Thread: spark plug gap range is best?

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  1. #1 spark plug gap range is best? 
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    specs on my car:
    98 grand prix gtp 8.5:1 compression ratio
    65lb injectors
    autolite 103 gapped at 0.036
    ZZP Z7 turbo kit with T66
    devils own controller 2bar with M7(?) nozzle
    using -20*F washer fluid when lazy or 80/20 methanol/water mixture
    17.5psi and 23* of timing

    right now i see on the grand prix forums the turbo'd guys are running plug gaps in the 0.030-0.034. however they're not running methanol but larger size intercoolers. im running the default moderate sized intercooler 22x8x3.5". im using a NGK wideband and in order to run near knock-free my AFR is 10.0-10.2. my commanded AFR in the pcm is at 11.8.

    my other question is what gap range should i consider running if i want to go to 18-20psi? i noticed when i try and run anything over 18psi at wide open throttle the car stutters and most likely is misfiring. i imagine im getting the misfire because of the add'l boost? again my AFR is still under 10.99.

    any suggestions and advice is greatly appreciated!! TIA
    old setup-Z7 Turbo Kit w/T66, A2A I/C, stock cam & valvetrain/LS1 MAF/Ported 99TB/PowrTuner/AFC/Devils Own/LS1M Scanner/PRJ FP/42# Injs=12.3@118mph street tires -
    (Sold)BACK TO M90 Vs cam w/3.5" pulley/meth/25* timing+bolt-ons
    01 Z28 A4 HP-self-tuned, LTs, FTRA, 3600stall 12.3@112mph
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  2. #2 Re: spark plug gap range is best? 
    DUI BABY Bio248's Avatar
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    run less boost and lean it out. your AFR is way too low.
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  3. #3 Re: spark plug gap range is best? 
    GTX Level Member tayl5645's Avatar
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    Quote Originally Posted by Bio248 View Post
    run less boost and lean it out. your AFR is way too low.
    What he said your richer than bill gates
    2005 GTP Grey

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  4. #4 Re: spark plug gap range is best? 
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    i could try to lean it to 10.6-10.8. remember im also running methanol/alky injection which will add/richen my overall AFR.
    old setup-Z7 Turbo Kit w/T66, A2A I/C, stock cam & valvetrain/LS1 MAF/Ported 99TB/PowrTuner/AFC/Devils Own/LS1M Scanner/PRJ FP/42# Injs=12.3@118mph street tires -
    (Sold)BACK TO M90 Vs cam w/3.5" pulley/meth/25* timing+bolt-ons
    01 Z28 A4 HP-self-tuned, LTs, FTRA, 3600stall 12.3@112mph
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  5. #5 Re: spark plug gap range is best? 
    DUI BABY Bio248's Avatar
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    exactly, you want your overall AFR to be where its supposed to be. you're now using the meth as a secondary fuel. your car will be tons faster with it being leaned out.
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  6. #6 Re: spark plug gap range is best? 
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    yea. however my main question is should i lower my gap or enlarge it if i want to go past 18psi? again, thsoe with no alky but with I/C run smaller gaps with more boost going in to prevent spark blowout. in my case of using both alky and I/C would going to a smaller gap could also cause spark blowout cause theres too much happening in the combustion chamber?
    old setup-Z7 Turbo Kit w/T66, A2A I/C, stock cam & valvetrain/LS1 MAF/Ported 99TB/PowrTuner/AFC/Devils Own/LS1M Scanner/PRJ FP/42# Injs=12.3@118mph street tires -
    (Sold)BACK TO M90 Vs cam w/3.5" pulley/meth/25* timing+bolt-ons
    01 Z28 A4 HP-self-tuned, LTs, FTRA, 3600stall 12.3@112mph
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  7. #7 Re: spark plug gap range is best? 
    DUI BABY Bio248's Avatar
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    smaller gap prevents the spark from blowing out. if that is your issue then by all means go with a smaller gap. however, it sounds like youre drowning the car in fuel right now as well.
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  8. #8 Re: spark plug gap range is best? 
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    hmmm...enough to cause stutter/misfire?
    old setup-Z7 Turbo Kit w/T66, A2A I/C, stock cam & valvetrain/LS1 MAF/Ported 99TB/PowrTuner/AFC/Devils Own/LS1M Scanner/PRJ FP/42# Injs=12.3@118mph street tires -
    (Sold)BACK TO M90 Vs cam w/3.5" pulley/meth/25* timing+bolt-ons
    01 Z28 A4 HP-self-tuned, LTs, FTRA, 3600stall 12.3@112mph
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  9. #9 Re: spark plug gap range is best? 
    The Blue One blueguy's Avatar
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    Your excess in fueling could also be fouling out your plugs...so I'd pull them and check them too.
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  10. #10 Re: spark plug gap range is best? 
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    i changed the recently a month ago anf the old plugs werent soaked but rather grayish-white. i'll have o double-check when i get the chance again. however, should i open the gap more then?
    old setup-Z7 Turbo Kit w/T66, A2A I/C, stock cam & valvetrain/LS1 MAF/Ported 99TB/PowrTuner/AFC/Devils Own/LS1M Scanner/PRJ FP/42# Injs=12.3@118mph street tires -
    (Sold)BACK TO M90 Vs cam w/3.5" pulley/meth/25* timing+bolt-ons
    01 Z28 A4 HP-self-tuned, LTs, FTRA, 3600stall 12.3@112mph
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  11. #11 Re: spark plug gap range is best? 
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    the plug gap being too small could be causing your rich condition. it COULD also be that you are running too rich (after meth and all) for the small gap.
    In either case, widening the plug gap is easy, quick, and free. do that first
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  12. #12 Re: spark plug gap range is best? 
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    Coils could be getting weak.
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  13. #13 Re: spark plug gap range is best? 
    GTP Level Member 01gpgt01's Avatar
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    whats your AFR Wot?
    2001 GT. A few here and there mods http://www.streetfire.net/video/2001...ynp_208097.htm

