If you have ever attempted to modify a high-performance car in search of lower elapsed times, one of three things always happens. The result that everybody aims at is where the modification is successful, the car is quicker, and that demands a celebration with your beverage of choice. The second possibility is that the change makes zero difference in performance. This happens sometimes and leads to head-scratching and the creation of unique theories that often share only a threadbare connection to basic physics. The third alternative, which is depressingly common is when your hero performs multiple modifications in the name of massive acceleration enhancements only to be rewarded with a slower e.t. It's called suffering from improvement—which is exactly what happened this time. The trick is determining which mods helped and which ones contributed to stomping all over our fragile drag racer ego.
If you recall, last month, we left our intrepid 4.8L LS-powered Chevelle running a best quarter-mile equivalent of an 11.40 at 119 mph after tickling the baby LS with a 150hp shot of nitrous, using our NOS Cheater plate system and a Lingenfelter nitrous control computer. The controller allowed us to ramp the nitrous solenoids from 30 percent to 100 percent over a period of 1.8 seconds. When we did this, it cut roughly three-tenths of a second off our 60-foot time, which made our 4.8L orphan truck engine look pretty good. Of course, as soon as that happened, we instantly assumed we were capable of more. We increased the launch percentage from 30 to 40 percent and moved the time to 100 percent from 1.8 to 1.7 seconds. The Chevelle initially hooked, then began to spin the tires, which slowed both the 60-foot time and the subsequent pass. The LPE nitrous controller was working exactly as promised, but it was clear that if we were going to run quicker, the Orange Peel Chevelle needed suspension improvements.
We started at the front, replacing the stock upper and lower control arms with components from Global West Suspension. We knew about a repaired crack in the passenger-side lower control arm, but that did little to inspire confidence for potential 120-plus-mph quarter-mile trap speeds. None of these first changes was really going to help the Chevelle run quicker—they were more for safety and reliability. So we converted to Global West tubular upper and lower arms, along with new springs that needed to be trimmed by cutting 11⁄4 coils to bring the nose down. Jim Sleeper at Global West's shop in San Bernardino, California, did all this work, along with an alignment and new QA1 double adjustable shocks. These shocks are more expensive, but we can now adjust compression separately from the rebound (expansion) movements.
Adding the double-adjustable QA1 shocks improved ride quality but more importantly allows
Normally, QA1's replacement rear shocks for our Chevelle would be a TN801, but since we have modified the rear suspension with Global's lower control arm anti-squat kit, we chose a slightly different rear shock. We wanted to make sure that we had sufficient shock absorber length to accommodate sufficient movement, so we opted for a rear shock from an S-10 truck that is nearly 3 inches longer in extended length than the stock rear Chevelle shock. This also means that the shock is 1.4 inches longer in fully compressed length, so we checked to make sure the shock would not bottom out before the rear suspension hit the bumpstops. If the shock bottoms out, it will be permanently damaged—something we'd like to avoid when they cost $240 apiece. The advantage now is that we can create softer rebound settings to allow the rear suspension to plant the tire quickly, while using compression valving to limit the amount of unload the suspension normally experiences to maximize average rear tire loading. In theory, we might be able to increase the amount of nitrous we can apply closer to the starting line, which will make the car quicker and justify the shock expense. It's also important to note that we didn't have time to install the BMR antiroll bar in the rear, which probably would have improved our traction efforts. That will be at the top or our list for next time.
While this work was being done, we also sent our NOS Cheater system to Steve Johnson at Induction Solutions, where he flow-tested our original plate and then made some changes. The first thing he did was to install an Induction Solutions nitrous solenoid and then flow-test the system to create a new jetting combination. His baseline horsepower combo for our plate is rated between 100- and 125hp, so we stepped up to the next bigger jets, which are for a 150 to 175 hp tune. Our original Cheater tune was a 0.063 nitrous jet and a 0.057 fuel jet with 6 psi of fuel pressure. Johnson's version for our plate is a 0.066 nitrous jet and a 0.044 fuel jet with the initial fuel pressure set at 7.0 psi. We noted that while the nitrous jet is slightly larger (a 9.8 percent area increase), the fuel jet is 0.023 inch smaller (a 44 percent reduction). This is slightly offset by increased fuel pressure. Induction Solutions recommended starting with 7 psi of fuel pressure and gradually reducing the pressure (we ended up at 6.5 psi), while carefully evaluating the plugs after each pass. Right now, our timing is set at 32 degrees total with 8 degrees of retard when the nitrous is triggered, and we're still running 91-octane pump gas.
We chose a longer rear shock from an S-10 truck to add about 2 inches of shock travel to t
We installed the front upper and lower Global West control arms to upgrade the nearly 50-y
Jim Sleeper drilled new holes in the Global West lower control arm brackets to give us an