Plug gap

I run a BF HC head with cylinder overbore that results in a calculated CR of 6.2:1 or so. With standard 6V ignition and coil, I get great performance with spark plug gaps of 0.035-0.025, it does not seem to make a difference as long as I have clean points and a distributor point gap of 0.019+.

As far as proper heat range goes, in my engine Champion W16Y, TT10, or original and repro Champion 3Xs were too cold and affected performance negatively. Champion W18s are burning at the proper heat range and performance is great at a gap of 0.030 which I set as an initial test point and see no need to change.

I would advise sorting out which plug gives proper heat range for good performance before sorting out plug gap.
 
I have a stock head and engine and have found the same thing as Rich. As I recall the well used temporary has Champion W16Y's and is burning a light tan, and never misses a beat. Any thing from .025 to .035 is fine with me.
 
I didn't have good luck with the Motor craft TT10 plugs, they were way too cold and flooded very easily. The W16Y Champion was also too cold for our type of driving. I use the Champion W18 , they run clean and make a noticeable improvement. I gap all of my model A spark plugs at .035. A weak ignition or coil will work better with a smaller gap, with a hot performance type coil, you can open the gap farther with good results.
 
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Rich: Are you running modern points or standard? Should there be a difference in point gap between the two? And, will it vary between a HC head and standard head?

Mike
 
I run standard, original points and as Tom said, no difference in gap for other points. I have worked on cars with the modern points plate but see no advantage to them and in fact they are more troublesome in my experience due to problematic connections to the lower plate and I find them more finicky while adjusting the points gap. Good quality condensers are available now, and the original rationale (I believe) for adopting the modern points plate set up which was to move the condenser to a cooler location is no longer tenable.

Finally, if the car sits unused for a month or more, cleaning the points by simply pulling some stiff paper through them never hurts. New (or used) old points that have been sitting for 40 years or so may have infinite resistance out of the box and need to be cleaned for use.
 
"problematic connections to the lower plate"

In the past, when installing the "modern" upper plate I always installed a longer pig tail wire to the lower plate first. Makes connecting much easier.
 
To the original question, this has been posted previously:

Spark Plug Gap
.035" (A6050A cylinder head)
.030" (B6050 cylinder head)
.025" (A6050B cylinder head)
 
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