Do Surface Gap plugs require a lot more voltage than standard plugs? Is the spark gap much larger on a surface gap plug? As in larger than .035"? Thanks, Jim
I’ve not heard of surface gap plugs and would like to learn more. Who currently produces surface gap plugs?
They were used in Mercury Marine applications, other apps, I don't know. Scroll down to the bottom for explanation: https://www.ngk.com/glossary/8/spark-plug/S
I ran surface gap plugs in a 276 Merc with Offenhauser heads in a '36 3-window I had about 25 years ago. I had a boat with a Mercury outboard that used them. The plugs in the Offenhauser heads are located above the exhaust valves and they can hit the electrodes and close up the gap if you don't have exactly the right plugs. I tried some surface gap plugs from the Merc outboard in the Offy heads, and they came down perfectly flush with the surface of the combustion chamber. I thought "What the hell", and bought a new set of surface gap plugs and installed them. The car ran excellently and I ran that same set of plugs for the next 6 years until I sold the car. That car had an MSD "Ready-to-Run" distributor with matching box and coil and had a very hot spark. Although I can't remember the specifics of those plugs, I will say that I was entirely satisfied with them in that application. As an aside, I will say that I have always been concerned with the shrouding of the spark plugs in a flathead, especially on those with aftermarket aluminum heads. These days, I am very partial to Edmunds heads, as they have the spark plugs relocated just enough so that they are not directly above the valve head. This allows me to use extended tip plugs with no interference. I have this head/plug combination on both of my flatheads, and again, am very satisfied with it. So much so that there is a set of new Offenhauser heads that have been gathering dust on a shelf in my shop for 25 years.
As to racing engines: Yes, they require a high voltage ignition system. In most cases, yes the 'gap' is larger than a traditional ground strap plug, as the plugs are engineered for the application. They are a 'cold' heat range designed for high combustion chamber temperatures and where high RPM and full throttle are where the engine spends the majority of it's time. They have been used in F1 engines for years and we ( Champion Racing Plugs Division) engineered plugs for the NASCAR engines as well around 2006 which proved to be a improvement over the 'angle-ground strap design' in their applications. In the racing engines, they are "typically" a bit hard starting cold, although with fuel injection and computers most of that is a non-issue. Glenn Retired
Thanks everyone for the replies. I was hospitalized for the last 2 weeks & couldn't respond. Best Jim
I had several Kawasaki ( three cylinder) motorcycles (two strokes) that came with NGK surface gap plugs. They had pretty potent ignition systems and always ran really strong. A friend had a Kawasaki also and he tried regular plugs...the bike ran like crap.
Retro, remember how the CD ignition would buzz when you turned the key on? I also had a new 1969 Mach 111. It never fouled a plug!! I agree I think you need a hot ignition to run them. Or a good Magneto. Lippy
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