GM HEI: Cheap and Extremely Effective Ignition Upgrade

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Pinhead
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GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby Pinhead » Tue Mar 15, 2011 10:19 pm

http://home.comcast.net/~loudgpz/GPZweb ... vCoil.html

Loudhvx wrote:This project is an ignition module design to replace the stock unit for a 1980 Honda CB 750 C motorcycle using aftermarket GM ignition coils commonly found on Chevy Cavaliers and many other GM cars instead of the stock coils. It also uses two GM HEI igniter modules. The parts for this project should not cost much more than $35, (not including the coils which are about $20 each). This module is designed to work with the stock inductive pickups. This project will also work as a replacement for the many other early 1980's Honda CB motorcycles that use the same pickups, rotor, as the 1980 CB 750 C. It uses a mechanical advancer unit. This project is not compatible with electronic-advance type ignitions.

Image


As of today I am running GM coils and 7-pin HEI modules on my '79 CB650 (couldn't find the 4-pin modules at the junk yard).

The idle is absolutely amazing. The bike starts up extremely easily. Very little choke is needed (impressively so, considering the generally "cold blooded" nature of the CB650). The bike can take off in 1st gear at idle without dying. The low-end (1000 to 2500 rpm) is as smooth as my CM400 that has CV carbs.

I'm running Iridium plugs which are gapped at 0.060 inches. As of right now, I'm not using any resistors in the plug boots (the resistor plugs are ~5k ohms each).

With my highly modified engine at 10.7:1 compression ratio, there is no detectable ping even going up a steep hill at 35mph in 5th gear.. Even if I go to WOT. (This is more-than-likely a function of my engine configuration more than the ignition.)

With the stock ignition I would have definitely been forced to down-shift as the engine would bog down otherwise (verified by a ride with the stock ignition earlier today).

I'd say this is definitely worth a try, especially since a pair of HEI modules and coils cost me less than $30 at a salvage yard.

EDIT: I had a hard time finding 4-pin HEI modules so I'm using the 7-pin modules. The wiring had to be slightly altered, however. The attached diagram shows how to wire the system when using 7-pin HEI Modules and Chevy Cavalier coils.

EDIT

When I was trying to figure this project out, I sent a few emails to the author of the mod and here is some background information:

Loudhvx wrote:The 4-pin has internal dwell compensation.
The 7-pin has no internal dwell compensation circuit. The 7-pin is just a two-mode driver.
B stands for bypass. You are using it in bypass mode when B, R, and E are unconnected.
R stands for reference. That is the signal from the module to the car's ECM. It can be used for a tach signal, which is how some people probably use it, but that is not the real purpose of R. The ECM uses the reference signal to determine dwell and timing. That ECM signal then returns to the module through pin E. E stands for ECM.

N on the 7-pin correlates to W on the 4-pin.
P on the 7-pin correlates to G on the 4-pin.

N and W are what I refer to as the negative side of the reluctor pickup (positive and negative are arbitrary labels, but I use them consistently, which is what matters, other sources may refer to them opposite from what i do). The main difference between the 4-pin and 7-pin is that the bias voltage on N is relatively steady, while the voltage on W changes greatly with RPM (based on reluctor signal strength and output's current limiter usage). (My full notes on the 4-pin are available from that link you referenced.)

If you are using Cavalier coils, (as that is what the link refers to, note there is a different page for using stock spark coils), then the W-pin does not get used, so the issue between W and N is irrelevant.

However, P and G also have a slight difference in their behavior. The thresholds are slightly higher on the 7-pin module. So there may need to be a slight compensation on the negative terminal of the pickups. The difference is about 1 volt. A 1-volt reference voltage should be applied to the negative sides of the reluctor pickups. That is the blue wire with white band, and yellow wire with white band. On the 4-pin page, those wires are just tied to ground. To use it with the 7-pin module, you will likely have to go with a simple voltage provider like that used on the Kawasaki version:
http://home.comcast.net/~loudgpz/GPZweb ... EImod.html

Use P in place of G. The white band wires would be the negative pickup wires, but try both polarities in case the timing seems off. This is in case someone swapped the white bands. Double check the timing with a strobe to make sure the polarity is correct (wrong polarity alters the timing).

If the polarity seems reversed, maybe there is a chance someone put the white band on the wrong wire.


EDIT 7/8/11: 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.

EDIT 7/10/11

0.080" gap seems to be the limit on my engine with the DIY Accel wires and factory plug caps; 85 thou causes spark scatter when the engine is under load.

220 miles before reserve on my last tank (0.080" gap) for right at 60 mpg, all highway miles.
Attachments
7-Pin HEI.jpg
7-Pin HEI Module Wiring to replace early '80s Honda TCIs.
7-Pin HEI.jpg (30.16 KiB) Viewed 26245 times
Last edited by Pinhead on Thu Nov 24, 2011 6:03 pm, edited 6 times in total.

