Thread: Winter mod list/ideas
12-26-2006, 07:21 PM #1
Winter mod list/ideas
Things I am wondering about and wish I had more info about the impact of on the RXP ...
grind out bilge pump bumps altogether?
Knife edge the nozzle veins? They are flat on top.
Droop snoot nozzle, lower thrust angle, lift bow up?
Vanes in nozzle are slightly 'off' – they do not match to the pump vanes perfectly – should they be bent slightly to be perfectly behind the pump vanes?
Nozzle length … check out this quote from a jet boat racing site: “For drag racing, high top speed is desired, so a higher pitched prop is used. The jet pump nozzle is selected according to the desired pressure. A longer nozzle will produce more pressure, resulting in more speed. A shorter nozzle will develop less pressure, which is good for lower speeds.” Just like guns, rifles develop greater pressure and bullet speed than pistols shooting the same cartridge due to the longer barrel. Hoss mentioned this once and nobody understood, but it is worth exploring. Think about this … we gain speed by going from an 83mm nozzle to an 81mm nozzle, but we might gain even more speed by staying with 83mm and extending the 83mm portion of the nozzle by a few inches … the effect would be similar, since a longer nozzle will increase pressure just as a tighter nozzle will, but it is possible that a longer 83mm nozzle would gain more thrust and speed than an 81mm nozzle. To try this we would have to modify the nozzle and all the linkages so that the steering/trim nozzle would still maintain the appropriate distance/relationship between the thrust nozzle and steering nozzle.
After adding the RE blockoffs, I could not get my ski to porpoise even tho I have a Riva 2 degree wedge. The RE blockoffs make a big change in the hull, possibly allowing 3 – 4 degrees of wedge and possibly increasing speed.
Pump – smooth out internally, eliminate imperfections and bumps.
Match the intake grate and pump shoe and make sure it is totally sealed and smooth.
What is the optimal distance from the impeller to intake vanes for top speed?? Looking at other pwc and impellers, it looks like too close might be bad for top speed, but I don’t know what the optimal distance from impeller blades to pump vanes is …
Grind down the impeller nose even more?? Many of us have gained speed from ditching the impeller nose cones, but would we gain a few additional tenths by machining down the nose of the impeller even more?
Try the new 3 blade – more speed than 4 blade 15/20?? Still not a lot of data on how this impeller works with Stage 2/stock ECU setups but it sounds promising.
More boost makes more horsepower and there are many supercharger options out there now. It sounds like there are turbo systems in the works, stainless steel headers, and maybe better intake manifolds. I would think that once we eliminate the stock intercooler that a more efficient intake manifold design might gain some horsepower.
On the GPR, the front ‘biting edge’ of the intake grate is not flat on the bottom like on the RXP. On the GPR, the intake grate is flat from 12mm back from the opening, but from 12mm forward to the biting edge, the grate rises approximately 4 mm up from ‘neutral’. This would slightly reduce the tendency to suck down to the water, and would allow more water to channel under the grate, possibly adding a bit of lift. The combination of the two would seem to free up the hull a little, and our RXPs have nothing like this, the intake grate is totally flat on the bottom.
I have not yet added Jerry’s skegs, so there is another possible .5+ mph there for me.
I could run 77.3 mph most days, with the seat on and ran a best of 77.7 mph, seat off. My setup is in my signature. Over the winter I will be switching from the Riva 3 inch air intake to a good rear air intake (possibly the Riva setup), and I am switching from crappy undersized 2.5” (flared ends) crush bent muffler pipe to the much bigger and better new Riva metal intercooler tubing. I will also likely be sending my SC to Jerry for ceramic bearings and possibly seeing if he can shim it to .015. The combination of these things should add some rpm … anybody want to guess how many rpms??
I am cleaning up my pump … not sure if this will add any speed, but I want to smooth out the imperfections in the pump and the slight mismatches between the tailcone and pump housing and between the Riva wedge and the pump housing (my Riva wedge actually hung down slightly below the top of the pump housing). I did a little light grinding to try to make sure the water flow does not encounter ridges or bumps. Speed or rpm increase?? Not sure, but it will help …
I am running an electric bilge pump, so I pulled out the plastic bilge pump spigots in the stock nozzle and filled in the holes with JB Weld last year. This winter I have ground out the bumps totally (filled the holes with JB Weld) so that the nozzle is uniform between every vane. Speed or rpm increase?? Again likely not much, maybe 30-50 rpms … but it all adds up.
