1991 Tuned Port Fuel Injection Installation

Adding that new crate engine to my 1981 Corvette just wasn't enough! Instead of rebuilding the old L81 computer controlled carburetor, I decided that Tuned Port Injection was what I needed. I basically bought a Speed Density system from a 1991 Camaro 305 V8 off of Ebay, replaced the 19# injectors with 24#, and reprogrammed the MemCal.

Here's a few pics of what the system looked like when I bought it. pic1 - lower intake (bottomside). pic 2 - lower intake (topside). pic 3 - parts layout

The first thing I did was bead blast all of the aluminum parts. pic 1 - throttle body top (this was caked with carbon deposits). pic 2 - runners (before & after). pic 3 - intakes (before & after) Notice the one on the bottom is the style used on Corvettes with aluminum heads. It has a separate EGR passage and rear water passage. The extra water port is to keep each end of the aluminum heads at even temperatures. After blasting, this is the one I keep and install.

I decided it was best to check the hole treads to make sure they weren't stripped. Some were a little tight, so I rethreaded them.

This is a diagram of how the fuel system was plumbed on the '81 Vette. It should work for most C3's. 81vettetpifuellines.doc The MSD 43mgh fuel pump was mounted directly behind the transmission crossmember underneath the passenger side seat. The fuel filter was mounted onthe passenger side frame just before the foot well.

A fuel hose connection was needed between the pump outlet 5/16" and the filter inlet 3/8". The old mechanical fuel pump and push-rod were taken off and a chrome block-off plate was installed. Flexable fuel lines (3/8"supply and 5/16"return) were mounted between the engine and the frame to allow for engine twist and vibration. I also added some wire loom for protection to all the flexable lines. As another bonus, I placed a fuel pump test button under the hood so that I could test the fuel pump/pressure when the engine wasn't running.

I mounted the two fan relays where the old engine relays mounts were located. Only one fan is being use now. A knock sensor was installed on the passenger side of the engine block just in front of the starter and engine mount. It connects to a water passage. This hole was originally plugged. Supposedly the location for the knock sensor isn't that critical as long as it's mounted to the block. I replaced the old 2-wire oxygen sensor with a heated 4-wire. It is very, very responsive and takes less than 3-5 minutes to reach temp.

For all TBI engines through 1992, all computer-controlled-carbureted engines, and all 1985–1989 TPI engines, a two-pulse (2000 pulses per mile) square wave (D.C. current) Vehicle Speed Sensor (VSS) was used. So, I had to upgrade mine to a four-pulse (4000 pulses per mile) sine-wave (A.C. current) sensor. These were used on 1990–1993 TPI, 1992–1993 LT1 engines, and 1990–1993 Camaro 3.1/3.4 V6 engines. It is mounted between the automatic transmission and speedometer cable.

Here is a pic after everything was installed and I began to tune the engine. Some things are still missing (i.e. distributer plate). Notice the placement of the 0-60psi fuel pressure gauge. It took some work trying to get the right fittings so that it would clear the MAP sensor and distributer. For now the K&N filter on the front of the throttle body is exposed to the hot radiator air, but later I will install a cold air induction system.