Sparkplug gap "retread" (not carpet related)

[Guest Anonymous]

Per the archives, this subject has been lightly covered. At the risk of repetition, what is the largest "workable gap" you people run and on what type of sparkplugs and ignition system?

My limited research suggests that most manufacturers have increased the spark plug gaps over the years to maximize efficiency, so that the fuel mixture

burns more completely thus allowing better fuel economy lower emissions and maybe more power. Larger gaps appear have become vogue as the car makers said goodby to MR. Kettering's points system and hello to transistorized "electronic" ignition. It seems that BMW was one of the few makers that did not up their gaps significantly. (My 318 had a recommended gap of .036).

Was it because of clearance issues? Fear of overstressing the secondary system?

I have noticed much smoother running and increased throttle response when I have increased the gaps in my 02. I am not advocating that anyone follow my lead. But I wonder, with all of the wealth of experience out there, have you ever noticed any serious "decrease" in performance by running larger gaps?

Anyone? JohnA? PaulW? PatA? Zen?

Thanks

[Napes]

I run 9.5:1 piano tops w/ a stock cam and use Bosch W8DCs gapped @ .024" and car runs great.

Bob Napier

[Mike87]

I am running an Electromotive DIS with a .045" gap. That is coupled with 318EFI system. It works great and I have never fouled a plug!

Prior to that, with the stock ignition, I could gap to .030 without any issues.

[steve k.]

crane hi-6 with fireball coil with bosch w7 at .044

i have not fouled a plug yet. but i think the fireball will fire through anything.

steve k.

[Guest Anonymous]

Thank you Bob for your response. Same goes to other responders!

At the risk of beating a dead horse, allow me to ask a followup or two.

You say your car runs great running the stock gap .024. Have you ever tried running larger gaps? Is this just a case of aint broke no need to fix. Again, I am NOT advocating that you increase your gaps.

A little background. Years and years ago I had a bone stock low mile 02 with a Solex 2bbl. that would not pass smog. Blamed the problem on Solex when friends at local dealership said the Solex was prone to internal warping making it virtually untunable. (Knowing what I know now, I rather doubt it.) In any event, I swapped solexes from an Audi/VW (had same jetting) and still couldnt pass smog. Tired fiddling with ignition timing - still no better. Tried Weber 32/36. After serious jet swapping, car would now idle and pass smog but would misfire with serious progression problems.

Having passed Smog, I attempted to make the car more drivable. Out of sheer boredom and because I fiddle from time to time with other cars and boats, I tried increasing the plug gaps. Engine ran remarkably smoother. progression problems either disappeared or were masked so I could not notice them.

For grins I even tried running one of the Solexes again. Good grief, car seemed to better too. Although, it leaned out considerably and missed at top end 5000 +.

As you might imagine, I have manipulated advance curves including initial and total advance and am no stranger to trying new miracle products and ideas and debunking old wives' tales. I've fallen prey to my fair share too! But over the years, the gap thing has always been one of the easiest and least drastic modifications, I've wondered if I have been missing something.

Go ahead, tell me what I'm missing! (other than new carpeting) Incidentally, since you live in the land of perpetual heat, do you take any additional steps to avoid vapor lock or other heat-related problems??

Thanks for you indulgence.

[Benz02]

Tom at Monterey Bay Motor works recomended gapping the plugs at a "tight 28." The plugs I bought most recently , however, were gapped to 32. Close enough, runs fine.

[TobyB]

With an MSD6al and a Crane coil,

I run .045 without problems.

But it really doesn't make too much difference.

Plugs last longer, but when they erode, performance

falls off much faster.

t

[Beaner7102]

I have a Pertronix and use Bosch W8DC plugs, the come in a pack of 4 pre-gapped to .8mm (.031"). No need to regap, and they run great, and very little burnt oil fouling (old valve seals) compared to pre Pertronix days. I have not tried a wider gap for comparison. Beaner7102

[Mike Self]

on both my stock, tired 69 engine, and my newly rebuilt '73 with 9.5 pistons...that gap works equally well.

mike

[nt7110]

1968 2000 NK:  Stock M10, w/ Beru Blue Coil, Solex 36/40 PDSI w/ Hotspark & Bosch Distributor...gapping my NGk plugs at .033 seem to run fine.

Edited January 20, 2017 by nt7110

[jireland2002]

Years ago we were doing some dyno work and tried various plugs and plug gaps.  The car had a MSD 6A ign. box.  Various plugs made no significant difference but we settled on NGK non-resistor plugs.  For street motors -NGK BP6ES.  On the race cars we use BP8ES.   We found gaps from .032" to .040" gave about the same results.  Larger than .040" did not produce more power although CD ignitions will fire the plugs at much larger gaps.  Gaps below .030" produced less power.  At .028" gap we had lost nearly 10%.   With a stock ign. or a pertronix type ignitor which is just a magnetic switch I'd suggest .032" to .035" gap.

[TobyB]

>>whoah<<< was that a flashback?

 

t

 

[thinksound_mike]

55 minutes ago, jireland2002 said:

Years ago we were doing some dyno work and tried various plugs and plug gaps.  The car had a MSD 6A ign. box.  Various plugs made no significant difference but we settled on NGK non-resistor plugs.  For street motors -NGK BP6ES.  On the race cars we use BP8ES.   We found gaps from .032" to .040" gave about the same results.  Larger than .040" did not produce more power although CD ignitions will fire the plugs at much larger gaps.  Gaps below .030" produced less power.  At .028" gap we had lost nearly 10%.   With a stock ign. or a pertronix type ignitor which is just a magnetic switch I'd suggest .032" to .035" gap.

 

I run NGKBP6ES in my car (stock motor with IE dizzy). Next time I change my plugs I'll try the .032 gap. I'm running a tighter gap now. I'd like to see if the power increases.

[zinz]

123Ignition electronic dizzy, red coil, NGK BP6ES gapped .034

 

Previously, I've run various dizzies with different types of electronic ignitors and gapped plugs at .034, as well.  Never an issue. 

 

Ed