I had a go at this on my TDR a while ago, only a much cheaper version (£15). The basic set-up was a 1.5L bottle, with a windscreen washer motor at the bottom. This fed through a one-way valve, a T-piece, and a couple of banjo bolts into the headers. The water was turned on via the horn switch (just like nitrous used to be done!).

I experimented with various things, and the best result came with no jets in the system, just a slow flow of water into the pipes (using small jets only produced a fast squirt, like a windscreen washer in fact, but flowed the same amount of water as open banjo's) I think the fast stream just squirted right through the gas and didn't vapourise until later in the pipe, wheeas the slow stream spent more time in the gas flow and worked alot better. (Yeah I know it should be a mist....but I'm not spending money on a high pressure pump and proper jets) There's no build up of water in the pipes, as the heat soon vapourises it (unless the one-way valve sticks as I found one morning with water spraying out the pipe as I started it..I got a proper valve after that)



I used it on my first set of pipes, which were a little more revvy than stock. With the horn button pressed power came in about 1000rpm earlier, and noticabley dropped off earlier, so I'd release the button at 8000 and it'd fly off through the top-end as normal. It worked quite well for a budget version, and quite a nice gimmick to brag about.

Since then I've made a new set of pipes which are alot better in the midrange, and so I haven't felt the need to try water into these yet, though I suppose it would make them even more grunty.

As a little experiment I found I could also increase the midrange a little by using 2-3 exhaust gaskets, effectively lenghtening the pipes and retuning their rpm range.