Spark plug selection

[68sportsatelliteragtop]

Time for a new set of plugs and was thinking with todays gas I should go to a colder plug. I have been running Champion resistor 12 heat range. I run 92 or 93 octane and the motor is .030 over 10-1 comp. 383 with 484 purple cam and 750 vac sec Holley carb. I run the MSD 6AL with MP distrib. and a .045" plug gap. Timing is set at 32deg. w/vacuum advance plugged..The plugs looked a little lean, more white then brown. Anybody got any ideas about brand of plug and/or heat range.

 

[WileE]

Unless you're getting knock, I'd leave the heat range where it is.

 

[scotts74birds]

This is really a subject that doesn't get a whole lotta discussion. I would have no idea on how to start to choose a plug for my car after big mods. Maybe some of the smart folks here can help us.

 

[Meep-Meep]

This is really a subject that doesn't get a whole lotta discussion. I would have no idea on how to start to choose a plug for my car after big mods. Maybe some of the smart folks here can help us.

I tend to stick to the factory HP plug for mildly modified engines. You figure the factory speced the plugs for roughly 10:1 CR and mild cams, expecting occasional track use. Race engines spend a lot more time at high RPM and that High RPM increases combustion chamber temps so a colder plug will be required. Also higher compression increases heat so again a colder plug in that case.

 

[oldbee]

Stock 383-440 were a J-11Y if I remember correctly..Should still work.Colder will foul out quicker because they run "colder" compared to stock. I used to put in "13's" to get a fresh race engine to fire off and then go back to 11's after it was broke in.

 

[oldbee]

I'm sorry- seems the answers never did answer your question. Tan color insulator is best,white next, black/sooty is too rich. I would say try a set of 11's and go from there. Used to be that the correct way to check plugs on a drag engine was to shut it down right after the lights to check plug insulator color(running back to the pits would skew the color a little bit). Hope this helps.Jeff

 

[lewtot184]

i've always felt that the j11y was the best plug for an iron head and i still use them. unfortunately they haven't been made for 20-30 years. i stashed some back years ago. an autolite 85 may be next best.