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How good is a factory HEI(76 time era) compared to todays popular hot rod ignitions? Is it worth it to change or can an HEI be upgraded? <P>------------------<BR>455 Ken

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  • 2 years later...

Don't qoute me on these numbers, but a points ignition system puts out around 19,000 volts and an HEI puts out closer to 450,000 volts. aftermarket coils and modules can be installed to the stock unit but make sure the wire supplying power is changed (points couldn't handle a full 12 volt supply and HEI needs all 12 volts) so YES HEI is definitly an improvement.

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The stock point type ignition puts out around 7,000-14,000 volts on a good day. These also use a breaker (points) to fire the coil which is difficult to keep in adjustment over it's life span. The HEI puts out around 50,000 volts (100,000 if modded) and uses a magnetic trigger to fire the spark, making for easier starts and better accuracy to about 5500 rpm. Anything above that and the spark begins to scatter. The HEI also allows you to run a bigger plug gap creating a more efficent burn.

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The original HEI-style ignition first appeared as an option on '72 Pontiacs. Prior to that, the top performance dog ignition from GM was the capacitive discharge system of the middle 1960s.

Point ignitions worked pretty dang good back then, with coils up to about 40KV ratings. OF COURSE, the coil will only produce enough spark energy to fire the plug and no more. If it takes 10KV to do it, that's all it'll produce on each plug's firing. In other words, you don't get a 40KV zap on each firing unless it takes it to fire the plug. Most of those stock point ignitions, single point or dual point variations, would hit in the neighborhood of 30-35KV. Seemed to be enough to fire compression ratios of 11.0 to one back then . . . The hard core racers used magnetos for their drag racing applications back then, which is a whole 'nuther ball of wax.

The dual points allowed for greater coil saturation before the coil fired. Supposedly better for higher rpms, but I believe that Pontiac proved that was not always the case back then--or mayabe they wanted to prove their single point systems were adequate for performance uses and saved a few bucks per vehicle.

Single points typically had a dwell setting of 30-32 degrees. Dual points went about 10 degrees higher.

When the GM HEI system was designed, one primary design criteria was that it would fire a .100" spark plug gap. As noted in a book I found back then, when the gap got wider than about .070", the condition of the plug wires became critical. In those middle '70s emission engines, there were many that used .060" gap for emissions purposes. They also were somewhat prone to fouling on the new car dealers' lots who moved them around every so often and didn't let them get fully warmed up, from what I read, resulting in a revised gap recommendation of .045" or so. Seems like Olds led the way with the .060" gaps back then as other GM divisions typically used .045" gaps.

In later times, it was found that the output of the HEI would start dropping off above about 4500rpms. Still had more power than the point systems after that, but not by much in the higher rpms. The cure is acknowledged to be an aftermarket ignition module and maybe matching coil. One name mentioned is MSD, but others might work as well with respect to the high rpm output curve.

Any electronic ignition will have increased spark stability compared to a point system. In many of the conversion kits of the early '70s, it was also noted that you could count on about 1 degree of ignition timing retard/1000 rpms when changing from a points system to an electronic system. Might be a minor point, but it was noted in the literature.

If there is spark scatter, it might be due to the ozone buildup in the cap so that's why many people drilled small air holes in the base of the caps. Other than that, it could be due to uneven loadings of the oil pump and the resulting flexing of the pump drive/distributor shaft or torsional dynamics thereof. But that would typically be in the above 5000rpm range.

What would be critical now, with respect to using a point ignition, would be the wear on the distributor cam (what the rubbing block of the points contacts) that determines when the points open and close. These will wear with time. Such wear can be verified with a dial indicator.

The other thing I've come across is that for a period of time, the ignition point manufacturers deleted the little vial of "point rubbing block grease" from their point kits. This grease is vital for the long life of the points and decreased wear of the rubbing block on the points themselves and the distributor cam. If the grease is not replaced/added when the points are changed, point life will deteriorate greatly as the dwell and point gap will change as the block wears prematurely. This point grease is still listed in the GM Standard Parts Catalog.

