How To Run 10s In A Stock Z06 - Maximum Acceleration, Part 2

I've never met a Corvette owner that didn't want stronger acceleration. That visceral yearning for improved performance isn't limited to hardcore racers, far from it. Acceleration has always been central to the Corvette mystique and ownership experience. The customary approach to better acceleration involves modifying the engine to get more power.

The approach I've taken is different. I've spent six years pursuing maximum acceleration in Corvettes by improving my skill as a driver. In this pursuit, I've shown that a stock Corvette with a manual transmission and skilled driver can easily out accelerate one with fifty more horsepower piloted by an average driver. In light of this, I offer a simple, direct approach: modify the driver before you modify the car.

The quest for maximum acceleration led me to an extended series of semi-controlled experiments with these specific objectives:

* Identify the key variables a driver must control.
* Optimize those variables through specific, discrete techniques that produce the fastest acceleration.
* Work relentlessly to refine and document those techniques.

Techniques for maximum acceleration can be learned; they work for drivers of any shape, size, or age, and the results are highly repeatable with practice.

So if you want stronger acceleration, you can have it simply by improving your driving skills. With that objective in mind, I suggest you study the techniques described here, and then practice, practice, practice to embed them in your routines and muscle memory. And, of course, you can apply your improved skills not only at the track, but also on the street in driving situations where bursts of strong acceleration are appropriate.
With that as a background, here are the lessons I've learned making 570 passes at the dragstrip in three stock Corvettes.

Eight things to do before arriving at the dragstrip
* Learn the Chevy quarter-mile specification for your car. It's a reference point you need.
* Buy or borrow an approved helmet; the rules at the dragstrip require one.
* Buy a pair of sport or driving shoes with thin soles and good grip. Thin soles transmit clearer feedback from the pedals, key to sensing what the engine, clutch, and rear wheels are doing. Good grip prevents the feet from slipping off the pedals during aggressive movements.
* Buy a glove for your shifter hand. One made for football receivers or baseball batters is ideal. A glove gives confident, positive control of the shifter even when your hand gets sweaty.
* Adjust the driver's seat and steering wheel for proper access to the clutch and shifter. Store these race positions in a memory pre-set.
* Using the race positions, practice shifting drills to improve shift speed and accuracy.
* Clean up your clutch fluid to inoculate your car against clutch pedal issues that bedevil C5 and C6 Corvettes driven aggressively.
* Manage your fuel load to arrive at the track with about one-half tank.

A prudent early goal at the dragstrip, particularly the first day, is just getting down the track safely without missing shifts or breaking anything. The next logical goal is targeting the Chevy quarter-mile specification for your car.

Until your driving becomes reasonably consistent, I suggest ignoring the car in the other lane and your reaction time at the starting line. Measurement of your elapsed time (e.t.) won't commence until the car leaves the starting beam, no matter how long after the green light that may be. Freeing yourself from those distractions will speed up progress on improving your driving. If you decide later to try bracket racing, you will already have reasonably consistent driving skills and can begin to focus on the competitive dimensions of drag racing.

On Arrival At The Dragstrip
* Present the car for routine technical inspection, show your helmet, and receive the window number that will identify the car and appear on your timeslips. Ask about the location of the facility's air hose; you'll need it at the end of the day.
* Lower the stock rear tire pressure to 25-26 psi (hot) before making the first pass. This allows more sidewall flex, improving traction, cushioning shock to the driveline, and reducing the likelihood of wheel hop, which can break rearend parts. Readjust the tire pressure before each subsequent pass because sun load will make the psi rise and become uneven side-to-side.
* Adjust the driver's seat and steering wheel to your pre-set race positions. Then do at least two sets of shifting drills to warm up the shifting muscles and refresh your reflexes.
* Get a quick briefing from an experienced racer on procedures in the staging lanes and at the starting line. Ask to be shown the racing groove in the track surface; for optimal traction you'll want to align your tires in the groove. Ask also about the location of the entry point for the return-road at the end of the track and the timeslip window.

Staging The Car
* Drive around the water box to keep the stock tires dry.
* Properly set the traction control system. A C5 should be in "Competitive Driving" mode and a C6 in "Traction System Off" mode. These settings allow the rear wheels to spin while keeping Active Handling available to help the driver retain control of the car if the rear end gets loose on launch or a shift. If that happens, best advice is to lift the throttle immediately; it is far better to abort a run and save the car than err colossally by hitting the wall while fighting to salvage a deeply flawed pass.
* When moving to stage the car for a pass, align the wheels in the racing groove. As the car moves forward toward the starting line, it first trips the pre-stage beam, which lights the top pair of small bulbs. From that point, inch forward very, very slowly. When the lower bulb pair lights, stop immediately. That position is called shallow staged. It's where you want to be. Next, prepare to launch the car.

