Pump Pressure Data

[Duke]

After rebuilding my ported 1300 I added a pressure gauge to moniter pump pressure. Very interesting findings just during breakin.

At 20/30mph the pump already had 10-15psi ! At 50mph the pressure had climbed to 20. Keep in mind this is with 2 3/8 lines bleeding pressure off at the 2" extension.

It was noticeable when the valves would open causing the gauge to flutter and rapidly drop but as speed increased to over 65 the pressure would start to rise around 30+psi again!

This came to quite a shock to me! Especially with 5 times the amount of area being relived as first thought necessary.

I will keep posted of full throttle results as the motor is broke in.

[JIM'S PERFORMANCE]

awesome testing Duke, Keep us up to date.

[Hydrotoys]

Pretty cool, to see the differences, isn't it!

[Hydrotoys]

• approx 10psi at 35mph.
• approx 20psi at 55mph.
• approx 40psi at 65mph, and up.

You could watch the needle "jump" right before the ski did over 40psi.

This was with a single 3/8" relief.

[Duke]

• approx 10psi at 35mph.
• approx 20psi at 55mph.
• approx 40psi at 65mph, and up.

You could watch the needle "jump" right before the ski did over 40psi.

This was with a single 3/8" relief.

Very intersting to watch whats going on in the pump. Yesterday was my second tank of gas through the new motor so I was still limiting myself mechanically by throttle adjustment to a little over half. However did manage to get into the low 70s a couple times but the pressure never went over 30psi. Most likely due to the 2 valves instead of one.

Another note is that I have gone 170 miles through the river and even took a couple shortcuts through some wet grass and the valves never clogged yet. I hope yours was a just a freak event on Lake Pleasent that day because I sure like the way the valves have worked so far.

[Insanediego Joe]

Im still not convinced this is the only answer to the buck. Not saying you guys are saying it is.

My ski 84.8 mph , no buc at all not even a hint. Two holes drilled under the intake grate and a modified 800 grate. Smooth as silk. I guess we will have to wait and see what happens at 85 plus to be sure. So far So Good!

[Duke]

Im still not convinced this is the only answer to the buck. Not saying you guys are saying it is.

My ski 84.8 mph , no buc at all not even a hint. Two holes drilled under the intake grate and a modified 800 grate. Smooth as silk. I guess we will have to wait and see what happens at 85 plus to be sure. So far So Good!

Not in any way shape or form trying to indicate this is the only way. It worked for me and proved it to myself back to back but surely there are better and more efficient ways. It does however reduce pump pressure with I think is very important to the lifespan of these hulls. Also boat becomes more stable at full speed the more pressure I relieve. No bounce at all.

[N8R]

Im still not convinced this is the only answer to the buck. Not saying you guys are saying it is.

My ski 84.8 mph , no buc at all not even a hint. Two holes drilled under the intake grate and a modified 800 grate. Smooth as silk. I guess we will have to wait and see what happens at 85 plus to be sure. So far So Good!

Joe do you have any pics??? the holes are they in the intake grate or the 1.5 from the sides in the bottom of the pump shoe?? do you notice any bottom end cavitation??thanks

[Insanediego Joe]

Joe do you have any pics??? the holes are they in the intake grate or the 1.5 from the sides in the bottom of the pump shoe?? do you notice any bottom end cavitation??thanks

Nate, the problem with the conversion skis is the torque. I can spin any prop as long as I want to out of the hole. So the real question is have I suffered any additional cavitation by drilling the holes? The answer is absolutly not. Let me see if IO can dig up some pics for you.

[Duke]

Nate, the problem with the conversion skis is the torque. I can spin any prop as long as I want to out of the hole. So the real question is have I suffered any additional cavitation by drilling the holes? The answer is absolutly not. Let me see if IO can dig up some pics for you.

Have you tried a Skat pump yet? If so what kind of speed loss if any? Did you try the DF in the Skat?

[Insanediego Joe]

I have not tried a skat as of yet. I sent Jerry my 12 vein skat and he ran a skat prop with a 1200 grate and the cavitation was less but still unacceptable during a full pull from a dead start. Im beginning to think that a 158 mm skat pump is the answer to the cavitation.

[Insanediego Joe]

Nate here are the pics.

[N8R]

Nate here are the pics.

that you very much Joe .... i think i will try it i dont have a buck but, figure it may give the ski a little lift if it cavitates on me i will fill back with marine tex.what size are the holes??

[Hydrotherapy]

joe does the rxp lump weigh more than the gpr lump in full running spec,could the weight gain over centre of ski help at all with you not seeing the buck,or is it so small its not going to help...

just thinking out loud and i am sure its a silly question..

[Insanediego Joe]

that you very much Joe .... i think i will try it i dont have a buck but, figure it may give the ski a little lift if it cavitates on me i will fill back with marine tex.what size are the holes??

Thats the beuaty of drilling th holes there. Its so simple to refill and go back to stock.