Spark plug recommendation

If NGK is what you're interested in, then look here (lower left corner of first page)

[ame]http://www.ngksparkplugs.com/docs/racingspecs2010.pdf[/ame]

The R5670-5 (#2298) racing plug is equivalent to the XR5 (#3332) standard plug. Either of these would be considered a stock heat range plug for a 440. As you go down the list, you drop in heat range. So, the R5670-6 would be one step colder which would be something to consider as your compression goes up. I think you'd be fine with the stock plug. The racing plug is non-resistor, while the XR5 is a resistor plug.

I run R5670-7 plugs (2 heat ranges cooler than stock) on my blown motor.