Spark plugs for Aluminum heads?
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Spark plugs for Aluminum heads?

  1. #1
    Can't re-Member 28Eliminator's Avatar
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    Default Spark plugs for Aluminum heads?

    516ci BBC, N/A
    8.75:1 Comp
    AFR 305 heads, CNC chambers
    Dart intake, 830HP carb
    Hyd roller, 228/235 @.050, 650/603
    5500 rpm max

    Lake boat with a Bravo drive.

    AFR says Autolite AP3935 or AP3932,
    NGK cross reference's with the 3932 as a 10 heat range... cold??
    the 3935 Cross references with a 7 heat range, closer to the BR6FS's I ran with the Iron headed motor.... Not sure where to start Shouldn't I be using a resistor plug??
    I'd agree with you, but then we would both be wrong

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    Bostick Racing Engines six-oh-nine's Avatar
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    Quote Originally Posted by 28Eliminator View Post
    516ci BBC, N/A
    8.75:1 Comp
    AFR 305 heads, CNC chambers
    Dart intake, 830HP carb
    Hyd roller, 228/235 @.050, 650/603
    5500 rpm max

    Lake boat with a Bravo drive.

    AFR says Autolite AP3935 or AP3932,
    NGK cross reference's with the 3932 as a 10 heat range... cold??
    the 3935 Cross references with a 7 heat range, closer to the BR6FS's I ran with the Iron headed motor.... Not sure where to start Shouldn't I be using a resistor plug??
    NGK 4554 is a good place to start... may be a bit cold being a 8 heat range. Actually, 4091 would be the 7 heat range and may be more of what you'd need.
    Last edited by six-oh-nine; 06-07-2012 at 01:13 PM.
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  4. #3
    steelcomp was here
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    Quote Originally Posted by 28Eliminator View Post
    516ci BBC, N/A
    8.75:1 Comp
    AFR 305 heads, CNC chambers
    Dart intake, 830HP carb
    Hyd roller, 228/235 @.050, 650/603
    5500 rpm max

    Lake boat with a Bravo drive.

    AFR says Autolite AP3935 or AP3932,
    NGK cross reference's with the 3932 as a 10 heat range... cold??
    the 3935 Cross references with a 7 heat range, closer to the BR6FS's I ran with the Iron headed motor.... Not sure where to start Shouldn't I be using a resistor plug??
    I'm thinking the 32 is way too cold.
    The 35 is better of the two.
    Canfield always recommended a 3924 as a starting point...even a little warmer yet (NGK 5) and it always seemd OK. I like to run as hot a plug as possible and still have it live and do it's job.
    Last edited by scott foxwell; 06-07-2012 at 11:14 AM.
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  6. #4
    Senior Member Futs's Avatar
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    Will to cold of a plug make it run alittle rich throughout the throttle or just at idle or WFO or any at all??

  7. #5
    Some guy obnoxious001's Avatar
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    I use some 3923 Autolites, couple steps colder than the stock 25, with no reported problems. I use them since they are readily available at parts stores, but I would run non resistor plugs if they were easier to get. Engine I just had on the dyno had NGK-7's, more compression and higher rpm than you are working with.

  8. #6
    Can't re-Member 28Eliminator's Avatar
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    Quote Originally Posted by six-oh-nine View Post
    NGK 4554 is a good place to start... may be a bit cold being a 8 heat range. 4091 would be the 7 heat range.
    The 4091 is the R5671A-7, which cross references with the 3935...

    Quote Originally Posted by steelcomp View Post
    I'm thinking the 32 is way too cold.
    The 35 is better of the two.
    Canfield always recommended a 3924 as a starting point...even a little warmer yet (NGK 5) and it always seemd OK. I like to run as hot a plug as possible and still have it live and do it's job.
    Another vote for the 3935's... I'll start with them.

    Quote Originally Posted by obnoxious001 View Post
    I use some 3923 Autolites, couple steps colder than the stock 25, with no reported problems. I use them since they are readily available at parts stores, but I would run non resistor plugs if they were easier to get. Engine I just had on the dyno had NGK-7's, more compression and higher rpm than you are working with.
    3923's are resistor plugs?? Is there a particular reason for running the resistor? I though it was just the radio thing... what about the type of ignition system?

    sorry, it's my first set of Aluminum heads
    I'd agree with you, but then we would both be wrong

  9. #7
    Senior Member TNYoungblood's Avatar
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    I call NGK tech support when I don't know and that boy damn near nails it everytime. Not sure his name but the same guy has always answered the phone.
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