67cougar Posted September 6, 2021 Share Posted September 6, 2021 Hello all. I rebuilt my 289 in my Cougar from the block up. Stock pistons. Ford GT40P heads. Lots of other performance parts. The question is do I run the standard plug for the GT40P head? As they did not come off a 289 engine. Or is there a way to figure this out? Any direction would be great. Thanks. Link to comment Share on other sites More sharing options...
JFranklin Posted September 6, 2021 Share Posted September 6, 2021 Since you built the engine you will probably have to experiment with plugs to find what works best in your configuration. At least plugs are cheap. 1 Link to comment Share on other sites More sharing options...
rocketraider Posted September 6, 2021 Share Posted September 6, 2021 Ignition, compression ratio and piston to plug clearance will influence which plug to use and where to set gap. These are the aluminum heads right? The plugs Ford Performance recommends for those heads would be a good start. Even though some powerful coils can fire a wide gap for a nice fat spark, I don't like to go much over .045 gap. Link to comment Share on other sites More sharing options...
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