Since both the fuel injectors and the fuel pump were about 20 years old, Bruce says they are definitely wear items, and you will be money ahead by replacing them before throwing large amounts of bolt-on cash into one of these cars.
Another recommendation is an adjustable fuel pressure regulator (AFPR), so we contacted Holley Performance Products (as the company seems to know a thing or two about fuel systems) and ordered the Holley adjustable fuel pressure regulator, a very impressive design featuring a large stainless wheel that can be adjusted by hand, no tools required. Although we had interference with the wheel against the bottom of our intake plenum that required some grinding for clearance, we would come to love our Holley AFPR for this hand-adjustable feature, which made fiddling around hot engine parts in the back of the engine bay a minimal hassle.
Baseline Testing - We took our GTA to MD Automotive where owner Mark DiBella loaded it onto his Dynojet chassis dyno to test our baseline performance parameters. After a few test pulls, Mark reported that we were running lean at lower rpm as we had reset the fuel pressure to the stock 42 psi after installing the Holley AFPR. But when Mark produced his own fuel pressure gauge, it read only 32 psi. We boosted the fuel pressure to 42 psi and ran it again. The fuel curve was better, flatter, and the hp and torque curves became flatter and more consistent.
The Mods - Our next modification was to be the Mufflex after-cat system, which is impressive in that it's a true 4-inch arrangement with an adapter from the 3-inch catalytic converter. We had originally intended to bolt on this system and have a go on the dyno. Our plans were foiled, however, by the fact that our original catalytic converter had been cut out and a universal replacement was welded in. In order for us to test the Mufflex after-cat, we would have had to weld the system onto the original universal cat, thereby ruining the nice adapter section supplied by Mufflex to bolt to the original cat converter. As we had also resourced a high-flow catalytic converter from MagnaFlow and a complete header/Y-pipe system from Hooker, our best option was to change the entire exhaust in one shot so that everything would remain bolt-on as intended to begin with.
We were pleased with the beautiful, polished, ceramic coating that our Hooker shorty headers had out of the box. This coating not only looks great and retards rust and corrosion, it's also a thermal barrier that helps keep the heat (energy) in the exhaust, thus benefiting velocity. As we have discussed, that will be very important for any gains on this package with its current tune.
Though we were less than giddy with our 180 rwhp and 245 lb-ft of torque at the rear wheels, it's about what we expected. This car has run a best of 14.7 in the quarter-mile at Carlsbad Raceway before that track was bulldozed into history, so back-up quarter-mile testing is not in the cards.
Having long been trained by smarter people, we never install headers that have not been gasket-matched and thoroughly detailed (see photo). With a die grinder and compressor, gasket-matching is a 15-minute job that stops the exhaust gases from running into a brick wall as they exit the ports.
More than just a restriction, when the exhaust collides with these "right angles," it sends a strong pulse back into the exhaust port, which kills a great deal of the exhausts' energy that is trying to push it out, akin to two ocean waves colliding from opposite directions, canceling each other out. This is a sure power killer, and being so close to the exhaust valve, could actually cause reversion, which is pushing exhaust gases back into the engine resulting in excessive heating and dilution of the incoming intake charge. If you own any Pontiac with headers, this is something you should consider.
We also noticed that the opening at the collector, which forms a ball-shaped union with the Y-pipe, necks down to 1 15/16 inches. This is probably there on purpose so a 305 won't lose torque with headers that sacrifice lower-rpm velocity for improved flow, as Bruce Hawkins warned us. We have a 350, and 1 15/16 inches just didn't seem big enough, so we used our die grinder to open these up to 2 1/8 inches. Our intention was to see if we could make modest increases in both horsepower and torque as opposed to sacrificing one for the other.
Tubing diameters are only slightly bigger all around for the Hookers, but all transitions,
To gasket-match the header flanges, we marked the areas showing inside the gasket opening
Because these headers are also for 305 engines (we have a 350) and use a ball-type collect
Although the headers slid in and touched nothing, they were close to some of the coiled br