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Thread: Spark Plugs

  1. #1
    Canadian Beaver Inspector jkindt's Avatar
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    Spark Plugs

    Why does Polaris list the NGK BR8ES for the 93 SL750, but lists the NGK BPR7ES for the 94-95 SL750s, and then the NGK BPR8ES for the SL780s.

    I don't have a clue which ones to use on my Sleeper project because it is so modified. It's not really a 750, but not really a 780, and doesn't have factory heads. In fact I have no clue where the compression is going to end up!!! I guesstimate it at about 150-160 psi, but I am not sure without it being together yet. What mods affect which plugs you use?



  2. #2
    ujustlost's Avatar
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    you may have to experiment with the plugs. With NGK The lower the number the hotter the plug.

  3. #3
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Quote Originally Posted by jkindt View Post
    Why does Polaris list the NGK BR8ES for the 93 SL750, but lists the NGK BPR7ES for the 94-95 SL750s, and then the NGK BPR8ES for the SL780s.

    I don't have a clue which ones to use on my Sleeper project because it is so modified. It's not really a 750, but not really a 780, and doesn't have factory heads. In fact I have no clue where the compression is going to end up!!! I guesstimate it at about 150-160 psi, but I am not sure without it being together yet. What mods affect which plugs you use?

    First, NGK numbers are backwards.. The lower the number, the hotter the heat range.

    Second, the "P" stands for projected tip.

    93 750 had less compression, the heads were a bit shallower. So my guess would be possible interference issues if you used a projected tip in the is instance.

    In 94-95, they went with a deeper dished head, so the projected tip was fine to use. Not sure why they opted for the hotter heat range with SLIGHTLY raised compression???

    Most feel the BPR8ES is a better plug to run inside the 650/750/780 because it's heat range is a bit more forgiving with the holed piston isssue.


    For your build with higher compression and more heat, I'd run the BR9ES plugs. The nonprojected tip will help with any concerns of contact, and the lower heat range will also help too. They recommend thses plugs on the PSI triple pipe installation because of the added heat.

    IMO, there's no performance difference between the projected and non plug tips.

  4. #4
    Canadian Beaver Inspector jkindt's Avatar
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    How do you tell if your plugs are too hot or too cold? Also, what the heck is indexing on these motors? The last time I ever heard of this was when I was building SB Chevy's and we wanted the plug electrodes faceing a certain way. But that had to do with the asymmetrical head shape. These have symmetrical heads!

  5. #5
    bowsniper's Avatar
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    Small block chevys? Man your old!!! I would just loosen the throttle plates screws a bit and the huge 4 -barrels would jump wide open off the line! dumping all sorts of gas down the that street cam!! ahh the good ol days!

    See full size image
    553 x 730 - 80k - jpg - dirtbike.off-road.com/.../232006/332655/4.jpg
    Image may be subject to copyright.
    Below is the image at: www.250r.net/forum/showthread.php?t=154


    I think Crazy A has a great thread on this subject.!! tells ya exactly how much, where, what, everything,, good post!


    Are autolite plugs good to use? no.63? I had great luck with those. they dont foul out easily, the ngk's get fussy sometimes. But i use the 8's myself.
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  6. #6
    Connecticut CrazyA's Avatar
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    Plugs
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  7. #7
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
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    Nice diagrams Art.

    Indexing the plugs is exactly what you described.

    Watcon sells plug indexing shims.

    You want the electrode opening facing the exhaust port.

  8. #8
    Matrix 200 suparoo's Avatar
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    I run the Iriduim NGK's 50 odd hrs on a set no problems. They look cool too.

    http://www.ngksparkplugs.com/product.../iridiumix.asp

  9. #9
    Connecticut CrazyA's Avatar
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  10. #10
    bowsniper's Avatar
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    Thanks Crazy A!

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