We used to get over 25000 miles on a set of properly setup points, back when those cars were newer. That was usually when the spark plugs needed attention too. As I mentioned, they did a very credible job back then on those engines.

Now that the cars have aged since then, and people like to add things like nitrous oxide (which increased compression pressure in the combustion chamber and also increased the voltage needed to fire a plug in that environment), the spark's environment is much different on those modified applications. Factor in the fact that few good distributor cores with good distributor cams are around, plus the lack of maintenance factor, and the electronic systems make more sense.

But if you've got a stock distributor that's still working well, unless there are wear issues (other than bushing, which can be possibly addressed without much problem) such that the dwell will not set correctly with the stated point gap spec, I don't see any reason to change something that's working just for the sake of changing something.

One thing now working in favor of the spark capacity of the old point systems is that spark plug manufacturers are now addressing the minimum voltage that it takes to fire their plugs. Higher energy electronic ignitions have given way to systems with more precision (coil on plug, etc.) such that mega KVs are not needed to fire the plugs in a stock application. These Iridium plugs and such are reasonably new and might not be available for the more vintage applications, but usually the "fine wire electrode" plugs might be, in platinum or similar.

Ease of starting was mentioned as a benefit and reason to change to electronic ignition. Only exception to that is if the battery is weak. Many electronic systems have a minimum battery voltage requirement before they'll fire the plugs--period--whereas the points would always do something if there was even just a little juice left in the battery. Might not be a significant point, but one to consider.

Some of the higher performance boxes need a solid 10 volts to work, but I think the MSDs will go a little below that. Not sure about on HEIs, though. As mentioned, the HEI just takes a straight lead (no ballast resistor) to it to work.

Hope this might help,


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I am not sure what you mean by 'factory hot rod" ignitions. HEI is superior to points type. However, it is misunderstood why voltage is needed and what the function is. My auto electronics instructor always beat home the idea that secondary ignition only needs enough voltage to jump the gap and create spark for ignition. If it doesn't need 40,000 volts it won't use 40,000 volts.

Of course the students didn't care - we all read Hot Rod and knew our instructor was wrong. So he proved it out many times using the Sun meter. The reason higher voltage is needed is when there is higher resistance to the ability for the spark to jump the spark plug electrode.

If the coil and points system is only able to put out a certain amount of voltage energy and a person is running a high compression engine then in fact the voltage output may not be enough to overcome the pressurized combustion chamber at the exact time you need it causing a misfire condition.

On the other hand HEI will provide a higher voltage response to the "request" of timing to jump the gap in a higher combustion ratio performance engine and will do so through a rise in the rpms.

In higher performance applications - and with a points system - the voltage will actually increase to it's maximum and yet still not be able to jump the gap or do so in time with the motor.

That is the reason HEI is superior. Your iginition system should not be running at idle using 40,000 volts or else something is wrong. Modern cars I work on I typically see idle level voltage demands in the 20,000 to 25,000 range. (This is coil over plug or similar systems)

I would go with HEI but also make sure everything else is up to snuff. My 72 Buick Electra which runs points I have the spark plug gapped at .040. I would not recommend gaping the plugs at more then factory specification even with HEI. The wider the gap the more voltage you need and the quicker components will burn out - and the hotter they will run. There is no performance advantage over a wider gap - this is a falacy. Of course, a smaller gap will offer more eficiency for the secondary ignition but basically the factory engineers set the gap to offer the best compromise between fuel economy & performance for each engine. A "fatter" spark is an impossibility. Timing of the spark is far more important then "fatness". Remember, all it is trying to do is ignite the air and fuel mixture. Once the combustion starts, taht's all that matters.

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Back in the early '70s when I had plenty of time to gap the J-14Y Champion plugs on our '66 Chrysler 383 2bbl (9.2 to 1 rated compression ratio) just "so-so", when we'd check it out at the local Chrysler dealer on their Sun scope, it'd run about 8-9kv at idle with an air/fuel ratio approaching 14.0 to 1. That was with a .035" gap. If we put it in gear and loaded the engine against the brake, I don't recall the spikes going much past 15kv, but that's been a while ago. I mention that as a point of reference.

