LT1 Spark Plug gapping

Cadillac Forums | Help Us Help You | Advertise | Cadillac Parts | Cadillac News | Cadillac Classifieds

Cadillac Technical Archive | Cadillac Dealers | Cadillac Reviews | Cadillac Dealer Reviews | Cadillac Vendors is the premier Cadillac Forum on the internet. Registered Users do not see the above ads.
+ Reply to Thread
Results 1 to 4 of 4
Like Tree1Likes
  • 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.

  2. Remove Advertisements

  3. #2
    Stingroo's Avatar
    Stingroo is online now Wagon/Audio Enthusiast
    Automobile(s): 92 Caprice Wagon LS1/T56 | 98 Civic 5spd | 01 Sonoma 5spd
    Join Date
    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.

  5. #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.

Quick Reply Quick Reply

Register Now

Please enter the name by which you would like to log-in and be known on this site.

Please enter a password for your user account. Note that passwords are case-sensitive.

Please enter a valid email address for yourself.

What Cadillac(s) do you own? (Or type NONE)

Please select your insurance company (Optional)

Your date of birth and age are displayed in several places on the forum. Only the administrator will have access to your date of birth should you choose to hide it via the privacy option below.


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.


Cadillac Posting Rules

  • You may post new threads
  • You may post replies
  • You may not post attachments
  • You may not edit your posts
Read about Lincoln | Buick | Kia Forte Forum
Need products for your Cadillac? Check out your options at the links below:

custom floor mats | Cadillac Chrome and Black Chrome Wheels | window tinting