I see some engines with their sparkplug wires zap-strapped (plastic tiewrap)together for neat appearance, then seperated as needed. Then I see other plugwires using wire seperaters, intentionally keeping them apart. My friend says that the wires need to be kept apart and that it is very important that they are! What determines the differences, and what problems can it cause?
Thank-You!!
Gerry

There's a phenomenon known as crossfire with spark plugs wires, particularly with parallel running wires to plugs that fire consecutively, where the firing impulse from one wire can cause the adjacent wire to fire. I don't even pretend to understand the physics of it, but plug wires are supposed to stay at least 1/2" apart during parallel runs, and actually be wrapped around one another at some point, generally where they attach at the distributor. With small block Corvettes and their metal shielding, you may find the wires intentionally wrapped around one another as they go to their respective spark plugs to avoid crossfire.

I think besides avoiding the crossfire phenomenon, many of the seperators are there to make for a nice, orderly appearance under the hood.

Crossfire between plug wires is a real thing. It's caused by magnetic induction. Every wire is a transmitter, and every wire is a reciever. Wires running parallel tend to transmit and recieve in the same electrical plane, making induction paths easier. If you spark plug gap is .035 inch. there really is not much of a problem if the wires are in good condition and of good quality. Even a .045 plug gap does not create too much of a problem with good wires, but chances go up.
As the wires age crossfire is more likely. Atmospheric conditions are also a factor. High humidity is a contributor to the problem. If the wires are 1/2" apart and in good condition, there should be no problem. Using the zip ties can also work, but the wires are much closer.
Crossing the wires disrupts the electrical induction pattern and reduces the effects. Many 90's and newer cars have twisted pair wiring for computer multiplexing (not spark plug wires). The twisting reduces interference. There is more to it than that, but that's the basics. You don't have to cross the wires multiple times and multiple points. You can keep it to a minimum and still make clean neat looking wiring. Either way will work. But parellel very close is much more likely to cause crossfire.
I have used both methods (1/2 gap, crossed paths)with good success. If you use poor quality or the wrong spark plugs, or have too high of a spark plug gap, the problem gets much worse.
If you had Distributorless Ignition System (DIS) you need to run the wires exactly as the factory did. Even if the plugs don't crossfire, the induction can mess with the computer sensors and computer operation. DIS is very powerfull at up to 100,000 volts with a couple of amps at max output. It can seriously hurt you, so be careful of it. You can land in the hospital, or worse. HEI ignition produces 40,000 volts, and points ignition produces 20 - 25,000 volts. Both of the latter with low amperage. It smarts, but you'll be okay if you get nailed.

I hope this helps. I can get more detailed if you wish.

Ken Styer

Thanks for explaining crossfire, Ken. I knew it's a real phenomenon, and what was needed to eliminate it, but just really had no understanding of it. Your explanation made it easy. Thanks again.

Ken --
Do you work for NASA ? ? ?

No, not NASA, LOL. I teach automotive repair at Stark State College of Technology in North Canton OH. I am a ASE Master Auto, Master Truck, Master Paint and Body, Advanced Engine Performance, Engine Block Machinist, Engine Assembely, certified tech. (a couple of these have expired, and I need to renew them. I need to renew every 5 years) I am listed in the Automotive Hall Of Fame in Detroit as an ASE Triple Master. One of less than 1000 nationwide. I have served on the ASE commitee for writing Engine performance questions in 1990. I have written over 90 articles published in Import Service, Import Car, and Autobody Magazines. I hosted a call in talk show called "Car Time" on 1590 AM WAKR radio in Akron for 5 years. That was about 6 years ago. I have made my living with cars for over 30 years. I have been teaching for several years.
I worked for Chevrolet as a tech for over 6 years in the 70's and 80's and LOVE C3 Corvettes. I have been accused of having gas instead of blood. They may be right LOL.

Still I don't have anywhere near all of the answers. I help where I can. I will be counting on you folks for some answers as I put my recent purchase back together. A 75 C3 bought from e-bay. No paint, interior removed, most of it there, stored inside for 5 years and not started. It now runs again. I won't do a lot until it gets warm outside. It's sitting on plastic and under a car cover. Hard to believe, I don't have a garage at home. Go figure.

Ken Styer

Thanks for the indepth explaination Ken!! It is GREAT to have you aboard with all of your knowledge and experience!! Again, Thank-You!!So I have 8mm Taylor plug wires, do I need to concern myself with this? A tech from MSD told me that I can extend my plug gap to .050" for a better burn! I'm sorry, I'm still in the FOG!

The 8mm plug wire has better insulation and better resistance to induction and crossfire. Running a stock coil and wires .050 could be too big a gap. The initial KV (energy) to fire the plug would be too great and not leave enough energy to maintain a good spark. The initial KV goes up due to the increased resistance. The burn time would be very short, and not much fuel would be exposed to the spark, and you would have poor combustion.
Burn time is how long the plug actually maintains spark.
When initial KV goes up it uses more coil energy so there is less energy left to maintain the spark. When initial KV goes down, there is more left over and the burn time increses.
With a higher output coil this changes. The high output coil will allow a greater gap and still maintain a good plug burn time. Then the larger gap can be a good thing. Hotter spark due to the larger gap creating more resistance, creating higher firing KV, creating hotter spark, without loosing burn time. These systems work. The key here is system. If you only do part of a system, mixing with original or aftermarket original replacemet parts, the high energy parts overpower the others, and problems occour. These include crossfire, misfire, arcing etc. All of which make the car run bad.
Do a matched set of coil, wire, cap, rotor, spark plugs, or very good components that can handle what you are doing. Don't confuse burn temperature with heat range. Heat range of a plug is how hot the porcelain on the end of the plug stays. This affects pinging, fouling, etc. and can affect cylinder temp. Burn temp is the actual temp of the spark itself, and directly affects how the fuel is lit. It can't be too low or fuel won't properly light, even with a long burn time. By increasing resistance, i.e. bigger plug gap, the burn temp goes up which is always good, as long as the burn time does not get too short, or the porcelain gets too hot. That can be compensated by a lower heat range. A stronger coil helps this a lot. But a stronger coil increases posibility of arcing, shorting, and crossfire if the wires, cap, and rotor are not good enough quality.
Hope this helps. Let me know if you need better or more explanation.

Ken Styer