GM HEI: Cheap and Extremely Effective Ignition Upgrade

If it's broken or just needs tweaked

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

Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby Pinhead » Tue Jul 26, 2011 6:23 pm

klougnot wrote: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?


Could you get me a link?

What kind of trigger is he using to fire the coils? Definitely not points, as they would very quickly melt... Or is it a DOHC ignition firing the Cav Coils?

I'd be really hesitant to try without first finding out what kind of dwell the ignition is producing. Much over 1.4ms of dwell will waste power and unnecessarily heat the coils and triggers.

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 9:35 pm

Here is a copy of the post and the author is claming that the C849 coils work as it with the stock pickup and spark units on a 1980 CM400T. He says the primary resistance on the C849 at .7 is just about the same as the .5 on the CM400T.

http://www.hondatwins.net/forum/viewtop ... =60&t=7571


Ok, so I had been looking around over on the CB750C site, looking for some issues my friend was having with his bike, when I came across this mod and decided to try it on my bike, a 1980 CM400T. Never seen it done on our bikes, but figured it was worth a shot. Using a Wells C849 coil (used on so many GM vehicles I won't even attempt to list them all), and some universal individual plug wires, we can have a brand new, high output ignition for our bikes for around 35 bucks! And to top it off, it took me longer to get the parts than do. The coil I bought has a .5 ohm resistance. Sounds low, but the one I took off was only .7! So in the grand scheme of things, not enough difference to matter.

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

Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby Pinhead » Wed Jul 27, 2011 12:48 am

klougnot wrote:Here is a copy of the post and the author is claming that the C849 coils work as it with the stock pickup and spark units on a 1980 CM400T. He says the primary resistance on the C849 at .7 is just about the same as the .5 on the CM400T.

http://www.hondatwins.net/forum/viewtop ... =60&t=7571


Ok, so I had been looking around over on the CB750C site, looking for some issues my friend was having with his bike, when I came across this mod and decided to try it on my bike, a 1980 CM400T. Never seen it done on our bikes, but figured it was worth a shot. Using a Wells C849 coil (used on so many GM vehicles I won't even attempt to list them all), and some universal individual plug wires, we can have a brand new, high output ignition for our bikes for around 35 bucks! And to top it off, it took me longer to get the parts than do. The coil I bought has a .5 ohm resistance. Sounds low, but the one I took off was only .7! So in the grand scheme of things, not enough difference to matter.


Ah yes, the CM400 is actually a CDI ignition while ours is of the Kettering type. CDI coils have a low primary resistance which is very close to the C849.

Completely different type of ignition than what the SOHC4s and the DOHC4s have.

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

Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby klougnot » Tue Aug 02, 2011 10:27 am

I am struggling to mount these coils under the tank without it interfering with the cabling. The tank tunnel on the old CB750s is much narrower than on the CB650s.

Is it ok to mount the coils in front of the down tubes if I am careful to make sure all the connectors are sealed up tight? This way they are out of the way if I ever need to change spark plugs.

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

Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby Pinhead » Tue Aug 02, 2011 3:31 pm

I mounted mine lower than the factory position, more below the tank than in the tunnel. As long as all of your connections (both at the harness and on the back of the coil) are water proof, you should be fine.

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

Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby klougnot » Tue Aug 02, 2011 3:35 pm

Did you make up some brackets to mount under then tank? Do you think you can post a pic when you get some free time.

I would have had the new pickup plate last week, but the guys CNC machine broke down. Should be ready this week though.

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

Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby Pinhead » Tue Aug 02, 2011 3:38 pm

I have pics on my phone but keep forgetting to upload them. Hopefully I'll remember tonight. It aint pretty (with the tank off) but it works.

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

Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby klougnot » Tue Aug 02, 2011 7:48 pm

That's ok this is not beauty contest. It's what she can do with the lights out that matters! Performance trumps beauty any day. Just don't want em fall off when I am going down the highway.

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

Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby Pinhead » Wed Aug 03, 2011 1:58 am

Here it is, in all of it's glory. :lol:
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klougnot
Posts: 149
Joined: Wed Jun 02, 2010 1:05 pm

Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby klougnot » Thu Aug 04, 2011 9:11 pm

Looks good Pinhead thanks for the pics. I am too the same conclusion myself for a mounting point. Didn't like it interfering with plugs 2 and 3 though.

So here is the pickups installed in the CB750 engine with new CNC machined back plate. A local machine shop really did me a favor on this one. I did run into a slight problem with the cam being a tad too thick for the original advance so I had to shave a little off with the bench grinder.

It was a rather slow process as I would have to keep testing out the advance with the retaining nut to make sure it had good action. Took about and hour or so to work that one out.

Here is what she looks like.

Now I just need the rest of teams help wiring the whole mess up.
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elballoonrat
Posts: 4
Joined: Thu Aug 18, 2011 11:41 am

Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby elballoonrat » Thu Aug 18, 2011 11:47 am

Will this work on a 1972 cb450? any advice on how to hook it up? I have been trying for days to hook this up with no luck.

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

Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby Pinhead » Thu Aug 18, 2011 12:46 pm

elballoonrat wrote:Will this work on a 1972 cb450? any advice on how to hook it up? I have been trying for days to hook this up with no luck.


You would have to use the CB650's ignition plate like klougnot's picture shows above.

elballoonrat
Posts: 4
Joined: Thu Aug 18, 2011 11:41 am

Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby elballoonrat » Thu Aug 18, 2011 7:38 pm

I thought this worked with points ignitions though? klougnots looks like a electronic ignition. would the cm400 cdi be an easier swap and then I wouldn't need an HEI unit?

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

Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby Pinhead » Thu Aug 18, 2011 8:18 pm

elballoonrat wrote:I thought this worked with points ignitions though? klougnots looks like a electronic ignition. would the cm400 cdi be an easier swap and then I wouldn't need an HEI unit?


You can use the HEI modules, triggered by points, though in that configuration you definitey won't be able to use the DIS coils; the dwell parameters would be entirely too long. Using the factory coils, however, you should get a slight boost in ignition performance and your points will last a LOT longer.

This should be discussed in it's own thread, though...

The CM400's CDI system requires a special stator in the alternator to produce the high voltage spike to fire the coils. I don't think the system could be adapted to other bikes and if it could, it'd require a LOT of work.

elballoonrat
Posts: 4
Joined: Thu Aug 18, 2011 11:41 am

Re: GM HEI: Cheap and Extremely Effective Ignition Upgrade

Postby elballoonrat » Thu Aug 18, 2011 11:52 pm

what if I used this ignition...

http://www.cb750ignition.com/CB450.htm

it says it uses a hall affect sensor, could I use that in conjunction with the HEI unit and DIS Coil?

another idea...
What if on the stock ignition I used two hei units and two coils, I'd have to cap off one wire tower on each coil but it would be worth it I think if it worked.

Long story short I work at GM in Michigan and would really enjoy riding to work on a GM coil. The guys at the office would get a kick out of it.

Plus my coils currently are fried and I don't feel like spending 60 dollars on a stock looking and performing system.

Cheers, thanks for the insight, obviously I'm a newb.


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