When it comes down to it, the difference between a 9-second car and a 10-second car can be as much as a full second, or as little as a few measly hundredths. In terms of street cred, however, some goons feel that the difference between 10s and the single-digits is just as substantial as the gap that separate a 14-second slug from an 11-second screamer. Your author just happens to be one of those goons. So when our big-block-powered '93 Mustang project car laid down a string of 10.0-second passes, the experience was a bit bittersweet to say the least. Progress is progress, however, and we knocked off a solid three-tenths of a second since the first wave of testing began. Here's how it went down.
Back to the Track
Our last trip to the dragstrip with Project Fox ended prematurely due to a minor mechanical glitch. Tightening a few loose bolts got the car back on the road, and we headed out to Lonestar Motorsports Park in Sealy, Texas, on a warm October afternoon for a private test session. Located on the premises of Hennessey Performance (www.HennesseyPerformance.com), LMP is a hot rodder's wet dream come true. Owner John Hennessey was kind enough to lend us his facility for the day, and we weren't disappointed. Offsetting the less-than-ideal 35-mph headwind and 2,700-foot density altitude was a track surface that proved outstanding throughout the day.
One of the drawbacks of driving a street/strip car around the block on supersticky drag ra
Due to the temperamental nature of our Mustang's 275/60-15 Mickey Thompson ET Street radials, we programmed the MSD 6AL-2 ignition box with a conservative timing curve that pulled 12 degrees of advance out of the hole and progressively ramped it back in by 5,000 rpm. Leaving off the footbrake at 2,000 rpm, Project Fox laid down a 10.53 at 134.81 mph. The underwhelming first pass of the day was two-tenths off of the car's previous best, and it was obvious that we set the ignition tune way too conservatively from the moment we hit the gas. The car dead-hooked and felt like a dog coming out of the gate, reflected in its painfully slow 1.79-second 60-foot time. A slight carb stumble didn't help matters, either.
For the next pass we hooked the laptop back up to the MSD box and ramped the timing in much more aggressively. Whereas the prior tune didn't reach full ignition advance until 5,000 rpm, we put all 28 degrees of total timing back in the motor by 3,500 rpm for the second pass. Just in case the drag radials decided to spin, the air pressure was lowered from 18 to 16 psi. The recipe was just what the big-block notchback ordered. Launching once again at 2,000 rpm, Project Fox busted out a 10.03-second pass at 137.70 mph. Our organic accelerometer registered a much more pleasing launch, reaffirmed by the car's 1.54-second 60-foot time. In addition to the Mustang's new all-time best quarter-mile e.t., it posted new bests in eigth-mile e.t. and mph (6.46 at 110).
On our second-to-last pass at Lonestar Motorsports Park, Project Fox posted its best 60-fo
Pleased with the gains from the prior run, we left the setup unchanged for the next pass. With an identical launch technique, Project Fox backed up its prior run with a 10.04 at 137.07 mph on a 1.51-second 60-foot time. Determined that a slightly harder launch would net a 9-second pass, we lined the car back up after 20 minutes of cooldown time with plans to stall the converter up even higher. Interestingly, the same torque converter that seemed too loose during shakedown testing felt too tight this time around. Maybe the cooler weather had something to do with it, but the highest we could load up the converter off the footbrake was 2,100 rpm. At anything beyond that, the tight converter combined with the stock drum brakes to spin up the tires, making the car creep through the staging beams. Nevertheless, on the next run Project Fox busted off a 10.01 at 137.89 mph on a 1.47-second 60-foot time.
So close but yet so far, Project Fox developed a knack of running consistent 10.0s at LMP.
