I swapped out the plugs in my 300-6 today, before doing so I checked and they were all pre-gapped to .040" so I went ahead and installed them then went on a test drive and the truck ran great.

After checking online I come to find out the spark plug gap should be .035" for my engine. This is an electronic ignition (stock) not a points ignition. Will .005" really make any difference? The plugs are easy to pull but I'd rather not if the .005" difference is of no consequence.

 

In general, higher gap means higher secondary voltage and more electric load on the cap/rotor/wires. If gap and load/voltage are higher than what the system was designed for life and reliability will be reduced. I would double check specs for your system... if .035" is called for I would re-gap to spec for reliability (personally).

 

After researching more info/pics online I discovered my ignition system is not original to the truck, a phone call to the previous owner confirmed my suspicion.

He apparently upgraded the ignition to the later version with the larger two piece distributor cap, which also required different plug wires and coil.

In his opinion he stated I would be fine with a .040" plug gap, but not to exceed .045" is this an opinion you would concur with, or should I re-gap to .035"? Thanks.

 

I'd leave them in. If you're going to pull the plugs, then gap them to 0.045". The larger spark gap does increase secondary voltage but it should still be far below what your system was designed to withstand. Increased plug gap size makes a larger flame kernel which increases combustion efficiency/reduces misfires and might even cause a small increase in fuel mileage.

I've run totally worn out plugs at 0.060" measured gap with 100K mile old spark plug wires. After replacing plugs and wires with new high-quality pieces I measured exactly zero increase in mileage. What a disappointment.

Even your truck's original stock system would fire 0.045" gap plugs effortlessly.

R.

 

Sounds like it was upgraded with Duraspark II components. Recommended plug gap is .040-.043" from memory so you should be OK with .040".

 

Thanks for your feedback! As you and others have advised i'll be keeping the plug gap at .040"

I've noticed the engine even "fires off" quicker with the increased plug gap, I no sooner turn the key to start and the sleeping beast is awaken!