The Launch Has Three Components
1 ::: The launch rpm is held steady during release of the clutch. This pre-selected rpm is the maximum you believe prevailing track conditions will reward. An ideal launch rpm will produce just a small amount of wheelspin before the tires hook. A higher rpm would produce too much wheelspin, and a lower rpm would cause the motor to bog. With stock rear tires, the launch rpm will generally be in the range of 2,400-3,300. If you are unsure, start at 2,400 and, based on the results, adjust upward or downward in 200-300-rpm increments on the next pass. After a few runs, you will find the sweet spot that gives the right balance between wheelspin and bog.

2 ::: The clutch release should be very fast, but less than a pop or side step. The clutch pedal should be out fully before the car has moved more than 3-to-5 feet. Some drivers favor a literal pop of the pedal, termed a clutch dump. I find this more likely to break driveline parts than my approach. Other drivers prefer a slow release of the pedal to produce significant intentional clutch slip and keep the rpm elevated during the launch. I also avoid this approach because it increases clutch wear and generates unwelcome heat that can glaze the clutch entirely or cause pedal woes during the pass. This is a particular concern on the C6 Z06 because the LS7 clutch is intolerant of intentional slip at an elevated rpm.

3 ::: The throttle squeeze requires modulation and calibration to track conditions. The instant the clutch release is complete-and not before-quickly squeeze the throttle to the floor. This motion is not a stab or stomp, that would provoke excessive wheelspin, something to definitely avoid since it will slow you down and greatly increase risk of driveline breakage. Rather, the motion is a firm, deliberate squeeze with your senses focused on what the clutch and rear wheels are doing. The goal is to have the initial wheelspin from the clutch release transition quickly to a rapid rise in engine rpm without a loss of momentum or bog. Once the tires are hooked, you want the fastest squeeze achievable without provoking renewed wheelspin. The faster the squeeze, the faster the launch and 60-foot time will be. Generally, the throttle is on the floor within 20-30 feet of forward movement, depending on track conditions.

Using this three-element launch procedure, an average Corvette driver will attain 60-foot times in the 2.0s. With practice to synchronize these movements and react correctly to feedback from the car and track surface at the ragged edge of traction, a good driver will dip into the 1.9s and an excellent driver into the 1.8s.

Gear shifting should be performed fast and at the correct rpm, but more on that in a moment. A fast shift of a Corvette manual transmission can be completed in about 200 milliseconds (two-tenths of a second). So three fast shifts in a quarter-mile run (the 1st-to-2nd, 2nd-to-3rd, and 3rd-to-4th) consume six-tenths of a second with the clutch disengaged and the car not accelerating. In contrast, an average driver without the fast-shifting skill will need 400-500 milliseconds per shift, consuming 1.2-to-1.5 seconds for the three shifts; that is six- to nine-tenths slower than the fast shifter. The way to avoid the slow-shifting penalty is to practice until the act of repetitive shifting is fast, precise, confident, and, essentially, automatic.

Shift points are crucial to maximum acceleration. The ideal shift point in stock Corvettes is just before invocation of the rev-limiter or fuel cut-off. This conclusion comes from my calculations, verified by personal experiments at the dragstrip. Shifting before the ideal rpm-termed short shifting-produces slower acceleration adversely affecting both e.t. and trap speed. Conversely, perfect shift points can shed two- to three-tenths of a second in e.t. compared to very good ones.

If 6500 is the target shift point (for a Corvette with the LS2 or LS6 engine), the driver must get the clutch in at an actual 6500, ease the throttle, complete the shift, release the clutch, and reapply the throttle. Because engine rpm at wide-open throttle climbs at a different rate in each gear, the driver must calibrate clutch-in and associated movements to hit each shift point correctly. Special attention must be paid to the 1st-to-2nd and 2nd-to-3rd shift points in C5s because the tachometer needle lags behind the actual engine rpm at wide-open throttle. There is very little tach-lag in C6s.

If you overrun the target shift point, the penalty for barely kissing the rev-limiter is usually around five-hundredths of a second. But hitting the limiter squarely under wide-open throttle will cost at least a tenth, and even more if driver recovery actions are not extremely quick.

Finally, after the shift to Fourth gear, be sure to remain at wide-open throttle until beyond the final timing beam that marks the end of the quarter-mile.

The foregoing discussion provides proven recipes for good launch, strong shifts, and correct shift-points-the crucial ingredients of max acceleration. Knowing what to do is certainly a prerequisite, but actually performing all steps correctly and smoothly integrating them for a successful pass takes seat time and practice . . . a lot of practice.

A reasonable expectation is you will need 30-50 passes to find your personal lower limit for e.t. in a particular Corvette platform. You will need fewer passes if you are a gifted athlete, fast learner, or have previous race experience in a traction-limited, manual-transmission car. some drivers deeply committed to beating the Chevy spec for their cars manage to accomplish that goal in 20 passes or less. keep your expectations realistic. CF

Editor's Note: John "Ranger" Armstrong is producing a DVD on the aforementioned techniques for maximum acceleration in Corvettes. Scheduled for release the fourth quarter of 2007 via his web site (www.rangeracceleration.com), the DVD is intended to help Corvette owners get the most from their cars in a straight line, on the street, and at the dragstrip.