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AC 45S vs Champion RJ12YC

mhnbonne

New member
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This is not so much of a question as a “Heads Up” information.
My ‘65 389 just was not running very well. The engine deteriorated to the point that it would not idle. It smoked pretty bad.
I sent it out to a rebuilder and had my carb rebuilt as well. The carb was built to run on todays non leaded gas.
I got the motor back, installed it and installed the rebuilt carb.

The motor ran, but not very well. It idled and accelerated roughly.
I noticed that I had Champion RJ12YC spark plugs, they are all new. I dont remember installing them, I guess that the engine rebuilders installed them.

I checked and I see that the AC45S (which I have used since 1970) does not cross to this part number.
Whats more, resistance from tip to electrode varied from 30K to over 100K
My new set of AC45S are all about 2K

After installing 8 new AC45S plugs my 389 runs absolutely perfect, idles like a kitten, accelerates lime a lion.

Hope this helps somebody
 

melsg5

Staff member
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Thanks for the post. The Champion number you listed is a resistor plug. The AC number you listed if 45S is a non-resistor plug but if you meant R45S that would also be a resistor plug.
Which AC number did you intend?
Did you install new plug wires during this rebuild?
Did you install new cap, rotor, points and condenser?
Did you use a new ignition coil?
 

mhnbonne

New member
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Thanks for the post. The Champion number you listed is a resistor plug. The AC number you listed if 45S is a non-resistor plug but if you meant R45S that would also be a resistor plug.
Which AC number did you intend?
Did you install new plug wires during this rebuild?
Did you install new cap, rotor, points and condenser?
Did you use a new ignition coil?
1. I have always used 45S, not R45S and with great success
2. Wires were not replaced.
3. Cap, rotor, points and condenser are new.
4. Coil is new

I checked the resistance on the Champion plugs, the values varied widely from 30 K ohm to over 100K ohm. All of the new 45S were about 2K ohm.
What a difference it made using the correct plugs.
Thanks for the quick reply.
 

melsg5

Staff member
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The point I was trying to make is there maybe a weak component in your ignition system, using those Champion resistor plugs should not have caused that problem. As an example the standard exceptable resistance in carbon core plug wires is 1000 ohm per foot of wire thus the 100 ohm reading on a plug is acceptable. You may want to test your wires.
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cammerjeff

Member
563
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18
Belleville MI
I always tend to run the original make of plugs in my cars, from my personal experience Champion plugs do not work well with GM Engines, they do work well in Chrysler engines, and most lawn Mowers (that is not meant to be a slight on Chrysler engines, sorry if it came out that way)
 

mobileparts

Member
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The problem is of course: finding non-resistor 45S AC plugs -- you can pay big money for them... R45S is of course, still in production, made in Mexico... You are definitively compromised to some extent...
Resistance means less performance traditionally, and Mexico vs. U.S.A., of course....
And, you are right, since the days when AC and Champion "split up":
G M vehicles should use A C ,
Chrysler vehicles should use Champion,
& Fomoco vehicles should use Motorcraft.

Incidentally, I have some N.O.S. DELCO Distributor Caps with Copper Contacts!!!!
 

mhnbonne

New member
14
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1
The point I was trying to make is there maybe a weak component in your ignition system, using those Champion resistor plugs should not have caused that problem. As an example the standard exceptable resistance in carbon core plug wires is 1000 ohm per foot of wire thus the 100 ohm reading on a plug is acceptable. You may want to test your wires.
I measured all wires, all were 8000 (8K) to 11K ohms. No wire is more than 3 feet, some less than 2 feet.
Although have seen a tremendous improvement in accretion, the engine is not smooth a 600 rpm idle.
I guess its time for a plug wire change. Now, ALL ignition parts will be new.
Improvement should be another leap forward, I hope
 

mhnbonne

New member
14
0
1
The problem is of course: finding non-resistor 45S AC plugs -- you can pay big money for them... R45S is of course, still in production, made in Mexico... You are definitively compromised to some extent...
Resistance means less performance traditionally, and Mexico vs. U.S.A., of course....
And, you are right, since the days when AC and Champion "split up":
G M vehicles should use A C ,
Chrysler vehicles should use Champion,
& Fomoco vehicles should use Motorcraft.

Incidentally, I have some N.O.S. DELCO Distributor Caps with Copper Contacts!!!!
The AC 45S plugs that I used to replace the Champions are poorly made where the ground electrode is too short after gaping the plug to .035"
Out of the box, the ground electrode is parallel to the tip, however, the gap is less than .020 (the smallest gauge tool have). After bending up the electrode to .035", the electrode is now at an angle over the tip (about 20 degrees). T are this right, you would have to completely straighten out the ground electrode and bend it at a different position, however, it would then be too short to reach over the tip.
______________________________
 

melsg5

Staff member
SUSTAINING MEMBER
20,076
114
63
The AC 45S plugs that I used to replace the Champions are poorly made where the ground electrode is too short after gaping the plug to .035"
Out of the box, the ground electrode is parallel to the tip, however, the gap is less than .020 (the smallest gauge tool have). After bending up the electrode to .035", the electrode is now at an angle over the tip (about 20 degrees). T are this right, you would have to completely straighten out the ground electrode and bend it at a different position, however, it would then be too short to reach over the tip.
How long ago did you buy these 45S plugs?
Where did you buy them?
The reason I'm asking it appears AC-Delco no longer makes them so they may be knock offs.
They only make R45S.
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