Can someone pleae explaing to me what a HEI distributor is? And how it works. (In laymans terms please) I am I've tried a search but it just confuses me more. What is a Tach drive distributor? Is it different? I have a 68 with a points (orig) distributor out of the 327/350 in the 454/425 under the hood right now. My tach bounces all over the place upon acceleration but does settle down when I'm cruising. Would a new HEI distributor be easier to tune-up? Easier starting in cooler weather? (I live in northern Canada)

Also what would be invovled in changing it over. What system should I go to? Do I really need to change the tach? What are my options?

I'm not sure if I am supplying enuf/or right info so if you need more please ask.

shmoky

 

HEI is GMs version of High Energy Ignition. Generally it is a distributor with a Coil in the distributor cap instead of an external coil and they are electronic instead of points.
There are several versions, with different ignition control modules etc.
TACH drive means there is a gear output for a mechanical tach for some cars, I have no idea what years, but the C1 and C2's and I presume some C3's had them
In general Yes an HEI would eliminate a lot of tuning issues for a non gear head kinda guy and make starting easier if your starting issues are due to ignition, but then again fixing what ya got would do that too.
I personally like HEI, its very good stuff and I would not hesitate to convert a points non NCRS show car over, in a heartbeat.
You can get an HEI distributor with the tach drive so you do not have to change the tach, a clean well lubed cable might fix your jumpy tach

 

The cable drive tachs are a super PIA, the dist gear set in there for the cable take off is constant headache, the cable is not all that reliable, and the tachs themselves at this age need overhauling...frankly, I would go electronic tach, out of a '75-77 vette, and HEI....HEI will require replacement of that wire going to your coil plus terminal with a heavier wire, as the original points dist had a special wire in there called a resistor wire, so will NOT WORK with HEI....

You probably find an decent old HEI from a junkyard that should work fine with your setup....but it will need a complete overhaul and set up with springs, shims....run like a charm though....

 

You can get a brand new HEI for about $55 off ebay that is ready to go. Just find a hot wire that is hot with the key on and not hot when the key is off and hook it to the "BATT" spade on the dist, but your cable tach is not going to work anymore
Plus you have to have new plug wires and plugs also.

 

First, I've never installed HEI in a '68, so others will need to chime in if there are parts interference.

That said, HEI is a General Motors electronic ignition system, the points and condenser were replaced by electronics. A magnetic pickup coil inside senses when a tooth on the distributor shaft passes and sends a signal to the control module (also internal) to fire the coil then to the spark plug.

There are 2 kinds of tachs, mechanical and electronic. A mechanical tach is driven by a cable from an engine accessory that rotates such as the generator or distributor. In a '68 the tach is driven by a cable from the distributor (tach drive distributor). A bouncy tach is most likely is a cable problem or a distributor problem.

A tach drive distributor has a different housing and shaft than a standard Chevy distributor due to the tach drive gear required for the tach cable connection.

An HEI distributor requires less periodic maintenance than a points distributor. An HEI still has a cap and rotor that wear and still requires a timing setting and can be fine tuned by changing vacuum and mechanical advance settings.

To convert to HEI you would need to purchase an aftermarket tach drive HEI distributor from for example; http://www.hotrodsusa.com/store/product2158.html. To hook it up you would run a new power wire from your ignition switch to the distributor.

HEI is an excellent distributor and very reliable. Unless you put high miles on your car, you probably won't see any maintenance benefit over your points distributor. The HEI has a better spark than your present set up, longer plug life, and you won't need to set the dwell any longer as the points wear. You'll need to adapt your upper ignition shielding to a '75 style because the HEI is larger in diameter and your stock shielding won't fit.

 

The HEI is an excellent electronic distributor. It is used often in low buck performance applications, because it is relatively inexpensive and because it works very well. They are now even available with a tach drive to be able to use your stock tachometer. There are also electronic conversions available for your current distributor if you want solid state capability but original looks. And there are even conversions for your tachometer so you can use the electronic drive from an HEI distributor.

As for your tach bouncing, that is a common problem with the stock mechanical tach-drive distributors. It's normally caused by the driven gear in the distributor bouncing back and forth in the housing. There is a kit available from many of the FORUM vendors that addresses this problem very well.

http://www.corvette-paragon.com/cata...A-690CDA444A81
It is relatively easy to install and very effective. I installed one in my 1973 (L-48) many years ago and it has given very reliable service and settled the tach down very well.

Good luck... GUSTO

 

I installed a HEI Tach drive distributor in my 1970. Had to use different
plug wires because of more spark - I believe it is twice as much -
a coil is about 25,000 but a HEI coil is about 50,000. Now I have a
souped up small block that is driven on weekends - I tend to drive two
lane back roads at the limit. The reason I changed is because the
tach gears on the original distributor were bad. But, I got the HEI with
a tach drive gear - if you get a standard HEI that means electronic
speedo like in a 1975. Do you need it - Based on my driving it is not
necessary and I would stay with the stock unit.

 

Just to confuse matters, there are a handful of HEI distributors with separate coils - the F-body small base unit from the late 80s/early 90s and some early I6 HEIs.

 

This is not an attempt to hijack your thread, but, I also have the same dilemna. I have looked at three options on "that auction site". I don't know which, if any would be better.

item no. 230157991574
item no. 140145751513
item no. 140145941771

I can't tell any difference between the three except a little price;
All are new, not rebuilt.
All have a warranty.
All are American made.

Any help or advise would be greatly appreciated.

Thank-you, in advance,
STEVE

 

I've sold more than a few of same TDHEI distributors ... I don't believe any of the above are "American made" ... I believe all are both manufactured in and imported from Asia. Still, any of the 3 are probably a good value.