Spark plug wire routing?

[LAC_STS]

I got my OEM OMC manual today. Its day and night to the crappy Seloc one.


I was just looking through it when I saw some charts for trouble shooting problems.

One has a part that says Engine vibrations and noises ---IGN ---Improper spark plug wire routing.


Maybe its in here but I havent found anywhere where it says a specific way to route the plug wires.

Is the routing of the plug wires important? Important where is could cause vibrations and noises?

 

[Alpheus]

Re: Spark plug wire routing?

Well the rule is on small block chevys or any engine that has a similar firing order
1-8-4-3-6-5-7-2 you are not supposed to cross the #5 and #7 spark plug wires...

 

[LAC_STS]

Re: Spark plug wire routing?

Thanks

Do you mean cross as in dont put the #5 wire on the #7 plug and vice versa?

I figured you couldnt cross any of the wires. I was wondering if they meant the actual routing of the wires,

 

[wire2]

Re: Spark plug wire routing?

Well the rule is on small block chevys or any engine that has a similar firing order
1-8-4-3-6-5-7-2 you are not supposed to cross the #5 and #7 spark plug wires...

Ok, I'll bite; why not?

Now, did you mean "don't interchange 5 with 7", or "don't let the wires overlap"?

The 1st is an obvious no-no, but I'm curious what *might* happen if they do cross?

If the wires are in good condition, it's doubtful that the spark energy from one can induce enough voltage in the other to do anything.

 

[Alpheus]

Re: Spark plug wire routing?

First rule I was taught when I used to build high HP SBC engines.

The electrical Principal is called 'Induction'.
The electromagentic field created in the first plug wire in the firing order will fire, the electrical field generated will 'Induce' a fire in the plug wire it's lying next to.

If it's firing a cylinder that is on the exhaust stroke, no worries...
If it's firing the next cylinder in the firing order, it's setting the burn off 90 crankshaft degrees, plus what ever advance is in the original ignition cycle!

That means the second cylinder is getting fired 90 to 130 degrees too soon, and the burn is trying to force the piston back down the way it came instead of letting it reach the top of the cylinder.

#5 & #7 fire one right after the other in SBC and BBC engines.
#5 has the momentum in the intake runner, so it starves #7 for fuel, racers have always known that #7 on a SBC will run lean no matter what you do...

In a low performance low compression boat engine it can just cause popping and sputtering out of the carb or vibrations. This has been reduced by the introduction of newer more insulated plug wires, but its just a good idea not to cross those wires because the potential is there...

 

[LAC_STS]

Re: Spark plug wire routing?

So does this mean that we need to use those spark plug wire things that space out the wires and make them neat?

Or just make sure the #5 and 7 plug wires are not all over each other?




Thanks

 

[Alpheus]

Re: Spark plug wire routing?

You should always have your plugs wires ran neat and as far from each other and hot surfaces as you can. This can and will cause premature wear and tear on your plug wires do to burning and chaffing. But the main thing is not to cross/overlap the #5 and #7 plug wires...

 

[wire2]

Re: Spark plug wire routing?

Ok, that's where I thought it was going. Are you aware of instances where it was observed to actually happen?

I'm quite familiar with induction, have been a licensed electrician since 1972.
I suspect it's become an "urban legend" that #5 firing can induce a spark in #7 (or any other wire) by just the proximity of the wires.

At best, it's a very inneficient 1:1 transformer, with an air core,(not iron laminations to conduct magnetic lines).

The intensity of the magnetic field around a current carrying conductor depends on the amount of current. A coil draws ~ 5 amps @ 12v, so by Ohm's Law, that equates to 6 milliamps @ 10Kv. If you subtract the heating loss of the coil, it drops to 2-3 milliamps.

I find the concept somewhat dubious.

However, I can accept that the spark from 5 can jump to 7 IF the wires are in poor condition.

 

[LAC_STS]

Re: Spark plug wire routing?

Thanks guys.

My wires are not too neat right now. They are running from the plugs under the manifolds to the dist.

I will buy some of those wire things and fix em up.

 

[sethjon]

Re: Spark plug wire routing?

I got my OEM OMC manual today. Its day and night to the crappy Seloc one.


I was just looking through it when I saw some charts for trouble shooting problems.

One has a part that says Engine vibrations and noises ---IGN ---Improper spark plug wire routing.


Maybe its in here but I havent found anywhere where it says a specific way to route the plug wires.

Is the routing of the plug wires important? Important where is could cause vibrations and noises?

Most important is make sure the wires aren't pinched or touching anything hot.