Originally posted by Alec
I recommend .048-.050.
Based on what?
Im no EE, but...
Fords ignition systems are good, and a big gap if you have the power will provide a big fat spark, more complete combustion, power etc.
I would gap the plugs to the factory specs on most plugs in a stock or close to stock engine. No reason not too, unless you are running some outrageous compression or maybe forced induction. Even then todays ignition systems should be able to handle the bigger gap.
Gap creates a certain amount or resistance combined with the fuel/air mix- more resistance the more power it takes to overcome it, the bigger the spark. The Air/fuel in the CC makes it a bit harder for the plugs to spark. Gaps too small and you get less bang, gaps too large and the ignition system may not have enough uumph to get a decent spark across the plug.
Too Large or Small and you will get misses and incomplete combustion.
If the plug mfr has a reason to run a specific gap thats different from the factory I would give them a call and ask them why? Make sure its tailored to your vehicle and not just a generic recommendation.
Anyway, I would stick with the stock specs, or if the plug manufacturer recommends something different try it - you can change it if it doesnt work well. But I would call them and ask first.