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Homemade Water injection (ideas?)

I've been considering a water injection system for my 94 S4. With all this
talk on IC design and water injection on the Quattro motherlist, I thought
I'd jump in.

There are 2 basic WI designs:
1. Pressurized Reservoir Design
Reservoir pressurized with manifold pressure and injected with a washer
pump. This is the most common homemade system, and is what Spearco is
selling (with a nice aluminum tank). The Spearco kit costs about $150.

2. Fancy High Pressure Pump
This involves using a high pressure (>4 BAR) pump that draws fluid from
the washer (or other) reservoir, and injecting at high pressures. ERL
sells a system like this (see link attached) for about $500.

I like option number #2 since it should provide higher injection pressures
and a finer mist - But there is no way I'm willing to pay that kind of
coin for a fancy pump, a $10 pressure switch, and $10 worth of injector

I invision my homemade system working as follows:  
- manifold pressure switch set to desired boost level (about 14 psi)  
- cockpit switch to turn on system
- relay to provide power to pressure switch if cockpit switch is on AND
washer reservoir low switch is not tripped
- pressure switch wired to pump
- when the cockpit switch is enagaged, the reservoir is full, and
the manifold pressure is above the setpoint, water is injected into the
cross over pipe just before the intercooler

Since I use a boost controller in my car, I will wire a set of NO contacts
off the relay to the scramble signal of the controller to turn up the
boost a few pounds. I also plan to install an EGT gauge to make sure I'm
not going overboard.

The only missing piece of the puzzle is where to source a small high
pressure pump? Can I use a high performance fuel pump or will water cause
it to sieze?

Any other suggestions or ideas?

For those who don't like the idea of water injection, I suggest you have a
quick look at the attached link for actual performance results and

Dwayne Cosby
94 S4

From: Trevor and Cara Frank <tcfrank@home.net>
Subject: ERL Aquamist water injector

I have looked at these things in the past but have no experience with
them.  I came across this system a while back when looking at components
that major rally teams ran.

One of the U.S. distributors