TPI Bolt-Ons for Speed

The new SLP system is actually slightly cleaner than the stock dual-catsetup.

Aftermarket intake runners are the soup du jour for TPI guys, and SLPmakes a set that are actually easier to install than the stock piecesbecause of the thicker mounting flanges. These things are worked to makepower by enlarging the intake tubes and removing the first inch or so ofmaterial between the runners where they mate with the plenum,essentially extending the plenum area. More plenum, more torque. Thenext trick is to cut the plenum divider and the gasket to match, but wedecided to keep the first set of mods strictly bolt-on.

Exhaust: No Parts Runs!

If you are going to do one thing to your TPI car it should be installinga good set of headers. We've seen 0.60-second gains at the track on a305 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 centralizedtube that takes a 45-degree turn into a small collector. It's like GMhated it. The new SLP tubes slide in from the top pretty easily afteryou pull all the emissions stuff out of the way. We switched thespark-plug wires to 90-degree-boot style with a generic Summit set andbolted them up. The collectors use a doughnut combined with a variationof 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-thickprimary flange and the trick collector they're not gonna leak.

Both tips exit on the driver side. Here we dropped one tailpipe anddented it so it wouldn't fit. We threw it in the trunk for the mufflerguy to fix.

Beyond that, it's worth the $89 to get the SLP header-installation kitthat converts the dual-cat system found on '89-'92 cars into a bigsingle. It makes it so you don't have to go to the parts store, not evenonce. The two-into-one pipe from the headers joins a 3-inch elbow thatconnects to the cat. We used a Random Technologies 3-inch catalyticconverter that bolted directly to the after-cat via another ball flangebut required a weld where the SLP elbow met the Random inlet. Since wealso needed to weld up the A.I.R. tube and seal the unused bung on thecat (it's universal), we took the Pontiac to Speedway Muffler in Gardenawhere Wayne zipped it all up for $35.

The after-cat needs no explanation other than it bolted directly to thefactory mounts, has both tips exit on the driver side, and sounds mellowlike a refined version of the old Turbo IIs you liked in high school. Atfull-throttle there is no harsh glasspack rattle.

Second Run: 14.66 at 92.82

We were hoping for 0.50 off the first run because that's what a goodexhaust system will bag you on these cars. We missed it by a bit andhere's why: In the past, we've used a system that basically equates to astraight shot from the back of the cat to a tail pipe using what isreferred to as "adjustable" exhaust. It's loud. Also, as we mentionedbefore, the intake runners will benefit from the plenum porting. Thosetwo restrictions likely cost us a tenth or two. We ran 14.75 at 92.01mph with crazy wheelspin, then bolted on a set of 26x11.50-16 ET Streetson '91 Z28 wheels, set the timing to 15 degrees, and found a 14.66 at92.82 in it that corrects to 14.19 at 95.94.

So we're zoomin', and tenths away from a 13-second pass with only acouple of bolt-ons. The other news is that we're bummed that we alreadyspent about $2,500 to get the thing to run right, but that will changewhen we add a few more parts that will take advantage of the intake andexhaust mods and go fast. Love it? Tell us on CarCraft.com.

The Cost of Cool