Exhaust: No Parts Runs!If you are going to do one thing to your TPI car it should be installing a good set of headers. We've seen 0.60-second gains at the track on a 305 five-speed Z28, and when you see the stock stuff, you'll know why. The cast-iron manifold feeds all the exhaust ports into one centralized tube that takes a 45-degree turn into a small collector. It's like GM hated it. The new SLP tubes slide in from the top pretty easily after you pull all the emissions stuff out of the way. We switched the spark-plug wires to 90-degree-boot style with a generic Summit set and bolted them up. The collectors use a doughnut combined with a variation of the ball-flange design that matches the stock stuff. The sting is the $654.95, but they're already thermo-coated and with a monster-thick primary flange and the trick collector they're not gonna leak.
Beyond that, it's worth the $89 to get the SLP header-installation kit that converts the dual-cat system found on '89-'92 cars into a big single. It makes it so you don't have to go to the parts store, not even once. The two-into-one pipe from the headers joins a 3-inch elbow that connects to the cat. We used a Random Technologies 3-inch catalytic converter that bolted directly to the after-cat via another ball flange but required a weld where the SLP elbow met the Random inlet. Since we also needed to weld up the A.I.R. tube and seal the unused bung on the cat (it's universal), we took the Pontiac to Speedway Muffler in Gardena where Wayne zipped it all up for $35.
The after-cat needs no explanation other than it bolted directly to the factory mounts, has both tips exit on the driver side, and sounds mellow like a refined version of the old Turbo IIs you liked in high school. At full-throttle there is no harsh glasspack rattle.
Second Run: 14.66 at 92.82We were hoping for 0.50 off the first run because that's what a good exhaust system will bag you on these cars. We missed it by a bit and here's why: In the past, we've used a system that basically equates to a straight shot from the back of the cat to a tail pipe using what is referred to as "adjustable" exhaust. It's loud. Also, as we mentioned before, the intake runners will benefit from the plenum porting. Those two restrictions likely cost us a tenth or two. We ran 14.75 at 92.01 mph with crazy wheelspin, then bolted on a set of 26x11.50-16 ET Streets on '91 Z28 wheels, set the timing to 15 degrees, and found a 14.66 at 92.82 in it that corrects to 14.19 at 95.94.
So we're zoomin', and tenths away from a 13-second pass with only a couple of bolt-ons. The other news is that we're bummed that we already spent about $2,500 to get the thing to run right, but that will change when we add a few more parts that will take advantage of the intake and exhaust mods and go fast. Love it? Tell us on CarCraft.com.