About to tune up my 250HP 327 and wondering what spark plugs are available these days for this engine. Any suggestions for normal driving?
Thanks,

 

Read Duke's postings.

 

All C2 small block OE spark plugs, were non-resistor AC 44. The first four indicates a 14 mm thread and the second four is the heat range that ranges from 1 to 6. For those like me and John Hinckley with over 60 years experience with these cars we figured out at least 55 years ago that for normal road driving including long distance freeway drives at not too much over the legal limit, the 44 is too cold, and the AC 45, one heat range hotter, is a MUCH better choice to avoid premature fouling and misfires.

AC no longer makes non-resistor plugs, so the R45 resistor type is your choice if you insist on "AC", but remember, AC-Delco no longer manufactures ANYTHING, and I have no idea who manufactures "AC" plugs.

My choice would be the NGK B4 or Denso W14-U, which are non-resistor equivalents to the long out-of-production AC 45.

It's my understanding that all Corvette engines dating back to 1997 have Denso plugs as OE. If anyone has a modern Corvette maybe you can confirm what's called out in the owner's manual

All C2 iron head big blocks were OE AC 43N, and the best current "AC" replacement is R45XLS or a non-resistor equivalent in another brand.

Spark plug selection must be based on the engine's average load NOT peak rated power. Since Corvettes are relatively light cars with high power engines they are loafing most of the time at low load, so they need a fairly hot plug, but if you plan on hot lapping a race track all day install a set of AC heat range 2 or 3 or equivalent in another brand.

If you're going to replace the points, read my breaker points article... easy search, threads started by me.

Duke

 

Thanks Duke. Already using NGK B4 pugs in my L84, but this is my first go-round with the 250 horse engine and wondered if it needed something different.