I will be cleaning up the pump tunnel a bit (I got a bit sloppy reinforcing with West Marine epoxy and carbon fiber last winter) then continuing on into the intake and pump shoe, where there is a noticeable mismatch. I will also be looking at whether I need a little JB Weld there to fill in the mismatch perfectly.
We only have two options to increase speed: 1. Eliminate water ‘friction’ by making sure our undersides are as smooth and efficient as possible, 2. Increase thrust. Time spent sanding and smoothing covers number 1 on our RXPs since there are very few options, try to eliminate any edges or ridges that water encounters. Increasing thrust involves adding hp to the motor, or making the pump more efficient. The engine options are pretty straight forward bolt-ons mostly, but maximizing pump efficiency is not as straight forward or obvious. We now have some good 3 blade impeller options, but not a lot of data yet on whether they unquestionably add speed over available 4 blades, but it sounds promising so far.
I think just with the air mods I will do over the winter I should be able to hit 78.0 mph with the seat on. Then playing with the underside, the pump, 3 blade and 4 blade impellers and tweaking the trailing edge as needed, nozzle changes, more wedge, skegs, and possibly other changes that become available, I hope to hit 79+ mph at 8100 rpms (80mph would be even better) with the stock ECU. Not sure how close I will get, but I wanted to share ideas that others might be able to test before I can. Winter sucks …
12-26-2006, 08:52 PM #2
did you go to an A kit impeller right away, or did you have a vortec/riva prior to? Just wondering what gains you would see from a 1st run riva to an A kit impeller.....
12-27-2006, 12:03 AM #3
Steve, I went from a stock impeller to an A kit later. I ran 76 mph with the stock impeller and eventually ran 77+ with the A kit, so I think the A kit added roughly 1 mph. I never ran the Riva/Vortech first gen impeller. The A kit is better, but my friend Dan ran 77.5 mph with a similar setup to mine except he was running the first gen Riva impeller, but also a good 4" rear air intake setup. So the difference is not huge, maybe .5 mph would be my guess. There is more speed in all the fine details and setup I think. Part of the reason Dan hit that speed was his better air intake and cooler air and water.
One other thing I noticed that I will be addressing is that there is a sizeable ridge that intrudes into the pump just after the impeller liner. The outer pump diameter appears to be smaller than the impeller liner and although the graduation is machined, it is a pretty abrupt change. I intend to smooth out the transition and make it much more gradual.
12-27-2006, 12:50 AM #4
12-27-2006, 02:26 AM #5
Vern.... your ideas are always on target with all the things churning in my mind.
I've tackled 'making' a different intake manifold already, results still TBD
I also wanted to find a way to make an extended venturi and keep the diameter of the nozzle larger... other skis run far larger than 81mm
i've decided it's not even worth talking about these things anymore... where there's a will, there's a way! .... just make it yourself before someone else does and releases it to public for a tremendous price... you make the same product, and it might bite u in the arse and someone makes the exact same thing and sells it, but at least you made it and know what goes into it and what makes it 'work' and it cost you nothing but materials.
... we need rideplates without a built-in heat exchanger
... extended venturis
... i've already done the same as you with the bailer removal and a uniform venturi
... intake manifolds with less volume, or at least better directional air flow (i made one myself)
keep up the brainstorming, you have awesome ideas, but now brainstorm how you can make it yourself and put the ideas to paper, to the work bench, and onto your ski
12-27-2006, 10:42 AM #6
I wish i had a garage to tinker with more stuff when i get those ideas in the middle of the night. Brian already looks at me funny when i show up randomly at his house to tool on the ski.
12-27-2006, 12:04 PM #7
Thanks Steve, nice to hear you are noticing a lot of the same things. Unfortunately I don't have easy access to any facilities to do fabricating so my contributions often can only be sharing ideas, hoping others might agree and maybe have a better chance of fabricating. I will be doing a lot of minor work over the winter, but you are right, I think a longer but slightly larger venturi might really work well. Have you seen the jet pumps and nozzles on V-8 race jetboats?? The nozzle necks down and stays necked down for a long ways ... and those boats haul a$$.
Did you notice any gain from the 'optimum venturi'? I know the Yamaha guys typically gain 30 - 50 rpms when they remove the bailer spigot from their nozzles.
The difference in grates is very visible in the thread on the black and green GPR on the Yamaha side ... the one picture of the pump shoe/grate area shows very clearly how much the GPR grate rises toward the grate opening.
12-28-2006, 08:19 PM #8
- Join Date
- Apr 2005
While your working on your pump fill in the area where the cone is bolted on. You can knock them out if you want to get the cone off.
02-23-2007, 07:20 PM #9
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