Other Pump cone & Exit nozzle Basics

[FlightPlanDan]

Found nothing in Tech Faq section.
Looking for some education on the subject. I realize that there are 1000 set-ups for different motor/pump combo's, but, there must be some basic rules of thumb.
Bored nozzles vs. stock nozzles, stubby cones vs. stock cones, and combinations of both.

 

[JetManiac]

Bored nozzles vs. stock nozzles

Larger nozzle increases the flow through the pump. It makes the prop seem shorter. So if you want to spool up faster then a larger nozzle will help.

Stubby cones vs. stock cones

Shorter pump cone will also increases the flow through the pump. It makes the prop seem shorter. So if you want to spool up faster then a shorter nozzle will help. Shorter cones are more for low and midrange and dont work well at high flow rates. The longer cones work better at higher flows and speeds.

 

[JetManiac]

Shimming the prop forward from the stator vanes will also 'loosen' pump when tuning and cutting back a prop and moving it closer will 'tighten' response. The closer to vanes is more efficient all things being equal.
But there is no perfect setup for any given setup. It is best to start what has worked on a comparable setup and then tune from there.

 

[FlightPlanDan]

Swapping out cones is simple enough to do on the beach.
The exit nozzle's not that big of a job either.
Gonna have to try a few things in the water.
I think my current set-up might be "too many mods" and not enough motor.
Can't say for sure til I swap things, but I think I've actually lost thrust with the bored nozzle along with the stubby cone and the cutback impellor.

 

[JetManiac]

What impeller? Your new XS motor?

 

[FlightPlanDan]

What impeller? Your new XS motor?

12/17 Skat swirl

This was going on b4 the motor work. Have not had it in the water since rebuild. It's getting turfed now, then it will be done.
It's gonna be very different in a lot of ways.
I won't likely change anything until I get used to it.

It's now 737, ported top to bottom and side to side.

 

[Quinc]

I put on a blowsion stubby cone and didn't notice a difference compared to the stock cone. Not sure if that means I should bore the nozzle or change impellers etc though.

 

[kevbo]

I put on a blowsion stubby cone and didn't notice a difference compared to the stock cone. Not sure if that means I should bore the nozzle or change impellers etc though.

Stubby cones on stock pumps make no difference. Boring the nozzle will increase thrust, I use 85mm. The small hub 12/17 is about right for most 701/760 cylinders. the exhaust port height, pipe, compression, and ignition timing will determine how responsive it will be. A high port/low compression engine may need a flatter impeller.

 

[Quinc]

Stubby cones on stock pumps make no difference. Boring the nozzle will increase thrust, I use 85mm. The small hub 12/17 is about right for most 701/760 cylinders. the exhaust port height, pipe, compression, and ignition timing will determine how responsive it will be. A high port/low compression engine may need a flatter impeller.

Running a Solas I 13/15 and the pump is blueprinted. I also have a swirl 12/17 large hub I am thinking about trying.

 

[KTM434]

Can't say for sure til I swap things, but I think I've actually lost thrust with the bored nozzle along with the stubby cone and the cutback impellor.

Make sure your pump is sealed properly. Those changes you listed as long as you didn't change impeller pitch should gain thrust (quicker response and hookup) since cutback impeller improves pump efficiency at impeller to stator section and the nozzle/cone combo reduces resistance of exiting water. Your current listed setup should be best for your riding unless you're wanting a narrower pitch for gained response or a more loose feel by shimming the prop more IMO