The motor of choicethe Rat. With only a couple of exceptions, everyone in Factory St
James Tharps 70 Camaro is one of the few cars running a leaf-spring rear suspe
Theres hope for leaf springs. One trick is to remove the bottom leaf (arrow), which
Another must-have with leaf springs is traction bars. The Slide-A-Link bars from Competiti
We dont think BFG intended the Drag Radial to look like this, though every racer agr
Ruth Spires 93 Camaro uses six-cylinder rear coil springs to soften things up.
Donny Williams 79 small-block Malibu runs 10.02 at 133 mph. Part of his succes
Tuning is everything. Joey Harris (see our feature story Southern Sanctity) ha
In the world of drag racing, happiness is a low e.t. Horsepower helps, but there is more to quick quarters than just gobs of torque. A major key to quick e.t.s is a low 60-foot time, which combines both power and suspension. So we took a peek under some NMCA Factory Street cars to see how these guys are hooking up when required by the rules to use radial tires. With 1.40-second 60-foot times and 10-second quarters in 3,500-pound, stock-suspension behemoths, these guys must know something. Sound impossible? Read on.
The first question to answer is simple: Do I want a canyon-carver or a drag machine? The bottom line is that if you want best possible e.t.s from your boulevard bruiser on street tires, you will need to adjust your suspension accordinglyadjustments that will probably adversely affect handling.
Every racer we spoke to agreed that when it comes to hooking up, Its all about weight transfer. This comes down to two things.
First is the front suspension. Here you will want to make the front suspension as loose as possible, which will entail the removal or disconnection of the front sway bar and the installation of a drag-type shock like the Koni or Lakewood 90/10. Some of the racers also recommended installing a set of tall drag springs, though many of them have retained the original front springs. All of these changes allow the front suspension to rapidly lift and transfer weight to the rear when the car launches.
With a loose front suspension, the second step is to make the rear suspension work. Here, the key is keeping the rearend planted. A stiff suspension may keep your canyon-carver hugging the road, but a certain amount of squat is desired when youre working with a stock suspension. As far as suspension upgrades go, most retained the original springs (coil or leaf) and simply bolted in set of soft rear drag shocks. You may need to play with a few sets of shocks to get the right combo; every car is different.
Leaf Spring Vs. Coil Spring
For the leaf-spring, rear-suspension crowd, the suspension aid of choice is Cal Tracs traction bars. Infinitely tunable, the Cal Tracs work, though they do require a fair amount of tuning for them to work properly. If youre running a street car, a great traction aid is Competition Engineerings Slide-A-Link bars (see Tails of Traction, May 2000). Matched with a pair of adjustable shocks, this combination can be made to work. (A softer spring pack was recommended by one racer.)
Styled similar to a four-link, GMs coil-spring rear suspension works well with some mods. One of the major weaknesses of this setup is the control arms. Notorious for their deflection, boxing both the upper and lower arms is a must. Or if its within the budget, tubular arms from Hotchkis, Lakewood, Global West, or Chris Alstons Chassisworks are excellent alternatives to minimize twist. The stronger tubular design and urethane bushings are designed to minimize deflection.
Whether youre running leaf or coil springs, deflection is your enemy. In order for your suspension to work to its potential, urethane bushings are a must in the rear suspension. Energy Suspensions and PST (Performance Suspension Technology) both offer this type of bushing, or check out Global Wests Del-A-Lum bushings that greatly minimize deflection. Just remember: The more you eliminate deflection, the more accurately your suspension will work.
Full Of Air
For ease of tuning, every car we investigated had airbags. When independent air lines are routed to the bags, airbags are the most valuable tuning tools. Not only do they allow you to set preload on the suspension by varying air pressure from side to side (usually more on the right), they will also enable you to set the total amount of squat that is attained in addition to suspension stiffness. Most of the racers we polled run an average of 13 pounds in the bags. One racer said he ran as low as 3 pounds in the left side and 8 pounds in the right side. Ultimately the bite in the track will determine the amount of pressure used in the bags. Lower air pressure will provide more bite in most cases.
Based on the NMCA rules requiring a radial tire for Factory Street, the BFGoodrich Drag Radial T/A was the only tire currently available. According to every racer we spoke to, the tricks in making the tire work are air pressure and tread depth. Most set the pressure at 13 to 15 pounds. Vehicle weight and track conditions will affect the exact pressure used. As for tread depth, hands down everyone answered bald. Looking similar to a slick, the Drag T/A seems to work best with no tread. Unfortunately, for street use most officers will not be amused with no tread pattern, so this may not work as well on the street. Also getting tire temps up with a static burnout is critical.
The Secret Summary
There is a lot that can be applied from the Factory Street racers. The basic theory of weight transfer is applicable to all cars. Additionally, setting up a loose frontend and soft rear suspension works in most cases. The most important thing to understand is that every car is different. The Factory Street guys have spent countless hours testing and tuning to come up with a combo that works. So check out the sidebars, then get out there and tune.