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Thread: Will plug/gap change help mileage?

  1. #1
    Advanced Tuner coachcrow56's Avatar
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    Will plug/gap change help mileage?

    I have been driving a 2002 Firehawk---6 speed for the last 3 weeks and only averaging 20 mpg per tank---79 mph down interstate. The car has QTP long tube headers----3 inch dual exhaust---NGK V power Racing #8 plugs gapped at .030. I think its the wrong plug to get decent gas mileage.

    If I change to a TR55 and gap them at .050, will that help mileage?
    Last edited by coachcrow56; 07-17-2015 at 02:46 PM.

  2. #2
    Tuning Addict 5FDP's Avatar
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    Is stock gap near .040 or .060 on those motors?

    I know it's .040 after like 01-02 for silverado's and that what I run in my truck with TR5's.

    Too cold of plug will reduce mpgs and doing 70mph might help the miles per gallon also.
    2016 Silverado CCSB 5.3/6L80e, not as slow but still heavy.

    If you don't post your tune and logs when you have questions you aren't helping yourself.

  3. #3
    Advanced Tuner coachcrow56's Avatar
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    Owners manual recommends a .060 gap. The NGK plugs in it now (colder plugs) are for a 200 shot nitrous set up, which I don't plan to use for a while. The speed limit on I20 here in Texas is 75 , at which the engine only turns about 1700 rpm.

  4. #4
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    I used to gap TR6's to the stock spec on my 2000 F-Body. It was an M6 car with QTP long tubes, LS6 intake, true dual exhaust and a lid...nothing special. I averaged 25 mpg commuting to work with that car for years...most of my commute was cruise control set at 75 mph on the highway. When I played with DFCO settings I got it up to about 27 mpg.

    Using the cruise control helps a LOT. When you think you're maintaining the speed yourself...you're not LOL. Set the cruise control on 75 and see how the car reacts.
    2010 Camaro SS M6. Stock Bottom End, Heads/Cam/Intake/Headers/Exhaust.
    2005 Silverado RCSB. Forged 370 LQ9/Borg-Forced Inductions T6 S484/Jake's Stage 4 4L80E with D3 Brake/4WD.
    2023 Durango Hellcat

  5. #5
    Advanced Tuner coachcrow56's Avatar
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    I always use the cruise on the Interstate. I read on several forums that GM changed plug gaps to .040 for many cars in 2003, using TR55 iridium plugs. What gap did you use on the TR6 plugs?
    Last edited by coachcrow56; 07-17-2015 at 08:50 AM.

  6. #6
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    Stock gap spec on that car was 0.060...and I wasn't doing much in terms of additional cylinder pressure over stock, just bolt on stuff, so I left it at stock spec...never had any issues blowing out the spark at full throttle, and it drove great.
    2010 Camaro SS M6. Stock Bottom End, Heads/Cam/Intake/Headers/Exhaust.
    2005 Silverado RCSB. Forged 370 LQ9/Borg-Forced Inductions T6 S484/Jake's Stage 4 4L80E with D3 Brake/4WD.
    2023 Durango Hellcat

  7. #7
    Advanced Tuner coachcrow56's Avatar
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    Ok---for those who would like to know! Using the correct spark plug makes a difference in your mileage. I installed a set of NGK TR55 Iridium plugs, and gapped them at .055. (Changing plugs on an LS1 is a pain in the ***!)

    I have made 2 trips down I20, and my mileage has increased from 20 to 23---3 miles per gallon. I was hoping for more, but with 3.42 gears and cruise set on 78, I guess it will do for now.

  8. #8
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    Quote Originally Posted by coachcrow56 View Post
    I have been driving a 2002 Firehawk---6 speed for the last 3 weeks and only averaging 20 mpg per tank---79 mph down interstate. The car has QTP long tube headers----3 inch dual exhaust---NGK V power Racing #8 plugs gapped at .030. I think its the wrong plug to get decent gas mileage.

    If I change to a TR55 and gap them at .050, will that help mileage?
    If your tuning it yourself,

    You can add some timing to the area you're cruising in. you can also add +2 to the dwell table.

    Outside of that, has it been tuned at all?

  9. #9
    Advanced Tuner coachcrow56's Avatar
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    No---totally stock tune--or whatever SLP may have done---if anything.