Pump pressure/cold pipe

[burton2323]

Bill, I know your not exactly fond of rossier pipes, but I have a question or rather a scenario and wanted to see if it makes sense with you..

The stock prop in my 96 XP was pretty chewed up. The leading edges were all dinged up and the trailing edges were slightly bent. I was seeing 7150-7200 rpms @ 59.5 - 60.5 mph gps, with a 105 jet in the midpipe and a 185 in the stinger. My gf's brother has a 96 XP and bought a solas XO, so I threw his stock prop in mine in place of my chewed up one. His stock prop I threw in was literally new looking, all edges perfect no dings or bends at all. With the mint stock prop in I now see 6700 - 6800. Highest I saw was 6850 @ 59.3. The pipe stays ice cold after a WOT run also, when it used to get decently hot. Now for the question..

Would it make sense that I could lose almost 400 rpms because the perfect stock prop is creating much more pressure in the pump therefore cooling the pipe more?

I put a 100 in the midpipe this afternoon but the river is so choppy I cant hookup at all, I need to wait to near sunset when its glass. I also have a 90 that I can try if the 100 doesnt help..

[Mr. Bill]

Re: Pump pressure/cold pipe

Bill, I know your not exactly fond of rossier pipes, but I have a question or rather a scenario and wanted to see if it makes sense with you..

The stock prop in my 96 XP was pretty chewed up. The leading edges were all dinged up and the trailing edges were slightly bent. I was seeing 7150-7200 rpms @ 59.5 - 60.5 mph gps, with a 105 jet in the midpipe and a 185 in the stinger. My gf's brother has a 96 XP and bought a solas XO, so I threw his stock prop in mine in place of my chewed up one. His stock prop I threw in was literally new looking, all edges perfect no dings or bends at all. With the mint stock prop in I now see 6700 - 6800. Highest I saw was 6850 @ 59.3. The pipe stays ice cold after a WOT run also, when it used to get decently hot. Now for the question..

Would it make sense that I could lose almost 400 rpms because the perfect stock prop is creating much more pressure in the pump therefore cooling the pipe more?

I put a 100 in the midpipe this afternoon but the river is so choppy I cant hookup at all, I need to wait to near sunset when its glass. I also have a 90 that I can try if the 100 doesnt help..

First, I have nothing against Rossiers pipes. In fact Charlie sent me one to mess with as soon as he got the first castings machined.
I bolted it onto a limited class 95 or 96 XP and headed to the lake. My rpm was about 6900 with the XO or the Skat Trak impellor installed ( cannot recall which prop but I never used rthe X1 but once, and that was on a different 96 XP with a FPP Spec2.

I called Charlie told him what I had and asked him to give me suggesstions to pull some rpm out of the pipe. He had a few ideas that I tried and none did better than the way he shipped it.

So, I tried a few of my own ideas and eventually got 7150 rpm after a few tries.

There were no Jetworks valves back then, so everything we did involved hoses, fittings and jets

I removed the WR from the muffler and placed a brass fitting with a jet in it into the WR hole in the muffler.

I put a 1/2 x1/2 x3/8ths Tee spliced into the main water line from the jetpump. At the end of that hose, I used a 3/8thx1/4x14 Y. One for the stinger and one for the muffler hoses.
Then I started trying combinations of jet sizes. I cannot recall the size jet at the pipe, but I think I had a 65 in the stinger and a 140 in the muffler.

I believe my range of pipe jets was between 125 and 90 and I settled on one of those jets.

It makes perfect sense that you would lose a ton of rpm with a non bent impellor.

It also makes perfect sense that the water pressure went up, probably by about 30 psi.

An oem impellor is very good at making water pressure, as at idle, the water psi is around 5 psi and over 40 psi at 6700 or more.

The psi will change with different pitch impellors, but all provide plenty of water pressure unless they are bent or cavatating.

When the pump is cavatating, very little water is pushed into the engine.

59.3 and 60 mph is not worth haggling over, if it took 400 extra rpm to see that 60 mph.

Do you have stock nozzels on your boat ? I ask because your GPS MPH readings sound too high for a '96 XP using an oem impellor turning the same as stock 787 rpm.

I have been tuning these boats since they were new and I have yet to ever see a boat go faster than stock when it has an oem impellor and it turns oem rpm. How is that possible ?

Either somehow your hull as a lower drag factor as it crosses the water, or the jetpump is producing more than oem thrust.

The average 1996 XP top speed when new was below 57 mph.

If you have a 1995 XP 800 Limited version in stock form, the best I ever saw was 58.1 on the radar, but usually more like 58.5 mph. And that was on one boat, the other three were at 57.6 to 57.9 mph.

All Radar tests were using the normal sitting position with riders in the 150-185 lb range.

6850 + oem impellor = about 56.8 on a smooth water pass at Sea Level, but you can gain almost 1 mph if on salt water.

The problem with GPS readings is in order to get perfect calculations for the GPS to convert distance and time to get speed numbers is the item being measured has to travel in a perfectly straight line.

All of my tests were done in the exact same format at least 3 passes and all were recorded on a stationary mounted Stalker Pro Radar gun with all of the bells and whistles availible at the time of purchase, including the software and cable to connect to a laptop. The readings were averaged to achieve a honest evaulation of the speed of the 1996 XP.
My radar gun was recalibrated by the California Highway Patrol several times and each time it was reading exactly what it was susposed to be reading. It was a $2250.00 purchase directly from the manufacture. It was not some K band radar or something.

