its best ever) and blasted an incredible 7.26 at 96.03 mph. That equates to a quarter-mile time of 11.40 at 119.08 mph. We were stoked and decided we needed to back this up. Now empowered with our newfound control of the nitrous beast, we bumped the initial hit to 38 percent, achieving 100 percent in 1.7 seconds. All this was in an attempt to improve our 60-foot time. Basically, after 1.7 seconds, the nitrous system works just like any simple nitrous kit, so our best opportunity for a better e.t. was to improve our 60-foot times.
From the start of this test, the Chevelle was running these Global West anti-squat bracket
The car launched hard and hooked, but then we could feel the tires spin slightly, and the time clocks recorded a slightly slower 60-foot time of 1.763, which meant our overall time slowed to a 7.420 at 96.44. But this still equated to an 11.64 and improved the trap speed to 119.58. It was clear we needed suspension work now if we were going to go quicker. While we have a relatively small 8.5-inch-wide tire, there are plenty of cars running a lot quicker than our high 11s on these same tires.
While we were thrilled with that first quick pass at Irwindale, there is more e.t. to be gained. On that pass, the bottle pressure was low due to an intermittent bottle heater that only worked when it wanted to—bottle pressure was around 875 psi on the final two passes. Despite that, the Orange Peel has run much quicker than we ever thought possible—11.40s. We have a list of about a dozen things we’d like to try, including headers, a 4.10:1 gear, and a nitrous plate blueprint, among the more popular ideas. The obvious choice is to just hit our little LS with more nitrous, but that’s too easy. We’re not ready to talk about running in the 10s yet, but low 11s certainly seem possible. We still have to be wary of our stock, cast pistons.