It’s time to start giving George some pep to his step! I was looking around the forum for simple upgrades to his old and tired 350 while I give him an over due tune up and I came across a thread talking about using junkyard HEI units to replace the points system that originally came in these trucks. I felt this would fit right into the realm of recycling and upgrading the spark in my truck.
There are several different types of HEI units available, some which are controlled by computers (4wire), some that have computers and sensor wires (5 wire) and the original 2 wire setup. I went with a simple 2 wire setup. All that is needed is a full 12v power source, there is a tach wire that comes from the unit that helps to tune the advance, but you only need the power wire to run the HEI. So I called a mechanic buddy of mine to ask where to start looking for one and he had one just layin around so he gave it to me for FREE! But nothing is free so off to O’rilley I went. New Accel rotor and cap $42, cheap wires $18 (I will upgrade later), Mr. Gasket curve kit $17 and the cheapest tach they had $20 just so I can tune it (I will upgrade later as well).
If you have not done this to your old truck, you are missing out! First thing I did was replace the cap and rotor in the HEI unit, this involves removing the coil from the old cap and installing it in the new cap with a new electrode and screwing on the new rotor. While I was in there I also installed a re-curve kit from Accel.
The Accel kit has replacement bushings for the weights, modified weights and three different sets of springs to adjust how fast and aggressive the advance engages, all of this allows you to increase rpm faster than the stock setup, increasing horsepower and timing. With the new bushings, springs and the modified weights my timing begins to advance much faster than stock, about 800 rpm.
So after all of the parts are replaced in your HEI you need to get rid of a few things in the engine bay. I began by taking off the negative terminal on the battery, removed the cap from the old distributor and marked the location of where the rotor is pointing on the manifold by placing a piece of tape on the manifold and remove the rest of the distributor assembly. Next step was to insert the HEI rotor with the cap off in the same position as marked with the tape, place the cap on the new unit, run the new wires and gap all the plugs to .045 (with all of the extra spark you get from the HEI you can run a wider gap and get better burn in the combustion chamber, POWER!!). The last step I needed to do to install the unit is dig into the loom that runs across the firewall under the hood, remove the white braided resistance wire and replace it with a red 12ga wire to powers the unit.
Points style coils could not handle a constant 12 volt power source or they would burn up, but they needed 12 volts to start the vehicle, so GM installed the white braided resistance wire to knock the voltage down to about 9 volts at the coil and a wire that ran from the starter solenoid to the coil to give it 12v to get it started. The HEI unit needs 12 volts constantly, so by pulling the spade for the resistor wire at the firewalls harness, replacing it with a new spade attached to a12ga wire, running the wire through the loom (or in my case rewrap the wires in electrical tape), and removing the lead from the starting solenoid all that is needed is to connect the new 12ga wire to the red wire on the HEI plug.
After reconnecting the negative battery terminal, a few pumps of the gas pedal and a turn of the key the truck was running. I then took my timing light and advanced the timing to 14*. With a hotter spark from the coil, and an adjusted timing and the modified curve the 350 has lost allot of the sluggishness that it had with points.
Pages on how to tune an HEI unit-
http://67-72chevytrucks.com/vboard/s...05#post5189005
http://www.73-87.com/7387garage/drivetrain/hei.htm
http://www.chevyhiperformance.com/ho...438/index.html
The first picture is the old coil and distributor, the second picture is the new HEI installed and the third picture shows where I removed the white resistor wire on the firewall mount and replaced it with a red 12ga wire.