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Spark plug wire length and routing


TheBMan

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I purchased a set of reproduction spark plug wires for my 72 Monte Carlo (small block). Since the wires are different lengths, especially two oddballs that I wasn't sure about, I wanted to be sure I got the routing and position correct. It's not as cut and dry as it appears. It's deceiving because, of the eight wires, six of them are matched pairs. This would make you think that they go to opposing cylinders on opposite banks. Nope, that isn't true. And what are the two oddballs for?

A while back, @jft69z posted an image of the routing and the factory part numbers for each wire. This is immensely helpful. That post can be found here: https://www.firstgenmc.com/forums/index.php?/topic/22499-spark-plug-wire-looms-holders/&tab=comments#comment-215443

In the wire set that I purchased (from https://www.lectriclimited.com/) was a sheet that specified the length and position of each wire. I thought this might be helpful as well if someone was making their own wires or wanted to use it in addition to what Joe T. posted. Attached is an image of that page and a picture of the wire set. Use it combined with what Joe T. posted and you can't go wrong.

I hope this helps anyone who is going to replace or make their own spark plug wires.

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Glad the picture helped you out Bryan!

After looking at the part numbers the factory pic listed, and the wire lengths that are on your instruction sheet, it looks like there's a little difference?

The factory looks like it has 2 sets of 2 with the same number, one set of 3 that are alike, and one single wire with a different part number.

The replacement ones show 3 sets of 2 alike, and 2 different lengths after that. 

Granted, the factory pic is a very early one they used, and who knows how many updates happened as production progressed. Did you run into an issue with it, or did they fit like a glove?

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21 minutes ago, TheBMan said:

@jft69z I haven't installed them yet! I'll update here when I do.

Yeah, do that, I'm curious.

Seems like any time I get a set of wires, even though they're 'application specific', I end up cutting at least a couple & re-terminating them to get them to route the way I want it to run. Just got a new set of MSD BBC wires sitting on my dining room table, I know I'll be trimming them to fit, lol.

Oh, scrutinizing those numbers a little further, it appears that your #6 wire is the odd one compared to the factory pic. It's maybe 2 inches longer (at 26"), compared to the #5 & #7 wire at 24". That's based on the GM part numbers, and seeing which cylinders had the same part numbers (GM shows 5,6 & 7 with the same part number).

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9 minutes ago, cny first gen 71 said:

I think anything you buy in the aftermarket they add a little length to, maybe to fit other applications too. They always seem a little long.

Yeah, seems you could wrap the wires around the distributor a couple of times on some of them, lol.

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I guess I need to go through the manuals and check my routing. The engine builder put them on when he ran it on the dyno and it all fit in the looms ok so I never messed with them. I will now. Thanks for the info 

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47 minutes ago, TheBMan said:

Sorry @Brew, didn't mean to wire shame you. ;)

Add me to the shamed list, I still need to clean mine up around the dizzy 🤣

From my experience in the past I just order the wires I want (not pre-made) and build'm as I run'm. I'm not a concours guy tho. 

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1 hour ago, SPLATT71MC said:

I've always use the trim to fit kits with great results.

I use these also my son in-law has the crimping tool specifically for spark plug wires 

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On 10/11/2021 at 1:44 PM, Leghome said:

I use these also my son in-law has the crimping tool specifically for spark plug wires 

I just got tired of the precut sets either having that one wire that no matter where you put it was way too long and the one that was way to short to go anywhere.

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Here's an update after I got the wires installed. I would have to say that this set from Lectric Limited fits as good or better than any I've seen before. I'd recommend the set. I also purchased new valve cover wire looms/holders. I'm looking for two special looms for the left bank that I'll create a different post about.

@jft69z

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  • 3 months later...

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