Intro

I have never met Randy, except in cyberlife, but we have people we know in common. Mark Dent, springs to mind, his Dyno design & manufacturing company is literally 10 min. walk away from my place. Both of them are Horse Power freaks, I truly believe that Mark designed his own Dyno & started the company to build them, simply to save time after "tweaking" his bike. :-}

Randy is just as "possessed" and has dug deep in the books and pulled up really esoteric stuff, used it, tweaked it, and re tweaked it ( cut a long story short:-  see this ). He has covered most of the usual porting / pipework I am sure but what I like is his work on "different" subjects like "still air box design" and the piece I present here:-

WATER INJECTION

By Randy Norian

An old trick, injecting water into the exhaust pipes is a very effective way to cool the pipes and lower the operating range of an expansion chamber. I obtained a copy of an SAE paper 931506, expanding the torque curve of a Two Stroke Motorcycle race engine by exhaust water injection", by Robert Fleck at QUB.

In this paper, they built a simple system to inject water into the head pipe of a 125cc test motor and recorded power gains of up to 24% in the lower midrange. I decided to copy their set-up and was able to reproduce their results on the dyno. After that, I decided to built a usable system that would function smoothly on my street / race bike.

But first, some numbers.:-
Fleck recorded pipe temps at several points along the exhaust pipe. In the diffuser, without water injection, he recorded gas temps rising from 425 Deg C at 9000rpm, to 510 Deg C at 10800 rpm. With the water injection active, the same sensor recorded temps of 150 degrees Cat 9K RPM, rising to 420 Deg C at 10800 rpm.

Lets go back to the equation for tuned length.
If we consider a stock RG500, this distance is about 84cm, (33 inches) and Exhaust opening is 188 degrees. Using Vs of 1700 fps, this formula predicts a peak power RPM of 9684 RPM. This is a pretty good estimate, as my bike peaked at 9500 rpm in stock form.
Now we consider Vs with water injection active, let's say we have a mean 200 degree C drop in gas temps. If we use Vs of 1700 fps with no water, this figures to a new Vs of about 1430 fps with water.

Plug that into the equation for tuned length, and our same exhaust pipe is now tuned for a peak of 8150RPM. So we have been able to shift our peak power down almost 1500 rpm, by injecting water. Obviously, this will reduce the peak rpms of our motor, so the trick here is to turn off the water at some point and let the engine rev out normally on top.

If we were able to cool the pipes all the way down to room temperature, the stock Gamma would have a peaking RPM of just 6270 RPM. Clearly, pipe temperature has a huge role in determining the rev range of a pipe / port combination.
Controlling pipe temperature is an effective way to alter the tune of a 2 stroke.

This is how I have the water injection system installed on my bike:-

I use an NOS rpm switch, which senses the tach signal on the blue / white wire, and arms the system between 6000 and 8400 rpm. In order to inject water, the motor must be between those rpms and also there are 2 switches that control the system, one senses when the powervalve is in the high rpm position, and the other is a throttle position switch. So, half + throttle, revs between 6k and 8400 rpm, and valves "shut" will inject water. The entire set-up is turned on or off by a master switch on the dash.

I use a variable exhaust valve controller made by BDK, and the dial for this is also on the dash. so, wherever I set the exhaust valve, the water will come on in synch with the valve. A 3 qt tank is mounted under the tail. this feeds a generic windshield washer pump (through a filter). The pump puts out 5 psi. This injects into the head pipes through #70 round head Mikuni main jets. Bungs welded onto the pipes accept brass fittings, which have jets tapped into them where they go into the pipe, and have 6" of 1/8 steel brake line leaders coming out to keep from melting the plastic water lines.

I have 3 psi check valves installed just upstream of the jets to prevent water from siphoning into the pipes. I will get you the correct size of the brass fittings-The 3 qt tank has a low level indicator, which lights up the side stand indicator when the water is low.

This set-up will provide about 180 seconds of injection to 4 pipes. That sound like a lot, but it lasted hours in frequent use in mountain riding. On the track, 1 qt doesn't lasted me through a 20 minute practice session.
The only real problem I have anymore is the switch on the powervalve, which is cheap and keeps failing one way or another. I guess I need to drive PAST radio shack, and get a real switch.

When the water kicks in, there is not a violent burst of power, more of a quick whoooosh, like a turbo spooling up rapidly. It has been very manageable so far, it only remains to fine tune the throttle opening/rpm combination to get the water dialled in exactly. If I were to get trickier, I might pulse the water system, or find a way to taper off water flow so that we might extend the advantage to the highest possible rpm range.

As it is, I simply ran the bike on the dyno with and without water, saw where the crossover points were, and switched the system there. More sophistication is possible, but at this point I feel I am getting 90% of the benefits of a water system. I'm not sure its a good use of my time to chase the last 10% of this set-up!

 This Dyno graph shows, same engine, back-to-back, with water and without.

Next set of internal stingers will just have to have some water bleed outlets, or something, I dunno, but I aim to make the water injection a part of daily life with the TZ barrels and their comparative lack of midrange. I am changing to a 2-stage water injection set-up, prolly with 1/3 -2/3 split of the water, 1/3 system in early and out late, half throttle or maybe 1/3 I dunno,2/3 in the middle of the used range, and at larger throttle openings.

The idea is to taper the water in, and out, to extend the useful range, as it rather kills your top end. Also, at part throttle you don't have enough heat in the pipes to vaporise the full volume of water, this ought to really extend the range on a tank as well, during street riding.

This second Graph shows one of the curves when I first started to dabble.
Unfortunately all my other graphs were lost when the computer got stolen 
from my dyno operator (and he did not take a back-up)

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