Holy spark plug gap - More MPG research

[90Haccord]

And here comes another installment of MPG research for CB7's

Latest issue "SPARK PLUG GAP"

So I tuned up my old gal, new spark plugs new wires the whole 9 yards. All NGK and to correct spec.

There is a 45mile stretch to my parents house that is 100% highway driving, I set my cruise control to 55mph, I yeilded 31.25 mpg

Then I did the tune up, the spark plugs were OLD, at least 60K on them. When I took them out they were gapped to 0.052, WTF? When I put them in I gapped them to .044. I thought odd, installed the new spark plugs and gapped them to .044( in spec).


I drove the same 45mile stretch, almost identical to previous conditions with CC set to 55mph, I only yielded 27.6 MPG

Now both are over the EPA for a 1990 automatic

However, I have to wonder....will spark plug gap really do that?

Anyone know or wish to comment? I'm about to go regap the new plugs to at LEAST .052 as the old worn out plugs were since they yielded more MPG but I want to make sure I'm not crazy first.

And for those wondering, I always fill up at the same gas station so its not the gas(shell).

[accordaffair]

Can you do an A-B-A test by regapping them to .052 and repeating the test?

[90Haccord]

I'm seriously considering it, but wondering if anyone else has experienced this with respect to cb7s.

I've heard some old muscle car guys say its possible with respect to spark plug gap to increase MPG.


But needless to say i was shocked at what my tune up did to my MPG.

[benji]

I'm seriously considering it, but wondering if anyone else has experienced this with respect to cb7s.

I've heard some old muscle car guys say its possible with respect to spark plug gap to increase MPG.


But needless to say i was shocked at what my tune up did to my MPG.

Yes, spark plug gap can do that, but it is at the expense of everything else in your ignition system. More gap means more resistance to spark - the coil will have to generate higher voltages in order to jump that gap. That leads to more wear on the ignitor, cap, and rotor. Higher voltages in the ignition wires leads to a greater chance of the spark jumping out somewhere other than at the end of the plug, which leads to misfires.

I can't say how long it would take to start burning stuff out, but it will happen eventually. The question is, is it cheaper to run more gap (better MPG), even though you will most likely be replacing other (high dollar) parts sooner than you should be? Not to mention the fact that you will probably see less performance out of your engine.

[accordaffair]

true, I go by honda since they have the smart engineers

[Losiracer2]

yeah I'm not gonna mess w/ the gap. I'll just leave it at .044 or whatever Honda recommends and only use NGK plugs. I'm averaging about 30mpg on the highway so I'm pretty happy w/ my plugs where they're at.