With our test session coming to a close, we were tapped out of ideas on how to improve the car while at the track. Clearly, the engine and chassis combination had leveled off in the 1.5-second range, and all it needed was a bit more grunt coming out of the hole. Unfortunately, the converter and footbrake combo wouldn't oblige. If not for the nasty headwind, or the extra 20 pounds of processed Big Macs and cheesecake hanging off the driver's midsection, it's quite possible that the Mustang would have picked up the two-hundredths of a second it needed to post a single-digit pass that day. We were that close. Lame excuses aside, the truth of the matter is that whether Project Fox ran a 10.01 or a 10.99, it's still just a 10-second car.
On the cusp of 9s, we determined that the cheapest and easiest way to knock our 60-foot times down was with a transbrake. Based on how hard similar combinations to our Mustang launch, with an optimized chassis tune and torque converter, Project Fox should be able to pull 1.3- to 1.4-second 60-foot times all day long. To get Project Fox part of the way there, we ordered a transbrake from TCI. By engaging First gear and Reverse at the same time with a solenoid, valve, and an electric switch, a transbrake offers several advantages over footbraking. The most obvious benefit is that it holds the car stationary in the staging beams, allowing an engine to rev to a higher rpm for a more aggressive launch off the line. Furthermore, transbrakes eliminate the loading of the chassis and suspension that results from holding back driveline torque with a footbrake. The result is cleaner, more consistent launches. The TCI transbrake bolted right up in a couple of hours, and then we headed out to San Antonio Raceway for another round of testing.
It doesn't look much different from a standard Turbo 400 valvebody, but the TCI transbrake
Expecting great things, we staged the car, stalled up the converter to 3,500 rpm, and popped the transbrake button. Presumably due to the additional shock of the harder launch, the Mustang shook the tires so violently that we had to get out of the gas. The car registered a miserable 1.84-second 60-foot, and we didn't bother driving it out the top end. Of the dozen or so passes the car had logged thus far, this was the first time it experienced tire shake, which happened to coincide with launching off the transbrake for the first time. It didn't take a genius to figure out that the two were related, so we convened with the Bill Buck Race Cars crew to try to correct the situation.
Although vehicles as diverse as street/strip machines, 2,500hp Outlaw drag cars, and 6-second Pro Stock machines have all been battling tire shake for decades, eliminating it is still somewhat of a black art. After a tire's sidewalls distort and wad up at launch, the energy released as they "unwind" back into shape sends violent shock waves through the tires and chassis. This affect is greatly exacerbated with drag radials compared to bias-ply slicks due to their stiffer sidewall construction. With marginal track conditions where a slick would still hook, radials have a greater tendency to go into tire shake. In essence, the chassis and engine tune in a car that experiences shake isn't so far off that it blazes the tires, but it does allow for enough spin to create the condition in the first place. That's just a fancy way of saying that Project Fox's setup was close, but not quite all the way there. "Tire shake can be caused by not having enough power, having too much power, or hitting the tires too hard out of the hole," says chassis expert Bill Buck of Bill Buck Race Cars. "Drag radials and slicks require different setups to prevent tire shake. With drag radials, setting the rear shocks too soft or running the air pressure too low is usually the problem."
Replacing our original semi-automatic valve body with the TCI transbrake unit was very str
Back in the pits, just as Buck suspected, the air pressure in the Mickey Thompson radials was way too low. Cooler weather conditions caused the pressure to drop down to 12 psi, so we aired them back up to 18 psi. Likewise, since we had never experienced tire shake before, the rear shocks were set at two clicks from full loose. Project Fox's single-adjustable Competition Engineering shocks feature 16 clicks of adjustability, so we tightened them up to eight clicks from their stiffest setting. Furthermore, since we were unsure of how high the TCI transbrake would allow the motor to rev up at the line, we left the timing curve in the MSD box unchanged from our prior test session at Lonestar Motorsports Park. The tune was set to ramp in all the advance back in by 3,500 rpm, and since the transbrake allowed loading the converter up to 3,500 rpm, that meant that we were leaving the gate with all 28 degrees of advance. Just in case the motor was overpowering the tires, we dialed in 10 degrees of retard at 3,500 rpm, and ramped it back in by 5,000 for the next pass.
