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Thread: 3 stage jet - performance improvement scenario

  1. #1
    Join Date
    Dec 2007

    Default 3 stage jet - performance improvement scenario

    Trying to make an educated decision instead on the impact of a couple different modifications to my current configuration:
    wooly classic
    350 fi
    standard posi nozzle
    19 overlap 19,24 - rebuilt impellers in good condition(rebuilt about 20 hours on em).
    WOT almost 42
    falls off step around 32
    cruise 34-37 depending on load - typical load is 4 souls plus gear and dogs for the weekend cabin trips 70 gallons fuel.
    Observations in a friends boat running a carbed 350 on a 500 mile trip:
    running 22,22,22 impellers
    changing out posi and using a T3 (so larger "throat" on the nozzle and crappy steering):
    Increased speed at a given RPM
    Increased Fuel efficency
    What will happen to WOT,Cruise RPM,and Speed?
    Scenario 1:
    re pitch middle impeller to 22 (no other change)?
    Scenario 2:
    replace posi with a scott/flo-pro and open up to 96mm (no other change)?
    Scenario 3:
    Re pitch middle impeller to 22 AND replace/bore out POSI to 96?

  2. #2


    The one thing that you have not put into this. The only true comparison is if you have the same boat to compare to. Different boats will preform different with the same eng. and jet set up. A change in your boat may effect it different that the same change in your friends boat.

  3. #3
    Join Date
    Jul 2010
    Fairbanks, AK


    I have a 21' Wooly classic with a 6' wide bottom. I built up my 302 to about 330-340 hp (about the same as the EFI 5.7) and had to re-pitch. I went from 19 in the back pair to 22 and kept the same overlap up front since it was oversized for what I had anyways. With 2 people, 2 dogs, 60 gal. of fuel, and a few days worth of gear, and on the ocean, I was getting on step at 28-29, cruising around 32-33, and maxing out at 42. Unloaded with two people I averaged around 7-7.5 gph running around Valdez arm/PWS over a three day period. I did try hard to keep the 4 bbls from opening. Hope this helps any. Also, I have noticed that my Wooly loves everything loaded in the back. I've tried to "Balance" the loads like all my buddies with Extreme Shallows and other Jon style boats and she hates it.


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