Part II: Drivetrain And Suspension
Now that you've applied the knowledge given in last month's "Pure Stock Prep School" on engine preparation, you need to know how to put all that potent Pontiac muscle to the ground. This takes several steps, starting with the trans and continuing on to the rear end, exhaust, suspension and tires.
Why is the chassis the most important place to start when preparing for the Pure Stock Drags, assuming you already have a well-maintained and running musclecar? If the Pontiac can't apply the power it's already making, what good does it do to add more?
Pure Stock racers have reaped...
Pure Stock racers have reaped very good performance and reliability benefits from the Centerforce Dual Friction clutch.
To use a few examples from the '07 Pure Stock Muscle Car Drags (PSMCDR or PS) run in September, we have the slowest GTO at the event and a well-dialed in AMC from a seasoned racer. The two cars have nearly equal specs. Both are four-speed cars, with 3.55 and 3.54 gears, and similar engine size. The GTO actually had a slightly higher trap speed of 98.98 vs. 97.22 mph for the AMC. The GTO qualified with an e.t. of 15.265, while the AMC qualified with a 13.875. With most things equal, the GTO driver, with his extra 1.5 mph, should have been running even faster than the AMC instead of being nearly 1.4 seconds slower. As this GTO is already making reasonable power, it's obvious that it can gain more from controlling what it makes than trying to add more. If it finds the traction it needs, the Pontiac could run well into the 13s.
Both automatic and four-speed transmissions have their strong points. The automatic is much easier to work with in PS racing, given the tire requirements. It'll generally provide a 0.2 quicker e.t. than a four-speed car, but usually gives up about 2 mph to a four-speed car for a similar e.t. Why bother with a four-speed if it's likely to turn a slower e.t. and get roundly beat in the all-important first 60 feet? The few people who can really make four-speeds dance have matched the best auto drivers by using the extra mph they provide down the track. To do so, the four-speed driver must have eliminated the advantage the auto has by the 330-foot mark or earlier, which is no easy task.
A four-speed trans is trickier...
A four-speed trans is trickier to get the lowest e.t.'s, but a proper rebuild prior to racing will help to ensure top performance. Then all you'll have to do is master your launch and shifting techniques.
Automatics add a few more tuning options. Make sure your trans is functioning properly first, and if it is, then you have two choices. One is the torque converter-the maximum allowed is a 2,400-rpm stall speed for GM products. That doesn't mean you want 2,400, though. Feel and quick lockup are important in PS racing. You have to walk the cars off the line and roll into the gas as quickly as possible. A tighter converter does that better than a loose one. A 455 H.O. may work better with an 1,800 stall than a 2,400 because it has large doses of low-end torque. The tighter converter lets you sense traction and meter out that torque quickly. Conversely, a '69 350 H.O. with a Turbo 400 would get pulled off its torque band with a tight converter.
The next tuning factor is whether you should install a shift kit. These cars run modest-sized tires and the B.O.P. versions of the Turbo 400 already have firm shifts. They weren't called "bang screeches" for nothing. If the trans is shifting too abruptly, it'll only cause the tires to break loose on each shift. Every time the tires spin, it's burning up e.t., and Pontiacs, in general, need little improvement in this area. A good quality shift kit that's not biased towards drag slicks is the most you will need.