fourload

I am thinking .25 on these new sp534's. Running a 5star 91 tow tune and seeing almost 19lbs of boost settling down to about 17.5. Most other turbo forums regardless of brand recommend .25-.28 when running that kind of boost in a higher compression motor like the ecoboost. Anything above that results in spark blow out!!

SkiSmuggs

I would go with .028. I have only seen .025 recommended with the Brisk Silver Racing plugs. Motorcraft recommendations have been ,028-.030.

brucesears

I had been running .028 on my SP534's since June with zero problems and smooth idle. Monday I pulled them and narrowed the gap to .025 just for grins and giggles. Now mine seems to hold boost better at highest boost and I may even be getting a little better mileage. This on limited amount of driving.