Topic: Ignition Upgrade using GM HEI Modules

[TwoTired]

Are you still using the wasted spark?  If so, realize that the, gap is doubled across two spark plugs. .065 +.065 is .130 total gap the spark must jump.  For the auto's case, the gap is the spark plug plus the distributor to rotor gap (whatever that is).

Cheers,

[Pinhead]

Yes, still using wasted spark.

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" and I'm hesitant to go any further since you pointed out that the gap is actually 0.140" which is quite wide.

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.   

[Skunk Stripe]

So what is actually used as the trigger to fire? I am at work and have only glossed over most of it so I might have missed that.
Otherwise, this sounds like excellent spark you have. I have the Dyna S right now and while happy with it, I certainly would think about something better.
What is the current draw from something like this? Will it shave things pretty close?

[Pinhead]

I only have experience with the CB650 which uses the factory reluctors to trigger the HEI modules. I haven't measured average current draw but the alternator on my '79 has no trouble keeping up.

[Skunk Stripe]

Hm, do you think the S would trigger things?
The ignitors trigger the hei which then fires the gm coils right?
If that is the case, then maybe the S would work inplace of the ignitors.

[Pinhead]

Hm, do you think the S would trigger things?
The ignitors trigger the hei which then fires the gm coils right?
If that is the case, then maybe the S would work inplace of the ignitors.

Probably not; the GM coils have a resistance of 0.7 ohms and very low inductance which only need a dwell of 1.4ms. The S would produce a much longer dwell than needed which will cause very high current draw and overheat the coils as well as overloading the electrical system (and burn out the Dyna S).

[Pinhead]

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).

Strangely enough, while testing 75 and 80 thou, I noticed that the ping that I had at WOT 3000rpm is gone when I was I flogging it up and down the highway trying to get a misfire. I have two theories about this 1) The wider gap is delaying the spark discharge and causing a slight reduction in timing advance, and 2) The larger spark is causing the combustion event to be completed more quickly which reduces the chance for detonation.

Or a combination of the two.

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

You CB650 guys should really try this. It's definitely a winner!

[fmctm1sw]

I see the 650 specifically mentioned.  Is there any reason this won't work on the older Hondas (350/550, etc)?

[Pinhead]

I see the 650 specifically mentioned.  Is there any reason this won't work on the older Hondas (350/550, etc)?

The HEI modules can be triggered by your points and fire your stock coils but you can't use the low-resistance Cavalier coils on the older Hondas. The 650 is special because it came with electronic ignition from the factory (as with all of the rest of the '80s Hondas). The factory reluctors are required to make this work optimally.

[Skunk Stripe]

Wonder if I could snag an ignition from a 79-82 cb750 and drop it on.

[trueblue]

Hey Pinhead, how and where did you mount your coils, I have everything I need to put one of these setups on my 650 but I can't figure out where to mount the coils.

[Pinhead]

Wonder if I could snag an ignition from a 79-82 cb750 and drop it on.

That would work if you can get it mounted; it's the same ignition system as the 650.

Hey Pinhead, how and where did you mount your coils, I have everything I need to put one of these setups on my 650 but I can't figure out where to mount the coils.

I have 'em stuffed under the tank in my '79. They're a bit too wide to fit in the factory location so I dropped them down between the tank and the head. I had pics on my phone that I was going to upload if that phone hadn't gotten ran over by a car.  I'll try to get some pics up. NOTE: My wiring and mounting is ugly with the tank off, as it was experimental when I installed them. But you can barely see them with the tank mounted.

[trueblue]

Ok thanks, pictures would be appreciated. It doesn't matter if the wiring looks ugly, it's more the location of the components that I'm interested in 

[Pinhead]

Burned up a full tank between yesterday and today at 0.080" without issue. It seems that 80 thou may be close to the limit, though; I saw an ever-so-slight spark tonight at the top of one of the plug boots when I first fired it up after dark (one spark at initial start but none after that). *NOTE* these are 30-year-old oil soaked plug boots. The gap can probably go wider if the wires and plug boots could hold the voltage. Looks like that'll be my next upgrade before I see how much further the ignition can go.

[japscrap]

can someone put up a link to the proper wiring for this setup on a cb500-4?

I'm all about getting better spark and more burn.

Pinhead,how did this mod affect your gas mileage?

[Pinhead]

You can't run the GM coils on your bike unless you want to fit a CB650's trigger plate and reluctor to replace your points.

Running the stock plug gap it didn't make much difference on mileage. Once I opened it up to .080" though, my mileage went up by a good consistent 5mpg.

[japscrap]

I was wondering about using my stock coils with the 4 pin module on my cb 500-4 I know I cant use the chevy coils.
what has to be done to make this work?

5MPG more is quite a gain,i like.

[Deltarider]

Forgive me for being dumb... but this GM HEI thing is nothing but a transistor ignition module is it? I've used the wiring diagram of a Velleman kit and built one myself 12 years ago. And then there's Hondamans... What's so special about this one? Did I miss something?

[Pinhead]

Forgive me for being dumb... but this GM HEI thing is nothing but a transistor ignition module is it? I've used the wiring diagram of a Velleman kit and built one myself 12 years ago. And then there's Hondamans... What's so special about this one? Did I miss something?

When using the stock coils and points, the HEI modules have no advantage over Hondaman's unit. I'd personally rather run his box if I were staying with the stock coils and points.

The HEI modules hold a distinct advantage, however, when coupled with the CB650's trigger plate (which does fit the SOHC 750s) and GM DIS coils. This combination produces an exceptional spark which allows 0.080" (and possibly wider) plug gaps.

[Spanner 1]

I think your askin' for trouble @ 80 thou. gap.......... fine in dry weather and with 'pristine' HT wires, run it @ 80 in the wet and with some 'seasoned' plug wires might be a different story , IMO.

[Pinhead]

I think your askin' for trouble @ 80 thou. gap.......... fine in dry weather and with 'pristine' HT wires, run it @ 80 in the wet and with some 'seasoned' plug wires might be a different story , IMO.

That's what I thought, too... Luckily, though, I was able to test the theory the other day on my way home during a rain storm and didn't have a bit of trouble.

I do realize, though, that the widened gap will force replacement of the wires sooner rather than later. Luckily the kit that I bought was for a V8 and I've got 12 extra wires (the wires were long enough to make two sets of each wire).

[binder56jd]

hey guys--good stuff here

my question is how to make this work on a 1983 honda vt750c--i want to use the gm hei in place of the ignitor box--i need 2, so i am thinking to use 1 hei per cylinder

mr pinhead--can u hook me up

many thanks

jd

[Pinhead]

Welcome to the forum!

I'm not specifically familiar with the vt750 and my quick internet search didn't turn up anything really helpful.

Does the VT have mechanical advance? Or does the ignition control module electronically control timing?

If the ignitor box controls timing advance, the HEI modules won't work, as they will operate at fixed advance.

If the ignitor box doesn't control timing advance, then I also need to know what the reluctors and pick-up coils look like (to see if they're the same as used on the 650 and DOHC4s).

If the pickup coils are not the same components used in the bikes I'm familiar with, I have no idea if the HEI combo would work without attaching an o'scope to the output of the modules in order to verify the produced dwell time...

[binder56jd]

ty

will get that info

[faux fiddy]

damnit jim,the geocities page is longer available,does anyone have this they could send me.im really interested in it.pm me if you have it.thanks

Bump.

 This is on my friends computer as a favorite that I portal in on.