When this '82 was new, its performance was somewhat short of exhilarating -- Chevrolet just didn't build in the go to match the classic looks. In stoplight sprints, the drivers of less respectable vehicles (read: Mustangs) would wave goodbye as they ran away from the 200 horsepower, 350 cubic inch, automatic transmission-equipped car. This had to stop!
Read on if the thought of hotrodding a Collector Edition Corvette brings joy to your heart (not tears to your eyes) because changes are definitely in store!
Over time, I've built and installed a 418 cubic inch stroker small block Chevy with ported heads and roller cam; swapped a Richmond 6 speed in place of the 700R4 automatic transmission; bolted up headers, dual pipes, cats, and Flowmaster mufflers; beefed-up the brakes and suspension with Vette Products and Koni parts; mounted sticky BF Goodrich Radial/TA tires; and so on... you get the idea. The car has been transformed from a stone into an impressive and very driveable street performer. One of my major modifications, described here in detail, was swapping out the intake and fuel injection system, which netted unbelievable torque gains.
The stock General Motors throttle body fuel injection system (TBI, also known as Cross-Fire Injection) just couldn't coax any really pavement-scorching power out of the big new V8. Port matching, enlarging the throttle bodies to over 2 inches, and modifying the computer PROM still left the TBI system weak. It could only flow enough fuel and air to achieve a respectable yet disappointing 350 lb-ft of torque and about 350 gross horsepower. Oh, sure, with the pedal to the metal it got hard to reach the radio controls, but I was looking for the kind of gut-wrenching, tread-frying thrust that warps space and sends you to the delta quadrant!
As you may remember, GM switched to TPI in the mid 80's Corvettes and immediately achieved impressive torque gains in their factory engines. When the new F.I.R.S.T. (Fuel Injection Research Systems Technology) tuned port injection (TPI) system was marketed as a do-it-yourself kit by a (sadly, now out of business) company named Airsensors / Impco, and was said to be capable of over 450 horsepower and unspeakable torque, I knew I had found the right way to feed my hungry small block the healthy diet of fuel and air it so desperately needed. This, then, is the story of how a F.I.R.S.T. TPI found a home in a Collector Edition that definitely does not collect dust.
Included were a mass-airflow (MAF) sensor, throttle body, TPI plenum, runners, intake manifold, fuel pump, computer control system, wiring harness, plumbing, filters, gaskets, hardware, and an absolutely top-notch instruction manual. One thing that was immediately obvious was that the runner and intake passage sizes are a good bit larger than the GM TPI units, supporting the claims of high torque and horsepower capability.
After making a number of measurements, I determined that filtered air would have to be delivered to the TPI MAF sensor at a point just above and behind the radiator. There was no hope that the excellent (but huge) conical K&N Filtercharger air filter supplied with the kit would fit anywhere in the tight Corvette engine compartment, so I checked to see whether any stock or aftermarket parts could be used in its place. While a late model Corvette TPI air duct was close, it didn't meet the tight hood-to-radiator clearance requirements of the '82, so I knew I would have to fabricate an acceptable substitute. Although it would mean removing the engine-driven cooling fan (leaving only a radiator-mounted electric fan), I decided to make an air filter box just above the radiator that would feed air into the MAF sensor. The new TPI system would just fit under the hood bump after the inner wall was removed.
Removal of the stock manifold was next. I unplugged all of the wiring, disconnected the fuel and return line fittings, and removed all vacuum hoses. Then the top plate, to which the throttle bodies are attached, was unbolted and lifted off.
The manifold bolts came out next and the manifold was lifted away, along with the old gaskets. Cleaning the head and block surfaces ensured the new TPI manifold would seal properly, and a shop vacuum helped me remove bits of loose dirt from the heads and lifter galley. I laid in some paper towels to catch anything I might knock in later.
With the manifold down on the heads, the next problem was getting it to sit far enough back to line up properly. The oil pressure sensor was in the way, so I had to move it out. The addition of male to male and female to female couplers moved the oil pressure sensor out just the right amount to avoid interference with the TPI manifold, yet still clear the firewall.
With the intake in its proper position, I looked through the bolt holes and found it necessary to elongate them slightly upward/outward to ensure the bolts could be torqued down without interference. I later learned that a slightly thicker set of intake gaskets would have made this modification unnecessary.
The edges in the throttle body casting got some attention, so as to improve the CFM capacity of the system. I made these mods using a carbide burr for cutting aluminum, some sandpaper rolls, a steady hand, and some patience.
Using an intake gasket as a template, marks were made to serve as a guide in port matching the intake (the heads had already been ported to match the gaskets). The die grinder was used to carefully enlarge the ports to match the gasket marks.
F.I.R.S.T. provided both a front and side mount for the throttle body on the TPI plenum, and a plate to cover the opening not used. The side throttle body opening was covered, the bolts also securing the throttle cable bracket. The throttle body was bolted to the plenum. You can see where the die grinder was used to smooth the surfaces inside the throttle body.