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

Postby MEHall » Wed Mar 16, 2011 3:26 am

Nice find there! :wink: :D
When i saw the schematic i came up with a simpler idea to get an troublesome bike to start when cold!

See link:
http://www.airsoftglobal.com/shop/image ... 0-L-AG.jpg

If you bypass the standard cable to the coils, only when you start up the bike, whit a relay and plug in that kind of nimh battery you can achieve the same in fact. But i must point out that you need to recharge a Nimh battery with a charger that is for NiCd or NiMh batteries. :wink:
Riding bikes? I ride where ever i want and whenever i want. :wink:

Online manual: http://cosky0.tripod.com/

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

Postby Volker_P » Wed Mar 16, 2011 4:51 am

Interesting. This seems to imply that the typical poor cold starting behavior is not really a fuel system but rather a weak ignition problem (lean mixture ignites harder?).
So cleaning 30 year old ignition system contacts is on my list now. :)
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forum links to common technical issues

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

Postby Pinhead » Wed Mar 16, 2011 4:25 pm

Volker_P wrote:Interesting. This seems to imply that the typical poor cold starting behavior is not really a fuel system but rather a weak ignition problem (lean mixture ignites harder?).
So cleaning 30 year old ignition system contacts is on my list now. :)


Definitely. This morning it was 45°F when I started the bike. Normally I would have had to crank the engine over for a second, fully choked, before it would fire up. This morning, no choke, it started right up almost like the engine was already warm and I rode away 20 seconds later.

The best part is, due to the automatic dwell control on the ignition modules, the entire system uses about the same amount of power from the electrical system; the dwell is perfect for the coils regardless of RPM.

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

Postby MEHall » Wed Mar 16, 2011 9:22 pm

I must agree because I'm educated to a car mechanic and know about electrical power systems.
I understand that when starting an engine in an older typ ofe car or motorcycle, the starter can draw so much power so it might not be sufficient for the ignition system.
So an extra battery separately to the ignition can be helpful in cases like this. :wink:
You have really found a clever system that works a little in the way I originally had on my mind. :wink:




8)
Riding bikes? I ride where ever i want and whenever i want. :wink:

Online manual: http://cosky0.tripod.com/

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

Postby Volker_P » Thu Mar 17, 2011 2:21 am

MEHall wrote:So an extra battery separately to the ignition can be helpful in cases like this. :wink:
I saw a nice (probably stock) solution in some old japanese van. The coil has a series resistor which however is bypassed when the starter is turning.
The CDI of my dirtbike has a pin for the starter, but here no idea what it really does.
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forum links to common technical issues

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

Postby Pinhead » Thu Mar 17, 2011 4:12 pm

Volker_P wrote:
MEHall wrote:So an extra battery separately to the ignition can be helpful in cases like this. :wink:
I saw a nice (probably stock) solution in some old japanese van. The coil has a series resistor which however is bypassed when the starter is turning.
The CDI of my dirtbike has a pin for the starter, but here no idea what it really does.


A lot of old Ford and Chevrolet vehicles had the same "ballast resistor" in-line with the power to the coils. This was because they used slightly lower resistance coils that will produce a strong spark when the resistor is bypassed. However, running without the resistor for an extended period of time, the coil or the points will burn out.

The GM HEI configuration outlined above used a coil with <1 ohm of resistance. The sparkers on our CBs produce about 1.4ms of dwell, which is almost perfect for the coils. Therefore no ballast resistor is needed.

I have no idea how the stock spark boxes work with regards to dwell, however.

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

Postby Pinhead » Thu Mar 17, 2011 9:19 pm

This HEI conversion has greatly increased the low-speed at idle. Whereas before the rebuild the engine wouldn't idle any lower than 900 rpm, now it will idle much lower (can't tell exactly with the mechanical tach)

So I am curious if this is a function of the mods that I've done and the strong ignition, or if any freshly rebuilt SOHC4 can idle like this.

VIDEO:
http://www.facebook.com/v/10150159079641974

Let me know if you can't see the video...

I suspect that the ignition has the most to do with it, as I was unable to do this with the stock ignition even after the engine rebuild.

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

Postby klougnot » Fri Apr 08, 2011 10:16 pm

Nice Job! I think you maybe onto something here I a have never seen able carb bike be able to maintain a 500 RPM idle! Does this put a drain on your batery/charging system. Are you able to get 13.5+ plus volts out at the battery at 4000 RPMS. If so I am putting in my order for a plug and play version with all the connectors prewired. Let me know how much you would want to do it.

Thanks!

