Does a closer gap mean more mpg, but less power? Or does it make a difference? I know that as a plug ages the gap widens. But I was always told to run a bit closer gap to provide better mileage. Any ideaS?

 

I have also wondered about the effects of different gapping. My old truck, a Ranger with an 8 plug head, was so hard to get at the [pluggs I left it fro 2500-km and finally changed them out of guilt. The gap on the plugs was huge, near .070!, but the truck ran fine. My new truck is a 93f 150 with a 5.0 and I recently changed plugs wires and rotor and cap in a quest to cure a missing problem(i didn't). I gapped the plugs to the recomended gap on the sticker on the hood,.044. The truck still misses. I tried a test plug hooked up to view the spark and it seem very weak, kind of pinkish not a fat blue spark that I would expect to see. Even my lawnmower has a better looking spark! Perhaps my coil is going south. I did try different gaps on the test plug but to no avail, still wimpy. I Do believe that the larger gap gives a hotter burn if the coil is up to it. Most modern engines use a bigger gap than they did years ago where .025 was the norm. My new plugs seem to be of a nice cafe au lait color with no deposits on the as were the old ones I took out. The gap on the old ones had worn into .050. The truck runs fine except for an idle miss and a miss when going up hill, but this miss corrects itself after a while. I am at a loss now so I will get the coil tested if I can to see if it is o.k. Any other suggestions? P.S. the engine light doesn't come on at all.

 

Ive always gapped the plugs on my engine at the upper range . The range is 044 to 046 . You always want the widest gap possible to produce the best spark , At least with conventional plugs . Another thing Ive found is the gap really doesnt change a lot in 15 to 20K miles . Thats about the life span of any Motorcraft spark plug .

 

 

I've read that a larger gap produces a larger spark for improved combustion which equals more power and better gas mileage. But as in all things there is a trade off. With a wider gap, you have to change the plugs more often and your ignition system has to be in tip top shape. The factory gap is a happy medium in plug life span and power/gas mileage.