GM Distributor tech....

Oh sure, there are lotsa really cool aftermarket distributors and "hocus pocus" ignition systems available to the rodder who elects to run a GM V8 (Chevy, Olds, Pontiac, Buick) in their ride...but let's not overlook the inherent low-buck value and backyard, home-built appeal of the factory distributors. Essentially, they fall into two groups for V8 engines of the "semi-modern era" (Mid 60s - Early 80s)....

DELCO SINGLE POINT

Yes, factory dual point and capacitive discharge didtributors WERE available from the factory on special high performance models such as the Corvette, but we want to keep our eyes focused on what the average home builder might be working with.

The cool thing about GM's Delco single point distributors (also found on some AMC V8 engines) is that the cap features a "window" with a slide-up "door" to allow for adjustment with the engine running. This greatly simplifies periodic dwell settings at tune-up time.

With a single point distributor, there really isn't much that can go wrong. The points act as a mechanical switch to saturate and discharge the ignition coil, and they will do their job without falter for a good long time...although regular inspection and service are required.

Various sources will recommend different service intervals for points-equipped distributors, but my rule of thumb is to install new points and a condensor at an oil change, check the dwell at the next oil change (3000 miles), then replace the points and condensor at the following oil change (6000 miles). You can go further on a set of points for sure, but they are inexpensive, and I like to avert trouble by replacing them a little more often than most folks do!

When replacing the points and condensor in a Delco distributor, I always like to install what is known as a "uni-set", a small ***embly that contains the breaker points and the condensor in one part. These uni-sets can be installed as a direct replacement in applications that were originally equipped with seperate points and condensor. It makes replacing them as a unit a no-brainer.

When installing a uni-set, I've never seen one come out of the box that wasn't set close enough to allow the engine to fire. Once running, hook up a dwell meter and adjust the dwell through the window in the cap to spec. Remember to dab a SMALL amount of the lube provided with your new points onto the rubbing block that actuates the points.

(ALWAYS set your dwell first, and THEN set your timing. Dwell affects timing, but timing does not affect dwell. You'd be surprised at how many experienced mechanics get this wrong!)

Your Delco distributor will also feature mechanical and vacuum advance mechanisms. It's a good idea to inspect the weights and springs at tune-up time to insure that they move freely without sticking or binding. The vacuum advance chamber can be checked for proper operation with a hnad-held vacuum pump and a small length of vacuum hose. Pump it a few times and look for the action, and watch to be sure it doesn't leak down quickly. Replace the vacuum chamber if it is leaking or inoperative.

When hooking up your Delco distributor to the engine, remember that the wire coming from the distributor goes to the NEGATIVE (-) side of the ignition coil. The other side (POSITIVE or +) is fed from the ignition switch through resistance wire (or a resistor) to keep the points from burning out prematurely. In addition, there will also usually be a wire running from a post on the starter solenoid to the positive side of the coil. This provides a full 12 volts to the coil DURING CRANKING ONLY to help guarantee quick start-ups. It's as simple as that, folks! No mysterious wiring involved!

PERFORMANCE MODS & TUNING

You will find that a properly tuned and functional stock single point distributor will work well in most street driven performance cars. However, there are ways to wring out even MORE performance from this old favorite.

To start with, aftermarket companies such as Accel offer replacement caps and rotors for your Delco single point that are made of thicker plastic and contain br*** contacts to increase conductivity.

Performance ignition coils are also available to help boost the secondary voltage to your spark plugs when needed. Accel, Mallory, MSD, Jacobs and others all offer universal style performance coils for single point ignition systems. Hook-up is the same as a stock coil, though some may require a different or additional resistor as recommended by the manufacurer.

Aftermarket points from Accel can also be purchased with increased spring rates. They install like any stock uni-set, but the higher effort spring rate will hold off "point bounce" until a higher rpm level. This will allow for higher revs, but may accelerate rubbing block wear slightly if not lubed properly. Stock points are good for about 4500-5000rpm in most cases, and performance units will carry you to 6000rpm without bounce.

