Good treah from bill, for stock X4 also when he tested an rossier pipe
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Jun 2008
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Re: Pump pressure/cold pipe
Quote Originally Posted by burton2323 View Post
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
Last edited by Mr. Bill; 06-21-2011 at 01:18 PM