If a person knows how to get max speed out of 2 seat runabout using his body position/weight to his advantage, usually there is an extra mph that can be had on any 2 seater or sport class boat.

Bill O'Neal
WCM

[burton2323]

Re: Pump pressure/cold pipe

Cool, thanks Bill you answered every question I had dead on.

Yes I have r&d 85/88 nozzles, and the 59.3 run was the best I EVER saw with the perfect non bent OEM impellor. If I can remember absolutely correctly that was at 6850, but very possible it could of hit 6900 for a second.

My waterbox is plugged, and I have a 185 in the stinger with a jetworks valve. With the new OEM impellor I have tried a 105, and a 100 in the midpipe. Im going to go throw the 90 in now and see what I can get rpm wise, my GPS is dead.

Any tips on installing midpipe jets while the headpipe is still on the ski? Cant get a flathead at the right angle in there to start threading it in, so Ive resorted to stabbing a toothpick down the jet and starting to thread it in like that

[Mr. Bill]

Re: Pump pressure/cold pipe

I have never been a fan of placing a hole into the core of the pipe right behind the water hose fitting, and even less of a fan if it is an obscure place that is difficult to work with.
I absoulety do not remember where that jet hole is, and what your screwdriver is hitting that keeps you from being able to get a straight shot at it. If I knew that, I might be able to suggest something else other than the toothpick. I can only imagine the difficulty it is to rejet a pipe using a toothpick and not being able to even see where the threads are. I like Charlie alot but he must not have known better to allow it to be placed there.

They probably used an engine in a dyno to design the pipe, using the stock pipe as their guide for where stuff like mounts and such all line up when installed. The water fittings on oem pipes are not always easy to get a clamp onto when the engine is in the hull and the pipe barely clears the gas tank.

I have slid the gas tank forward on many jobs that required removing the flywheel. The trick to moving the tank forward is to lift the front of the tank about 2 inches, then move it forward or have someone push it forward from the engine bay. Remove the strap for the oil tank as it stays where it is hanging from the oil tank filler hose. You might want to unhook the front strap on the gas tank too, but not the rear strap unless you have to. It is easist if you siphon out the gas first.

Bill O'Neal
WCM

[burton2323]

Re: Pump pressure/cold pipe

Cool thanks for the tips. yeah its a pain in the a$$ to change midpipe jets on a rossier pipe while its in the ski. Im referring to the brass elbow that is connected to the front head fitting water line. I can get a flathead bit in a 7mm socket on a 3/8ths ratchet in there to tighten and loosen the jet but as you know jets are brass and unmagnetic. They thread in about a good half inch past where you can reach/touch. If there was something to grab onto and thread them in that would be great, but I have no idea if there is. Hence me thinking of a toothpick to just start the thread then get the rest with the ratchet.

[Mr. Bill]

Re: Pump pressure/cold pipe

Mikuni makes some tools for rejetting their carbureators, it is possible that they have one that you can insert the flat screwdriver into the jet, twist the handle, and have the middle of the flat blade turn 90 degrees to latch onto the jet.

I know that a tool like that exists because I have one, but because mine is straight and about 6 inches long, you would not be able to use it while the pipe is in the boat.

Mikuni has one with a bend in it that might just work, I just do not know it it has a device to hold the jet like my screwdriver has.

I think there may be a picture of it on the Hot Products website in their catalog. It might even be in the Mikuni manual for the SBN's that we so often talk about here. I think I downloaded the Mikuni manual from the link at the Sea Doo fourm for Free OEM Manuals where the service manuals for all of the models of Sea Doo's are found.

The Superstore here sells the oem Mikuni jets, kits, N&S's and the Mikuni Tools and maybe you can see it in their catalog.
You guys should be supporting the Superstore over alot of the other places to get parts because they gave you this forum for conversing with others about technical problems. Their discounts are pretty good too on everything they sell.

Bill O'Neal
WCM.

[burton2323]

Re: Pump pressure/cold pipe

absolutely, and I get everything from the superstore. it's just the smallest main jet they have is a 105..

they have the best shipping too

[Mr. Bill]

Re: Pump pressure/cold pipe

I do not know anyone that carries a main jet below an 80 or so. I have most main jet sizes above the 75 or 80 up to 180 or so in my personal jet storage box that I use myself. Well, I mean Chris has it now at my shop for his use.

If you bought something from us, he might send you one, as otherwise it would cost us about $10 just to mess with it. If he has one he could send you, it may have been used or it could be new. I know I have used those sizes many times during my pipe rejetting and testing days, as I was the very first pwc shop that sold pipe jetting kits for Sea Doo's. I quit after a few others got into it because it is hardly worth the time to put a kit together and sell it for what some of my copycats were selling them for a year or two later.

Plus, water jets in pipes can burn up alot of expensive parts when they get clogged up, and it only takes one grain of sand to clog a pipe jet. But, the carbon buildup on the jet can also clog a pipe jet, even if each jet is filtered. I hate selling stuff that I know people will neglect to clean everytime they ride their boat, or get near the beach sand or a sandbar. Been there done that, do not recommend it to recreational riders.

Bill O'Neal
WCM