Re-curve kits containing new mechanical advance weights and springs are also available to help you dial in your optimum advance rate. The kits will contain an ***ortment of springs in various tension ratings to provide faster or slower centrifugical spark advance. The best way to set up your ignition curve is on a distributor machine, but you can do the job at the track with a timing light and by noting ET changes. As always...be carefull to avoid getting too much advance too soon, or detonation (spark knock) will wreak havock on your engine! Good idea to up your octane rating when altering your distributor from stock.

Crane sells replacement vacuum advance chambers that are adjustable to control how much advance is provided by engine vacuum. Many racers elect to plug or disable the vacuum advance unit, but it is essential for all around street driveability and maximum economy. The vacuum hose is routed from the chamber to a manifold vacuum source on the intake manifold or carburetor.

When tuning your GM V8, I like to set the dwell to 32 degrees as a starting point. You can go a little bit more, or a little less, based upon what you find your engine to like, but 32 degrees works well for me with most stock or very mildly modified Chevy and other GM V8 engines.

HEI DISTRIBUTORS...

In the early-mid 70s, GM replaced it's points-equipped distributors with a new factory electronic distributor dubbed the HEI, or High Energy Ignition system. Feared at first by staunch supporters of the age-old breaker point systems, the HEI has come to be regarded as a landmark in performance and reliabilty. Today, it still enjoys wide popularity a****st street performance enthusiasts.

The HEI distributors can be quickly identified by their m***ive size in comparisson to their single point cousins. They also feature an ignition coil mounted in the distributor cap, amking for a unique and self-contained ignition system without the need for a coil wire.

The HEI units use a magnetic pick-up coil and an electronic control module to do the job of the old breaker points. They accomplish the same task...saturating and discharging the ignition coil, only they do it without moving mechanical parts.

Being pretty much maintenance free, there really isn't alot to DO with an HEI at tune-up time. There is no dwell to set and there are no points to replace. Until you experience an ignition failure, or wish to perform upgrades to your HEI, there really isn't much that you will need to do!

When an HEI equipped vehicle fails to fire due to an ignition problem, you have three prime suspects to investigate. The pick-up coil, the module, and the ignition coil. Most times, the module or the pick-up coil will be your culprit.

(Unlike points systems, HEI ignitions can fail without warning rather than giving you 'hints' in the form of deteriorating performance)

To replace the pick-up coil is the most difficult task, because it involve removal of the distributor from the vehicle. It is located in the bottom of the distributor, below the plate that the module mounts upon. To remove it requires that you dis***emble your distributor.

Once removed from the engine, you will need to drive the small pin out of the distributor gear so that the gear can be removed and the shaft can be slid upwards and out of the housing. At this point, the pickup coil can be removed and replaced as needed.

Replacing the module is a far simpler task. It mounts to a plate below the rotor and advance mechanism and is easy to get to and remove. It is held in by two small screws, and has wires at both ends. Before installing your new module, clean the metal surface below the old one on the distributor plate and spread a small amount of di-electric grease on the bottom metal portion of the new module. Then, simply hook up the wires and screw it down securely.

The ignition coil is contained in the cap and can be easily removed and replaced as needed or desired. There are two wires on the coil that go into a little "box" on the side of the cap. One is for a 12v positive feed from the switch, and the other is for a tach or test hook-up, if used or desired.

As with a points system, be sure to inspect your mechaincal and vacuum advance mechanisms for proper operation when servicing your distributor.

Hooking up an HEI distributor is as easy as it gets...one 12v wire run from the ignition switch to the cap does it all. No need for a resistance wire or anything else...a true "one wire" hook-up, making it a popular choice for rodders where the is ample room for firewall clearance.

PERFORMANCE MODS

Although an HEI distributor will work dynamite in stock form, it can still be tweaked for more performance if desired. Starting with a good aftermarket cap and rotor is an ideal upgrade, as with your points distributors.

Aftermarket ignition modules are also available to boost performance in an HEI application. They are programmed to provide a longer saturation time (dwell, essentially) to induce a hotter spark. They install just as a stock module would, and make for a very quick and easy performance upgrade.

