By on January 29, 2013


Zack writes:

Hi Sajeev,

I’ve been following a series of discussion on a MK3 Ford Focus forum; in particular I’ve been following the technical discussion about how to squeeze more power from the MK3’s new 2.0 GDI motor. Of course, this involves talk of CAIs, Cat-deletes (inadvisable), and free flow exhaust. One of the more curious things to emerge is…

…the notion that re-gapping the spark plugs can account for +5whp. I’m dubious to say the least that something seemingly inconsequential could generate that much power. It’s almost seems akin to slapping turbo badges on the rear lid expecting some similar black magic. This being an internet car forum there is much breathless back and forth, but few actually explanations. I was hoping you might have heard of this “trick” and whether or not there’s any validity.

I think for questions like this we need a carforum, but then again we have you. Thanks in advance!

Sajeev answers:

You sir, have made my day.  Putting me on par with Snopes is a high honor indeed. That said, now I wonder if Snopes is as horribly inaccurate and clueless as yours truly on many, MANY occasions. (sad trombone sound)

Now about the spark plugs: I won’t say that a re-gap cannot possibly increase horsepower.  I will say that it isn’t very probable.  At all. Two things:

  1.  Spark plug gap can make a huge difference, especially in forced induction (turbo or supercharger) applications where adding extra boost is on the table.  But that low hanging fruit (i.e. extra power) is usually not there in factory setups: they normally hide the power in tame air/fuel/timing parameters in the engine computer’s tune.
  2. If it isn’t backed by a dyno sheet from a local tune shop, this is pure, un-stepped on, pharmaceutical grade bullshit.

Look, I’ve been messing with Ford products for a looooong time. And while not everything I do has been proven with dyno results, there’s always that low hanging fruit proven many times over with other’s dyno sheets: conservative factory computer tunes, intake boxes with inlet tubes significantly smaller than the engine’s throttle body and mediocre (i.e. quiet and restrictive) mufflers on inadequately shaped crush bend exhaust tubing (older models only).  The first is solved with an SCT tune, the second is free (remove something) or requires a trip to Home Depot for a slice of PVC pipe/glue/black paint,  and the latter is not a big deal with an exhaust shop and a muffler from a 2005-present Mustang GT.

But spark plug gap? The forums never show that as a credible performance modification.   Perhaps GDI motors are a game changer, but I doubt it.  That will be optomized to perfection by Ford’s engineers, the low hanging fruit will be the things mentioned in the previous paragraph.

Best and Brightest, you go right ahead and prove me wrong. Snopes ain’t got nothin’ on me. Or not.


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23 Comments on “Piston Slap: Hocus Pocus…Focus???...”

  • avatar

    I know I will regret asking this, but why does the Focus (presumably a front wheel drive car) in the picture have its rear wheels on the dynamometer?

  • avatar

    Brain-chance-of-scattered-showers here…

    What if changing the spark plug gap is sensed by the computer (ie. change in resistance or spark temperature or whatnot) which prompts the computer to change the air/fuel/timing parameters?

    Older cars have taken signals from otherwise completely unrelated systems before. Why would a newer car not take a much more improved diagnostic signal and change the operating parameters? Would it yield more HP or would it yield a trip to the dealer to unlock it from safe mode? I don’t know…that is why this was a brain-chance-of-scattered-showers and not a brainstorm.

    • 0 avatar

      I think the only way diagnostics could use a spark plug would be to measure how much juice it takes to jump the gap ( compared against an operating window). Well directly at least unless some other inferred measurement can be used.

      Anyways I wonder if the ecoboost engines use a fairly conservative plug gap to avoid blowout when the wick is turned up or is the boost low enough and ignition robust enough to run plug gaps commonly seen on NA engines?

      • 0 avatar

        Stock the 2.0 EcoBoost in my ST was about 18 PSI, IIRC.. Tuned I’m seeing like 22ish… The 3.5 V6 EcoBoost in our Flex was more like 10 PSI stock… tuned I’m more like 14 to 15 PSI.. Still running the stock gap in both… no mis-fires…

  • avatar

    All the computer can detect from a gap change is any difference this makes in terms of knock count. which I don’t think a simple gapping will alter. Not unless the person in question had spark plugs so far out of spec before the re-gap that they were misfiring.

    That said, an ultra-lean burn direct injection motor is likely to be more sensitive to incorrect gaps than a regular motor, so there may be something there.

    • 0 avatar

      Not true; by analyzing the current trace during & after the spark, some cars’ ECUs can see if combustion took place. They’re called ionization detection modules (at least for the Saab 9-3), and what they detect would probably be affected by spark gap changes. IDK if the focus GDI engine has something similar, or whether fooling this module would cause the ECU to advance timing, add fuel, or do something else that would affect power, but generally all they do is check for combustion, and if there isn’t any, then they trigger the CEL.

      • 0 avatar

        Ford was one of the first to monitor the back EMF induced into the primary windings by the secondary windings to monitor the voltage that was required to make the spark occur. The voltage required to make the spark occur is directly related to the spark plug gap.

  • avatar

    Widening the gap will do either of two things:

    1. If the system is capable of generating higher voltages, this will happen automatically with the wider gap. There will be more stress on the ignition system and it will likely fail earlier.

    2. If the system cannot generate a higher voltage, mis-firing will occur and obviously this is detrimental to power production.

  • avatar

    As Sajeev said, wider gap – no, but indexing the sparkplugs has shown to add small gains in horsepower.

    Indexing is a legitimate motor building trick of placing the open gap in the optimal spot of the combustion chamber, I don’t know if it’s worth the time for the small gain but then I don’t build race engines.

  • avatar

    Crank up the boosts!

  • avatar

    Nothing to contribute automotive-wise, but I wanted to congratulate Sajeev on his reference to the best damned Dutch yodeling instrumental ever made. Well done!

  • avatar

    Wait what? This seems like one of those things where next the claim that putting the “Twister” air disruptor in your intake will give 20 more hp.

  • avatar
    Spanish Inquisition

    If the ST is anything like the Mazdaspeed 3, you’ll want to replace the downpipe.

    Turbo cars like fat downpipes and exhausts anyways.

  • avatar

    OMG…The answer is so clear: shave springs by 1.5 inches ( 2.26 cm. :) ) add an aftermarket fin on back bumper then coffee can sized fart muffler. To make it faster add some bullet hole stickers. This was so obvious! How could you waste Sajeev & Steve’s valuable time? Tschaaa!

  • avatar

    Increasing spark plug gap on a boosted engine particularly if the boost level has turned up. The amount of voltage needed to create a spark is determined by a number of factors. The primary factors are the spark plug gap and the cylinder pressure. The higher the cylinder pressure the higher voltage requirement, the larger the gap the higher the voltage requirement. That is why it is common to reduce the spark plug gap when turning up the boost or adding boost to a previously non-boosted engine.

  • avatar

    Always ask the question: why didn’t the engineers – who have done extensive testing and likely know more about the details of this engine than anyone else ever will – do this? If you can’t come up with a reasonable answer, then don’t even think about it any further. When considering performance modifications, the typical answers would include: emissions, low-rpm driveability, NVH, and cost. Good luck tying a spark plug gap to any of those. Emissions aren’t going to get worse by making the spark ignite the air/fuel mixture more efficiently.

    “If it isn’t backed by a dyno sheet from a local tune shop, this is pure, un-stepped on, pharmaceutical grade bullshit.”

    I wouldn’t even trust that. All they’d have to do is heat soak an engine for the first run then wait long enough to test with a cooler engine on the second run to show a big gain.

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