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
In an ideal world, we would test each of these suspension and nitrous upgrades individually to evaluate their effect on the Chevelle's elapsed times. But, since we test on Thursday night with everybody else, we stacked up our best-guess combination and headed to the track. Though, we retained our best previous nitrous controller setting. Our first pass proved the point that you should not make more than one change at a time when we ran a whole quarter-second slower than our previous best 7.26. It's difficult to point to any one change as the culprit, but if we had to guess, it appears that changing the instant center by raising the rear control arm location may be where our lack of traction originated. Conversely, the shocks noticeably improved how the car handled even when it was spinning the tires hard. Unfortunately, those spinning tires killed the e.t., so we softened the initial hit back to 30 percent (from 36 percent) and slowed the total time to 1.8 seconds. This only made the Chevelle run slower (see Track Times, next page). The only consolation was that these first two passes produced the fastest mph our little 4.8L has ever run: 97.31 mph (96.03 previously) in the eighth-mile. This computes to the equivalent of 120.66 mph in the quarter-mile. We attribute this entirely to Induction Solutions' nitrous plate tuneup.
To improve traction, we decided to try the non-linear nitrous curve (see Nitrous Tuning sidebar, above). By maintaining the 30 percent initial hit for 0.4 seconds and then bumping the percentage to 60 percent, the Chevelle ran even slower, so we pushed the initial hit up to a 40 percent launch with a jump to 60 percent at 0.50 second. This produced our best run of the night with a 7.712-second, 95.95-mph pass that equates to 11.50 at 118.98 mph. This is still roughly a tenth of a second slower than we had run before all our changes. We were making slightly more horsepower now as indicated by the increased trap speed, but traction was still the problem. We tried a longer burnout to heat the tires better and a more aggressive nitrous hit with a quicker ramp after a shortened 0.35-second delay, but this just spun the tires even harder, slowing the Orange Peel to a 7.577 at 96.39 mph. We ran out of time to try again.
Looking back at the results, we think that going back to the more aggressive anti-squat location on the rear lower control arm may be a solution to planting the tires better on the starting line. If we can make them stick, then it's possible to maintain traction throughout the rest of the run. It also appears that our previous 7.26 was likely a Hail Mary run that worked, but one that will be difficult to surpass. We didn't use the wider M/T tires in this session because we really wanted to try and run quicker with the narrower tires. But we'll take the easy way out and include the wider 26x11.5x15 tires on the next test session. We'll also include the new BMR antiroll bar, which should also improve suspension efficiency.
In terms of raw power, we are still only spiking the 4.8L with roughly a 165hp shot. We could easily upgrade to a 200hp tune—but that's too easy. We'll save that for when we're desperate. It's worth mentioning that of all the parts we've added to the Orange Peel cost more than the original 4.8L engine. In fact, the Induction Solutions' nitrous plate tune was our only engine modification in this session. At $200 for that 4.8L long-block, the engine has literally become the least-expensive part of this entire effort. We thought about building a 5.7L iron-block version, but we had trouble justifying the cost, especially to do it with forged pistons and good connecting rods. While a 5.3L would run better with its 30-plus-ci displacement advantage, we've grown attached to our Tiny Dancer engine. We have lots more ideas, but we'll save them for the next installment. The overall goal is to run quicker without grenading the 4.8L in the process. That would be bad form.
On our best run last month, we started with a 30 percent hit on the starting line and ramped the duty cycle up to 100 percent by 1.8 seconds using a straight, linear curve. The Lingenfelter computer illustrates this curve with a simple display right on the box that we've duplicated in our accompanying graph. When we changed the tune to a 40 percent hit with 100 percent at 1.7 seconds, the car initially hooked but then spun the tires about 20 feet out. We mentioned this to Joel Orme at Orme Brothers a few days later when we were refilling our nitrous bottles, and he offered an intriguing alternative to our linear duty-cycle application of nitrous. His suggestion was to go back to the 30 percent initial hit and maintain that as a flat line for 0.40 seconds and then produce a more vertical duty cycle to hit at 1.7 seconds. The concept is to allow the car to create wheel speed before hitting the tires harder with more nitrous.
We've created several versions of this idea on a graph to make it easier to visualize. Curve A is our original idea—note its simple, progressive approach. Curve B is the delayed nitrous application, where the initial 30 percent flatlines until 0.4 seconds and then radically increases the duty cycle up to 60 percent. Note that as the line moves vertically, it increases area under the curve. This area represents additional engine power. At first, this didn't work with our little 4.8L engine because it needed more help right on the starting line. So we applied 40 percent duty cycle to the engine on the starting line as with curve D, which produced our best run of the night (still slower than our best 7.26). We then tried shortening the time before steepening the curve to 1.30 seconds, and that caused quite a bit of tire spin and a much slower e.t. Obviously, we will continue to experiment with variations on these ideas to make the car quicker. As we increase power, this places more emphasis on tuning the front and rear suspension to be able to convert this additional power into traction.
1⁄8-mile e.t. x 1.57 = 1⁄4-mile E.T.
1⁄8-mile mph x 1.24 = 1⁄4-mile MPH
||1⁄4 E.T. (est.)
||1⁄4 MPH (est.)
*Weight (with driver): 3,650 pounds, TH-2004R trans, 3.55:1 rear gear, 12-bolt
1) Best normally aspirated pass from Part I
2) First nitrous run: spun badly off the line; NOS jetting: 63 nitrous/57 fuel
3) Second nitrous run, no changes: delayed nitrous start—best e.t.
4) Best previous nitrous run with NCC controller; 30 percent initial hit
5) New suspension, shocks, and nitrous tune—same linear nitrous control: tires spun badly
6) Softer nitrous hit with linear control: didn't work, slower yet
7) Stepped nitrous control (curve C), lower tire pressure—minor tire spin: best pass of the session
8) More aggressive nitrous control, 1 pound lower tire pressure
9) Even more aggressive nitrous step (curve not shown): spun hard; slowest 60 foot of the night
|Used 4.8L long-block
|Comp Cams timing set
|Hooker exh. manifolds
|Edelbrock Perf. RPM
|NOS Cheater system
|Fill 10 lb. bottle
|NOS blow-down tube
|NOS bottle heater
|Induction Sol. solenoid
|MSD Ignition box
|Global front upper arm
|Global front lower arm
|Global front coil springs
|Global anti-squat kit
|QA1 front double adj.
|QA1 rear double adj.
|QA1 T-bar kit
|Summit jacket, 1 lyr.
|Crow Belt re-certify
|AEM A/F meter
|LPE nitrous controller
|Autolite race plugs
|M/T ET Street tires
3406 Democrat Road
6198 Hwy 12 East
Holley Performance Products
1801 Russellville Rd.
Orme Brothers Inc.
18453 Parthenia Place
39 Old Ridgebury Road
Mickey Thompson Performance Tires & Wheels
1900 Compton Ave., Suite 101, Dept. GMHTP
QA1 Precision Products
21730 Hanover Ave.
Global West Suspension
655 S. Lincoln Ave.
2700 California St
Lingenfelter Performance Engineering