The Stovebolt Site Forums The Shop Area General Truck Talk HEI vs Point. Dist.

Coils based systems need 8 volts and use a resistor wire to drop the voltage...HEI needs 12 volts.... - Is this statement true?

Yes, if you are referring to the GM HEI system. Other makes & conversion solid state systems sometimes use resistors.
George

Coil based systems can run on 12 volts, but the points contact will wear quicker. Points system do use full 12 volts on the start circuit, them drop to 8 or 9 in run circuit byway of the resistor wire. GM used a 12 gauge wire to feed the voltage to HEI, so they wanted to make sure it had full battery voltage.

Aftermarket HEI or conversions differ from vender to vender.

Ok - The truck - 1967 250 Cu In has a GM - HEI, reason unknown, bought it that way....So is it 'plug & play'? or does the wiring have to be adapted.....Incline to go back to point distributor.....

GM replaced the point distributors in 1975 with HEI distributors in all of their vehicles including the 250 6 cylinder. It appears that the PO installed one in your truck. It's a common upgrade, if it is installed correctly, and it works OK, leave it alone and drive it.
Fred

Key word...'Installed Correctly' ...well its not off a tooth, and its sitting firmly on the block....I guess its installed correctly.....I'm just Ole Skool.....My 292 has a point distributor and I'm good with that.....Wondering if these HEI upgrades is due to not knowing how to set points, as silly as that sounds......

No, HEI came in because of increasing federal emission demands to burn cleaner, with this you get hotter spark, wider plug gaps that lead to longer life/less problematic ignition components to just name a few

Old School is OK. If you like points, go back to points. There is nothing to bad mouth about a GM HEI. It's better and it is way more reliable. Nothing is easier to wire than GM HEI. They are not installed because someone does not know how to set points.

Aftermarket "HEI" mods to stock distributor is another story for another time.

Just make sure that whoever wired the HEI did not use the resister wire from the original wiring harness which is for the points system. This wire will only provide 8-9 volt and will not work reliably to power the HEI.
Carl

HEI require a large 12v wire, the old feed wire will not do it.

Ed

OK - will check the wire out....So its a single wire,.... what gauge wire should I be looking for?

12 ga. from ignition switch to HEI. All resistance wire or ballast resistors removed. Some folks can have trouble if they have an ignition switch/system that has a separate start and run circuit. They will need to maintain 12V to HEI during start. Some older switches do not have 12 volts on the ignition run terminal in the start position.

Also, you should have a 12 gauge wire feeding the ignition switch. It does no good to have small wire feeding large wire. If you find your ignition switch does not supply battery voltage in start position, use the factory wire off the starter solenoid ( I ) terminal and splice it in to the distributor feed circuit. It's the same wire the points system uses.

HEI’s actually draw very little current.
In talking to Tom Langdon about why Chevrolet used such a large supply wire, he told me it was to prevent electrical interference from outside sources.
I have seen many HEI’s work just fine using much finer wire.
Full 12 volts is required.

I would not repeat that theory too many times. The larger wire does not shield against EMI. The larger wire will help with voltage drop and amp surges. Even though HEI draws pretty low amps most of the time, it does have higher draws.

The plug wires have EMI protection.

The wiring diagrams say 12Ga. Possibly a safety factor included. 10ga is used by many on here.
A 14 gauge will probably work (one size down). But what's the point? Wire the HEI per GM instructions.

American Autowire provides a 12Ga wire. They are the leader in wiring harnesses.

"The average current draw isn't large for HEI. But for a short time, each time the coil begins to charge, they draw a lot of current. It's called "instantaneous current draw" and it's the real reason why GM used such a large wire for HEI systems. Plenty of people have learned by experience that too small a wire diameter can cause problems with the way the truck runs."

Was able to eye ball the truck today & took these pics.....Looks to me the yellow wire, is on the same wire connector as the heavier 12 gauge pink wire....and the yellow wire also goes to the starter....The installation of the pink wire on the junction box looks to be more recent than the rest......Not understanding why the pink & yellow are connected together???

It appears to me that the pink wire is terminated with a spade connector and wedged into the plastic housing making contact with the power side of the HEI unit. The yellow side should be for a tachometer. Cobbled up for sure.🛠

Little bit of a contradiction here....There's no tach to eliminate any confusion....If I understand this correctly...It should be a one wire preferably, 12 gauge from the junction block on the firewall to the HEI ??? Here's my issue to shed some light on this...The truck starts and runs on choke...To get any RPM the gas pedal needs to be pumped....then its spits & sputters...won't idle & quits...The carb has been taken apart twice & I'm 99.9% sure there are no plugged passages....There's good vacuum & the timing is set.....I also had the ignition switch out of the truck for a cyl & key replacement as the PO lost the key and was starting it with a screwdriver....Now another question why would a new ignition switch be any different in design? - wouldn't a replacement be the same????

A new cylinder and key does not change the contacts in switch. So you didn't get a new switch. The difference in design is as I said earlier. The old switches do not have continuity between the "Ign" terminal and the "Start" terminal. The newer switches do. That means on an older switch if you hook the HEI to the Start terminal, it would start then shut off when you let go. If you hooked the HEI to the run terminal it would not start unless you pushed the truck. Old design and new design. The wiring you show looks like you have an older switch.

Looks like they have it correct. They have it wired for the case I mentioned. An old ignition switch where run is not connected to start when switch is in start position. The violet wire to solenoid "S" terminal is from the ignition switch "start" terminal. The pink is from the ignition "ON" to HEI and the yellow is from the solenoid "R" terminal to HEI. They are connected together so that HEI gets 12V while starting and while running. If you ever get a new switch, you won't need yellow from "R".

If you have a separate issue with spits and sputter, I suggest another post.

This thread has been allowed to run on too long.