gpr 04 vs 05-07

[wishihad1]

i am wondering what the difference between an 04 and an 05-07 gpr...
i kno they put in a new pump, but what gave in the extra 5 hp?

[Chrisrokc]

Power Valves in 2003 and 2004. No power valves in 2005+


Power Valves are a pain but produce better numbers usually I think.

[r33pwrd]

So did the extra 5 hp come from less moving mass of no PV's?

[philip_gpr]

Good question.

Port timing was changed a bit. The header pipe was changed. The PVs were removed. Not sure where the 5 hp came from - anybody know?

[smackwave]

I was under the impression the extra five horses came from improved fuel mapping - at least that's what the Yamaha guys were saying back when the '05s came out. The changes to the exhaust port height and header pipe were to compensate for the removal of the PowerValves. Without them compromises needed to be made to make for a smooth RPM curve and to keep the intake charge in the cylinder at low RPMs.

r33pwrd - the PVs are electronic, not mechanical, so they're not parasitic to horsepower.

[smackwave]

Hmm... R&D is claiming 10HP increase for 03-04 GPRs from swapping in the 05+ header pipe and their exhaust power sleeve. See the bottom of this page:

http://www.rd-performance.com/perfor.../performer.asp

Since I've never heard of anyone actually achieving any performance gains from the power sleeve I'm leaning toward calling BS on this. The part number they give is for the short section of exhaust between the manifold and horseshoe section - about a $300 part OEM. If I can find an inexpensive used/salvage part that's easy enough to swap out and test.

So... I might have to eat crow on this one if the pipe change is helping produce additional HP in the 05+ 1300s.

One other nice change in the later skis - HydroTurf mats from the factory.

[flyboy]

water box is defferent too