Can I get a "cliff's notes" version of how the water injection into exhaust works?

[scooper77515]

I understand that the water regulator allows water into the exhaust at low speeds, then shuts the water flow off at high speeds. I would think it would be the other way around.

How about the water injected up just after the exhaust manifold?

I just had one burn up on me and want to better understand how it works so I can better watch it in the future.

I think I need to keep the exhaust cool to the touch at all times, right? Even at wide open throttle?

 

[Dr Honda]

First... the water shouldn't be cut completely otherwise you melt things.


OK... the cliffs notes version.


2-stroke engines work on the scavenging principle, and tuning the exhaust can yield HUGE gains in power. One of the effects is how the pressure wave travels though the pipe. A cold pipe lets the wave travel slow... and a hot pipe lets it travel fast. So... when the RPM's are low, you want to slow wave so it is in time with the engine speed. Then inversely, you want that wave to speed up, as the engine speed climbs.

The result is good low end torque, AND high speed scavenging.


On something like a dirt bike, or snow mobile... you have to chose where you want the peak power to be with your tuned pipe... but in a water craft... we can move it around by injecting water.

 

[scooper77515]

Alright! Makes sense.

So based on that i can tune (at least a little) how much water is injected and impede or increase performance.

So can i use pipe temp as a tuning tool? I have rebuilt the entire cooling system and when reassembling the water regulator i set it as the book states(3 turns out) and would like to keep the pipe cooler a touch even if i lose a bit of top end.

At least that is what i am thinking at this point in time...

 

[Dr Honda]

Alright! Makes sense.

So based on that i can tune (at least a little) how much water is injected and impede or increase performance.

So can i use pipe temp as a tuning tool? I have rebuilt the entire cooling system and when reassembling the water regulator i set it as the book states(3 turns out) and would like to keep the pipe cooler a touch even if i lose a bit of top end.

At least that is what i am thinking at this point in time...

I haven't looked at the regulator too much... but honistly... if you wanted to stay cool, and didn't care if you lost a few HP up top... then you could remove it, and just put a fitting with a changeable jet. The smaller engines (like a 720) don't have the regulator, and just have a fitting with an orifice to control the overall water volume.

 

[scooper77515]

I have read about that but since i already have "a fitting" there and it is adjustable, I figured i would adjust it to where I like it to be.

At least I found that it wasn't my regulator that overheated my engine, but a clogged line.

But I figured maybe I could mess with the regulator while I am making adjustments.

 

[WAJetboating]

2-stroke engines work on the scavenging principle, and tuning the exhaust can yield HUGE gains in power. One of the effects is how the pressure wave travels though the pipe. A cold pipe lets the wave travel slow... and a hot pipe lets it travel fast. So... when the RPM's are low, you want to slow wave so it is in time with the engine speed. Then inversely, you want that wave to speed up, as the engine speed climbs. The result is good low end torque, AND high speed scavenging.

That is the best and most concise explanation of that principle I've ever seen. Excellent summary!