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  1. #1

    ? about heat range/spark plugs...

    Ok, the way I understand it is you need to run 1 heat range colder when using a few mods such as Power pipe/thru hulls, air box mods/filter kits, with and without IC`s. I was reading some tech stuff on one of the plug sites NGK/Denso and basically their interpretation was if you have 75-100 increase in HP from whatever, you would need to use colder heat range to prevent detonation, I`m guessing...
    So: Do the mods, "bolt-ons" really add up to 75-100 hp increase to require a colder plug? Could you still use a standard/stock heat range plug (4-tec) DCPR8E, and does it depend on the water temps or riding area? Will the colder plugs actually get to their optimum operating temps?, just curious to here some proof`s or testimony...PR...


  2. #2
    Legend in my own mind Sirhc7897's Avatar
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    The colder/denser the air the more this will come into play as well. On the domestic Polaris 1200's we used to run 8's in the summer and 9's in the winter (stock called for 9's)...Now once we started modifying we went to 9's all the time...

    Realize that normally the reason for a plug swap to a cooler range as soon as you start modifying is becasue most manufacturers run a plug right on the edge of the range in stock form. That means there's not a lot of wiggle room and you can quickly fall into the range of needing a cooler plug with just one or two "minor" mods...

    Also realize that each plug is designed for a specific range. Just because that plug is in your ski and your at 600hp now (random number for example) doesn't mean you have until 675hp before you need the cooler plug. The specs of that particular engine and that particular plug may be such that it's range is 550hp to 625hp which would mean you'd already be close to needing a cooler plug...

  3. #3
    daverxp4's Avatar
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    i thought denso iridium ixu27 was not an NGK (NGK/Denso)?

  4. #4
    Quote Originally Posted by daverxp4
    i thought denso iridium ixu27 was not an NGK (NGK/Denso)?
    I was looking for plug cross references on those 2 sites in particular, NGK and Nippon Denso, the IXU27 are Denso`s and the DCPR8E are the NGK`s.

    Sirch, will damage occur with the stock heat range plug?

    let`s put a few things into the equation: water temps, 70-75,
    air temps 75-90, comparing to those who run in the south, which is much hotter all the time. I see your point about the 2 heat ranges for the dif temps per year...PR...

  5. #5
    Legend in my own mind Sirhc7897's Avatar
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    All depends on the level of modification (sorry there's no straight answer)...We won't even worry about hull modifications (even though they do affect motor load but usually everything that's a pursuit of speed reduces the load in this regard)...

    I would imagine just a CAI would be no big deal. Probably in truth neither would the Riva/Vortech SC imp as the added power is minimal...Going to the lower operating temp thermostats will help as well...I also doubt the thru hull would cause a problem...(don't quote me on any of these)...

    Now once you start talking external intercoolers, several pounds of additional "boost" (be it through the rotax imp or the Les stuff) I think you almost have to go 1 range down just to be safe...I mean the $30 it costs for a set of plugs is just good cheap insurance vs running the risk of leaving a plug in there that can't disipate the added heat being built and it acting almost like a glow plug and causing serious deto...

    For me props would fall into this category as well since a steeper prop is loading the motor but that tends to go hand in hand with the mods as mentioned above...

    The added rpms of the ECU's would probably fall into the "go a range cooler" category as well. Think about it...You turn an extra 300-500rpms with them and that's just that many more times per minute that cylinder fires and generates heat...

  6. #6
    Sirhc: well said, I do have the IXU27`s in my modded ski, I am amazed at how many dealers (locally) or the marina`s do not stock the plugs we use. The only one I found were the DCPR8E`s, which is stock. No Denso`s, and no NGK 9`s anywhere. If I were in a pinch for immediate set of plugs, I`m beat ...I have almost all of the aforementioned mods you quoted except the RR ecu, I`m installing the RXP ECU soon, thanks for the info!...PR...

  7. #7
    PWC Rider & Racer RXPBeast's Avatar
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    So running a stock RXP with nothing but a 4" air intake with a big filter would not be necessary to change plugs? ( but may not be a bad idea? )

  8. #8
    i have s45x HKS on my ski that the same spec to denso'ixu27
    they do best
    but...they gone in competition just from 3/4 moto

    i run my ski with
    1.reflashed ecu
    2.rr thermostat
    3.rr s/c clutch and power filter
    in ixu27 and hks s45x have about 0.031 oe gap but stock dcpr8e has0.028

    1from3 plugs, the iridium center electrode was collapse-lean down that increases the space between cemter electrode and ground electrode.

    so i turn back to NGK DCPR9E or IX

  9. #9
    Novice: how are you able to use the DCPR9E`s, the ends of the plugs are solid, they don`t unscrew? what ski do you have?...PR...

  10. #10
    they come w/o nut like the dcpr8e from brp so u can run it on 4tec
    denso comes w/o nut too

    my ski is 05 rxp

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