Spark plug help

[ted johnson]

Steve, on NGK, the higher the number, the COLDER the plug. Ted

[steve miller]

Yes sir...7 pretty hot... I never ran one.. never any hotter than 8...so with akly you run one step hotter than gas correct...????

[ted johnson]

Steve, alky wants a cold plug.

"Methanol: Since it has a higher octane level than standard gasoline, methanol delivers more complete combustion. As a result, you’ll need a colder plug to transfer more heat from the combustion chamber."

Credit to Summit Racing Tech Tips for the quote. B9's are good for modified alky burners. If you consistently foul B9's go to the next hotter B8. My West Bends are happier with B9 plugs. Also, when you "up" the compression for alky, cooler plugs are indicated.

Here's the website for the NGK code: https://www.ngk.de/en/technology-in-deta...-ngk-code/

go down the page and click on the little icon in front of the "how you crack the NGK code" It'll take you to a very useful PDF. TJ

[steve miller]

Aahhhh gottca...I don't run alky...but figured since motor runs cooler need hotter plug...now if I ever try alky now know...thanks TJ..

[doug tenney]

I'm glad that Mel asked this question.

On the "old" forum I recall that someone recommended Autolite 303 for the older 3/8" reach McCullochs.

So, we've been running the 303's in my son Alex's Mc91.  However, the 303's have been showing damage from heat.  (Bone white, with spalling of the porcelain of the center insulator.  One even had partial melting of the center and side electrodes.)

Dave's cross-reference site shows that the Autolite 303 to cross over to:
NGK B6S, B6Y, B7C, B7S
Champion J4C, J5 J6C, J6J. J9 and J9J

From the earlier posts in this thread, clearly the Autolite 303 is "too hot," but I wonder if it's THAT far out to cause the problems we're seeing.


FYI:
We don't have any obvious air leaks, although I haven't pressure tested the motor, at least not lately.
We're always careful to run rich, and we're getting lots of blue smoke in the exhaust.  We're inexperienced running with a pipe (RLV 101 with 10-1/4" from piston to start of diverging cone).
We run alcohol with 16:1 castor oil.
The spark plug boot is good, with no obvious cooling problems.

[doug tenney]

By the way, a while back I found a different NGK decoder chart.  See attached.  I make no claims about which is better!

BTW, their numbering system is ambiguous.  For example, for B8S, the "S" could mean 9.5mm (3/8" reach) OR standard 2.5mm electrode.

[ted johnson]

Doug, I'd never run anything hotter than the B8S  or B8HS (depending on whether it is long or short reach), and a B9** may be safer. It's been 40 years since I ran a Mac with a pipe, so maybe someone like SteveO will chime in on that. TJ