In the 1960s when the first capacitive discharge aftermarket conversion kits came out, the main things the various makers talked about was "joules" of energy and the duration of the spark (in milliseconds). At that time, there was some discussion on these issues and how much difference they'd really make in an engine's performance. They used lesser voltage across the points so the points lasted longer before they'd get corroded or pitted. But, in general, there was no compelling reason, back then, to "go electronic" as the point systems worked just fine, even in the old super stock drag racers with 13.0 to 1 compression ratios. If there was "point bounce" at higher rpms, you just got a higher performance set of points with a stronger spring in them.

By the time that electronic ignitions became popular on factory vehicles in the early 1970s, the compression ratios were in the 8.5 to 1 range. That might be one reason that GM's HEI system seemed to be so "ultimate" with all of its powerful capabilities when compared to what Ford and Chrysler were using, which was basically the same setup they'd used with point ignitions, but with electronic ignition distributors--meaning still about 35kv output. Still, these systems were capable of firing .045-.050" plug gaps on those motors with the lower compression ratios. Adding cylinder pressure, either via mechanical compression ratio increases, different camshaft profiles, or nitrous oxide injection does increase the power required to fire the plug in that more dense environment, but that max cylinder pressure only happens at WOT. End result, unless the resistance of the plug wires, cap/rotor combination, etc. increase markedly, the ignition system will not be straining under normal operating conditions as there's no need for it to produce max output under those conditions.

I believe that it's now generally accepted that .045" gaps are the best compromise between added power from a wider gap and "wear and tear" on the igniton system. I feel that the J-gap plug modification will benefit at most any gap setting as it will expose more of the spark to the mixture, which is what the wider gaps will do anyway, and do it in an efficient manner.

Interestingly, in the NGK literature I found on their V-groove ("V-Power" in the performance versions), they had a graph of the mixture vs. gap size that the plug would reliably fire. It showed a leaner mixture could be fired at .035" than at .045" gap. This might explain why most of the newer vehicles use .035" gaps again.

Other than the maintenance issue, the main benefit of the electronic systems is their spark accuracy. Yet, as Smokey Yunick mentioned, the placement of the distributor at the opposite end of the camshaft as the timing chain introduces all of the torsional dynamics of the camshaft into the accuracy of the spark timing. This is why the coil-on-plug computer fired system is needed for the ultimate of spark timing on modern emission controlled vehicles. It's also why front of the engine distributor placements are better.

We used to have a Sun scope, but it seems that OBDII has obsoleted that. The computer has misfire detection built in and the computer will also store the operating parameters when it happened. If misfire is suspected, there's a special tool to check the spark output of the suspect cylinder, basically a super wide gap spark plug with a holding fixture.

As mentioned, the HEI conversion on a Buick V-8 of the '70s is an easy thing to do. Plus you can readily buy HEI wiresets that should not require any modifications to use on the earlier engines. If you care about the original look, then the Pertronix or similar might be the best bet.



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Great post, It took me back to auto electronics I! Pretty much what we were taught in tech school. I clearly remember experimenting with the Sun O'scope and watching the raster pattern. I was fun to find out which cylinders weren't performing properly by eliminating them one at time and watching the results (RPM drop) on the scope. You could really tune a car with that.

I used a Pertronix system on my 72 Lincoln MkIV as it's an easy drop in replacement. Just pull out the points and condensor and screw it in. Hook up the wires to the coil (use their blaster coil) and find 12 volts. Tip, they make two versions, the cheaper one is what I used. It is not advisable to leave the key in the "ON" position without the engine running. I'm told this might damage the coil or processor. The Pertronix II system has supposedly overcome that problem, but costs a little bit more. I think the whole deal was about $100. Retain the old distributor so the thing looks stock. Takes about 45 mintues to change and check timing.

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I use a Holley Annihilator Laser Shot coil, which mounts in the stock HEI cap. It has 30% more voltage than the stock unit ant is good up to 6000 rpm before fading out. The also sell internal upgraded parts such as the pickup and the module. i run my plug gap at .060 and the plugs come out clean every time......hope thes sheds some light in Hot Rod ignitions.

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