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I just thought I's share with you all the very helpful response I had from Aquamist about water injector sizing...

My question:


I've recently installed a System 1s on my Saab 9000 2.3T. It's running up towards 1.5bar/300hp (it has reprogrammed ECU and uprated intercooler) and I was wondering what the most appropriate size of injector to use would be. I've heard conflicting advice- some say use 0.8mm for maximum cooling; others say use the smallest possible as you're displacing fuel with water that doesn't burn.

Fuel/air ratio has been checked and is good.

I'd be grateful for any info that you have on how to determine the most appropriate size of injector.

Many thanks

And the response (I particularly like the last comment):

Hello Mark,

We normally recommend running between 8-15% of fuel. For 300 BHP, you will
probably require 1.5 litre of fuel so a 0.4mm or 0.5mm water jet will be
good for normal day top day usage.

These rate need to be increase if you intend to run a a/f ratio less than
12.5:1 or your EGT is higher than 900deg C or you experiencing some

Since you have an updated intercooler, you may not require too much inlet
cooling but you may require some in-cylinder cooling to avoid the onset of

Rule of thumb- if the EGT is in excess of 900C, it will probably means that
the "excess heat" can be used to generate steam from the injected water and
produce more torque rather than being destructive. So more water over our
normal rate if you experience high EGT or detonation.

Since water has six time the latent heat of fuel, image injecting six times
amount of fuel to lower the equivalent EGT and think how much "un-burnt
fuel" is displacing the normal fuel, the result will probably mean that you
will be bellowing out tons of black smoke as well as fouling your spark

So the answer is get the EGT reading first. If your EGT is below 900C and no
detonation, you know what, you are not running enough boost !

Richard Lamb
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