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  1. #1
    TheElite0ne's Avatar
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    VTech Tune - What is Max RPM for stock fuel system

    With summer here already in Florida I've lost almost 300rpm due to the increase in water and air temperature. In efforts to save a few bucks I was toying with the idea of putting the stock prop back on to bring the RPM back up. I'm guessing my RPM will be in the 8600 range with my current mods on a stock prop.

    I was going to try the 48 8650 169 36 38 AGR 101 tune.

    Would this be safe? I have the SuperTech Valve Spring & Retainer upgrade so I know the valvetrain can support the RPM... but what about the stock fuel system? I do not have an AFR gauge. Does the stock fuel system have enough fuel to support ~8600rpm with the stock X-Charger?

    Anything else I should consider?


  2. #2
    Autism Speaks. Its Time To Listen gOt BoOsT's Avatar
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    you shoukd be fine fuel wise with the stock 48's and x charger, but you need a wideband to be sure a/f is in line

  3. #3
    GOO$E Mongoose2's Avatar
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    you'll be fine

  4. #4
    JFizzleJR's Avatar
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    Quote Originally Posted by TheElite0ne View Post
    Does the stock fuel system have enough fuel to support ~8600rpm with the stock X-Charger?

    Anything else I should consider?
    You won't have to worry about the fuel pump maxing out. Before that happens you can go with larger injectors. But as the others said above it should be well within the safe range, especially since the map is made for the injectors you have already.

  5. #5
    Nothin' better than Doo'in it! BigDaddyRXP's Avatar
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    Before you do anything.... I would highly recommend two things.

    1. Adjustable fuel pressure regulator

    2. a/f gauge

  6. #6
    GasResearch-VT.SE's Avatar
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    Quote Originally Posted by TheElite0ne View Post
    With summer here already in Florida I've lost almost 300rpm due to the increase in water and air temperature. In efforts to save a few bucks I was toying with the idea of putting the stock prop back on to bring the RPM back up. I'm guessing my RPM will be in the 8600 range with my current mods on a stock prop.

    I was going to try the 48 8650 169 36 38 AGR 101 tune.

    Would this be safe? I have the SuperTech Valve Spring & Retainer upgrade so I know the valvetrain can support the RPM... but what about the stock fuel system? I do not have an AFR gauge. Does the stock fuel system have enough fuel to support ~8600rpm with the stock X-Charger?

    Anything else I should consider?
    Short answer. Yes.
    I've done this setup 3 times now and 2 of them I've checked on AFR after and found both to be low 12's on WOT.

    But this setup is on the limit of injectors with sometimes an overrun of 100% DC.

    Bite the bullet and get some VT11's, fuel pump and AFR setup (Even if its cheap and temporary).

  7. #7
    VinceC's Avatar
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    Quote Originally Posted by GasResearch-VT.SE View Post
    Short answer. Yes.
    I've done this setup 3 times now and 2 of them I've checked on AFR after and found both to be low 12's on WOT.

    But this setup is on the limit of injectors with sometimes an overrun of 100% DC.

    Bite the bullet and get some VT11's, fuel pump and AFR setup (Even if its cheap and temporary).
    Could you explain this for dummies like me?

  8. #8
    dnielsen's Avatar
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    Quote Originally Posted by VinceC View Post
    Could you explain this for dummies like me?
    He said he has ran that setup on two different skis before and found that the engine ran lean as hell (you could melt the pistons from excess heat). He suggested you run larger injectors than the stock 42s along with an adjustable fuel pressure regulator so you can tune the engine AFRs to a desired mix. Raising and lowering FP will change your Air to Fuel mix. He also highly recommended you install an O2 sensor with a gauge attached so you will be able to see what changes you are making or otherwise what AFRs you are running.

    12.9 AFR = 12.9 parts air to 1 part fuel mix = LEAN (very hot)
    11.8 AFR = 11.8 parts air to 1 part fuel mix = GOOD
    10.5 AFR = 10.5 parts air to 1 part fuel mix = RICH (too much fuel)

    The above is only for you to understand what the AFR is all about and is typical for our forced air (supercharged/turbo) applications and will vary with different RPMs (WOT), boost ranges (some have extremely high boost and RPM ranges requireing even more fuel at WOT).

  9. #9
    VinceC's Avatar
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    Perfect. Thank you. I don't want to hijack this discussion here but I'm ready to do a Vtech upgrade to a stock ski. I heard about possibly needing to do a fuel regulator and sensor and want to understand more.

  10. #10
    Brd-Prey's Avatar
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    Quote Originally Posted by VinceC View Post
    Could you explain this for dummies like me?
    Get Ed to do it!
    Plus your ski has 48 lbs injectors, you will only have a problem if your fuel rail pressure is significantly below 58psi which some factory ski's have been found to have.

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