MTFCA Forum

Recently I got some new Champion X plugs to swap out the old A25's in our touring car. The instructions said that their engineers recommended 0.025" gap, but most familiar with the T shop manual know that it calls out 1/32", or 0.031". I decided to try 0.025". My coils and carb are in good shape. What I found was that while it would drive OK, the idle was not smooth. I started wondering why people said that these are great plugs.

Further forum reading indicated that it can be car specific on what gap is best. Some love .025; others .030 or even more. The common lesson was set it to where your car runs best. I decided to regap them to 0.030 and saw a noticeable difference on how well it idled; more like it did with the A25's which were also gapped to .030.

Anyway, it was a good lesson for me that there is not an exact value that plugs should be gapped to, but rather an acceptable range for a starting point. The best value for each car will likely be determined by experimenting a bit.

Lesson learned about Model T ‘s is that each T is NOT exactly alike! Same goes on carb settings, spark plug gap and a few other things. Engine oil is another story!

I found that my car idled better with a larger gap too. Also Champion X plugs.

If you have a higher-compression head, you might want to try .035".

It's just a stock 21 head.

I once thought to do my T something good and installed new, aftermarket Champion X's - and the car run worse than ever before and after when I reinstalled the old 'motorcraft' plugs.
So you recommend to experiment with the gap and that will do it ?
What else might be necessary ? Changing the ignition setting ?

So you recommend to experiment with the gap and that will do it ? What else might be necessary ? Changing the ignition setting ?

Based on my experience, I would definitely recommend increasing the spark plug gap on the Champion X spark plugs and trying them again. I would not change your timing setting, because you will set the timing lever to where it runs the best no matter what plugs that you have installed. You can also adjust the mixture knob if necessary.

ONE NEEDS TO REMEMBER HOW THE GAS HAS CHANGED OVER THE 1OO YEARS, TO DAYS GAS IS PRODUCED TO BURN SLOWER, GIVING MORE POWER, THAT'S THE DEFERENCE BETWEEN HI TEST AND REGULAR ,HAVING HAULED MANY MILLIONS OF GALLONS OVER THE YEARS FOR A LARGE OIL CO, I LEARNED A LITTLE ABOUT WHAT I WAS HAULING, IT COST MORE TO PRODUCE HI TEST, MORE ADDITIVES , THERE FOR THE T IGNITION SYSTEM IT SET UP TO BURN THE LESSER, TO DAYS AUTOMOBILES WITH THERE HI COMPRESSION ENGINES WITH PLUG GAPES UP TO 60 THOU, SHOULD TELL US WE NEED TO WIDEN THE GAP FOR TO DAYS GAS, MY FORD PLUGS ARE GAPED '30 AND RUNS VERY GOOD AT BOTH ENDS OF THE THROTTLE. WIDENING THE GAP DON'T MAKE THE SPARK ANY HOTTER THERE IS MORE OF IT, GIVING THE LOW COMPRESSION ENGINE A LITTLE JUMP THAT'S NEEDED TO COMPLETE THE COMBUSTION PROCESS A BIT SOONER. [ARE YOU USING A LEAD ADDITIVE] UNLESS YOU HAVE STAINLESS SEATS AND VALVES YOU SHOULD BE, THOSE OLD VALVES CANT STAND TO DAYS GAS TEMPERATURE. ALL THE MORE REASON FOR THE WIDER GAP.

Interesting stuff. I’m running my X’s at .025.

Now I’m wanting to try them at .030. I estimate that I’ve put in excess of 500 miles on the car since I returned it to the road. So, it’s a good time to pull the plugs and clean/gap them.

Don,

I'm currious to heard your feedback at 0.030 if you will notice some differences.