Holley's adjustable fuel pressure...
Holley's adjustable fuel pressure regulator (left) offers a unique oversized thumbwheel that makes adjustments a breeze, even on a hot engine.
The stock fuel-pressure regulator...
The stock fuel-pressure regulator top and diaphragm were removed as shown. Holley's unit simply bolts on using the same T10 tamperproof Torx bolts, and a T-40 Torx is required for removal of the plenum.
The rear bottom of our plenum...
The rear bottom of our plenum needed to be clearanced to make full use of the thumbwheel adjustment. On the left, a second unmodified plenum is shown for comparison.
The ceramic coating is optional...
The ceramic coating is optional from Hooker. Primary diameter size of the shorty headers is 1.625 inches.
OK, we'll be the first to admit that the Tuned-Port Injected cars, and Third-Gen F-bodies in particular, don't get much respect. Eschewed by traditional car collectors because they are too new, corporate-powered, and high production, Third-Gen Firebirds are often cast aside by the all-out power junkies as well because their performance was significantly eclipsed by the generations preceding and following them.
So why would HPP decide to do some tech on one of these automotive Rodney Dangerfields? Because the value of classic-Pontiac muscle has put those cars out of the reach of many, especially the younger readers. Speaking of the younger generation, our test car seems to be irresistible bait for the import-boy racers around town and has effectively smoked all but one in purely stock form, so why not build an import-eater?
Our GTA looks great against four-cylinder buzz bombs and on paper with its port-injected 350 L-98 V-8, factory oil cooler, 700-R4 four-speed overdrive auto trans, 3,380-pound curb weight with a half tank of fuel, 16x8-inch wheels, four-wheel disc brakes, WS6 suspension, digital dash, air adjustable seats, and power everything. This Pontiac should be really fun to drive, and it is, but it has its compromises that are part and parcel of the era in which it was designed.
At the dawn of the Reagan years, meeting government-imposed emissions requirements and corporate average fuel-economy standards were paramount concerns of automakers, and electronic engine controls were still in their infancy. By the mid '80s, engine packages were improving from both a power and efficiency standpoint. A highlight was the newly designed Tuned-Port Injection (TPI) of GM. It incorporated an integrated-systems approach to designing an engine to maximize torque and fuel economy, while meeting emissions requirements. Problem was, modifying the engine for more power upset the balance with the other matched components, and the power increases from typical bolt-ons were not as robust as they had been with earlier engines. This earned the TPI engines the reputation of being difficult to modify. When the TPI 350 debuted, the problem was somewhat exacerbated.
The 305, for which the Tuned-Port intake was originally designed, used the same 3.48 stroke as the 350 but with a much smaller 3.74 bore, so the 13.65-inch-long runners from the intake plenum to the heads were designed to maximize what little velocity the small-cammed, low-compression, small-bore, and slow-revving 305 could create, and it did exactly what it was designed to do: make low-end torque. But on a 350, while there is an impressive 330 lb-ft of flywheel torque, there's only 230 flywheel horsepower. So the GTA has great low-end torque, but it can't breathe at higher rpm, which is necessary to make the power that this engine design should be capable of with its larger bore.
This, coupled with restrictive heads, smallish valves, a tiny cam, and the aforementioned massively long intake runners almost guarantee that no matter what bolt-ons we throw at our Third-Gen, it's not going to suddenly awaken from its slumber and climb the Empire State building to swat some hapless airplane out of the sky unless the whole engine is upgraded to breathe at higher rpm. But you have to start somewhere.
All this being said, we still strongly believe that these are great cars for an entry-level gearhead to learn on, and if you pay attention and make the right modifications, you can serve up helpings of humble pie to the legions of "Fast and Furious" fans who try to treat your Pontiac with disrespect.
Some Advice - HPP consulted with Bruce Hawkins at Hawks Third Gen Parts who provided some general warnings regarding Third-Gen TPI cars: "The 305s don't like large-tube headers or open exhausts. They lose velocity and the torque falls off, and although it sounds impressive, the car will be slower." He also cautions against steep gearing. "Third-Gens like taller gears. They are torquey, so steep gears and big converters will give poor results."
Following Bruce's advice, we wanted to be sure what we already have is working properly. Fresh plugs, wires, cap, O2 sensor, oil change, coolant change, and making sure there's air in the tires came next. OK, it idles better, but it's a long way from fast.