-Kyle

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

Postby Pinhead » Sat Apr 09, 2011 2:48 am

klougnot wrote:Nice Job! I think you maybe onto something here I a have never seen able carb bike be able to maintain a 500 RPM idle! Does this put a drain on your batery/charging system. Are you able to get 13.5+ plus volts out at the battery at 4000 RPMS. If so I am putting in my order for a plug and play version with all the connectors prewired. Let me know how much you would want to do it.

Thanks!

-Kyle


For the idle demonstration, look no further than HERE.

It seems that the HEI system doesn't use much more power than the stock system; the HEI modules, themselves, dissipate about 3 watts at peak usage. But the HEI ignition system doesn't effect the ability of the alternator, however, so some rpm is still needed to charge the battery.

Having said that, I'm not having any charging/voltage problems, even with a known weak battery. But I have re-wired the charging system with a Ford regulator and universal rectifier, all wired straight to the battery (so it's not losing voltage through the wiring harness).

As for me putting together a plug-and-play solution, I'd have to find a different mounting system than what I'm using right now; currently their home is where the stock regulator/rectifier would normally be mounted.

The mount that I'm using is 5 inches wide x 4 inches long x 0.5 inch thick and that seems to be about as small as I can make it with the modules side-by-side.

I could possibly mount the modules back-to-back (one on either side of the metal heat sink) which would drop the package down to 4x3x1.25 inches or so. I haven't tested this so I'm not sure if they would overheat when mounted this way.

My gut tells me that they shouldn't have any trouble with heat, though, as they're designed to be mounted inside the distributor on top of a V8 engine which should surely be a much hotter environment than virtually anywhere on our bikes.

I think a couple of good places to mount would be between the battery and the right-side cover, or somewhere underneath the gas tank. It may even be possible to use the factory mounting point with the modules mounted back-to-back... I'll have to take a look at that.

Anybody have any other ideas for mounting the modules?

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

Postby klougnot » Sun Apr 10, 2011 8:45 am

I don't think I can come up with any better mounting points for the HEI than you have already suggested.

Do you think you can take some pictures? I would really like some pictures of the connectors and the wiring you have done. The blueprint is nice, but a picture of the actual wiring job would be a big help in doing this myself.

I am still very new to electric and seeing a picture of the wires and each connection would make a big difference. I would like a picture of all the hookups start button, HEI, coils, pickup, resistors etc...

Thanks!

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

Postby Pinhead » Sun Apr 10, 2011 11:08 am

You don't want a pic of my current wiring, as it looks like a rat's nest. :oops:

Now that I know the system works (and works well) I'm going to get OEM plugs for the modules so I can eliminate the spade terminals that I'm using.

But since you asked... Pay no attention to the slew of wires running everywhere. Like I said, this was purely experimental so I didn't tidy any wiring.
Attachments
GM HEI.jpg
GM HEI on CB650.
GM HEI.jpg (224.36 KiB) Viewed 26451 times

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

Postby klougnot » Sun Apr 10, 2011 7:07 pm

So let me get this straight. Our Honda CB650 has 2 inductive pickups with 2 wires that go to the HEI Modules and to wires that go to the coils. Is this basically correct?

Also, it looks like from the diagram and from what you said in you post that there are 2 separate circuits.
1. A starting circut with the built in resistors for easy starting.
2. A running circut that is powered by the ignition switch.

To Summarize
2 wires from each inductive pickup to each HEI and 2 wires from each HEI to each GM coil. HEI is grounded to heatsink, and heatsink is grounded to the frame. Start boost comes from a couple resistors that amplify the inductive pickup signal when the start button is pressed. Under normal driving the HEI is powered by +12v from the ignition switch.

Does this sound about right?

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

Postby Pinhead » Sun Apr 10, 2011 10:00 pm

klougnot wrote:So let me get this straight. Our Honda CB650 has 2 inductive pickups with 2 wires that go to the HEI Modules and to wires that go to the coils. Is this basically correct?

Also, it looks like from the diagram and from what you said in you post that there are 2 separate circuits.
1. A starting circut with the built in resistors for easy starting.
2. A running circut that is powered by the ignition switch.

To Summarize
2 wires from each inductive pickup to each HEI and 2 wires from each HEI to each GM coil. HEI is grounded to heatsink, and heatsink is grounded to the frame. Start boost comes from a couple resistors that amplify the inductive pickup signal when the start button is pressed. Under normal driving the HEI is powered by +12v from the ignition switch.

Does this sound about right?


Mostly correct. However, due to crosstalk between the two reluctors (inductive pickup), one side of the reluctor goes to ground and the other side goes to the HEI modules.

NOTE: The circuit must be modified when using 7-pin HEI modules due to some slight internal differences in the modules themselves. I'll draw a diagram showing these changes (the only difference is a pair of diodes).

cb650
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Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby cb650 » Mon Apr 11, 2011 6:29 am

Pinhead u going to meet the CO group on the sohc4 relay?
Did you clean the tank out?!?!?!?!


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