To engage reverse with the touch of a button, the transbrake relies on an electric solenoi
The tweaks definitely helped, as the tire shake was far less violent on the next pass, and the 60-foot time dropped to 1.72 seconds. A nice improvement, yes, but it was still poor enough to warrant an aborted run. On the next pass, we decreased the launch rpm from 3,500 to 3,000, netting a 10.21 at 137.49 mph timeslip on a 1.67-second 60-foot time. While the tuning changes helped reduce the severity of the tire shake, it wasn't entirely eliminated. The next logical change is to adjust the instant center of the rear suspension. Project Fox's Competition Engineering lower control arm relocation brackets feature three different sets of boltholes, and Buck thinks that raising the rear of the arms from the lowest setting to the center setting will help soften the hit to the rear tires. Unfortunately, our test-and-tune session came to a close before we had a chance to change the instant center, so we'll have to save that for our next round of testing.
A Track In Your Own Backyard
For decades, Hennessey Performance churned out some of the most powerful late-model performance machines in the world. Its fire-breathing Dodge Vipers are what first put Hennessey Performance on the map, but these days everything from LS-powered Camaros and Corvettes to new-age Hemi cars and mod-motor Fords fill its 30,000-square-foot facility. A cool 1,000 rear-wheel horsepower is very much the norm at this joint. The kicker is that testing these beasts out at the dragstrip requires just a 500-foot drive through the parking lot. Like every hot rodder has fantasized about-John Hennessey has his own dragstrip in his backyard. He acquired Lonestar Motorsports Park several years ago-located 45 minutes west of Houston-and built a brand-new shop right on the same facility. Hennessey has already expanded the track to a full quarter-mile, and is also putting up a new road course and karting track. Lonestar Motorsports Park hosts regular test-and-tune nights and special events, and as we found out during our test session, the place hooks hard. The one-two tandem of a premier performance shop combined with a dragstrip make Hennessey's impressive compound one of the most unique facilities in the country. For anyone in the Houston area, it's definitely worth checking out. -Stephen Kim
|PROJECT FOX: THE FINAL TALLY
|'93 notchback Mustang
|Sold old wheels, tires, engine, trans
|532ci big-block Ford (SAM)
|Phoenix TH400 trans
|Strange 8.8 rearend
|Comp Engineering rear suspension
|AJE front suspension
|Bill Buck custom 10-point 'cage
|Engine and trans install
|Russell fuel system
|Wheels and tires
The TCI Thunderstick shifter in Project Fox already had a button in place on the shift kno
What We Learned
In retrospect, compared to our prior test session at LMP, the combination of a harder launch and a different track surface all contributed to tire shake and disappointing e.t.'s. The effectiveness of the transbrake and finicky nature of the drag radials simply require a different chassis setup than we were accustomed to running. Furthermore, our trip to San Antonio Raceway revealed that our prior timing curves were way too conservative. While the tires shook, they were never even close to boiling to a haze, even when feeding in full ignition advance off the transbrake. Presumably, we were castrating the motor way too much in our prior tests, contributing to its less-than-stellar 1.5-second 60-foot times. If we were smart enough to feed in more timing at LMP, instead of pulling out 12 degrees out of the hole, it's quite possible that we could have run 9s off the footbrake. At the end of the day, Project Fox is extremely close to entering the hallowed single-digit territory, but for now it's still just a 10-second car. That fact is both painful and extremely motivating, as we plan on using what we learned running off the transbrake for the first time, making the necessary adjustments, then heading to the track again as soon as possible.
|WHERE THE MONEY WENT
With the transbrake in place, the first pass of the night at San Antonio Raceway shook the
Stiffening up the rear shocks and increasing tire pressure on the next pass reduced tire s
On the final pass of the evening at SAR, dialing back the launch rpm from 3,500 to 3,000 r