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  1. #1

    Join Date
    Dec 2005

    GP1530R Stage II+++ Step by step instructions

    My black ski, a Stage II+ 2000 GP1530R

    Over the past couple years I have had a lot of help from other forum members. I used all of this input when putting together this ski - as always - thanks guys. A special thanks to HopatcongGPR for his help with setting up the motor and to 2fast4u for all the help he has provided me setting up the handling components. Thanks to Mark for explaining the pump stuffing issue to me.

    Safety Issues

    The GPR has several major areas that have to be addressed when building a modified ski capable of 80+ mph.

    1) Intake grate

    The stock intake grate is unsafe at any speeds above 65 mph

    There have been numerous reports of Riva/R&D intake grates breaking

    The ski has been known to buck using a stock Worx or Pro-tec grate

    This means there really isn’t a safe intake grate available. On my ski I have resorted to building my own intake grate using billet aluminum pieces welded together.

    2) Intake Grate Bolts

    The intake grate bolts need to be upgraded to the next larger size

    3) Inserts (pump shoe, rideplate and intake grate)

    All of the OEM inserts need to be replaced with replacement inserts that are made from flat pieces of aluminum. The flat bars spread the force over a large area making it impossible to pull the insert through the hull.

    4) Pump Tunnel Reinforcement

    The pump tunnel needs to be reinforced. This can be done with a fiberglass reinforcement piece, a R&D carbon fiber reinforcement kit or with layers of fiberglass cloth and Epoxy resin. With the SMC hulls any glue or resin used must be epoxy based in order for it to stick to the hull. If you have a 2003 or newer hull I would suggest you use the fiberglass reinforcement piece or the R&D carbon fiber tunnel reinforcement kit.

    5) Pump Pressure Relief

    The faster you go the more water gets forced into the pump tunnel.

    The more angle you put on the rideplate, the higher the front of the hull rides in the water which opens up the pump tunnel more to the water which forces more water into the pump tunnel.

    These 2 forces act together and cause the pump to get over stuffed – this commonly happens at speeds around 78 – 80 mph. When the pump over stuffs the ski bucks, it is like you ran over a log, the rear bounces up, here is where it gets real nasty, sometimes the front chines dig in and the ski does a violent left turn.

    One fix to this problem is to add pressure relief fittings to the 2 inch pump spacer.

    6) Steering Nozzle

    Steering nozzles. The cheap plastic POS that sits in the sun everyday needs to be replaced every couple years or switch to a R&D or Pro-Tec aluminum model.

    Modified Rideplates – a few comments

    After a R&D or old style Riva rideplate has been modified by Jim or Island Racing quite a bit of material has been machined off the plate. Doing this significantly reduces the strength of the plate. I believe it is inevitable that one of these plates will fail at high speed. It might fail on its own or maybe it will be helped by hitting something floating in the water, but fail it will. For this reason I will be working with a new style Riva plate. This style plate does not require as much material to be machined off.

    My Black Ski – Overview

    To make the HP I wanted I decided to use 90 mm pistons while retaining the OEM exhaust. The crank was also stroked 2 mm. This resulted in a displacement of 1527.

    These 1500 cc motors make a lot of HP. I saw a 500 rpm gain (this translates into approximately a 35 HP gain) when compared to my unported 1300 motor. My 1300 is no slouch either, it has all of the common bolt-on upgrades including 48 Novis, VForce reeds, Riva head at 170 lbs and Riva CDI.

    The 1500 motor spins a Solas Dynafly impeller pitched at 14/27 a respectable 7170 rpm.

    With a Solas Concord VX110 impeller pitched at 18/24 the rpm is also in the 7170 range.

    Using trim tabs, with a 1200 grate it is an 80+ ski. With an 800 grate it is an 82+ ski.

    On HopatcongGPR ski, with no trim tabs, his best was 84+ .

    The motor – 1530 cc

    GP1200R cylinders bored to 90 mm and ported by Lowell Horning
    GP1200R OEM machined to provide .035 inch squish and 165 lbs compression
    One layer of a GP1300R head gasket - 1300 gasket proved to seal better than the 1200 gasket when opened up to 90 mm
    Power valves locked in place - working PVs are not required with 90 mm pistons
    Pistons – custom 90 mm Wiseco pistons (designed by HopatcongGPR)

    Water Cooling- Reverse Flow

    Double cooling was added to the pump. Cooling water is routed directly to the cylinder head from the pump, from there it exits the exhaust manifold using 3 custom fittings, 2 lines are routed from the manifold to the exhaust pipe and the 3rd line from the manifold is bypassed overboard.