    2009 Hummer H3 Solar flare premium
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  14. #14 Re: spark plug gap range is best? 
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    Quote Originally Posted by fst View Post
    im using a NGK wideband and in order to run near knock-free my AFR is 10.0-10.2. my commanded AFR in the pcm is at 11.8.
    this
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  15. #15 Re: spark plug gap range is best? 
    GTP Level Member 01gpgt01's Avatar
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    Quote Originally Posted by matt5112 View Post
    this
    Ding ding ding. You're running a 10.0 afr and wonder what the issue is lol. 10.0 is the lowest most widebands read aswell. So who knows where your at
    Last edited by 01gpgt01; 01-29-2011 at 05:36 PM.
    2001 GT. A few here and there mods http://www.streetfire.net/video/2001...ynp_208097.htm

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  16. #16 Re: spark plug gap range is best? 
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    Quote Originally Posted by fst View Post
    specs on my car:
    98 grand prix gtp 8.5:1 compression ratio
    65lb injectors
    autolite 103 gapped at 0.036
    ZZP Z7 turbo kit with T66
    devils own controller 2bar with M7(?) nozzle
    using -20*F washer fluid when lazy or 80/20 methanol/water mixture
    17.5psi and 23* of timing

    right now i see on the grand prix forums the turbo'd guys are running plug gaps in the 0.030-0.034. however they're not running methanol but larger size intercoolers. im running the default moderate sized intercooler 22x8x3.5". im using a NGK wideband and in order to run near knock-free my AFR is 10.0-10.2. my commanded AFR in the pcm is at 11.8.

    any suggestions and advice is greatly appreciated!! TIA
    I am the tech manager at Autolite, have alot of experience with these cars. I also agree with the other posters on your afr, fix that first. My coworker is a former owner of DHP. .028-.032 plug gap when running high boost with stock ignition to avoid blowing out the spark
    Last edited by blueguy; 01-31-2011 at 08:57 AM.
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  17. #17 Re: spark plug gap range is best? 
    youtu.be/xhrBDcQq2DM FoSHO99's Avatar
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    Also take into consideration stock valvetrain at 18+psi of boost. If you were to hop on a dyno I bet you would see some characteristics of valve float.

    Get it in the 11.1-11.5ish afr range for the street, that way if your methanol fails, you should be able to tell and back off safely before it goes any leaner. You also should work on matching the commanded afr to your actual afr with the methanol if you are going to be using it all the time.
    2001 GTP PT61 Turbo, E85, Stock Motor
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