Some months ago I read a discussion about sidegapping spark plugs...maybe at this site or at F150 online. I read the web-link article with the discussion and thought 'how much difference could that make?' Well, got bored today after finding an old set of autolite plugs in my garage and decided to experiment. These plugs came out of my 4.9L six before the Splitfires went in a few months ago. Took the old plugs out to the shop, put each in the vise and hacksawed about 1/16 to 1/8th inch off of the tip of the electrode bar...leaving the tip just over the tip of the electrode. Double checked the gap, installed them and went for a test drive. WOW! Thought I was driving my 69 F100 with a 360 V-8 again! Can't burn rubbber, but engine runs smoother, accelerates faster and better and now my E40D tranny waits until 55-60 mph to shift into OD...before it would hit OD between 45-5 mph, kind of aggravating when you're trying to get around a blue-hair or an old fart just plugging along. I know sidegapping reduces plug life, but if it gains me 1-2 mpg along with this peppier performance, I'll be a happy puppy. I'll post back in about a week with mpg results...I drive about 30 roundtrip to work each day and normally burn almost 3/4's of a 16-gallon tank per week...a week's worth with the sidegapped plugs should tell the tale on mpg improvement, if any. If mpg does go up, I'm going to keep sidegapping...plugs are cheap compared to current hi-test gas prices. Any opinions (long-term) from those who have tried sidegapping in the past?

 

This sounds interesting. Im not exactly sure what you do, could you please post some links or pictures?
Thank You!

 

Well there used to be a good pictorial on side-gapping plugs at the performance unlimited web site, but now its gone. Let's see if I can describe sidegapping in simple terms. When you look at a profile view of spark plug with the electrode up, you see the electrode bar extending all the way over the top of the center electrode, right? The Spark jumps between these two points. On a side-gapped plug, the tip of the electrode bar barely extends over the edge of the electrode, so the spark essentially jumps sideways (kind of) to the electrode. Some folks grind the electrode bar shorter to achieve this, but I had good luck with a hacksaw and vise...just went slow and carefull. Does anyone else know of a web link with photos of sidegapped plugs?

 

Sounds like a great idea. More horsepower, torque, and better fuel economy is always better when it is free. I'm going to give it a try as soon as I get home from work. I found this site that has the pictures of a side gapped plug. I think the pics would have been more useful if it was a straight shot at the electrode just to show how much of the arm was left. So here is the site and I hope it helps. http://performanceunlimited.com/illustrations/sparkplugs.html

 

as a regular guy who changes oil and plugs himself, is this the kind of job I should undertake myself? It looks really easy, but are there terrible hidden consequences? Like the ceramic insulation burning and cracking and the chips falling into the cylinder? Does this minor change with good quality effects, risk disasterous side effects? (Murphy's law and all) The photos of the chipped insulation made me think of $800 repairs because I decided to have a little fun one afternoon... and how long do the side gapped plugs last?

 

The plugs won't last as long, because of the uneven wear. but look at it this way, it saves you money, so it really isn't a big deal to replace the plugs more often. I would advise doing it to a set of cheap plugs like motorcraft or autolite.






Evan A.K.A. PastMaster
1993 F-150 302/E40d XLT
1989 F-150 302/Aod 4x4 XLT Lariat

 

Well, I finally got around to sidegapping my plugs. I didn't do it in my truck, so my car (1992 Plymouth Sundance 2.5l non-turbo) was the guinea pig because it had half as many plugs and half the price to replace them if I screwed them up. I took a Dremel tool and ground the grounding arm down with a 1/8" thick grinding wheel. It was fairly effortless. Doing it this way, I could avoid bending the arm making it weaker. Then the running test came. Performance wise, there was a very noticable difference in pickup. Also, maybe due to my imagination thinking it was some magic miracle, the throttle response seemed greater. I haven't checked the mileage however and I will post the results as soon as they are known. Right now I get 24 m.p.g. average so it would be great to jump to 26 or better.

fire23
1989 F-150 XLT Lariat 4X4 302

 

Just to let you all know, the end product of grinding away the ground electrode until it barley extends over the center electrode, is allready designed into a sprak plug that has a part number dedicated for a two stroke application, such as a dirt bike plug or a chain saw plug. If you look into the Autolite or Champion catalog on the pages of the specs for the plugs,not the applications, you will find foot notes about this feature labeled as 'unshrouded' or 'for two-stroke apps.'or 'cut-back' and simular. Allthough the tapered seat plugs that live in the late 6's and V-8's were never OEM on any type of two stroke application, you will find the older gasket seat plugs available with the tip cut back right out the box,you just need two study the spec charts in the back of the catalog for the proper part #. Also, there is a racing plug spec chart back there as well that may point out such features as that as well. I wish I had a catalog with me now to verify part #'s for these out of the box side gapped plugs,but they do exist.
Phillip

 

Another thing you want to do is when your tighting up the plug itself,get the opening of the plug between the valves when tight.Indexing.....I have a plugsocket that has a line grinded up and down it.I face the opening to it and when I tighten plug I try to get it where I want it between the valves when fully tightened.

 

So did either of you testing this see a jump in mpg also?

 

I've done side gapping on my truck and I saw a 10-12% jump in mileage. I also side gapped and indexed the plugs and my son's oval track 4 cylinder and he picked up some good power and about a tenth and a half on the track (that's an awesome jump).

Slik