This was a good time, with the manifold out of the way, to run the wiring harness through the fiberglass fire wall and install the TPI computer. I placed the computer in the glove compartment and secured it to the bottom using bolt holes on its base. With a hole saw I cut a hole in the fire wall, then fed the computer connector through from the engine compartment and plugged it into the computer. A rubber grommet, a little fiberglass cloth, and resin sealed the cable opening nicely.
The TPI computer fit nicely in the glove compartment. It can be reached easily by the driver, and doesn't show unless the door is opened.
Ready to install the TPI manifold, I removed the protective paper towels and vacuumed out the lifter gallery again. RTV sealer was applied to the front and rear rails, and rubber seals were inserted carefully into the guide holes. I then coated the head surfaces lightly with gasket sealer around the intake ports and water passages and put intake gaskets into place. Finally, I put a layer of RTV on top of the rubber seals and more gasket sealer lightly on the gaskets.
The gaskets were secured to the heads with sealer, and the end seals were put in place. Note the elongated fitting for the oil pressure sensor.
I very carefully lowered the manifold down, so as not to move the seals or gaskets. A visual check down several of the bolt holes was made to verify gasket alignment, then I threaded in the manifold bolts at the four corners and hand tightened them to keep the manifold properly positioned. The rest of the manifold bolts were threaded in and torqued down to the recommended 20 lbs-ft in a pattern starting at the center and working toward the ends. Note: It is important to remember that whenever an intake manifold is installed, the rubber end seals may try to squish out of position -- watch carefully for this. Some engine builders don't even use these seals, but rely on a thickly applied bead of RTV to avoid this problem.
With the manifold mounted, I routed the wiring harness under the fuel rails and plugged-in all injectors. The power, exhaust oxygen sensor, fuel pump, MAF sensor, and idle air control wires were all placed in their appropriate locations then locked neatly into position using nylon tie-wraps. The distributor presented a tight fit during reinstallation, so I filed its base a tiny bit to allow it to clear the manifold and turn easily.
Because the manual suggested that it should be done before the runners were installed, I threaded hose fittings into the two fuel rails and clamped on the high pressure fuel hoses supplied with the system. Also, I found a good home for the fuel pressure regulator on the alternator bracket.
The plenum-to-manifold runner installation came next. The F.I.R.S.T. runners are very large (in comparison to stock GM TPI runners), and are cast together in pairs, each marked with its proper location (for example, "Driver Rear"). The 4 castings were fitted to the manifold and the bolts were threaded in, but not tightened (the bottom bolts were a little hard to get to, since the runners fit close to the valve covers). I then placed the TPI plenum assembly down between the tops of the runners, threaded in the remaining bolts, and tightened them all. The final shape of the TPI fuel injection system was taking form!
F.I.R.S.T. provided plenty of vacuum connections to the TPI plenum, and I hooked- up all of the vacuum lines, leaving connections I didn't use covered with small rubber caps. The stock throttle cable fit perfectly into the throttle body linkage. Note: The stock cruise control cable would not fit, however, and was left off.
Knowing this beast would need to breathe clean air, I began the creation of an air filter box. First, the stock plastic air guide was unbolted and removed from above the radiator. Originally responsible for directing air up into the hood passage, this part would make a good platform on which to build the new box, since it already had mount points to the car and was generally in the right place. Next, since the TPI MAF sensor would need to "plug" into something, I obtained a short piece of heavy rubber 4 inch hose from a local boating supply house and cut a small ring. I also bought a rectangular Fram CA3903 flat air filter element. A section of the guide was cut away, then it and the hose ring were secured in their proper relative positions on my work bench. I made a "skeleton" out of hardware cloth (wire mesh) which would connect the two and provide a casing for the air filter. Finally, it was a simple, although time consuming matter to lay on layers of fiberglass cloth and soak them with resin.
While the fiberglass was curing, I swapped the car's electric cooling fan motor with a more powerful late-model Corvette unit, and installed a small engine-driven flex fan. Note that I have since replaced these fans with a high capacity Flex-A-Lite Black Magic cooling fan with integral shroud. After the air guide turned filter box had hardened, I painted it and bolted it into the car. To make it fit, the top portion of the stock fan shroud had to be cut away, after which it slid easily into place.
The MAF sensor tube was to be installed next. It pushed snugly forward into the air filter box. F.I.R.S.T. advised me to isolate the sensor from mechanical engine vibration, so I cut a short piece off of the end of the rubber air-duct hose supplied with the kit, and using two hose clamps connected the hose section to the tube and throttle body. The air filter was then inserted into the air box, its rubber lip sealing around the edge. Although the F.I.R.S.T. people didn't recommend it (essentially due to lack of testing), I would be retaining the stock GM computer to continue management of the spark timing. This required the reinstallation the throttle position (TPS) and coolant temperature (CTS) sensors. I made a simple mount for the TPS using a piece of steel bent into a "Z" shape and attached it to the right side of the throttle body, but found that the throttle turned it the opposite way from stock. This was not a problem, however, as the TPS is in fact a simple linear potentiometer (two-way variable resistor), and functions backwards if its electrical connector is reversed. The coolant temperature sensor threaded easily into one of the holes provided in the front of the TPI manifold.
