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We like to write easy to read technical articles on some of the common topics discussed by our customers and forum members. We post these in our blog. Our latest is a discussion of spark plug heat range, spark plug gap, and how it relates to the Focus ST.

Have a look at the link below and if you'd like a topic discussed post up:

Blog : Spark Plug Tech : Stratified Automotive Controls
 

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We like to write easy to read technical articles on some of the common topics discussed by our customers and forum members. We post these in our blog. Our latest is a discussion of spark plug heat range, spark plug gap, and how it relates to the Focus ST.

Have a look at the link below and if you'd like a topic discussed post up:

Blog : Spark Plug Tech : Stratified Automotive Controls

So you recommend a 0.25 - 0.26 gap for stock plugs and aftermarket plugs?

Could too large of a gap cause negative ign correction on one cylinder?
 

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So you recommend a 0.25 - 0.26 gap for stock plugs and aftermarket plugs?

Could too large of a gap cause negative ign correction on one cylinder?
We recommend a 0.025 - 0.026" gap with any spark plug on this car. The larger gap can cause misfires and you would feel this as the engine not running smoothly.
 

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I've been getting a miss fire and was wondering why. Good to know thanks!
 

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Hmm I gapped mine at .028, is it worth it to regap a bit tighter?
 

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Once again thanks for sharing such great information! It is very much appreciated and I've learned a lot from reading your blogs and forum posts :).

I'm contemplating running one step colder plugs after reading that blog post but I have yet to check my stock plugs for the proper gap or for fouling.
 

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Once again thanks for sharing such great information! It is very much appreciated and I've learned a lot from reading your blogs and forum posts :).

I'm contemplating running one step colder plugs after reading that blog post but I have yet to check my stock plugs for the proper gap or for fouling.
Happy to contribute! I don't think you'll find fouling on the OEM plugs as they are suited heat range wise for the stock motor. I run a one step colder plug simply because I push the car hard and it is cheap insurance against pre-ignition. I don't think pre-ignition is very common at all however even with the OEM plugs. Since you're pulling them out to regap and if running the car hard it's a good idea to replace them with a step colder.
 

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Would you recommend one step colder plugs on a car with intake, Roush exhaust and bov only? I usually shift in the 3-4k range and generally avoid redline but like to hit it every once in awhile up to 5k when it strikes my fancy.
 

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Would you recommend one step colder plugs on a car with intake, Roush exhaust and bov only? I usually shift in the 3-4k range and generally avoid redline but like to hit it every once in awhile up to 5k when it strikes my fancy.
From the link in the first post:
For the Ford Ecoboost we still recommend a plug that is one step colder than OEM for mildy bolted cars especially since 21+psi of boost is quite common. For highly modified cars that see a lot of heat it is advisable to try a plug which is two steps colder than OEM. The Ecoboost motors seem to be able to manage colder plugs better than the Mazdaspeed motors.
Just make sure your gap is 0.025 – 0.026″ range and you should be fine going one step colder. Id suggest adding a set of feeler gauges to your tool box that include those sizes: Amazon Best Sellers: Best Feeler Gauges

Next, get yourself an upgraded intercooler and a tune :)
 

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From the link in the first post:

Just make sure your gap is 0.025 – 0.026″ range and you should be fine going one step colder. Id suggest adding a set of feeler gauges to your tool box that include those sizes: Amazon Best Sellers: Best Feeler Gauges

Next, get yourself an upgraded intercooler and a tune :)
Thank you! Those are definitely on my list of mods, just gotta get my next raise first lol.
 

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Got the plugs changed today. Here's my factory plugs. The gaps we're as follows: #1 .039, #2 .037, #3 .039, #4 .035. what a difference the new plugs make. Installed the NGK at the factory heat range all gapped to .025. Right away, the idle is smoother and she's more responsive.
376697
 
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