GM HEI: Cheap and Extremely Effective Ignition Upgrade

If it's broken or just needs tweaked

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Pinhead
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Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby Pinhead » Fri Jul 08, 2011 10:57 am

The HEI ignitions' plug gaps were originally set at 0.080" but turned back to 0.060" because the distributors and wires weren't lasting long enough. We don't have a distributor to arc over, or wires overlapping to cause cross-talk which are the two of the HEI's problems. The GM DIS ignitions (where we get the Cav coils) are factory-gapped at 0.060 inches so the plugs can last 100,000 miles. By the time they're changed I've seen the gaps as wide as 0.100 inches and still firing.

Right now I'm running at .060" with no problems, and going to open it up to .065" today to see how it runs. I'll widen the gap by .005" until I get a miss at WOT and then back it down to the last best setting. There was a study by a prominent ignition company that said 0.100" is the optimum plug gap for kernel expansion if enough spark energy is available. We probably won't be able to get quite that far, but the closer the better. :)

Also note that if I can easily go to 0.060" on my bike, you guys can go a lot further; high compression and lean mixtures are more difficult to fire than low(er) CR and stoich mixtures. I'm running 11:1 CR and trying to maintain lean cruise which makes it much more difficult to fire the plugs than the factory 9:1 CR.

Pinhead
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Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby Pinhead » Fri Jul 08, 2011 2:31 pm

So far today I've increased the gap by 0.005" increments and each time the results have been positive. My latest setting is 0.070 inches.

However, I've examined the various types of ignition systems, and this actually should be called a GM DIS system instead of a GM HEI system since there's no distributor and the coils fire two plugs.

I've seen 100k mile plugs wore down to 0.100" each (which is 0.200" total) using these same coils (GM DIS), and they were only misfiring due to bad/dirty plug wires, not due to insufficient spark energy; the required voltage was high enough to cause the spark to jump from the plug boot to the head.

So far at 0.070" there seems to be absolutely no misfire through the entire rev range at WOT or cruise. The transition from idle to acceleration is smoother, as well, when compared to the 0.060" gap.

I think I'll drive it for a bit at 0.070" to make sure everything is still working correctly, and if so, increase to 0.075" tomorrow. :shock: :twisted:

Just as a testament to the power of this ignition, remember, that's 0.070" at each plug, which means 0.140" total spark gap... In an engine with 11:1 CR... And I haven't found the limit yet!

Pinhead
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Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby Pinhead » Fri Jul 08, 2011 7:18 pm

I couldn't leave well enough alone and got to 0.080 inches. I can't tell if it made a positive difference or not, but it definitely hasn't hurt anything (no spark scatter or misfire at WOT).

There definitely has not been a loss of power anywhere in the rev range as I've opened up the spark gap.

Does anyone else have any experience with this system yet? How is it working out for you?

Pinhead
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Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby Pinhead » Sun Jul 10, 2011 1:03 am

The last 9 tanks have been better than 55 mpg and each consecutive tank has been higher than the last. Tonight's tank was 60.49 mpg. Mostly 55-60 mph, though there were probably 5 sprints up to 95 mph or so while testing the ignition's capabilities. I've had to settle for 0.080 inch plug gap because my plug wires and boots aren't up to the task of holding the voltage of a much wider gap (aiming for 0.100" if it's possible). Each increase in plug gap from 60 to 80 thou (in 5 thou increments) has netted a slight improvement in MPG.

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Volker_P
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Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby Volker_P » Tue Jul 12, 2011 1:25 am

All right, now things improve. Did you fix your accelerator pump yet? Did you provide these gaps for side gapped plugs?
Cosky's great (free) online manual: http://cosky0.tripod.com

forum links to common technical issues

Pinhead
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Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby Pinhead » Tue Jul 12, 2011 10:48 am

Yes, the plugs are side-gapped at 0.080 inches. Accel pump works marginally; the rubber is stiff but it sprays some.

Wow I just looked at my mpg figures for the last two tanks, talk about consistent!

3.378 us gal
204.3 mi
60.48 mpg

3.746 us gal
226.6 mi
60.49 mpg
Last edited by Pinhead on Wed Jul 20, 2011 2:18 pm, edited 1 time in total.

klougnot
Posts: 149
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Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby klougnot » Wed Jul 20, 2011 11:40 am

Hi Pinhead,

I need some ignition advice for my latest project a 1976 CB750 which came with what appears to be a Dyna ignition with stock coils. When the system works is really hauls! They rest of the time I am lucky to get it firing on 2 to 3 cyclinders. I have done timing with a light and switched coils to a nearly new set with only 3,300 miles on them. Still it is not reliable enough so I switched back to points. The problem I have read is that the Dyna does not shut off and is on 80% of the time which heats up the coils, drains the battery and causes issues. If I buy the Dyna blessed coils I will have to pay $150 bucks!

Pamco is $240 and Power Arc sopposedly the best is $350 too rich for me. I probablly could affor the pamco, but $240 is alot compared to your solutions which comes in around $100 with all brand new stuff. Less if I go the junkyard route.

My question is this if stock points is on 50% of the time, Dyna is on 80% of the time, and Pamco is on 30% of the time what percent of the time is the HEI unit on?

The above numbers are from Pamco Pete. Please give me an idea of how the HEI compares to the other ignitions above.

Thanks!

-Kyle

Pinhead
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Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby Pinhead » Wed Jul 20, 2011 2:38 pm

klougnot wrote:Hi Pinhead,

I need some ignition advice for my latest project a 1976 CB750 which came with what appears to be a Dyna ignition with stock coils. When the system works is really hauls! They rest of the time I am lucky to get it firing on 2 to 3 cyclinders. I have done timing with a light and switched coils to a nearly new set with only 3,300 miles on them. Still it is not reliable enough so I switched back to points. The problem I have read is that the Dyna does not shut off and is on 80% of the time which heats up the coils, drains the battery and causes issues. If I buy the Dyna blessed coils I will have to pay $150 bucks!

