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1966 Chevy Chevelle - Tiny Dancer, Part III

Suspension Changes for our Nitroused 4.8L Mini LS

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Track Testing

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.

Nitrous Tuning

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.

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