Thread: 3.5 setup... what is the best spark plug? Can't figure out heat range...

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  1. #1 3.5 setup... what is the best spark plug? Can't figure out heat range... 
    SE Level Member MM704's Avatar
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    So I have a 2000 GTP with 117k miles. It has a 3.5 inch supercharger pulley, PLog, 3 inch downpipe, CAI, 180* thermostat, and Overkill tune. I'm currently running AC Delco 41-104 plugs (from CTS-V, ZL1, ZR1) gaped at .045, which was personally recommended by Will Overkill for my setup. My KR numbers are very low, usually under 2 at WOT.

    This set up worked fine for the first few months during the fall but once winter came I started having some RPM hesitating/chugging issues with light throttle while driving on the highway, particularly uphill. I put in a beefier set of spark plug wires (AC Delco wires > cheap wires) and that definitely lessened the problem but it's still there. I'm willing to bet my spark plugs are too cold.

    My question is what spark plugs should I be running with this particular setup? Based on what I've read Autolite 605's with a .050 gap is the most consistent answer, but I'd rather stick with AC Delco Iridiums if possible because they last the longest and GM engines seem to respond to them very well. Would 41-993 (from 4.3 Vortec/Blazer) be the heat range I'm looking for? I'm assuming I want 1 heat range colder than the stock 41-101's.

    Please let me know what you think. Thanks a bunch!
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  2. #2 Re: 3.5 setup... what is the best spark plug? Can't figure out heat range... 
    Schooner Tuner ADrugDealer's Avatar
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    Frankly most guys here will say 1 of two things:

    Stock for 99% of things
    AutoLite 104/105s for 1% of other things

    I currently run 104s in my Turbo GP and have been considering stepping up one more heat range.
    2008 G8 GT - IOM - LSA Blower, Intercooled, Ported Heads, Cam, Flex Fuel Conversion, Tuned - 550whp - 11.5 @ 124 -
    2000 Regal - Winter Beater
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  3. #3 Re: 3.5 setup... what is the best spark plug? Can't figure out heat range... 
    GTP Level Member 99GT2dr's Avatar
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    I have almost the same setup as you right now, but with an ssic, I'm running 104's @ .055. No issues under any conditions, 104's are good for a pretty wide range of mods.
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  4. #4 Re: 3.5 setup... what is the best spark plug? Can't figure out heat range... 
    GTP Level Member Impala131's Avatar
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    Go with the 605's... I have switched back and forth between 104's and 605's many times on 3.5/3.4 setups, and have never been able to add timing or increase AFR based on swapping plugs on those pulley sizes. Heck, 606's might be more appropriate for a 3.5, but I haven't tested that extensively.
    2003 Grand Prix GTP.... the journey begins again....
    E85 Self Tune with HPT, 80# Injectors, Gen V 3.4 pulley, SD Headers, AL605 Plugs
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  5. #5 Re: 3.5 setup... what is the best spark plug? Can't figure out heat range... 
    Killa Bee Scottydoggs's Avatar
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    being every car takes mods differently, try the 104's gap em a few times, 55, 60 53, 50 see what feels better. 0.45 seems small. try 0.50 for your plugs now. if that dont work swap plugs. copper core plugs seem to work best too.

    no kidding i had my plugs in and out like 10 times over a weeks time playing the gap game. 104's gaped at .50 feel the best in my car.

    98 Buick Regal GS, F body brakes, Caddy STS wheels, tinted tails L36 bottom end, lightly ported heads, 1.95 roller rockers, headers, gen 5 N* 3.0 pulley, FSIC, 42 lb injectors, a BrandonHall rebuilt trans, DHP tuned and AEM water/Meth injection https://goo.gl/gpV5kW
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  6. #6 Re: 3.5 setup... what is the best spark plug? Can't figure out heat range... 
    Schooner Tuner ADrugDealer's Avatar
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    and here I am, ran stockers until a 2.8 :P
    2008 G8 GT - IOM - LSA Blower, Intercooled, Ported Heads, Cam, Flex Fuel Conversion, Tuned - 550whp - 11.5 @ 124 -
    2000 Regal - Winter Beater
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  7. #7 Re: 3.5 setup... what is the best spark plug? Can't figure out heat range... 
    SE Level Member MM704's Avatar
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    This is great stuff thanks everybody
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  8. #8 Re: 3.5 setup... what is the best spark plug? Can't figure out heat range... 
    GrandPrix Junkie SgtMarshal's Avatar
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    try the copper tip plugs, I ran a set of iridium 104's and when I switched back to copper the car ran much better.
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