So I recently had to swap my 86 5.0 motor for one from 94 (also a 5.0). Went through the process of changing the gear on the distributors to fit so the 86 distributor would work. My question is the computer and distributor still think the truck is an 86 of course so do I use spark plugs gapped at .044. Or do I use the 94 gap of .054?

 

Why would you think of using the 94 gap?

FYI the wider the gap the harder the ICM has to work and that adds heat.
Also spark will always try and find the easiest way to ground.
If the gap is to large and the wires weak spark could jump from the coil tower to the neg side of the coil wire.
I have had this happen with just high resistance plug wires.

Now you can try different gap settings to see what the motor likes best but just remember what I said above.
Dave ----

 

I'd install them at .044 and that might have a cleaner handshake with the ICM in your truck. Over time, miles, the gap usually enlarges so you'll be drifting towards .054

The gap difference is small and for someone unskilled at gapping not knowing the difference between a tight fit or a light drag could be off by half the difference between the two specs. And to be fussy you need one of those graduated disk type because those gaps are not on a typical wire guage gapper.

 

If you want to get real fancy you can index the plugs so the opening points to the intake valve as they say that makes more power.
Dave ----

 

How about a feeler gauge set?


Then, you can be spot on!

 

Most feeler guage sets only go up to 0.035 so you'd have to stack some blades and that can introduce some slop. Get one of the round ones. They're cheap.

 

I don't know if that would make any difference you would notice... try it as they are, but you do know the plug wires have to be routed for the HO firing order correct?

 

That flat gauge is not for plugs either the wire type that also has the part to bend the end or as said the round disc type.
I like the disc type myself.
Dave ----

 

The wire ones are fine too. They will have .045 , .050 and .055 which are close enough. Even cheaper than the progressive round ones and straight forward to use.

 

If you have an Autozone store close by they have cheap wire ones with an .044 wire and the AZ progressive guage a buck cheaper!

https://www.autozone.com/clamps-and-...plug-gap-gauge

 

The wire type are for setting plug gap and why it has the part for bending the tip to set gap.
The round type is for plug gap.
The flat is for setting valve lash and ring gap when set in the cly.
I would never use the flat type for plugs
Dave ----

 

I have used the flat type feeler gauges for plugs since the early 80s and have never had any issues (that includes race engines). I have the wire type gauge just so I have the ability to adjust the electrode. My b-i-l and best friend are engineers. They're the ones that recommended using the feeler gauges as they're "more accurate" (their words, not mine). I'm going to continue with what works for me for ~40 years. If you feel more comfortable using a different method, that's cool. We can agree to disagree.

 

It's not so much the type of gap guage as much as the proper thickness. If you have a feeler guage that's .044 or .054 use it. The thickest I've seen is .035 and my set only goes up to .030

Many plug gaps are specified at .030 or .035 so fine to use a blade there.

I have a set of wire guages that I typically use and it has the electrode bender on it.