Technical Spark Plug Gap Question

Today as I was doing some reading on late 30’s Hudsons, I saw something I can’t quite explain. After unsuccessfully searching for an answer, hopefully someone has insight on this.

My 1937 Hudson (model 73) 212ci 6cyl engine calls for spark plug gap of .025” but in 1938 Hudson (model 83) with the exact same engine has the plug gap of .032” (same plugs, points gap, etc). The only thing I can spot that was slightly different was the distributor spec shown in the photo below. However, I’m not sure that difference is enough to cause a change in plug gap.



So if that isn’t really something that would be the reason behind the change in gap, should I consider increasing the gap on my 37 to the .032”?


Sent from my iPhone using H.A.M.B.

 

Did they change coils maybe?

They also may have found out a larger gap was beneficial

 

When in doubt, try it. What is the worst that can happen? In my cars I have found many
different gaps produced better results than what the spec. recommended.

 

Usually a larger gap will result in a greater spark

 

...but will require more juice to make the spark happen

 

.025” is easier to fire like Jim said especially with 6 volts. If the engine can stand an extended or semi-extended tip it will run slightly better and give better fuel mileage if easily driven. Most in the 30’s were not.

 

Between the two years I wonder if there might have been some changes in compression ratio, combustion chamber design, pistons, or maybe a different carburetor and /or intake manifold?

 

I cannot spot anything that really leads me to an answer other than gas continued to improve & they probably found the bigger gap helped the engine run better.

I’ve gone with a longer reach plug than stock & even made a wide cone cut at the plug hole to unshroud it within reason.

Original plug in head, you can almost see the plug but I circled the tip in red:


This is the end product I went with for plug & unshrouding.





Sent from my iPhone using H.A.M.B.