Pamco is $240 and Power Arc sopposedly the best is $350 too rich for me. I probablly could affor the pamco, but $240 is alot compared to your solutions which comes in around $100 with all brand new stuff. Less if I go the junkyard route.

My question is this if stock points is on 50% of the time, Dyna is on 80% of the time, and Pamco is on 30% of the time what percent of the time is the HEI unit on?

The above numbers are from Pamco Pete. Please give me an idea of how the HEI compares to the other ignitions above.

Thanks!

-Kyle


I have no personal experience with any electronic ignition other than the HEI/DIS and the stock ignition from the CB650.

The HEI/DIS system's "on" time doesn't change with RPM; it stays steady at ~1.4ms. Since that is the same amount of time that it takes to charge the GM DIS coils, there is no wasted energy.

The other systems' charge times are determined by degrees of crank rotation (which means the "on" time is reduced as RPM increases).

Stock: 195°
Pamco: 120°
Dyna: 315°

In degrees of crankshaft rotation, these systems reduce coil charge time as RPM increases, while the GM HEI/DIS system increases charge time (when compared to degrees of rotation) as RPM increases.

So the three mentioned systems can't be truly compared to the GM HEI/DIS system; the GM system is superior in every way.

The only problem is, I don't know if you can get the '80s TCI trigger plate and hardware to fit onto an earlier CB750. If we could figure THAT out, there would be a huge market for a clearly superior ignition system for the earlier CB750s...

klougnot
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Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby klougnot » Wed Jul 20, 2011 3:00 pm

Hi Pinhead,

I have a plate from a CB650 I am going to see if it will fit into the CB750 and will let you know how I make out with it. If it fits we can go from there.

Now just for learning sake can you explain how the degrees from the crank thing works.

So if stock: 195° what does this actually mean? Does it mean the coils start to charge at 195° degrees from the F mark or TDC mark? I am very confused on this one.

If the plate works out this could be a nice twist on what is becomming a well proven system. Nice part about the 750 is all the room for the coil packs and lots of places to stuff the HEI modules.

Thanks Again!

klougnot
Posts: 149
Joined: Wed Jun 02, 2010 1:05 pm

Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby klougnot » Wed Jul 20, 2011 7:14 pm

Ok Pinhead,

Here's the pics of the cb650 pickup in a 1976 cb750 engine. Basically I just took the cam lobe off the cb650 put it into the cb750 and installed the cb650 pickup in the 1976 cb750 engine. As you can see from the pics the cb650 back plate is a little smaller than the cb750, but does fit in nicely and does not make contact with the cover. The easiest thing to do would be to drill out the old cb750 back plate and screw the cb650 plate over it. The best part about this solution is the pickup contact line up just about perfectly. Should work good enough for testing. Bet if you had a 1979 or above cb750 it would fit perfectly.


Check out the pics and let me know what you think.

cb650_pickup.JPG
CB650 pickup
cb650_pickup.JPG (142.7 KiB) Viewed 8343 times


750_2.JPG
CB650 Pickup in a 1976 cb750 engine
750_2.JPG (144.53 KiB) Viewed 8343 times






I really like the cam lobe of the cb650 much beefier than the dyna setup which looks sickly in comparison. After taking the advance apart I now know what Volker_P was talking about! These things need cleaning and oil. Wasn't all that nice and snappy like it should be a little oil and cleaning made a big difference. I will never skip this step again.

Pinhead
Posts: 611
Joined: Thu Jan 04, 2007 2:26 am

Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby Pinhead » Wed Jul 20, 2011 8:06 pm

I'm really interested to see if the timing can be set correctly (if the timing plate fires in the same position as the points). If so, this is kind of a big deal!

When it comes to the other triggering systems' dwell parameters, basically the degrees indicate how many degrees of crank rotation the coils are held "on" before the spark; shutting "off" the primary is what causes the coil to fire.

If you look at the points and points lobe, you can see how this works: While the points are closed, the ignition is charging the coil primary, and when the points open the spark occurs.

klougnot
Posts: 149
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Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby klougnot » Wed Jul 20, 2011 9:44 pm

Why would it be a big deal?

Pinhead
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Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby Pinhead » Wed Jul 20, 2011 11:15 pm

klougnot wrote:Why would it be a big deal?


Because, IMHO, this the best ignition system out there. No wasted energy all the way to redline, with ample power to run huge plug gaps. Being able to run the GM HEI/DIS on the earlier CB750s creates an ample "market" for this system. ;)

klougnot
Posts: 149
Joined: Wed Jun 02, 2010 1:05 pm

Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby klougnot » Thu Jul 21, 2011 7:26 am

Ok, I understand what your getting at.

I think I will go to the junkyard this weekend and see if I can scavange up some parts cheap. I think I will leave out the booster to start. Just need basic wiring to test for now. The bike starts up good enough anyway, but might add it latter. Hopefully it will work. We'll see.

klougnot
Posts: 149
Joined: Wed Jun 02, 2010 1:05 pm

Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby klougnot » Tue Jul 26, 2011 10:14 am

Hi Pinhead,

I got the parts ordered and a local machine shop is making up a new timing plate. It 3/32" thicker hopefully this won't mess up the pickups too much. Gave me a very reasonable price on the machining work.

I saw a post on SOHC about a guy who just hooked up the chevy coils without the HEI and says it works. Any thoughts on this approach?


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