Z32 Oversized Valves and -B spark plugs

Discussion in 'Technical' started by Hulk30dett, Jun 2, 2020.

  1. Hulk30dett

    Hulk30dett Member

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    Hi All,
    I am using NA heads machined to suit TT
    The motor is back together and in, everything is running well
    I want to investigate going back to recommended plugs, just colder
    As you'd expect i didn't think ahead of time to check if the 3mm added length to the spark plug will hit the valves. I am using 9.5 lift cams with 1mm OS valves

    Has anyone checked these before with NA or TT heads?
    Attached are pics of mine at time of last build
    I even thought about the clearance, just to piston though :(
    20180325_160641.jpg 20180325_160646.jpg 20180325_160648.jpg 20180325_160650.jpg 20180325_160701.jpg 20180325_160706.jpg
     
  2. IB

    IB ?????

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    -11B plugs were for US spec z32. Jspec used -11. If you're planning to run higher boost, use the plugs without -11 for .8mm gap.
     
  3. beaver

    beaver southern zeds

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    The difference between the ngk -11B and the -11, is the 11b sits further into the chamber which ngk says produces a cleaner more efficient burn, I use the 11b's gapped to .8, try one wile the engine can free rotate.
     
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  4. jellybeans

    jellybeans Active Member

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    Hulk,
    Just some thoughts, no specific knowledge for you sorry.

    Valves hitting spark plugs
    i cant see those valves at that angle hitting the plug with only 9.5mm of travel.
    disclaimer : All measurements taken by eye, my old bloodshot eye and your photos are the closest i have ever come to seeing a VG head despite owning 2 VG's. I recently saw a nice looking DOHC V6 sitting on an engine stand and asked what it was. The mechanic told me it was a VG30. I just laughed, that stupid ugly plenum has hidden the VG so well I've never seen one.

    Checking the spark plug to piston gap
    This could be done with a threaded spark plug top dead centre tool. This would be able to be used to check the maximum spark plug length.
     
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  5. Hulk30dett

    Hulk30dett Member

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    Cheers Ian,
    That does make sense- most of the big write ups come from there and they are saying to run 0.6-0.7mm gaps
    This would be their plug sits further down in the bore along with the piston top (lower comp than 8.5)
    You wouldn't happen to know what numbers were cast on the US spec heads would you?
    I cannot find anything about them
    Garry
     
  6. Hulk30dett

    Hulk30dett Member

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    Cheers Beaver,
    Looks to be plenty of room
    Will put some plastaseen on the plug and see what comes of it
    Can i ask what boost you are running?
     
  7. beaver

    beaver southern zeds

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    base is 14psi high is 18.
     
  8. IB

    IB ?????

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    I don't think heads were different. Speculation back in early 2000's was that -11B were for California emissions. A couple of the Aus tuners around same time said the long plugs made more prone to detonation.
     
  9. Hulk30dett

    Hulk30dett Member

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    Perfect info peoples
    I am looking into the maps around 14-17 seeing some knock levels so the info on plugs is great- cheers
     
  10. geron

    geron National Petroleum Equipm

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  11. Hulk30dett

    Hulk30dett Member

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    Thaanks Geron
     
  12. rob260

    rob260 Moderator Staff Member

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    There is lots of conflicting information about plugs out there.

    NGK say the longer plugs are to stick the plug in the middle of the chamber to optimise combustion.

    There are other (well regarded) schools of thought that suggest the longer plug acts like a heat sink and increases the risk of pre ignition.

    Considering the operating parameters that the car was designed for I'd say both are correct.

    At 17psi you are pushing twice the boost that the car was originally tuned for. A colder plug will help combat the increased risk of detonation due to increased temps (no free lunch, you can't make more power without more heat). A tighter gap will reduce the risk of blowout (which occurs when the ignition system is not able to provide enough energy for the spark to jump the gap "against" increased pressures). If you are not experiencing blowout then a bigger gap is always going to be better (although whether it is measurably better is another thing).

    If you are wishing to combat detonation changing from OEM heat range 6 to a heat range 7 may be a good idea.

    If you are wanting to get the most performance out of the ignition system as is then changing from OEM platinum to an iridium plug may be a good idea. Iridium is a better conductor and more energy is therefore available for the electronic pulse to jump the gap and spark compared to a platinum plug. Again there is lots of conflicting information about copper/iridium/platinum out there on the internet but the dyno does not lie and the benefits of changing to an iridium plug can be measured and backed up.

    If you are still shopping for plugs I have heat range 6 with 1.1mm gap (OEM spec) and heat range 7 with .8mm gap in stock.

    Hope that helps.
     

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