tygr1

So what is the recommended plug gap for a 3.5; both OEM and YOUR recommendation and why? Engine is all stock with no tuner.

maplelakeduckslayer

I believe Ford reduced the recommended gap a time or two, don't remember what they currently recommend.

Stock I would go .030-.032. Many tuned guys are .025-.030. Some trucks like the really small gap, some don't.

Last time I put stock SP 534 plugs in they were all gapped about .030 out of the box.

Tothemax

I'm tuned and I run .030

klumb15

I'm tuned running .030 SP534 plugs. Will probably gap them at .028 when I load the XV1 tune.

killerrudy

when I was stock I didn't have any issues. Threw a 87 tune on it and it started to have hiccups. Checked the plugs and they were .34-.40 from the factory. Set them all to .30 and haven't had an issue since.

woody3

It all depends on the "effective" compression ratio, the more pressure you have in the combustion chamber, the harder it is for the spark to jump the gap. As long as the effective compression ratio doesn't exceed the engineering design compression ratio (physical CR + cooled air boost), the original factory plug gap will work just fine, Even better, more reliable mixture ignition (bigger "match") than a narrower gap.



The problem is/was that occasional "gulp" of water as you go from cruise to acceleration mode. That "gulp" of water/condensate, turns to steam as it enters the HOT combustion chamber, oftentimes raising the effective CR to diesel engine compression ratios.


Spark can't jump the original factory plug gap, to much "atmospheric" pressure, so it chooses a weaker point to "jump". Inside the COP, of down the plug insulator.


Drill a hole, go with the original WIDE spark gap settings.