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Thread: NGK BR6FS "vs" AC MR43T

  1. #1
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    NGK BR6FS "vs" AC MR43T

    Last spring after three faithful seasons on my AC 43T's I decided to try NGK BR6FS supposedly the direct replacement for the AC's. Boat has been running decent but I got a bug to check the NGK's, I put about 35 hours on last year. When I pulled the AC's out last spring I had that why bother feeling, they were spotless with -0- signs of tip wear. Upon pulling the NGK's it was easy they were a colder plug, they were a good color but a bit cruddy. They were not handling the 750 Holley well enough to suit me, they would be fine in a 650 or under engine. Bummer is I was handed a new set of NGK's over the winter so I stuck them in but will put my faithful AC's back in next season. Do no take this as knocking NGK they are a very good plug but BR6FS in not good for a 383 with a 750 Holley.
    No matter what your beliefs are "GOD BLESS AMERICA"

    Fully retired marine tech near 60 years in the biz.

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    I was a little suspect of my NGK's too, ran the same set of AC's for 3 years in a similar engine. Then when I built my 406 sbc w/Dart heads,770 Holley. I installed R5671A-7 NGK's. Now at least 2 plugs foul at the beginning of each season. Think I'm gonna replace the NGK's with an AC equivilant.

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    For a 2003 350/300 MPI engine I bought a set of NGK BPR6EFS today as NGK's always run well in my old BMW's. I'll try the AC plugs next time. The shop manual shows 41-932 for the AC plugs that apparently has been superceded to 41-993 in a platinum plug. I've seen posts that recommend the MR43LTS for small blocks. What AC plug should I buy next time?
    Thanks.

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    Smile

    There is nothing wrong with NGK's they make a very good plug, I did a little reading their heat range is wider I guess to cover more applications. I will not write them off and may email them for advice. Bonnie says I need to run harder to keep them clean, maybe she is right I tend to sit on about 3400 with only an occasional minute or two blast. Ooops now you know who the hot rod in the family is!!!!!

    Phil
    No matter what your beliefs are "GOD BLESS AMERICA"

    Fully retired marine tech near 60 years in the biz.

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    For almost all SBC's MR43T seem to be the most revered, I have never ever had a issue with them.
    No matter what your beliefs are "GOD BLESS AMERICA"

    Fully retired marine tech near 60 years in the biz.

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    Quote Originally Posted by MOP View Post
    Last spring after three faithful seasons on my AC 43T's I decided to try NGK BR6FS supposedly the direct replacement for the AC's. Boat has been running decent but I got a bug to check the NGK's, I put about 35 hours on last year. When I pulled the AC's out last spring I had that why bother feeling, they were spotless with -0- signs of tip wear. Upon pulling the NGK's it was easy they were a colder plug, they were a good color but a bit cruddy. They were not handling the 750 Holley well enough to suit me, they would be fine in a 650 or under engine. Bummer is I was handed a new set of NGK's over the winter so I stuck them in but will put my faithful AC's back in next season. Do no take this as knocking NGK they are a very good plug but BR6FS in not good for a 383 with a 750 Holley.
    Quote Originally Posted by cvx View Post
    I was a little suspect of my NGK's too, ran the same set of AC's for 3 years in a similar engine. Then when I built my 406 sbc w/Dart heads,770 Holley. I installed R5671A-7 NGK's. Now at least 2 plugs foul at the beginning of each season. Think I'm gonna replace the NGK's with an AC equivilant.
    Hey Phil & Jeff,
    You know the old saying: If it isn't broken don't fix it!

    My small & big block Chev's in both boats luv those AC 43 TR's too!
    This year I only replaced the cap & rotor after doing my ign check inspection.
    Think Fast, Live Long!
    Humor Helps.

  7. #7
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    pre vortec and post vortec and aftermarket heads ALL take different plug reaches..

    a catalog isn't going to show you what's best

    requires visual inspection for chamber orientation

    personally, I like Denso's
    Charter Member - WAFNC, SBBR, KWOSG
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    Quote Originally Posted by Walt. H. View Post
    Hey Phil & Jeff,
    You know the old saying: If it isn't broken don't fix it!

    My small & big block Chev's in both boats luv those AC 43 TR's too!
    This year I only replaced the cap & rotor after doing my ign check inspection.
    Seeing my error above, I should have written AC MR-43T for both of my engines.
    Think Fast, Live Long!
    Humor Helps.

  9. #9
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    Quote Originally Posted by MOP View Post
    There is nothing wrong with NGK's they make a very good plug, I did a little reading their heat range is wider I guess to cover more applications. I will not write them off and may email them for advice. Bonnie says I need to run harder to keep them clean, maybe she is right I tend to sit on about 3400 with only an occasional minute or two blast. Ooops now you know who the hot rod in the family is!!!!!
    Phil

    pre vortec and post vortec and aftermarket heads ALL take different plug reaches..
    a catalog isn't going to show you what's best
    requires visual inspection for chamber orientation
    personally, I like Denso's
    My neighbor use to work for Denso and did lots of testing with many plugs. He said the NGK's are better than the AC's because they have a wider heat range like phil said and they last a lot longer. He also said Denso makes most of the plugs out there from some autolite to ac's to motorcraft.

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