GM's first-generation Vortec engine was derived from its fuel-injected predecessor, the throttle-body fuel injection (TBI). Both the TBI and Vortec engines used only two injectors to supply fuel to the 350ci V-8. The differences between them are that the TBI had the injectors right in front of the throttle plate, where the Vortec placed the injectors behind the throttle plate; and the TBI was a speed density system, whereas the Vortec used a mass airflow system to manage the fuel-injection system.
Even though changing the fuel-injection system to a newer mass airflow system was an improvement, it still carried some faults. With the injectors moved out of the air stream, the engine can pull more air, but the two injectors still can't supply or distribute the fuel as efficiently as true direct port injection. The first-generation Vortec was GM's early attempt at an inexpensive port injection system.
The Vortec's two injectors spray fuel into a distribution block. This block has eight plastic hoses attached to it that carry the fuel to the end of each intake runner. At the end of each plastic hose is a spring-loaded check valve known as a pop-it valve. These pop-it valves open when the injectors pressurize the fuel block and hoses. The run on the Vortec 350 engine was relatively short: It hit the market in 1996 and was replaced with GM's new-generation engine line by 1999.
Due to the short duration and its limited-performance injection system, not many aftermarket companies spent the time or money making performance parts for the Vortec fuel-injected 350 engines. But, of course, that doesn't completely eliminate it from modifications. In fact, we found your typical filters, intakes, exhaust, and even big-mouth throttle bodies. We contacted Gibson for its dual stainless exhaust system, BBK for a high-flow throttle body and spacer, and Airad for a cotton-gauze filter to see how much power was left on the table. We dyno'd the engine and gained 9 hp and 12 lb-ft. You can see the dynamometer results: The upgrades follow the engine's powerband, but at higher power numbers.
Of course, you can't just buy parts and expect that they will give you great results. Every situation is different and this one had some basic fuel issues. The stock dyno pulls averaged a 12.12:1 air/fuel ratio, which showed that the stock programming with the stock components is really close to perfect. The performance upgrades are definitely holding up to their claims. After adding the mods, we found that the air/fuel ratio went to an average of 14.4:1, which is way too lean. Even though we find that the performance upgrades provided an increase in power, we know that there is much more to be had with a programmer that would enhance the fuel to accommodate the increased airflow.
Exhaust Install
1. Cut off the rear section...
1. Cut off the rear section of the exhaust pipe from the rear of the muffler. Pull the exhaust hanger from the rubber grommet and remove the rear segment.
2. Unplug the O2 sensor mounted...
2. Unplug the O2 sensor mounted behind the catalytic converter. Liberally apply some sort of penetrating lubricant on the O2 sensor to prevent damaging it, and then remove the sensor.
3. Unbolt the flange holding...
3. Unbolt the flange holding the after-cat exhaust to the catalytic converter. Remove the remainder of the exhaust system.
4. Put Gibson's exhaust flange...
4. Put Gibson's exhaust flange and first section of the after-cat exhaust.
5. Bolt the two flange plates...
5. Bolt the two flange plates together.
6. Slide on a U-bolt to the...
6. Slide on a U-bolt to the front section and set the new muffler in place, but don't tighten the U-bolt yet. Prop up the muffler so you can twist, push, and pull all the components into alignment before you start the tightening sequence.
7. Install the rear tube closest...
7. Install the rear tube closest to the center of the vehicle first.
8. Slide U-bolt clamps in...
8. Slide U-bolt clamps in place before sliding the tubes into the muffler. Install the second exhaust tube.
9. After aligning the exhaust...
9. After aligning the exhaust so it has no clearance issues - and looks cool - slide on the tips back to where you want them in reference to the body line, mark a lateral line on the tube, and tip for installation reference.
10. Tighten all the U-bolts...
10. Tighten all the U-bolts to lock the exhaust into position.
11. Cut off the end of the...
11. Cut off the end of the exhaust tube, leaving enough room for the tip to pinch the exhaust.
12. Install the tip; make...
12. Install the tip; make sure everything is tight and fire the motor to make sure the O2 sensor is still working. The check-engine light will come on if it was damaged in the removal and installation process. It's also a nice touch to spray a little flat black paint inside the tip for appearance's sake.
Throttle Body Install BBK's...
Throttle Body Install
BBK's power-plus throttle body
1. Remove the clamp and PCV...
1. Remove the clamp and PCV valve tube from the intake. Remove the thumb nut from the intake section covering the throttle body. Lift the back of the intake and slide it forward to remove this section of the intake track.
2. Making sure you don't let...
2. Making sure you don't let anything fall into the intake manifold, open the throttle plate with your hand and remove the cable linkage attached to the throttle body.
3. Remove the bracket mount...
3. Remove the bracket mount to the throttle body. Remove the bolt holding the throttle body to the intake manifold.
4. Unplug the idle air control...
4. Unplug the idle air control (IAC) and throttle-position sensors (TPS), then remove the throttle body from the intake manifold.
5. BBK's throttle plate is...
5. BBK's throttle plate is significantly bigger than the stock unit.
6. The intake manifold is...
6. The intake manifold is wide open - be very careful not to allow anything to fall in because you will damage the engine or need to remove the intake manifold to remove the debris. Covering it with a clean rag is a good idea. Carefully remove the IAC solenoid and TPS from the stock throttle body. Do not apply too much pressure to the screws because you will snap them off in the throttle body.
7. Make sure the gasket that...
7. Make sure the gasket that seals the throttle body to the intake manifold is in position and not down inside the intake plenum.
8. Remove any rags you might...
8. Remove any rags you might have put in the manifold to prevent debris from falling in and set the BBK spacer and throttle body in place.
9. Reinstall the stock screws...
9. Reinstall the stock screws to seal the throttle body to the manifold.
10. Plug in all the electronics.body...
10. Plug in all the electronics.body to the manifold.
11. Hook up the linkage c...
11. Hook up the linkage controls.
12. Reinstall the airbox to...
12. Reinstall the airbox to the intake tube and you're ready to rock.
Dyno Results
+12 LB-FT of torque
+9 horsepower
As far as the filter from Airad, it was the first modification completed and was already installed before we started this project, although we did clean it.