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

My question:

Hi,

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 detonation.

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 detonation.

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 plugs.

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 ! :cheesy: :nono; :cheesy:

Richard Lamb

That is very, very helpful. I was running an incredible 14:1 on the dyno last week and I sorely need the aquamist injection system (once I've bought: my house, new tyres, discs, pads, springs, dampers and reinforced clutch plate!). I was wondering about nozzle sizing and what he says sounds very sensible.

Alanb

Alan,

I'm afraid that water injection won't help if you're already running lean- all it does is stop extra fuel being dumped to help cool things!! I also found useful info on lambda sensors- here:

http://www.picotech.com/auto/lambda_sensor.html

and it may well be that yours is just out of spec. Whatever, I'd concentrate on getting your fuelling sorted out first.

As far as I know, the lambda sensor takes no part at full throttle, as the system is open-loop under these conditions. When I did my 305hp run, PE told me that mine was just atarting to lean out, so I think that's simply the limit of the standard fuel system.

I agree that water injection would only serve to allow Alan's car to run lean at that power level a bit more safely. However, more fuel would be required to increase the power level any further and I would think Aquamist is an expensive way of increasing the top-end power from 300hp to 311hp. To get my money's worth on the water injection, I'd be wanting to increase the power even further, which would still mean adding more fuel.

What about the crude but effective (?) idea of adding a fifth fuel injector before the thorttle body to come on at a pre-set psi (this would be somewhere near max boost, say 18 psi or so)? I think this is what is being discussed on the C900 board at the moment.

Alanb

Maybe. After all I've said about not liking the idea of an RRFPR, Mark seems happy with his. I just prefer something a bit more elegant, but I do accept that you might not have that luxury.

Theres an interesting thread on Scoobynet at the moment regarding rolling roads. They tend to read richer than the car would normally achieve on the road.

Alan, I would be very worried about your CO %age at the moment.

Yes, I'm trying to figure what to do about my problem quickly. I've done a bit of searching around and have found that Hoopers of Bristol can get a RRFPR kit for a 2.3T for GBP91.20 including VAT. This might be the way to go.

Mark seems quite happy with his.

Alanb

Removing the Dawes isn't an option :-??

Removing the Dawes isn't an option :!

I think the Daddy has a reputation to maintian.

Removing the Dawes isn't an option :!
:lol:

He'll have a reputation to live down shortly if he's not careful :o

As all daddies know, in front of the family one must maintain one's reputation by sticking to the original position - even if mistaken - and resist all arguments to the contrary. :lol:

Alanb