Home page

Topic: Phase 2 of installing EFI to my 75 Coupe

in Forum: C3 Fuel, Emission Control, and Exhaust Systems

Already a Member?
Not yet a Member?
Register for Free!

Phase 2 of installing EFI to my 75 Coupe (1/2)
 10/17/19 4:20pm
Standard Member
Send Private Message

Cana, VA - USA

1975 Stingray 71 350 engine Flat top pistons Sniper fuel injection Hyperspark ignition Vintage Air air conditioning Borgeson power steering box

Joined: 7/3/2016
Posts: 266


In an earlier post I described installing Holley’s throttle body electronic fuel injection on my 75 Corvette Coupe. Following is the rest of the story.

Now that I have the throttle body fuel injection installed and working, phase two is replacing the distributor with a system that allows the TBEFI to control the ignition timing. This involves a distributor that has no mechanical advance mechanism in it along with a high energy coil and ignition control box.

The first step is to install the coil and ignition box – or more accurately, finding a place to install them under the hood of a very small space. I made a bracket to hold the ignition coil above the air condition box and right in front of the cowl. This allowed it to be close to the distributor.

The ignition box was a bit more complex. This is about 4 inches wide, 8 inches long and 2 inches high. Other than mounting it on the inside of the firewall (which I didn’t want to get into because running the wires out through the firewall would be a pain), the only place I could find was beside the right fender, above the right wheel suspension. I had to mount it flat so there would be enough clearance for the suspension to travel. I made a bracket that mounted to the inner lip of the finder.

Once all the pieces were mounted, the next step was to set the engine at zero degrees on the number one cylinder, pull the old distributor and insert the new one. Holley provides very good instructions, but they are for a number of different types of ignition systems, and I had to do a bit of detailed reading to make sure I was configuring for the correct pieces that I had.

Next was to hook up the wiring harnesses. As you can probably imagine, there are a lot of wires going between the different components. Again, Holley provides very good instructions. The big challenge was to keep everything as neat as possible.

Once this was done, you turn on the ignition without starting the engine and use the touch-screen to configure for the new setup. Then start the engine, recheck everything and take a ride.

Initially, things did not go as well as I had hoped. The engine ran rough and misfired when getting on it hard. Since I now had a high-energy ignition coil, I suspected that there was leakage in the plug wires. I ordered a set of 8.5 MM MSD plug wires from Holley. They made the difference! After re-adjusting the hydraulic lifters again, the engine ran smooth.

A ride around the block blew me away! Throttle response was instantaneous, and the power was unbelievable. This Stingray was never this quick in the three years that I have had it.


Here are some pictures:

This is the bracket I made to hold the high-output coil:


This is how I mounted the ignition box:


This picture shows most of the components:

|UPDATED|10/17/2019 1:20:33 PM (AZT)|/UPDATED|



Our Sponsors help support C3VR
Re: Phase 2 of installing EFI to my 75 Coupe (2/2)
 10/16/19 6:16pm
Limited Member
Send Private Message

Overland Park, KS - USA

1973 Orange Metallic Coupe (orig owner), L82, 4 spd (WR), PS, (A/C & PW (I installed from wrecked 73)), leather, AM/FM Stereo, ran with '65 FI unit earlier & will again some day.

Joined: 7/9/2003
Posts: 740

Your comment about the instantaneous throttle response was the same as I had when I installed the 65 Rochester fuel injection on mine. Due to some teething problems and lack of local knowledge, eventually took it off but have since discovered some of the corrections for the problems and plan to reinstall it sometime.

Post some pictures of your install when you get a chance.

|UPDATED|10/16/2019 3:16:20 PM (AZT)|/UPDATED|


1973 L-82 4 spd

Our Sponsors help support C3VR