Does any one know, if I have to find and use the original AC48 plugs, in my, 46 Buick Straight eight? :confused:. Trying to find good accurate information seem impossible to find on a good substitute . I am running some NGK BP4HS plugs, but they are fouling on me. Are these to cold?:clonk:. Anyone out there got the inside info. for me?.:waving: Thanks in Advance.

In the street engine, we use AC R45 plugs, and they work well. In the race engine, we use AC R43. Don't know if the R45S plugs will work, may be too hot with the extended reach.
Doug

If you can find em, you may wish to try AC plug C49. There are two of the same number out there, check and make sure the size is not waaay too small.
The C49 is the commercial plug, and runs a little warmer than the 48 plug. If you are not doing over 50 mph for extended periods of time, they should be fine. I have used them in my 41 and 47. Just around town use. They work fine.

Does anyone know if the BP4HS plugs are to cold for the straight eight. I was wondering how far of correct I am at the moment. The eight is original, she has had no tweaking. Thanks again to those who have already replied. Thanks also in advance for any assistance.