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DuraSpark/TFI to HEI

#1 User is offline   Rollbar 

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Posted 15 January 2008 - 08:18 PM

DuraSpark/TFI to HEI Conversion.

Duraspark Controller, heated it up with a propane torch until the epoxy pulled away from the case and wrenched the old board out. Just drill some holes.

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HEI controller inside a DuraSpark box/ heat sink. And it plugs right into the harness. And if this ever goes bad you can use a spare DuraSpark controller.
Here is a little drawing...
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Interestingly the white wire, which is not used in this case, is to retard the spark while starting. This could be used as a octane selector later or for NO2 injection. It measures around 0.279 uF.

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Basically just get the HEI module from NAPA, just ask for one from a 76-82 GM 250. That's the black part in the pictures. You will need a heat sink like a big piece of aluminum angle iron or an old DuraSpark case. Use the leads off the box to make your connections.
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Here is a close up view.
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Some additional bonuses with a GM HEI.

If you turn your key to ON without starting it the module if "OFF" so no current passes thru your coil until you start your engine. This is good it you like leaving your ignition on when your working on your jeep. If you do this with a Dura-Spark setup then you will burn out your coil or your module.

The HEI learns as it is running.

Here is a picture of the GM HEI Module output right after the engine is started. Notice that the little bump at the end of the curve were it shows the current to the coil is reduced to protect the coil is missing.
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Now after a min. the blip has appeared.
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First here is the DuraSpark (DS) at idle.
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I want you to notice the last part of the trace were the curve is at it's lowest point. This is when the coil is charging.
Here is a drawing with Specifications.
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The dwell time here is roughly 3:1 (8ms vs 24 ms.
At 2500 RPM only the duration of the pulse changes but the dwell time is still roughly 3:1
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OR graphically,

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Now onto our GM HEI Module.
First at idle.
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Notice the dwell angle here is shorter for the GM HEI. Less time to charge up the coil.
Also notice the rise at the end of the low part. This is were the HEI module determines the coil is fully charged and ready to fire so it reduces the current into the coil to increase the life of the module and coil.

Drawn in detail like this:
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Our dwell ratio is almost 50% OK for idle.

Let's kick the RPM up a little to 1700RPM
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Notice how our dwell angle (ratio) has changed. The coil is turned ON longer to charge up and the "Holding" current is much shorter.
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Our ratio is almost 4:1 !!!

Now a little higher RPM or what I felt most comfortable at. 2700 RPM
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Now out "Holding" step has all but disappeared and out dwell ratio is at 6:1
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Now the DuraSparkII is suppose to do this also but we don't have those in CJ's Dura-Spark ignitions. They just runs at a fixed dwell angle.
Now one more picture.

This is were the HEI module fires in relation to the Pickup in the distributor.
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Interesting isn't it. I thought it would fire at the peak but i look like it is looking for a falling voltage and fires at a particular voltage level.

Thanks for the contribution John Strenk
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#2 User is offline   nero004 

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Posted 17 January 2008 - 09:08 PM

im kinda confused on the advantages to doing this, i will be working by this module this weekend but i would like to upgrade anything i can on my YJ, so what benefit will i get from doing this?
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Posted 17 January 2008 - 09:15 PM

Basically the spark is higher than stock, just like your HEI dizzy U are putting in etc.
*MY CJ IS YOUR yJ's DADDY*

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Support the Central Florida Bible Camp for kids

'65 CJ5 Navy; '74 CJ5; '80 CJ7; '84 CJ8; '86 CJ7
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#4 User is offline   nero004 

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Posted 17 January 2008 - 10:04 PM

so if i put the hei dizzy in do i still need the duraspark module or can i get rid of it??
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#5 User is offline   Rollbar 

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Posted 17 January 2008 - 10:21 PM

The HEI is a module.
Basically just get the HEI module from NAPA, just ask for one from a 76-82 GM 250. That's the black part in the pictures. You will need a heat sink like a big piece of aluminum angle iron or an old DuraSpark case. Use the leads off the box to make your connections.
Posted Image
*MY CJ IS YOUR yJ's DADDY*

*Who Needs A Stinking Manual When You Have A Fat Wallet For Tech Support!*

*What man is a man who does not make the world better*

Support the Central Florida Bible Camp for kids

'65 CJ5 Navy; '74 CJ5; '80 CJ7; '84 CJ8; '86 CJ7
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#6 User is offline   nero004 

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Posted 17 January 2008 - 10:55 PM

cool ill do it this weekend and add some pics
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#7 User is offline   nero004 

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Posted 18 January 2008 - 10:03 PM

i am doing this as i type, does anyone have any idea how to take that epoxy from the back off?????
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#8 User is offline   nero004 

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Posted 18 January 2008 - 11:26 PM

yea so i plugged it in and it doesnt work, i dont know if i did something wrong but im not even gonna try to fix it, im just gonna get a new duraspark box tomorow because my jeep wont start now, and i had a feeleing that my duraspark was already bad
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#9 User is offline   nero004 

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Posted 19 January 2008 - 01:33 AM

cancel i figured out what i have to do and did wrong
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