Accel also offers an HEI Supercoil that bolts into the cap in place of the stock ignition coil. Be carefull when selecting one, however...as there are TWO different applications...one for Chevy and Buick engines, and one for Oldsmobile and Pontiac V8s. The difference being that Chevy and Buick engines feature clockwise distributor rotation while Olds and Pontiac have counter-clockwise rotation. additionally, there are also special aftermarket distributor caps available with a provision for a standard coil wire in the center for those who elect to run a remote mounted ignition coil.

Good spark plug wires are a must with any performance ignition system, and are extremely important on HEI units, due to their high voltage potential. Don't overlook the wires when upgrading your ignition.

As with points distributors, aftermarket advance curve kits are offered to help you dial in proper spark advance, and the adjustable vacuum advance units are available as well. Much of the same rules that apply to modifying advance rates on points distributors carries over to HEIs, including vacuum hook-up and the fact that a distributor machine is the best way to go.

However, the overall mechanical advance is a little more limited on HEI distributors from the factory. Aftermarket weights and springs can help, but to do the job PROPERLY requires a knowledgeable touch, as some grinding work is required where the weights go to increase their travel. This is an operation best left to a pro with access to a distributor machine so that too much material is not removed!

EPILOUGE

In conclusion, it is safe to say that most gearheads can enjoy many reliable miles and great performance from their stock GM distributors with just basic common sense service and sensible performance upgrades. They are dirt cheap when compared to pricey aftermarket systems and components, and will equal their high dollar rivals at the track.

(To illustrate this concept, a buddy of mine with a tricked out Camaro drag car fried his fancy hocus-pocus crank-triggered black art voodoo ignition system and couldn't afford to replace it before going to the track on Friday night. I took a BONE STOCK HEI distributor (coil, module, advance, etc!) from my old Malibu and dropped it into his car. I set the timing for him and we loaded the car up and towed it to the track. It went ONE TENTH FASTER and fired up far easier than his old mega-buck mess did! Made a believer that day!)

So, consider that junkyard distributor for your GM powered ride...with a little effort on your part, it'll likely be all you need for a real world street-strip car or home grown hot rod project!

 

funny how none of this applies to a 2.8 v-6......

 

Great tech article Fat ... I may call you Fat, mayn't I?
Naww ... probably not, just doesn't quite roll off the tongue like FatHack does nor is the picture in my mind as cool....

Anyhoo, you pretty much hit the nail on the head with my next choice of distributor.
It's going on the to-be 462" Buick in the 31 on 32 rails roadster.
I run a Uni-Lite on the 32 and like it, but I have a newly rebuilt stocker I plan to use.

A couple of comments though.
More than likely the Uni-Set points/condenser combo comes with a fiber rubbing block.
If you're running the separate points/condenser setup, make sure you get a set of points with the fiber rubbing block.
The fiber blocks last a lot longer than do the plastic ones.
(Important for me cuz point contact life should be a lot longer as an MSD will be in use and the points will be a low amp trigger for same.)
Along those lines, toss the point lube that comes with the points and buy a tube of Silicon point lube. a $3.00 or so tube is about a life-time supply and the point block will last a lot longer with that.
True with my 4 cylinder Pinto. It ate rubbing blocks at a good rate, part due to the cam lobe is almost a square and the other part prior to my using Silicon lube.
About 6-7000 miles was it prior to using Silicon and about 10,000-11,000 after.

I enjoyed your Holley tech write-up as well and should have commented over there, but I note that here and in the Holley article you commented on using ET to monitor tuning/horsepower changes.
ET - in my experience - is a function of ch***is tune and MPH is a reflection of HP.
***uming of course, the engines runnning pretty good to start with.
Trouble with relying on ET to monitor HP increases is, a bad launch, slippery spot near the start etc. can affect the ET much more than it does MPH.

I like Carters and do run the Holley's from time to time.
Any plans for a Carter tech article?

And I"m still waiting for that 455 Buick engine article....

 

Fine tech as usual Hack.

 

You've had cars that'll beat a stock mustang Hack??? I don't believe it! Good tech stuff... Keep it comin!

Any Ideas on when we'll have tech on pink bikes???

 

AWESOME tech! Havent had a chance yet to read the Holley post but will soon.
Question - any trick to changing the bushings in the housing? I remember doing this in high school shop cl*** but cant remember the specifics, Thanks-