water injection can any one explain how it works pls

[joe23687]

water injection can any one explain how it works and advantages of it over a after market pipe with out ?

 

[Spimothy Leary]

water injection can any one explain how it works and advantages of it over a after market pipe with out ?

I can't explain the mechanical end of it, but on a 787 Factory Pipe (spec 1) when you turn off injection while riding its like somebody hit the brakes.....! i'm serious, it makes quite a bit of difference.

in general it pulses in water into the pipe and disrupts the sound, or pulse, or sonic wave, something like that, basically its tricking the motor to respond like it has more torque, you don't really get more top end, you just get there faster, approx from 3,000 to 5500 rpm's you get that extra pulse, and extra power.

i've never tried it or ran it with a stock pipe, but imo its worth it for an aftermarket pipe

 

[griz400]

its pretty intresting how the water through the pipes works, heres an article where a "dry" pipe may give a better low end and midrange, but if you read u suffer high end rpms gained by factory pipes
http://www.factorypipe.com/art_s720injection_chamber.php
also, it will be a quite bit hotter in your boat, on a hot day, me, i wouldnt do it on a ski, to hot on my ass

 

[Spimothy Leary]

water injection on my ski (96 xp) made absolutely no difference what so ever as far as heat is concerned, the only thing i noticed is that it went from 10mph to 50 before you could blink.

its seems like it would make sense on a boat, but from what i've read, the first boat performance mod should be the prop, not factory pipe.

 

[seadoosnipe]

I can't explain the mechanical end of it, but on a 787 Factory Pipe (spec 1) when you turn off injection while riding its like somebody hit the brakes.....! i'm serious, it makes quite a bit of difference.

in general it pulses in water into the pipe and disrupts the sound, or pulse, or sonic wave, something like that, basically its tricking the motor to respond like it has more torque, you don't really get more top end, you just get there faster, approx from 3,000 to 5500 rpm's you get that extra pulse, and extra power.

i've never tried it or ran it with a stock pipe, but imo its worth it for an aftermarket pipe

Your in the right direction. The water injection on the 787, per se, is a two part system. During low rpm's, water is injected at the tuned pipe, just aft of where your cooling system starts the pre-heat loop. This cools the exhaust gases, changing density and therefore, changing it's resonance. The sound wave is directly related to "back pressure". The pressure wave during lower rpms, isn't that far away from the exhaust, therefore, water is introduced closer to the manifold. At wide open throttle, the water injection at the tune pipe is shut off, and sent to the water box, at the water regulator. That's because at higher rpms, the sound wave travels further before it can bounce a usable sound wave to counter the next oncoming sound wave. The way the exhaust is set up, the gases actually pass through the water box and then, upward into the exhaust pipe, always having some source of backpressure. The systems without the water box, have a exhaust pipe that loops upward, over the shaft before it exits the boat. This keeps water in the lower end of the exhaust system.

There are probably a million different ideas on how resonance works. But, you can bet all the racers and high tech motors, use this sound wave to their advantage.

 

[Chester]

Some good basic information here. I'll explain it in further detail.
When the piston comes down and the exhaust port opens, the expanding exhaust gases escape as well as a sonic wave. As the piston goes down further, the transfer ports open and allow the fresh air/fuel charge to enter the cylinder. The piston continues down through bottom dead center and then as it goes up, it pushes some of the air/fuel charge out the exhaust port. The sonic wave travels to the end of the pipe (the convergent cone) then bounces back towards the cylinder and if it's timed right, the sonic wave pushes the escaping air/fuel charge back into the cylinder just before the rising piston closes the exhaust port. A longer pipe works better at lower RPM and will cause the sonic wave to take longer to return as it allows the piston to come back up. Conversely, at high RPM, a shorter pipe is more desirable as it reduces the time it takes the sonic wave to return to the cylinder. Also, the speed of the sonic wave depends greatly on the exhaust temperature. The higher the temperature, the faster it goes.
So, if you have a pipe that is tuned for high RPM (short pipe) you will have good top end but a mediocre low end acceleration. If you inject water into the exhaust stream at lower RPM, it cools the exhaust gases and slows down the sonic wave causing it to act like a long pipe. As the engine speeds up, the water injection shuts off allowing exhaust temperature to increase and the sonic wave to speed up. This gives you the best of both worlds.
RAVE valves also change the timing of the sonic wave. As RPM increases, the RAVE valves move up and the exhaust ports open sooner to release the sonic wave quicker.

Click the link. :coolgleam:

http://upload.wikimedia.org/wikipedia/commons/5/52/Arbeitsweise_Zweitakt.gif


Chester

 

[Spimothy Leary]

Some good basic information here. I'll explain it in further detail.
When the piston comes down and the exhaust port opens, the expanding exhaust gases escape as well as a sonic wave. As the piston goes down further, the transfer ports open and allow the fresh air/fuel charge to enter the cylinder. The piston continues down through bottom dead center and then as it goes up, it pushes some of the air/fuel charge out the exhaust port. The sonic wave travels to the end of the pipe (the convergent cone) then bounces back towards the cylinder and if it's timed right, the sonic wave pushes the escaping air/fuel charge back into the cylinder just before the rising piston closes the exhaust port. A longer pipe works better at lower RPM and will cause the sonic wave to take longer to return as it allows the piston to come back up. Conversely, at high RPM, a shorter pipe is more desirable as it reduces the time it takes the sonic wave to return to the cylinder. Also, the speed of the sonic wave depends greatly on the exhaust temperature. The higher the temperature, the faster it goes.
So, if you have a pipe that is tuned for high RPM (short pipe) you will have good top end but a mediocre low end acceleration. If you inject water into the exhaust stream at lower RPM, it cools the exhaust gases and slows down the sonic wave causing it to act like a long pipe. As the engine speeds up, the water injection shuts off allowing exhaust temperature to increase and the sonic wave to speed up. This gives you the best of both worlds.
RAVE valves also change the timing of the sonic wave. As RPM increases, the RAVE valves move up and the exhaust ports open sooner to release the sonic wave quicker.

Click the link. :coolgleam:

http://upload.wikimedia.org/wikipedia/commons/5/52/Arbeitsweise_Zweitakt.gif


Chester

nice post chester