When I put the distributor cap back on, I found that the Accel HEI Super Coil housing hit the TPI plenum. I removed a piece of the plastic coil cover with a hacksaw for a custom fit that would provide room for timing adjustment. Finally, I installed all of the spark plug wires and other electrical connections and snapped on the stock radio interference cover.
Accel spark plug wires carry the lightning from the modified HEI Super Coil to the plugs. This results in thunder.
Plumbing the connections for the radiator and heater was all that remained before I could straighten up from my position bent over the engine compartment. I found that a replacement thermostat housing was needed to get the top radiator hose to come out at just the right angle, but the installation of the heater hose simply required threading the connector into the front of the TPI manifold and clamping on the hose.
Time to close the hood! Or at least I thought so. The top of the TPI plenum hit the air passage wall in the hood, preventing it from closing. The plenum had to extend up into the hood bump, so I cut part of the inner fiberglass wall away with a small saw.
With the TPI installed on the engine, I turned my attention to the fuel system. The original throttle body injection system used an electric pump inside the fuel tank, which put out around 12 PSI of pressure. The stock fuel line on the 1982 Corvette would flow plenty of fuel, and the car already had a return line, so the job of switching over to the 60 PSI TPI system was to replace the fuel pump, plumb the fuel line connections to the TPI manifold, and strengthen the soft line sections (for example at the fuel filter) using the supplied high pressure hose. The fuel pump provided with the TPI system was designed to be immersible so I decided to mount it in place of the stock pump right in the tank.
The fuel pump, fuel level sensor, and filler spout were removed as an assembly through the opening in the rear deck. I took off the filler door and rubber guard and cleaned everything underneath to help prevent any dirt from falling into the tank. The hoses on the fuel, return, and vent lines were disconnected and the electrical connector was unplugged. Finally, I unscrewed the 8 bolts and extracted the filler assembly through the deck opening. It was a very tight fit, but with some twisting, fudging, and unkind words it came out, gasket intact!
The TPI fuel pump is about the same size and shape as the stock pump, so it was a simple job to swap the two. I soldered the power and ground wires to the lugs on the new pump to ensure a faultless connection. The fuel screen was removed from the old pump and cut to fit the new. Just to be sure it wouldn't collapse whenthe fuel flow was high, I pushed a small spring into the screen before clamping it onto the pump inlet. Finally, the pump-to-fuel line hose was clamped on and the assembly reinstalled.
The stock pump had been connected to the fuel line by a small piece of hose (with no clamps!) and slipped into the bracket at the end of the filler assembly. The TPI pump was almost an exact replacement for the stock pump.
I replaced the stock fuel filter, next to the right front frame rail, and plumbed the remaining fuel connections in the engine compartment. The only thing remaining now was to run a new fuel pump power wire under the car and up to the wiring harness in the engine compartment, which I did, using quite a number of nylon tie-wraps for security.
The TPI unit presents an ominous sight. This is how they should have built the car in the first place!
Nothing else obvious needed doing, but I put off the urge to start the engine just a little longer to recheck everything. I examined all of the plumbing and electrical connections, retorqued as many bolts as I could get hold of, and finally reconnected the battery. One thing I discovered was that I had forgotten to refill the radiator with coolant!
On the first try, the engine fired right up, but would not idle. I opened up the throttle a little bit with the idle adjustment screw, and tried again. This time the engine roared to life and greeted me with a fast idle at about 1800 RPM. At this point I checked the timing, which by chance was just about right. A little more work with the idle screw, and the engine slowed down to a slightly choppy 1000 RPM. The 417's 280 degree hydraulic cam (232 degrees at 0.050 inch) even with Rhoads lifters didn't idle smoothly, but with the old TBI system I could hardly get the car to idle below 1200 or 1300 RPM, so I was quite happy.
|Times In Seconds||Stock 350 with GM-TBI||417 with GM-TBI||417 with F.I.R.S.T. TPI||418 with F.I.R.S.T. TPI|
|0-60 Time||8.2 (per GM tech info)||6+ (approx)||about 5!||under 5 seconds!|
|Quarter Mile Time||16.5 @ 88 mph||14.0 @ 98 mph||13.1 @ 107 mph||12.85 @ 111 mph!|
This table shows how the Corvette's performance was upped by replacing the stock 350 with the 417, then further improved by adding the F.I.R.S.T. TPI system, then reaching its current peak by camming up the engine (and adding 1 cubic inch) during its rebuild.
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