2000 Yamaha GPR

If you have interest in sponsoring this project, with either parts or discounts, please email me at hydrotoys@yahoo.com

Intake System: I'd prefer a 4" system with the flame arrester buried up inside a splash proof area of the steering. I have a 3 to 4 reducer off of ebay. This will be one of the last things to get built.

Cooling System: The stock Rotax system is an automotive style closed loop system, utilizing the rideplate as a radiator. While very innovative, it is very limiting. In the GPR, I'm looking at two different systems to try. The first way utilizes the stock closed loop system, and replaces the rxp rideplate with a 80,000 btu water/water heat exchanger. The open loop cooling will cool the heat exchanger, which in turn cools the closed loop Rotax system. Obviously the other model to use would be an after market open loop panel, and cool the engine similar to a stock gpr. Light, and less parts, this may be the way to go. I will use 5/8" water lines from the pump... the largest I've ever used on a gpr to try and build pressure and volume within this massive unit.

The "other" cooling system, is a standard open loop lake water system to cool the intercooler, and pipe jacket. This is regulated by an orifice to control flow/pressure to around 38 psi at WOT. Eventually, I'll look into separating these two systems so that cooling water can be increased to the intercooler, without affecting the exhaust loop. The exhaust loop is purposefully kept very, very warm.

Exhaust System: The RXP waterbox sits at a near 30 deg angle to the engine and driveline, which means the "J-pipe"  between the manifold and waterbox is very short. Instead a Rotax Racing Waterbox was adapted. A modified Rotax Racing "through-hull" pipe was mated to the stock GPR exhaust outlet. GP12r Fuel Tank Modification: The XLT utilizes an 18 gallon fuel tank. I had hoped to install this in the gpr however, the RXP fuel pump is too shallow to sit flush against the bottom of the 18 gallon tank. I'm not sure if this is a problem or not, but I'm not willing to introduce more problems at this time so I'm sticking with the rxp tank.
Motor Mount System: The gpr uses a four point non-symetrical mount system with round retarded non-parallel runners from front to back. They are even a different height from each other... lovely. The rotax uses a 3-point symmetrical system. The gpr hull depth is close to 1" more shallow than the RXP which requires some inner hull trimming. The Rotax oil cooler hits the starboard stringer. In fact most of the engine hits the starboard stringer. The mount system is a tad bit short to clear the engine length. The starboard mount was moved back nearly 4" to clear the block. All of this, was to get a clean alignment for the drive shaft, as well as retain a weight distribution near the gpr, if not a few inches aft. The holes in the inner liner will be filled with a combonation of carbon fiber, fiberglass, and hole filler. Eventually, the mount system will be integrated into the hull for rigidity.
  Driveshaft coupler modification: The driveshaft system on the GPR uses a pretty standard rubber biscuit and bearing feed through. The RXP uses a type of feed through designed by cavemen and a doughnut. It utilized a crowned driveshaft to offset mis-alignment, with a hard floating seal that trys to destroy itself. There is no mid shaft support. It's all driven off of the engine and the pump. Very stupid sloppy design with built in failure. Popular discussions on the forums are how to repair it. Rotax Racing offers a two piece design, but it is too long for my application, and the rear driveshaft is not needed. A local spline company is designing a splined intermediate shaft adapter as well as modifying the RXP driveshaft to fit it, so that I can continue to use the stock gpr driveshafts and shaft  bearing supports.

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