Plugs

[Buick john]

Can anyone tell what's the best plugs to put in a spitfire engine straight 6. Mine has nkg b4 plugs and do anyone know what heat range these nkg plugs are

[greg g]

I would wager that NGK has some information on that stuff on their website.  A lot of us run AC 45,46, or 47's to good effect.

[Buick john]

Now these ac45-46-47 what colour do they run at. These nkg b4 run white all the time & I have no leaks anywhere so my thought is they must be a very high heat range

[greg g]

Where is your timing set?  Advanced timing is one cause of plugs running white rather than gray/tan.  The other is a compromised engine cooling system.  If there are any restrictions in the cooling passages in the head the plugs may be running hotter (actual temps not heat range) than designed.  This may or may not show as hotter than normal temps on the gauge.  If you have access to one of those point and shoot thermometer things, you might want to look for anomalies in temps at the plugs.   The NKG plug you referenced is a direct crossover to AC 45/46.  Those are the middle of theheat range that goes from cool at AC46 to hotter withAC47.  I would think you need to investigate timing cooling rather than plug heat range.

[Jeff Balazs]

I had the same problem with the NGK B4. It simply runs too hot. It may be listed as a direct crossover but I think this is incorrect. Autolite 306 seems to run well. I have not tried the AC plugs.

 

Jeff

[greg g]

Auto Lite 306is a crossover to the AC 45.

[Smokeywolf]

N9Y

[Niel Hoback]

Chryco CP1

[greg g]

champions are inferior in starting, smooth running to AC or Autolite. Lots of leakage of spark through around porcelain.

[Buick john]

Cheers guys I've taken done notes & will check everything over