Results 1 to 7 of 7

Thread: Spark plug fouling in a 2.7l RS spec engine

  1. #1

    Spark plug fouling in a 2.7l RS spec engine

    I’m having trouble keeping the Bosch WR5DC+ plugs in my 2.7l RS spec engine from fouling. Except for Weber carbs, ported heads and cams with more aggressive acceleration ramps, the engine is essentially built to ‘73 Carerra RS specs.

    This’s in the 914/6 I bought in 2020. Before shipment to North Carolina, I had it serviced at a well known, highly respected race shop. The only carb related work on the invoice read “Sync carbs and adjust idle and mixture“ for labor; nothing wrt parts.

    My operating conditions are not the best … so far confined mostly to stop & go driving in moderate traffic with speed limits of 45mph half the time. Despite the CDI, keeping the revs to 2000 at red lights and above 3000 while moving, the plugs are fouled for the second time in only about 300 miles since receiving the car. Under these conditions, and in today’s environment with cell phone cameras everywhere, etc., it’s impossible to do enough “Italian tune-ups” to keep the plugs clean ;-)

    How likely is it the Webers are already out of tune? (Not many miles, but 2 years later.)

    I’m curious what experiences others with similar spec engines may have with spark plug heat ranges … what you’re using vs how the car’s driven?

    I’m thinking the aggressive cam profiles, including the faster acceleration ramps, are playing a role, plan to try incrementally hotter plugs a step at a time until I get the fouling under control.

    Here’s a Bosch cross reference chart for heat ranges of popular brands:


    Regards,
    Bob
    Attached Images Attached Images  
    Bob Schaefer

    ‘67 911S Canary/Lemon yellow, sunroof coupe produced w/100L tank. Until determined otherwise, 306943S appears to be 1 of 1, and among the earliest 911’s with a 100L tank. The 911’s initial participation in a competitive event, the 1965 Monte Carlo Rally, was fitted with a 100L tank (#300055). Seeking additional info on earliest 100L tank fitments to 911’s.



    ‘70 914/6 (2.7l RS spec engine, but searching for 6404915 original)

  2. #2
    member #1515
    Join Date
    Mar 2009
    Location
    San Antonio, Texas
    Posts
    4,239
    That is a liberal interpretation of RS specs. Different cams, different porting and on carbs.
    I run BPR7EIX in my MFI 2.7 without any fouling. I don't know why you keep the revs above 2k at stops but 3k sounds low enough to qualify as lugging.
    I am not a fan of Bosch plugs.
    David

    '73 S Targa #0830 2.7 MFI rebuilt to RS specs

  3. #3
    Same as David, I have a carbed 2.0 and two 2.4's with MFI. I run NGK BPR7ES in all three, no plug fouling irregardless of idling time. Your problem may not be spark plug related.
    Early S Registry member #90
    R Gruppe member #138
    Fort Worth Tx.

  4. #4
    Senior Member Haasman's Avatar
    Join Date
    Apr 2011
    Location
    N.Calif., south of SF
    Posts
    1,965
    Ed- curious what are you gapping the NGK BPR7ES at?
    Haasman

    Registry #2489
    R Gruppe #722
    65 911 #302580
    70 914-6 #9140431874
    73 911s #9113300709

  5. #5
    The stock gap. I didn't see you in Utah last week?
    Early S Registry member #90
    R Gruppe member #138
    Fort Worth Tx.

  6. #6
    Senior Member Haasman's Avatar
    Join Date
    Apr 2011
    Location
    N.Calif., south of SF
    Posts
    1,965
    No Ed, really wanted to bust bugs in Utah with you all.

    Our country store had several employees come down with COVID. I canceled to help fill in. In the end we closed and I could have. Hope you all had a great time.

    Jeff
    Haasman

    Registry #2489
    R Gruppe #722
    65 911 #302580
    70 914-6 #9140431874
    73 911s #9113300709

  7. #7
    Thanks to those who replied with relevant spark plug heat range experience / info.

    I posted a similar thread on the 914World.

    Since opinions are somewhat varied, I plan to slowly try incrementally hotter plugs to see if that resolves the issue. It may be awhile, but I’ll report my findings.

    And btw, to add a little clarity to my cam configuration … it’s the Elgin 306/288-106, similar to the GE-60 pattern as reported by the PO.
    Last edited by Bob Schaefer; 05-26-2022 at 11:35 AM.
    Bob Schaefer

    ‘67 911S Canary/Lemon yellow, sunroof coupe produced w/100L tank. Until determined otherwise, 306943S appears to be 1 of 1, and among the earliest 911’s with a 100L tank. The 911’s initial participation in a competitive event, the 1965 Monte Carlo Rally, was fitted with a 100L tank (#300055). Seeking additional info on earliest 100L tank fitments to 911’s.



    ‘70 914/6 (2.7l RS spec engine, but searching for 6404915 original)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  

Message Board Disclaimer and Terms of Use
This is a public forum. Messages posted here can be viewed by the public. The Early 911S Registry is not responsible for messages posted in its online forums, and any message will express the views of the author and not the Early 911S Registry. Use of online forums shall constitute the agreement of the user not to post anything of religious or political content, false and defamatory, inaccurate, abusive, vulgar, hateful, harassing, obscene, profane, sexually oriented, threatening, invasive of a person's privacy, or otherwise to violate the law and the further agreement of the user to be solely responsible for and hold the Early 911S Registry harmless in the event of any claim based on their message. Any viewer who finds a message objectionable should contact us immediately by email. The Early 911S Registry has the ability to remove objectionable messages and we will make every effort to do so, within a reasonable time frame, if we determine that removal is necessary.