Spark Plug Wire Upgrade?

Spark Plug Wire Upgrade?

Shazam

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North Carolina
Vehicle(s)
1979 CJ-5 Renegade with '74 304 V8 & Edelbrock manifold & carb, Heddman headers & sidepipes, T-150 3 speed, Dana 20, Dana 30, AMC 20
Hi guys. Thinking of upping my wires from 7mm to 8mm but the price doubles for that 1 extra mm. As far as I know the ignition is a stock Motorcraft. A few questions:

Is it worth it or should I stay with the 7mm (I heard the extra mm is insulation only) Will I get better performance?

I know I'll need straight boots for the plug ends but I also have straight boots at the distributor - can I change to 90 degree with no issues?

Being an older (1974) motor, do I need a certain kind of wire for it to work best? I heard some new wires aren't as good as the "older" kind on some applications.

Thanks.
 
If it's stock or near stock ignition 7mm is what you want. 8mm will not produce a better spark or better performance. There is no point in putting 8mm wires on a stock ignition. It's the rest of the ignition that produces the spark. The spark plug wire's job is to deliver the spark and not to let the spark ground out through the insulation.
Now if you had a high performance MSD ignition then it may be producing such a high voltage spark that it could penetrate the 7mm insulation. In that case you might want to go to 8mm. But otherwise I say stick with 7mm.
 
More importantly than wire size is quality. I don't know why this is such a problem with spark plug wires but over the years I have had a lot of issues with aftermarket spark plug wires.
If you always ask for "OEM" quality parts when you go into a parts store you will get brake parts ,spark plugs and other auto parts that will last for many years. On the other hand if you ask for OEM quality spark plug wires you will get :dung:. Many times I have bought spark plug wires only to have them come apart the first time I try to remove them. Even if you pull on the boot the connector often pulls out. Then you need a specialized crimper to fix it.
Pay the extra money to get quality spark plug wires.
Oh and use dielectric grease.
 
Last edited:
Thanks. I was looking at Accel and will stick with the 7mm. Are they a good brand to use and does the 90 degree boot for the cap matter? Thanks again.
 
The professional mechanics around here tend to use the highest quality (blue) spark plug wires from NAPA...as long as it's an OEM ignition system.

Others with more experience will probably have an opinion about the 90 degree boot thing. I don't think it matters as long as you know for CERTAIN that it's reaching all the way into the cap and making a good connection. You can always slide the connector out of the boot and make sure it's connected good and solid into the cap, and then slide the boot back over the top.

Thanks. I was looking at Accel and will stick with the 7mm. Are they a good brand to use and does the 90 degree boot for the cap matter? Thanks again.
 
X2 on the blue Napa wires. I went to Kragen and another major auto parts store (can't remember) for new wires. Went to put them in one at a time, pull the old one, find the new same length one and put it on, and the last wire was too short both times. Took them back. Went to Napa and the set was correct. They get my vote. The blue color is kinda cool too.
 
Valuable input here - thanks to all.

I cannot find any 7mm wires that I don't have to cut myself - and I'm afraid I'll fubar it :)

I have found 8.5mm wires from Jegs (#40275). I know the 8.5 is overkill but I like the "plug and play" aspect of them. It won't hurt to use them will it - I may upgrade the ignition or coil one day. Thanks.
 
Valuable input here - thanks to all.

I cannot find any 7mm wires that I don't have to cut myself - and I'm afraid I'll fubar it :)

I have found 8.5mm wires from Jegs (#40275). I know the 8.5 is overkill but I like the "plug and play" aspect of them. It won't hurt to use them will it - I may upgrade the ignition or coil one day. Thanks.
I agree and I think you made the right choice.
8.5 is overkill but it won't hurt a thing.
 
Thanks guys. I went with the 8.5 set from JEGS. They are a little long considering they were for the AMC motor - but look and work great. I appreciate the knowledge you all shared. :notworthy:
 
I replaced mine with Beldon Max Power from NAPA, perfect length and boot angle. 1979 CJ7 w/304.
 
go to autozone, and ask for wires for a ford inline 6 (300ci) they are 8mm
 

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