symptoms of too short pipe length

[anthony_marquart]

Lets say you're running a boat at a given pipe length and you keep shortening it. Excluding difficult launches, what are the symptoms of getting too short?

Would you actually begin to loose top speed rpm? burn plugs?

I have a sp21 that i know is running a strong engine. IT's a 70mpg motor in the rigger. In my sp21, I have less prop, but I am running the same pipe length thinking of running in the same rpm range. I'm really not seeing the RPM or speed I think I should.

boat is a GP310, NR5p small volume head, AB 21 pipe, sholound x442 with some barcut,. 66% torco fuel.. would the pipe being too short lower rpm?

should I add length to the pipe or reduce prop to a 440 or 1440?

 

[Duck899]

X-440

 

[Kevin Krogness]

I had a tough time with a 1440 in my sport 20 with a go. It went pretty good with a 437 but knoing you have a strong power plat I would try a 1440 and keep playing with the pipe length.

 

[Greg Hahn]

shorter the pipe = less torque more R's the main symptom of short pipe is not enough torque to launch

 

[Brian Sorgente]

Is a sp21 a sport hydro?

 

[shoboat]

Tony,

What pipe? and what length?

Way more surface friction on a Sport 21, it will not allow you to launch more propeller.

Our pipes work much better after the mid-range kicks in. More boat set up and propeller

testing to do still. You may need a better pipe design. CAD design some new pipes?

Keep Working Different Combinations,

Mark

 

[anthony_marquart]

AB parobolic, at 2.5 back from C/L. No problem at all launching.,. I found a point with the S pipe on my rigger where if I had it too short it would lauch but fall of and kind of labor at top end.. The speed was way down from the parabolic pipe. I lengthened the pipe and it ran much better..

 

[Brian Sorgente]

A pipe that's set too short can do a few things but yes, for the most part the shorter it is the less torque you'll have. You will also see more top end revs with a short pipe.

When it's too short it can make the boat hard to launch but typically that just means you tossed it in too lean. Usually you can tell its too short if the boat falls off the pipe in the corner or doesn't really get on the pipe at all. Similar to being too lean but without a frosty plug.

Sometimes that can also point to prop load. Both too much or not enough prop load can limit rpm.. Sometimes it just takes some testing to figure out which way to go.

Brian

 

[Tim_Duggan]

What does it do with a smaller prop on it?