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Supercharged apex....won't spin past 9000rpm

Discussion in '4 Stroke Turbos/Supercharger' started by Woody255, Jul 9, 2019.


  1. Woody255

    Woody255 Veteran

    Messages:
    25
    Location:
    NW ON
    Country:
    Canada
    Snowmobile:
    Vmax4's
    Hi all,
    I have an Apex built for snow drags with an MPI s/c, stage 2...2 1/2. Running 18-19psi at 10,400 on pure C14+. PC5 with Autotune, POD300 data logger etc. This was built a few years ago and has dominated the local snow drags. At the end of the season, I began having a few issues with the throttle bodies coming lose, as I did not have them tethered down securely. That has been resolved, and all was good. At the last heat of the day, I could only run up to 9000rpm, and I still cannot figure out why. No abnormal noise, both S/c belts are good, throttle bodies secure etc. AFR readings are proper, clutches look fine...any ideas out there? Thanks. Woody
     
  2.  
  3. gouldsjett1

    gouldsjett1 Lifetime Member Lifetime VIP Member VIP Member

    Messages:
    185
    Location:
    maine
    Check your boost tube connections from the s/c to the front of the intercooler.
     
    Woody255 likes this.
  4. kinger

    kinger VIP Member VIP Member

    Messages:
    6,221
    Location:
    Clear Lake, IA
    Have you changed anything in the clutch recently?
     
  5. Woody255

    Woody255 Veteran

    Messages:
    25
    Location:
    NW ON
    Country:
    Canada
    Snowmobile:
    Vmax4's
    No, haven’t changed anything. It was working great, and the very next pass it wouldn’t pull the rpm.
     
  6. maim

    maim Moderator Staff Member Moderator Lifetime VIP Member VIP Member

    Messages:
    4,891
    Location:
    sudbury on
    Country:
    Canada
    Snowmobile:
    2016 apex xtx/ 2011 apex xtx/ 2009 phaser rtx/x/ 1997 et410t/r
    how heat soaked was the sled? where clutches hot?
     
  7. MrSled

    MrSled Administrator Staff Member Admin Moderator VIP Member

    Messages:
    18,265
    Location:
    Schofield, WI
    Country:
    USA
    Snowmobile:
    2017 Sidewinder
    I would do a leak down test. Don’t sound good. How much boost?
     
    74Nitro likes this.
  8. kinger

    kinger VIP Member VIP Member

    Messages:
    6,221
    Location:
    Clear Lake, IA
    Have you checked the throttle blades are opening fully at WOT?
     
    MrSled likes this.
  9. Woody255

    Woody255 Veteran

    Messages:
    25
    Location:
    NW ON
    Country:
    Canada
    Snowmobile:
    Vmax4's
    It did not get hot. Engine runs perfectly, just simply won’t climb to full rpm. My first though was a SC belt failure, but they are ok....I will do a compression test to be sure, but I do not think it’s an engine problem.
    Mr.Sled, 19psi
     
  10. mbarryracing

    mbarryracing TY 4 Stroke God

    Messages:
    1,729
    Location:
    Springville NY
    Country:
    USA
    Snowmobile:
    2006 Yamaha Attak Turbo
    2015 SR Viper RTX-DX
    1996 Vmax 600XT
    Does it rev / pull hard right to 9000 rpm then flat-line?
    Same with boost? Jumps up then flat-lines? If so, maybe if your SC has an internal sprag type clutch it might be that it's now junk / slipping when reaches a given boost level... Seen that happen on certain model MPI SC's (aren't repairable), and have that happening right now on a SC Wave Runner.
     
  11. Woody255

    Woody255 Veteran

    Messages:
    25
    Location:
    NW ON
    Country:
    Canada
    Snowmobile:
    Vmax4's
    Yes, that’s what’s happening. All seems well until I run 100% throttle. Happen to have any photos ? Thanks
     
  12. stone88

    stone88 VIP Member VIP Member

    Messages:
    510
    Location:
    Ontario
    Check for boost leaks
     
    ClutchMaster likes this.

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