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Discussion Starter · #1 ·
I just started my HEI conversion. Of course the first part is to locate one in the junk yard. There was one good post on what engine to get it out of, however, because it wasn't a jeep or Chevy small block, I was not exactly sure what the GM 250 looked like. Ends up that its a inline 6, I was looking for a V6.

Basically, there are two basic flavors of this dist, the only mechanical difference being the length of the shaft. The V6 version is too long and the oil pump drive is different. Of the ones that are the correct size, there are also 2 flavors, one with the coil in the cap, the other with the coil external to it. In my search I could not find a 250 that had the internal coil. After very close examination, I was able to use parts from the longer style to convert the external coil to internal.

The external coil has 2 wires from the base, the internal has 3. The 3rd wire is only a ground. You can take the cap, rotor and wire loom off the longer style and it fits just fine inside the short one. To be on the safe side I also swapped the electronics module since the part numbers were different.

As soon as I get the right gear I will get everything installed and let you know how (and if) it runs.

John......southern CA
84CJ7,3"lift,32"BFG
 
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Discussion Starter · #2 ·
ok, I'm going to feel like an idiot asking this, but if I don't ask I'll never find out. What is the point of an HEI? I know that they put out greater voltage, but how does this help? Once you get the gas to burn in the cylinder, why does it matter if you have 12,000 volts or 50,000? Help fill in an idiot here folks.

MudFlap 87 YJ POS!!
 

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DDAWG,
Don't worry, It'll run and it'll run good.

Jeeper131,
Here's my take on this: (I'm not as well educated as some who frequent this place) It boils down to efficiency. You have to ignite the fuel/air mixture at just the right time as well as you can. Your stock plug gap is about .035 with a tiny 12,000 volt spark and the HEI provides a 50,000 volt spark through a gap that's .045. The ignition spreads through the compressed gas faster making the explosion inside the cylinder (internal combustion) bigger and more powerfull and all at once, instead of still igniting while the cylinder is moving down on the power stroke. Plus the HEI is less affected by things like moisture and temperature. It was quite revolutionary when GM started using it in about 1975.

Loose nut behind the wheel
Another right-wing conservative.....
Born and raised in Jeep-Town
 

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Yes,..I agree, the HEI is a panacea for many ignition woes......it packs plenty of firepower......will fire unwilling(fouled) plugs.....in adverse conditions (lean mixture ......cold engine....poorly atomized intake mixture)...allows, as mentioned, wider plug gaps and is virtually impervious to environmental insult. All in a neat compact (well sort of) package. Cheap "drivability".

GeeAea

 
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Discussion Starter · #5 ·
To add to what was posted above. The HEI also takes the cpu out of the loop on the later 258's. So buy using a HEI and a weber or other non cpu controled carb or doing the nutter bypass you dont have the cpu running the timing and fuel mixture. I had the cpu carb and stock ignition. ran like crap didn't want to rev smooth over 3000rpm. with a weber and HEI is it much much better. revs smooth to at least 3600rpm. Never had it past there I don't think.

 

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/wwwthreads_images/icons/tongue.gif There was a post by LEVE on the old board about this, and my understanding was that there is not actually an explosion(we learned this in engineering skool/wwwthreads_images/icons/crazy.gif) but a steady burn which heats the air which expands and drives the piston down. The "plasma" produced by the HEI does a better job of "following" the burn as the gasses expand, thereby burning more of the fuel./wwwthreads_images/icons/tongue.gif

CJDave
 
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Discussion Starter · #7 ·
Where is LEVE? He has been MIA for close to a month. Anyone keeping in touch with him? If not I'll write him to see whats going on.

LarryM
85 CJ7, 350TBI ,T19 4spd
'00 TJ Sport, NV3550 5spd, D44, Teraflex system
 
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Discussion Starter · #8 ·
There is a bit of misunderstanding when it comes to upgraded ignition systems. A ignition coil, weather it be a HEI or a stock motorcrap, will only put out enough voltage to jump the gap in the combustion chamber. The amount of voltage necesary is related to the resistance across the gap. The more resistance, the more voltage. Plug gap, fuel mixture, and cyl compression are just a few of the things that effect the resistance.

 
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