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Discussion Starter #1
Hey all,
just wanting some feedback to my proposed water injection setup.

the main reason for the water injection is that in summer here (ie. now) the outside temp regulary hits 40°C or more. I am only able to use 91 ron unleaded here, and at present any outside temps above 28°C i can only expect base boost (which is set at 3 psi - 2 psi lower than stock) because of apc doing its job at reducing boost because of knock. now the main problem is that i am getting knock at around 2 psi of boost... so APC cant even prevent the knock that is occuring.. hence H2O injection.

I intend on using a fuel pump of sorts (have to find a suitable one first), the 5th injector out of my old C900 GLE that is now basicaly dead, the washer resivoir, and a boost switch set to 2 psi.

the pump will run with the ignition on (having a spil valve that vents excess pressure to the resivoir), and i would use the boost switch to open the injector.

I am toying with the idea of using a FPR like the one that is used on the fuel line to regulate pressure according to boost, therefore with the higher air flow at higher boost, i can get higher water flow throgh the injector.
anyone got any suggestions on this setup?
 

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I'd like you to reconsider using the cold start valve as a water injector. For water injection to be of any use, the spray must be atomised properly. The only proprietary water injection jet that is specifically designed for this purpose is the one from ERL/Aquamist (availabale in sizes from 0.5-1.0 mm - I'd suggest you start with 0.7 or so) and for the £12 it costs it would be false economy to try and use something different.

The fpr reasoning is a sound one except that doing thing tihs way merely means the same level of flow is mainteined with higher boost - the differential pressure between water jet and intake pressure remains the same where otherwise it would fall. You'll need a differential pressure of 3 bar at the very least for proper atomization with the Aquamist valve, ideally 4 bar or more. The fuel pump is normally lubricated by the petrol that runs through it - it will burn out on you at some point. I would make double sure I have full and unmolested APC protection, or rig up some kind of pressure based circuit that makes APC return to base boost whenever water pressure falls below a certain level. Without APC, you could use an electronic bleed valve in the line to the wastegate that opens whenever there's sufficient water flow.
 

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Discussion Starter #3
Thanks for the input...

My APC unit is onmly molested in the fact that it allows more peak boost than stock.... otehr than that the knock detection ability and boost reduction are both still the same as when it was made.
 

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Originally posted by Grentarc:
[qb]Thanks for the input...  

My APC unit is onmly molested in the fact that it allows more peak boost than stock....  otehr than that the knock detection ability and boost reduction are both still the same as when it was made.
     :rolleyes:     [/qb][/b]
Even when basic boost at the wastegate is left alone, a significant raise in peak boost per P/F pot tweaking will impair the ability of APC to dial back the boost to where it wants it to be, in the same timeframe as before, i.e. where it normally would have dropped to basic boost in X milliseconds it now cannot drop it further than to say 0.6 bar in the same X milliseconds.

This is due to the restrictions in the air lines of the APC system, most notably in the solenoid valve. The APC system is calibrated with these restrictions in mind. That's why, if you're overboosting, making the orifice in the plastic insert of the return line output of the valve bigger (or removing it completely) is sure to drop max boost one or more tenths of a bar...

Keep in mind: raising the 'ceiling' of the window APC operates in will result in the 'floor' also for all intents and purposes (if you give APC long enough it will of course always be able to return to the set base boost value, but then detonation could well have taken its toll on pistons and/or valves) even if you have not been tweaking base boost. Better make sure the new 'virtual' ground zero is one your engine set up can live with without harmful knock under all circumstances...

This is also why I don't feel there's any harm to raising the base boost level slightly in a tweaked APC set-up. The ability for APC to reach the original base boost level has been rendered somewhat academic anyways.

[edited several times - I hate keyboards with split space bars! ]
 

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Discussion Starter #6
well, my basic bost level is lower than it should be so therefore a stock APC unit is still going to have a problem in lowering the boost properly, but it seems that i cannot increase the boost pressure for one reason.. my wastegate rod is severly siezed (it seems that maybe the turbo place that reconditioned the turbo before i bought the car has loctite'd it or maybe just the heat has done it
)... ahh well aye?
Adrian.. thanks for that.. i have looked around there a lil before.

thanks for the help
 
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