LT1 Spark Plug gapping

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  • 2 Post By Stingroo
RWD 19xx-1984 DeVille and Fleetwood,
1985-1996 Fleetwood and Brougham Forum Discussion, LT1 Spark Plug gapping in Past Cadillac Vehicle Discussion; I've been educating myself on spark plug gapping for the LT1.. I recently did my plugs and wires with the ...
  1. #1
    Poda is offline Cadillac Owners Fanatic
    Automobile(s): 94 Fleetwood Base, 94 Fleetwood Livery-no vinyl top in sight
    Join Date
    Jan 2012
    Toronto, ON

    LT1 Spark Plug gapping

    I've been educating myself on spark plug gapping for the LT1.. I recently did my plugs and wires with the default "settings". Lately I find myself thinking I may be able to optimize the stock motor though.

    Manufacture req. is 0.050
    Default wires are 7.5mm

    I installed NGK TR55's, gapped to.050, with 8mm Accel wires. The wires were a mistake and I'll be swapping back to new 7.5mm's from who-knows-yet, but that's a whole other thread.

    The NGK's came pregapped at 0.058 for my application. I regapped to factory spec, then started reading up after the fact. Theory dictates larger gap=more power (but tougher on the optispark and coil), smaller gap is better for mpg. Too much either direction confuses the hell out of the PCM. I've seen recommendations for a stockish LT1 range from 0.045 to 0.058 (NGK default). I'd stay with factory spec, but manufacturers are notorious for uber-safe settings to appease regulations and I was wondering if anyone had any experience with a better gap for our cars than what GM recommends.

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  3. #2
    Stingroo's Avatar
    Stingroo is offline Cadillac Owners 10000+ Posts
    Automobile(s): 92 Caprice Wagon LS1/T56 | 1995 Lexus LS400 | Next: 16 MX-5
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    Jun 2009
    Port St. Lucie, FL

    Re: LT1 Spark Plug gapping

    On the Impala forum, .050 seems to be the consensus. Some also recommend AC Delco platinum plugs over the NGKs, but I can't comment on that.
    SilverCoupe and SilverCoupe like this.

  4. #3
    Pun90's Avatar
    Pun90 is offline Cadillac Owners Member
    Automobile(s): '97 Deville
    Join Date
    Sep 2009

    Re: LT1 Spark Plug gapping

    Hey Poda you should check out the . Much more information there related with Fleetwoods than I have seen here.

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  6. #4
    HUF's Avatar
    HUF is offline Cadillac Owners Connoisseur
    Automobile(s): 1995 FWB 100,*** miles CURRENT. 1991 Seville 175,000 SOLD
    Join Date
    Dec 2005

    Re: LT1 Spark Plug gapping

    I have been using NGK iridium plugs for a few thousand miles. They came with 0.0585" gap which I did not change. I have also replaced original AC Delco wires with the same exactly part number. Nevertheless, the resistance of the new set was significantly higher than the one of the old set. I do not know why they changed the specs. A lot of people use Tailor wires for LT1 engine.

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