Best Spark Plug


New member
What is the best spark plug for a Flathead on methanol. Do you like gapped or a gapless plug. What if you were able to put an autolite 3910x plug in it any advantages

If you can find them the champion QL57, seen it out pull the 411 and the denso plug on dyno pull with my own eyes even if its old.
for the gapless plug run the NGK BUH8. it's a bit hotter than the autolite

advantages of the gapless.
no indexing
air flow

tend to foul a bit quicker if you engine is smoking and not sealed up
I ran a 3910x in my flathead controlled stock last year with a 1/2in aluminum spacer and it worked well no clearance issues, Didn't dyno it with that plug so Icant say it made more or less power. My guess would be the engine flows better and ignites better I'm sure. And no worries on fowling. So it probably made a hair more power atleast on topend.