    Ported by Lowell
    For pistons 87 mm and larger the cases have to be opened up to provide clearance for the piston skirts.


    Work done by Crankworks
    Stroked 2 mm
    True and welded

    Misc items

    Flywheel – Vildar Charging

    Electrics – OEM electrics with Seadoo coils and MSD plug wires

    CDI – R&D CDI using their BB curve

    Fuel Tank - XL1200 Limited

    Fuel Sender - The black trap door was removed and both of the sender feed lines in the tank, main and reserve, were extended and “clunks” were added to the end of the lines

    Red fuel selector switch – removed. Both the reserve and main sender fuel lines supply the carbs.

    GP1300R 2 Inch Pump Spacer – installed and 2 pressure relief holes were added


    Old style Riva GP1200R ride plate.

    Rideplate mods I did:

    - machine (or grind) on the rear mounts to increase the angle
    - grind notches in the bottom of the plate so that it will fit around the bottom of the 1300 2 inch pump extension and pump
    - bottom riding surface was trued flat
    - angle the front of the sides of the plate (this is Carl's (Island Racing) mod 4 or Jim's FF mod)
    - grind on the leading edge of the plate where the notches for the transom are

    In order for the rideplate to fit, the bottom of the pump and the bottom of the pump nozzle had some material removed to provide additional clearance.

    When installing the plate I will be positioning it so the rear tip of the plate is somewhere between .930 and 1.00 inch higher than the bottom of the pump shoe.

    At the same time I ensure the sides of the ride plate don't sit lower than the pump shoe and hull. I always check this with a straight edge. It is OK to have a small step up from the shoe to the center flat section of the rideplate. My step, measured at the side of the plate is .025 inch or less.

    Rideplate Angle & Pump Shoe Discussion

    Skegs versus No Skegs

    Contrary to previously promoted packages there is current evidence that rideplates without skegs are faster than plates with skegs. Though there is no argument plates with skegs will corner with less slipping / sliding.

    Trim Tabs

    R&D trim tabs with the rear section of trim tab cut off. This makes the trim tabs the same length as OEM tabs. The R&D trim tabs are thicker and angled that is why I prefer them to the stock tabs.

    Tabs shimmed down .100 inch all 8 mounting bolts. For a more stable ride you can use a larger shim and/or you can add an extra .040 inch shim under the rear mounting bolts (ie .100 in front and .140 inch rear)

    I found with more than .100 inch in shims I lost speed.

    Filling Pump Shoe and Rideplate mounting holes with epoxy putty


    Danny’s Stepped Sponsons


    OEM D plate with the opening made .200 inch larger

    GP1300R waterbox and sound suppression box

    2005 GP1300R header pipe

    I drilled a whole in the exhaust mounting bracket. This allows you to see the tuning T handle on #2 carb.

    Exhaust manifold was polished (extrude honed).

    Jetworks Mod


    In addition to the Jetworks valve I use a manually adjustable valve that allows me to control the amount of water that enters the waterbox at WOT.

    Air to Motor

    In stock form the GPR motor is starved for air. You can raise you RPMs by allowing more air into the motor area. To fully satisfy the motor air demands it doesn’t take much.

    Air Opening

    Create an air opening on the right hand front cowling (to match the left hand cowling). Use a sharp exacto knife and cut away the black plastic as shown above.


    Storage Bucket

    I have also cut holes as shown above in the inside layer of the windscreen and in the top of the storage bucket. If you don’t want to make the holes in the storage bucket you can simply remove the storage bucket and leave it at home when you do speed runs. I have 2 storage buckets, one with holes and one without. I use the storage bucket without holes on rough water days when I am concerned with water intrusion.

    Do not cut holes in the windscreen and storage bucket if you ride in the surf.

    Steering Nozzle

    Protec nozzle - 9 mm longer than OEM - same diameter as OEM - oh yeah it is metal so it won't break like the cheap plastic OEM nozzle

    Protec Nozzle Test

    The cheap crappy stock one works fine - it just breaks and that was the reason I replaced it - I saw no speed gain from the Protec nozzle.


