For two strokes, in particular outboards, the spark plug was a critical component, with the development of CDI and surface gap plugs performance was vastly improved. Sales improved for foreign manufacturers such as NGK and Auburn due to specialization required by the 2 cycle engines.

I ran a dyno tuning shop in the late 60's and early 70's and there was a huge difference in the quality of spark plugs in those days. Some would not last a single pull on the dyno and others would surprise the heck out of you. One of the biggest brands was only suitable for filling a hole in a cylinder head.

I witnessed at the drag races a top fuel dragster with decals for one brand on the car and another brand going into the engine. You got paid for winning by the decal on the car. We were not sure what the difference was but the dyno and racetrack results were quite decisive.

When the dynamics involved are considered, spark plugs have a big job to do.

I had the side electrode fall off on a 2 stroke Villiers at speed. The electrode found the gap between the piston and cylinder wall and made a "keyway". The locked up rear tire made for a wild ride.

I agree they had a tough job and only the best came through. We worked mostly on muscle cars and competition vehicles and the demands were considerable. We could observe them on the oscilloscope under power and could see the plugs breaking down under heat and load. One drag vehicle with OEM plugs with one heat range would foul before it got to the line and with next hotter plug misfired before it got to the end of the quarter mile. With the other brand using street stock heat range there was no issue at all from start to stage to end of quarter mile. That was just one hemi for an example. The dyno with the scope and fuel analyzer was a fantastic learning tool. Now you tune with a laptop.

"One of the biggest brands was only suitable for filling a hole in a cylinder head."

Don't hold back, tell us how your REALLY feel.

With all the political rhetoric going around recently, it's a nice-ish change to get some brutal honesty. Would have appreciated a little more worning before such a line, I almost asperated my coffee when I read it. Although that might have been my fault for reading the forum before the coffee had started to kick in.

Since this was 40 years ago there is no sense in bashing history. The really bad ones started with letter C and the really good ones started with letter A and it was not AC. My mechanic was an avid snowmobiler and he had a misfire coming home across the lake, he had the C brand in the machine and did not have a new spare only some well used A brand. The A brand got him home and left a lasting impression and two strokes are very fussy on what is used to ignite the mixture.

I had the opportunity to work on a diesel powered generator that had spark plugs. The engine started on gasoline and switched to diesel, the plugs had their own chambers.

The BIGGEST progress in Spark Plugs was the switch to exotic metals that could stand the heat (metaphorically speaking) and physical wear (thermionic transfer)...today, most spark plugs last 100K miles or more.

I remember the mechs doing plug changes on the R1820's, the used platinum tipped plugs where returned to Pratt & Whitney. At least, that's what I was told.

That is a fact, not a military Urban Legend, because it's actually true.

The rare-metals (platinum, palladium, yttrium, iridium, etc.) contained in the center electrodes (not in the outside casing/shell) was "recovered" for recycling in USN.

There were two spark-plugs per cylinder in each of the four R3350-34 (18 cylinders) turbo-compound engines on our USN Lockheed EC-121 "Warning Star" aircraft -- that is 144 spark plugs per aircraft -- and those plugs were routinely changed quite often due to lead-fouling that resulted from the high content of Tetra-Ethyl-Lead (TEL) in the 115/145 AVGAS (purple) aviation fuel that we used.

I have a Franklin 4 banger in my little J-3, I keep a few extras around for the lead issue even now with the 100 LL in use. Lead is a pain.

Another fact, 115/145 taken from a fuel sample valve should NOT be used In a 1967 Chevy Nova.

I 'added' "water-sample" 115/145 AVGAS in my 1965 MG Midget to "enhance" the low-octane gasoline sold on base at Argentia, NFLD...and it left a nice creamy-white petina inside the exhaust tail pipe!