(sorry, can't help myself).
Converting to HEI help needed.....
Thread Starter
Le Mans Master
Joined: Oct 2005
Posts: 9,429
Likes: 44
From: Macon, GA
Converting to HEI help needed.....
Long gone is the label I put on the hot wire to the old coil when I snatched the old boat anchor motor. Question is this - Can't I just use any hot wire (with ign on) that's coming through the firewall?
Thanks.
SP
Thanks.
SP
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
make sure the wire gauge is correct, there shouldn't be too many wires in the harness there, look for a red one with a white stripe.....thats what it looks like what they hooked up on my 69 to an hei set up
Drifting
Joined: Jul 2002
Posts: 1,995
Likes: 110
From: Garland Texas
To do this correctly you need to trace the resistor wire back to the bulkhead connector and replace it with a 10 gauge wire. The coil wire is a non-fused circuit and independent of all other key-on power.
Mike
Mike
Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
If u don't bypass the resistor wire the coil will run on lower voltage and have reduced output. But i recall the '68 had a ballast resistor which is very easy to bypass - just short it out.Yep, HEI is just a 1 wire install and very easy upgrade from points and only 150 bucks too. But u will lose the mech tach drive - heck install a nice AutoMeter tach with shift light too.
cardo0
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Thread Starter
Le Mans Master
Joined: Oct 2005
Posts: 9,429
Likes: 44
From: Macon, GA
If u don't bypass the resistor wire the coil will run on lower voltage and have reduced output. But i recall the '68 had a ballast resistor which is very easy to bypass - just short it out.Yep, HEI is just a 1 wire install and very easy upgrade from points and only 150 bucks too. But u will lose the mech tach drive - heck install a nice AutoMeter tach with shift light too.
cardo0
Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
Do u know how to use a voltmeter? Just turn the ign on and measure the voltage at that wire. Should be 12VDC - well depending on how many contact voltage drops it should read close to battery voltage. If <12VDC then u have some resistance in the circuit.
HEI will still work on low voltage but your'e missing spark power that way. Free hp power for a little effort.
cardo0
HEI will still work on low voltage but your'e missing spark power that way. Free hp power for a little effort.
cardo0
Tech Contributor
Joined: Jun 2004
Posts: 20,905
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From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
I disagree with a couple items mentioned in the posts above. When using a voltmeter, you will only be able to determine if there's resistance in the line if there's current flowing (and noting an attending voltage drop). Just turning on the key will show roughly 12 volts regardless if there's a ballast resistor in the line or not.
Regarding the coil wire as "a non-fused circuit", that scares me. The original harness had the ballast resistance in it to limit coil current, but it also limits current in the event of a short in the coil or wiring leading to the coil. If you pull non-fused power to the HEI, there is a slight danger if there is a short circuit in the feed wire. Personally, I'm uncomfortable with unfused 12 volt lines. The HEI pulls less than six amps in normal mode (a twenty amp fuse should be fine), but its supply wire will allow a bunch of "toaster oven" current in the event of a short, with the potential to start a harness fire.
Just my two cents.
Regarding the coil wire as "a non-fused circuit", that scares me. The original harness had the ballast resistance in it to limit coil current, but it also limits current in the event of a short in the coil or wiring leading to the coil. If you pull non-fused power to the HEI, there is a slight danger if there is a short circuit in the feed wire. Personally, I'm uncomfortable with unfused 12 volt lines. The HEI pulls less than six amps in normal mode (a twenty amp fuse should be fine), but its supply wire will allow a bunch of "toaster oven" current in the event of a short, with the potential to start a harness fire.
Just my two cents.
Thread Starter
Le Mans Master
Joined: Oct 2005
Posts: 9,429
Likes: 44
From: Macon, GA
OK I've got 12.35 at the battery and 11.88 at the distributor wire lead. Is that going to be ok? What's all this talk about non-fused and fused wire? How do I make sure I'm good? I don't want to cook this thing.
Tech Contributor
Joined: Jun 2004
Posts: 20,905
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From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
Fused is just as it sounds. Find an unused place in the fuse box where you have switched 12 volts (hot during ignition AND cranking), install a twenty amp fuse,(a large fuse has a lower series resistance, but will still provide some protection) and run this to your coil + terminal. This should give you a protected low resistance feed to the HEI.
Race Director
Joined: Sep 2004
Posts: 11,874
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From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
its just low voltage thats all.....the coil will not have the same voltage as if it had a voltage source that was not running through the ballast resistor
edit:.........and it will probably work ok for you
edit:.........and it will probably work ok for you
Last edited by bobs77vet; Apr 15, 2007 at 04:05 PM.
Le Mans Master
Joined: Oct 2002
Posts: 7,098
Likes: 378
From: Las Vegas - Just stop perpetuating myths please.
It looks ok now.
The stock ign coil is energized until triggered by the dist reluctor - hense there is current flow (u can verify this by using that DMM ammeter function in between the coil and wire source). U can see this as if no current was flowing the full batt voltage would be at that wire and there is no voltage drop with no current flow - no that meter resistance/impedance is much too high to draw any measurable current. FYI Capacitance Discharge (CD) ign (MSD) use the reluctor trigger to energize the coil and the coil is not energized until triggered with a CD ign sys.
Now as far a 11.88VDC at the coil with 12.35 at the batt sounds ok considering contact resistance from all the wire junctions thruough the ign sw wiring path. My guess is the ballast resistor was already removed by previous owner and long gone (did u burn any previous coils?) - someone upgrade the wiring with the new eng?
If previous wire was not fused i would not change that configuration unless u know what u want to do and how to do it.
IMHO i think your fine sperkins.
cardo0
Now as far a 11.88VDC at the coil with 12.35 at the batt sounds ok considering contact resistance from all the wire junctions thruough the ign sw wiring path. My guess is the ballast resistor was already removed by previous owner and long gone (did u burn any previous coils?) - someone upgrade the wiring with the new eng?
If previous wire was not fused i would not change that configuration unless u know what u want to do and how to do it.
IMHO i think your fine sperkins.
cardo0
Drifting
Joined: Jul 2002
Posts: 1,995
Likes: 110
From: Garland Texas
You need to check the voltage with the engine running.
The ign circuit is unfused. Factory designed. But if you get a short circuit in the ign it will blow the fuse link on the starter and/or on the horn relay. The result will be all of the key-on power will be dead, ign and acc. The headlites will work but nothing else.
I should have said the independent ignition circuit is not fused but the entire key-on power supply, which the ign is a part of, is on a fuse link.
Mike
The ign circuit is unfused. Factory designed. But if you get a short circuit in the ign it will blow the fuse link on the starter and/or on the horn relay. The result will be all of the key-on power will be dead, ign and acc. The headlites will work but nothing else.
I should have said the independent ignition circuit is not fused but the entire key-on power supply, which the ign is a part of, is on a fuse link.
Mike