    Delta VForce II reeds with a reed spacer plate. There have been some failures reported for the VFII reeds. I am hoping with the spacer plate I won’t have any problems with them.


    48 mm Blackjacks

    Pilot 122.5
    Main 165
    N/S 2.5
    80 gram spring

    This motor uses a lot of fuel, I would strongly recommend using the larger XL1200 tank with a BB motor.

    Pump Plug Kit

    After installing a PPK you should take a long straight edge and see if the pump shoe is sitting down below the hull line. If it is, it needs to come off and be reinstalled. When I install the PPK I do not use the rubber pieces that sit in the holes in the bottom of the shoe. (this way I never have the problem of the shoe sitting too low) When sealing the shoe to the ski I focus my effort on ensuring the large gap between the pump shoe and the transom is filled.

    When mounted, I want the shoe to be recessed up into the hull. I found the sweet spot to be a range between .05 to .07 inch. By this I mean the shoe riding surface is .05 to .07 inch higher than the bottom of the hull. Coincidentally .070 inch happens to be the thickness of a nickel.

    Intake Grate and Shoe

    I am using an OEM pump shoe properly sealed with a custom hand made billet aluminum intake grate

    I am also using a modified Worx intake grate. (Do not use a stock Worx grate with a modified Riva or R&D rideplate)


    It is not safe to use the OEM intake grate on a modified GPR.

    Comments on OEM intake grate

    Impeller and Pump

    I am using a 2005 GPR pump with the VX110 bearings and VX110 short driveshaft. A second driveshaft was custom built which then allows this VX110 pump assembly to work in my GPR hull.

    The primary impeller I am using is the Solas Concord 18/24 designed for the VX110.

    I do not use an impeller nose cone.

    Pump Nozzle

    87 mm GP1200R nozzle.

    I added an electric bilge pump and I removed the pump nozzle siphon tube and blocked off that opening with JB Weld.

    The visibility spray hose was removed and that outlet from the nozzle was blocked off using JB Weld.

    To provide clearance for the angled rideplate the bottom of the nozzle had some material removed using a hand grinder.

    The mounting surface where the nozzles matches up to the pump was machined to increase the nozzle angle to 6 degrees.
    Last edited by philip_gpr; 07-26-2008 at 08:47 PM.

  2. #2
    Join Date
    Feb 2007
    Cape Town, South Africa
    Fantastic post. Any chance you can post some pics of the pump shoe, rideplate, etc ?

  3. #3
    mtrager's Avatar
    Join Date
    Jul 2006
    Orlando, Florida, United States

    Thumbs up

    As always awesome info Phillip.

    What a ride that would be.

  4. #4
    Quite interesting Philip, thank you for the info and please keep us posted on how it performs. Franks 1500 has serious holeshot problems, how's yours?

  5. #5
    Moderator RX951's Avatar
    Join Date
    Apr 2005
    League City, Texas

  6. #6
    Moderator OsideBill's Avatar
    Join Date
    Mar 2006
    United States
    Nice post Phillip. What type of BlackJack Carbs I-Body modified or SBN modofied? looking at the jetting I am guessing I-Body

  7. #7
    305coco's Avatar
    Join Date
    May 2007
    cape coral, florida USA
    phillip you run a riva head @ 170 lbs and a stock sound supression ?

  8. #8
    BLACK MAGIC HEADERS hydrojunkie's Avatar
    Join Date
    Jun 2007
    new york
    phil fantastic job on your post. i found very usefull ideas from your thread. great job

  9. #9
    spud's Avatar
    Join Date
    Jul 2006
    Oceanside, California
    Did you take any pictures of your intake grate? Did you perform any secondary treatments to it after the initial fab work (shot peen, normalize, etc.)?

    This whole intake grate thing has me wary.

  10. #10
    YudLuz2's Avatar
    Join Date
    Jun 2005
    Flowood MS
    Quote Originally Posted by VOODOO View Post
    Quite interesting Philip, thank you for the info and please keep us posted on how it performs. Franks 1500 has serious holeshot problems, how's yours?

    If you seen Frank's old prop you would know
    why. He has a new one now, should be
    much better.

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