The Stovebolt Site Forums The Shop Area Engine Shop Easy HEI ID ?

One of my trucks has a 1973 Chevy 350 in it. The distributor is an HEI, which probably isn't original.

How do I identify this HEI? It works fine, but I want to hook a tachometer to it, etc.

I haven't found anything yet that looks like a part number on the distributor.

About all I can say is that it does have vacuum advance and the big cap. It also has what appears to be a three wire connection to the outside world. One of the wires is yellow. (Too dark here to tell about the others.

I'd really like to know what it is so I can do some maintenance, and hook up the tach. Most of the discussions I have seen about HEIs only mention one wire. ??

starkweatherr,

Your description sounds like the standard GM HEI. If I remember correctly, with some magnifying glasses, you should see the word TACH embossed on that nub where the three wires connect.

Stuart

The three wires sound like an external coil. Did they use external coils on a V8? The external coil on my six has three wires (org, blk, brn) that exit the body from under the cap and go to an external coil. They only made the external coil for the sixes for two years 74 and 75.

Now if it has the "nub" with Bat and Tach on it, like Stuart says it is coil in cap.

HEIs don't require any maintenance to speak of. About all there is to do is check the bushings on the centrifugal weights.

Larry

It's definitely 'coil in cap'. I'm kind of confused by the 'one wire' that I keep hearing about. Does that mean that it only needs one wire hooked up, although there are other wires, or is there a model that actually only has one wire? Where would I look for a part number on it? That engine bay is so big that I have to get in with the engine to get to the distributor, and I'd like to spend as little time in there as possible right now.

The 3 wire connector comes out of the dist. housing & plugs in to the coil/cap. One wire is pluged into the bat. term. under the cover & a term next to it is marked tach & can hook to a tach or used for testing purposes. If there is any more wires then it is a computer controlled dist. & may not be compatible with your system. Check the centrifical advance for freedom of movement & wear in the weights & pins. Check the vacuum advance to make shure the dia. doesn,t leak.

There is only one vacuum advance/electronic timing control distributor that I'm aware of. It fits mid-80's 305 V-8 truck engines. There will be an oval connector coming from the distributor housing with 4 wires, plus the 3-wire connector that mates the module to the coil connectors. The module on that distributor has 5 pins, and requires a remote timing retard module and a detonation sensor that screws into the engine block coolant drain hole ahead of the starter motor. That system was worthless when it was new, and it hasn't improved with age!

Later model computer-controlled distributors have a 7-pin module, no vacuum advance, and the 4-wire computer connector. They require a full computer-control system for timing advance.

The pre-computer HEI system has a 4-pin module, a vacuum advance, a 3-wire connector from the distributor housing to the inner connector on the distributor cap, and two connections for external wires. One cap terminal is marked "BAT", and the other one says "TACH". Connect a #10 wire from the ignition switch to the BAT terminal, being sure to eliminate any ballast resistors or resistance wire in the process. The distributor needs full battery voltage and lots of current. If you want to trigger a dash-mounted tachometer, connect the trigger wire to the TACH terminal.

HEI systems have an open-circuit secondary voltage potential of 50,000 volts, so special coils and other high-performance gimmicks are totally unnecessary. With a little sneaky tweaking, I've run round track race engines on completely stock-appearing HEI distributors at 7,000+ RPM and 500+ HP.
Jerry

Related question, I just bought a 1952 GMC with a 1976 inline 6 cylinder bolted to a powerglide. It's being transported to my house but I'm curious as a kid on Christmas. Would it have the HEI distributor and what size 6 cylinder did they make in '76. Supposed to have been rebuilt completely 3000 miles ago. Any opinions? Thanks Terry1218

A 76 engine would probably have an early HEI system. possibly the one with a remote-mounted coil. Later ones went to the coil-in-cap setup like the V-8's. Displacement would probably be 250 cubic inches, with a possibility it would be a 292. 292 engines have the passenger's-side motor mount offset about 3 inches, while the 194, 230, and 250 engines all have mid-engine mounts directly opposite each other. All of the inline 6 engines newer than the 235/261 type will have the same bellhousing bolt pattern as the V-8's.
Jerry

Jerry

Thanks, HotRod Lincoln. I think that is everything I needed to know.