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  1. #1
    Kiwi spanner handler
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    thoughts on blown piston

    Hi,
    Just pulled this from a rxpx260 with a new xx2 charger and all the riva stage 3 things they recommend
    Went for about 10 mins most of that warm up and checking temp and rpm etc
    The top of the piston has opened the ring groove up by each valve relief and melted by the intake releif
    This is the front piston the other 2 look ok
    Really need to know why this has happened so it wont do the same again with new pistons etc
    Fuel was fresh and our highest octane pump gas.
    The ski had 27hrs from new all social riding and had the stage 2 set up for most of that with no issues
    Was running 8550 rpm and 74 degrees with the lower temp thermostat
    Thanks..



  2. #2

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    Waaaaaaaaaaaaaay too lean, irrespective of where the timing is

  3. #3
    boost junkie skidoochris's Avatar
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    classic death by detonation, your 95 octane (usa 90) is too low
    you learned the hard way, you must check the tune afr
    lean afr can also increase deto

  4. #4
    What did your AFR's look like? I assume with those mods you're not running blind?!?!

  5. #5
    JT jpt7779's Avatar
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    What tune were you using? Where you data logging? Where you monitoring AFR and logging it? FPR? What injectors?

  6. #6
    Kiwi spanner handler
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    This is a customers ski and was running 98 octane (NZ) which is same as 93-94 us. Riva states 91-93 us octane, the only reason he went for the riva kit was so he didn't have to use an afr gauge etc neither him or myself are comfortable playing around with maps etc and the kit is said to be ready to go
    Best case we would see 15 psi
    Using the riva 1000cc injectors
    The map we ran was specifically sent to us by tech support
    If the maps are that far wrong they shouldnt supply a map and just say must be tuned but they dont and you would think to be on the cautious side they would be richer not lean

    KXR60-SD10STG3-58psiP-308.MYp is the name of the map

  7. #7
    In theory, you would think it should be a complete plug n play system, but it isn't and cannot ever be when you're winding up the power output. At stock OEM is the 'safe' limit as decided by BRP. Anything more than stock, you need to dial in your specific ski to. There are so many variations between skis, conditions, etc. When you start moving into 'stage 3' mod level, you're deep into AFR monitoring, fuel controlling etc.

    The stock fuel pressure reg is notoriously poor, if the ECU / tune is pushing strong timing, there's no way it could pull the timing enough to save you from poor fueling - despite having knock detection.

    There is no such thing as a 'safe' out of the box standard mod. Sorry.

  8. #8
    GasResearch-VT.SE's Avatar
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    This is how I charge my customers for example:

    -Drop in map: 750-800 "Concrete warranty - You drive this off the concrete of the workshop, thats as far as the warranty goes"

    -Water tested with AFR drilled and adjusted map: 1100-1300 depending on the ski. Then I also give either a print out or a screen shot of the AFR chart to the customer as proof that due diligence was done. VTECH logged individual piston retard and AFR.

    Its just horsing around to think that you can drop maps in at Stage 2+ and hope it works. Maybe some tuners are more conservative too. I know that locally here in Melbourne it was known that 20 hrs was about the max you could get from a "race tune" on non afr tested ski before it went booom at another shop.

    Do it properly or don't cry about it when it doesn't work.

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  10. #9

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    Quote Originally Posted by skidoochris View Post
    classic death by detonation, your 95 octane (usa 90) is too low
    you learned the hard way, you must check the tune afr
    lean afr can also increase deto
    You're off your face if you think that damage has been caused by a couple of points low in octane .. It seems to be your generic answer to anyone overseas with an issue. Please find a new tune to play.
    We run our 91 in 260s with no issues.. It's only 15psi.. Our 95 pump is more than fine for it


    I know the fuel he is using.. Have have burnt many 1000s of litres of the exact same stuff. 99% of it on a dyno.
    There is nothing wrong with the fuel, it's basically the Motorsport standard in New Zealand.
    15psi on a 8.5:1 motor at 9000rpms is kiddies stuff..
    24psi, 9.5:1 and 9500 on an engine with a long rod will tell you if the fuels any good.. And it's fine.

    That piston has been REALLY lean. No ifs or buts, especially given the run time
    Either the fuel pump if falling over up top or the injectors arnt 1000cc assuming the tune is even close.
    I'm yet to see a classic detonation failure depicted by anyone- broken ring lands and rolled rings.
    Have seen a couple of cracks in 2 Pistons but inconclusive.
    I believe the simple reason for this is the rod ratio and lack of dwell, and hence why so much advance can be run.

    Post some macro photos of the plugs, valves and ports.
    Was the fuel BP or Mobil 98?

    Jason - I'm out of the county for 4 wks (flew this morning) but if you would like to PM me or when I'm back go through the setup just let me know.

  11. #10
    Kiwi spanner handler
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    Was BP 98 and injectors were new 1000cc will get them checked and have just drilled and tapped the exhaust for 02 gauge.
    Will get motor back in next week just waiting on rod bolts as on backorder. At this stage will go through the map work it out and add some more fuel then go check readings and fine tune from there.

    ps I didnt realize asking questions and seeking advice was considered crying!

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