News

Spark Plug Gap Importance

Discussion in 'Technical Q&A' started by Smiles, May 2, 2004.

  1. Smiles

    Smiles Moderator
    Moderator Owner

    Nov 20, 2003
    14,510
    Pittsburgh, PA
    Full Name:
    Matt F
    Hello, Ferrarichat members. Matt here.

    I'm using NGK BPR6ES plugs in my 330. I think that they're working really well. (They're one step hotter than the previous owner's NGK7's.) I gapped them to 0.025, which is what the owner's manal required of the original Marchal Type 34 HF plugs.

    A few other users of the same plug recommended a slightly larger gap, of 0.027. Interestingly, that's the Porsche spec for the same plug, used throughout a variety of their cars.

    The same NGK plugs come pre-set from the factory at 0.035.

    So... what would happen if I used the same plugs at 0.035?

    Or: What engine characteristics require a smaller gap, and which ones require a bigger gap? I know what happens if you go hotter or colder, what happens if you go wider or tighter?

    Thanks in advance!
     
  2. To remove this ad click here.

  3. Bryan

    Bryan Formula 3

    As I understand, a wider gap gives a bigger, more powerful spark; hence, better assurance of good fuel ignition. However, to jump a bigger gap requires more "oomph" from the ignition system. Too big a gap gives no spark. So, it's a balancing act.
     
  4. henryk

    henryk Formula Junior

    Dec 9, 2003
    479
    Door County, WI
    I have read that the spark plug gap is determined by spark plug manufacturer, not by the car maker. I have installed new platinum plugs in my TR, with whatever the gap was.......I would make sure that all looked the same. Had no problem.........I checked them after 5K miles and they looked great........not white, and not black.......just a very light tan color on the ceramic. The newer, more modern, plugs may not need the same gap as the original, older, plugs needed..........just my thoughts.
     
  5. FrostCS

    FrostCS Karting

    Mar 3, 2004
    65
    Vegas
    Full Name:
    Christopher
    Matt,
    The main characteristics of a spark plus gap is this;
    The Smaller the Gap, the stronger the spark.
    The Larger the Gap, the weaker the spark will be.
    With a strong ignition system, a larger gap will be recommended but the spark will be just as strong as a smaller gap on a slightly weaker system.
    The idea of having a longer spark is to increase the amount you can burn (almost like having two plugs instead of one).
    A smaller gap will increase power to a point, and give you a more complete burn in the combustion stroke.
    If the gap is too large, you lose some power, and the combustion stroke will be weaker as the result.
    However, you can gain "some" fuel economy from a slightly larger gap, but go too large, and you get blow-out, and you will then lose a lot of power due to.. well no spark ;).

    If the plug burns hotter then the stock ones, you can probably get away with a slightly larger gap, but if all is running well, and fuel economy is normal, I wouldn't worry about it. There is so many variables in an ignition system, I don't even know them all, and it will be a long time before I do. :)
    CS
     
  6. Smiles

    Smiles Moderator
    Moderator Owner

    Nov 20, 2003
    14,510
    Pittsburgh, PA
    Full Name:
    Matt F
    Great point, Henry.

    If the spark plug manufacturer sets the gap at 0.035, and everyone else (including the car manufacturer, Ferrari) recommends 0.025, who should I listen to?
     
  7. To remove this ad click here.

  8. henryk

    henryk Formula Junior

    Dec 9, 2003
    479
    Door County, WI
    If I where replacing "original" plugs, then I would go with the recommendations of the car maker. If the original plug is no longer available, and most are not, then I would go with the gap that came with the plug.......see how it runs, and check the plugs after 1K miles. Modern plugs have come a LONG way since the "good-ole-days".

    Can you even get original plugs for the 330?
     
  9. Fiat Dino 206

    Fiat Dino 206 Karting

    Apr 19, 2004
    144
    Mississippi
    Full Name:
    David
    Don't know if this site will help you or not, but there is enough information about spark plugs to confuse an engineer.

    http://www.centuryperformance.com/spark.asp

    Really a lot of information regarding what a spark plug does ... and about gapping etc.

    Best wishes
     
  10. Smiles

    Smiles Moderator
    Moderator Owner

    Nov 20, 2003
    14,510
    Pittsburgh, PA
    Full Name:
    Matt F
    Thanks!

    Thank link explained a few things, like not to exceed a 0.008" difference from stock. That in turn explains the 0.027 recommended by Porsche (vs. 0.035 stock) , and some other Ferrari guys I've talked to.

    I'll probably change them again for platinum plugs at some point, and may step up the gap a bit more.

    Thanks again.

    --Matt
     

Share This Page