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  1. #1

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    Screw the hull mod's. . .

    Screw the hull mod's. . .

    RXP folks have the disadvatage of a hull that's designed for rough water and ride-quality. It's been discussed here that the GPR folks go fast by reducing hull drag. The sacrifice is stability and rough-water capability.

    I have recently tried 2 hull mod's in an attempt to go faster with a fixed hp level.

    1) I built a custom intake grate that blocks off roughly 20% of the opening. The result was barely any increase in top speed, but a drastically reduced holeshot (would barely get on a plane at all with GPRyan as my witness).

    2) I read a book on hull design. It talked a lot about the purpose of chines and how they create lift. In order to increase the effectiveness of the RXP chines, I installed something similar to Skegs at the outter edges of the chines on the rideplate. This is to redirect the water that's split by the vee downward and create lift. They worked, as the rear-end of the ski rode noticably higher out the water than before. However, apparently, these tabs created more drag than they reduced. The result was a reduced top speed and some, let's just say, non-optimal handling characteristics. I almost bit the dust at 78 mph when I let off the throttle.

    From here on out, I'm will be going after speed the old fashioned way: Brute Horsepower. It's more fun that way, anyway. Plus, the acceleration is better. I've decided that I like the nice, stable, water-plowing RXP hull. I'm going to embrace what we have. If we wanted speed via low drag, we shoulda' bought GPR's.

    And besides, it's my nature to build hp to get speed, rather than the finesse route. I have a 4000 lb car that runs in the 9's in the quarter at nearly 150 mph, and a 5000 lb daily-driver truck that runs 13's stock. I guess it's just who I am... The GT32 turbo will be on the way soon. In keeping with the theme of the "Budget Bomber", I'll be going with a $750 non ball-bearing turbo rather than the $$$ BB units.



    Mike

    P.S. This post is mainly for entertainment purposes. Though, as they say, there's a little bit of truth in every joke.
    Last edited by engineermike; 07-13-2008 at 02:44 PM.


  2. #2
    Treemn's Avatar
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    Thanks for the great info.

  3. #3
    Brute horsepower..........I agree, it is more fun.


    I don't think the RXP hull is worth a damn in the rough though. The RXP-X is better due to the larger intake, but I think the only thing helping the RXP in chop is it's weight. It is a very stable hull though. I can't tip it.

  4. #4
    Website may not be suitable for small children WOT's Avatar
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    Quote Originally Posted by engineermike View Post
    Screw the hull mod's...From here on out, I'm will be going after speed the old fashioned way: Brute Horsepower. It's more fun that way, anyway. Plus, the acceleration is better...

    Hear hear.

    Let it be known by all ye not necessarily present either via silent acknowledgment or by nonexistent proxy that we will no longer be engaged in the fruitless pursuit of minimized hull drag and will instead employ methods of brute force to obtain the necessary terminal velocity and acceleration so dearly sought after in accordance with the Greenhulk credo of whose veracity we hold to be self evident:

    "The more boost you make, the more fun you are going to have..."

    Let it be said on this day, the 13th of July, of the year Two Thousand and Eight, that hull work is a girly pursuit best left to those who have minimal power or who are seeking speeds that can only be rationalized by an aberrant death wish. And, that real men prefer to be blown.

  5. #5

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    Now that's some funny stuff.

  6. #6
    Mike, I forgot to ask...what are your expectations with the GT32 turbo over your current turbo?

  7. #7

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    Quote Originally Posted by RXP-REX View Post
    Mike, I forgot to ask...what are your expectations with the GT32 turbo over your current turbo?
    As best I can tell from the compressor maps, my T3 60 trim (T series equivalent to a GT28R) is running about 67% compressor efficiency. At the same pressure and flow, the GT32 would be around 76% efficient. With ~10% more efficiency, the compressor discharge temperature will be around 20 deg cooler (250 deg F versus 270 deg F). And we all know what cooler IAT's are good for. . . [monster truck announcer voice] BRUTE HORSEPOWER[/monster truck announcer voice]

    Also, since the compressor is more efficient, then it will take less exhaust energy to spin it. Furthermore, with a larger, higher flowing turbine of the GT32 (~25% more flow area), the turbine will power the compressor while producing less upstream pressure. Less upstream pressure means the pistons aren't working as hard to push the exhaust out, which means more power to the prop at the same boost level. On turbo systems in general, the key to making big power is keeping the exhaust pressure down.

    All in all, I expect about gain about 30 hp over the current at the same boost level.

    Also, I'm going to build a bolt-on stainless water jacket to go over the turbine housing. In-hull heat is a real issue with these turbo setups.

    Mike
    Last edited by engineermike; 07-13-2008 at 05:44 PM.

  8. #8
    Gone in 3.0 seconds... RXPT400's Avatar
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    Quote:
    Originally Posted by engineermike
    Screw the hull mod's...From here on out, I'm will be going after speed the old fashioned way: Brute Horsepower. It's more fun that way, anyway. Plus, the acceleration is better...


    Hear hear.

    Let it be known by all ye not necessarily present either via silent acknowledgment or by nonexistent proxy that we will no longer be engaged in the fruitless pursuit of minimized hull drag and will instead employ methods of brute force to obtain the necessary terminal velocity and acceleration so dearly sought after in accordance with the Greenhulk credo of whose veracity we hold to be self evident:

    "The more boost you make, the more fun you are going to have..."

    Let it be said on this day, the 13th of July, of the year Two Thousand and Eight, that hull work is a girly pursuit best left to those who have minimal power or who are seeking speeds that can only be rationalized by an aberrant death wish. And, that real men prefer to be blown.
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    06 RXT - Metal washers, S3 SC, XS IC, Groco, 4" rear air, 42# Inj, Skegs, holes filled, intake grate ground flush ??? gps

    '07 Ultra 250X - Wife's ride Trailer drop mod (picked up .5 mph, go figure), Pump wedge, rideplate holes filled 67.3 gps
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  9. #9
    bron1c's Avatar
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    Quote Originally Posted by WOT View Post
    Hear hear.

    Let it be known by all ye not necessarily present either via silent acknowledgment or by nonexistent proxy that we will no longer be engaged in the fruitless pursuit of minimized hull drag and will instead employ methods of brute force to obtain the necessary terminal velocity and acceleration so dearly sought after in accordance with the Greenhulk credo of whose veracity we hold to be self evident:

    "The more boost you make, the more fun you are going to have..."

    Let it be said on this day, the 13th of July, of the year Two Thousand and Eight, that hull work is a girly pursuit best left to those who have minimal power or who are seeking speeds that can only be rationalized by an aberrant death wish. And, that real men prefer to be blown.
    Are you another one of those guys on extremeforum.net
    that hail from Smartassatoa?

  10. #10
    Moderator RX951's Avatar
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    CC'd to Yamaha for discussion
    http://www.greenhulk.net/forums/showthread.php?t=65167

    I tend to think that we do not lose or sacrifice much in the handling dept when more angle is applied to the rideplate. Other factors can be applied such as shimming out trim tabs to help with rough water handling. Rideplates such as Jim's performance give us the best of both worlds.
    The GPRXP is popular right now....eh.....

    .02
    Last edited by RX951; 07-13-2008 at 08:11 PM.

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