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Old 12-30-2008, 06:10 AM   #1
N3v
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Default Water injection questions

This is a post about me wanting to wander into the wonderful world of turbo.
I'm not afraid to sound like a noob, but I honestly had no idea what water injection was all about until I sat down and read up on it a little tonight. I thought it was all about simply cooling your intercooler with water spray. I've always thought it was bad to add water to your engine because of hydrolock stories. Aaaanyway, I've done a little reading now, and looked through the forums a bit, and I think water injection might be my solution.

So, I've got some questions:
1. does the manner of water delivery matter as much as say, nitrous? Or is the whole point to hit the air with a burst of cool air mist at any point while its travelling through the intake system? If you could set up a 'direct port' sort of system with four injectors for ITB's, would that be dumb or any more benefit than just injecting water inside the plenum?

2. what is the limit of such a system? Is the limiting factor how willing you are to mix expensive stuff into your water all the time, how much water the engine can handle, how much water you can use on a tune without running dry pretty quickly, or how low you can get the temperature of the air while using normal-temperature water and not sub-zero substances like nitrous?

Basically, to let the cat out of the bag somewhat, I ask because I'd want to boost a high compression engine and have the option of running pump gas. On a pump gas tune, it seems pretty simple to set the megasquirt to inject water/meth whenever the turbo starts making boost, I just need to figure out the best way of delivery with a setup like that!

Thanks. Feel free to rip me a new one.
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Old 12-30-2008, 06:26 AM   #2
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Some say you want to spray as early as possible (but post-intercooler) to let the water have as much time as possible to soak up heat in the intake stream. Whether the water does its work in the intake stream or in the chambers themselves is a question I wonder about myself. 4 nozzles would probably be unnecessarily complicated.

The limits of the system are how often you want to be filling tanks and how reliable the system is. I'd always have a fallback; a pressure switch in-line so if the pump fails, your boost controller shuts off, for instance. Magna (where is he anyway) was running stock timing and no intercooler and spraying something like 450cc/min of water into the motor. You want to vary the flow with fuel flow, something like 5 parts fuel to 1 part water. Of course, that changes with meth, since meth is essentially racegas being added to the motor as well and that will effect the AFRs (whereas water will have a minimal effect, if any).

You should be able to stuff 6-7psi into an 11:1 motor; I remember MarkP stuffing 10psi into an 11:1 motor and making 300whp with it, and I don't think he had water.
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Old 12-30-2008, 06:27 AM   #3
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awesome! This kinda solves my whole dilemma of high compression or turbo.
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Old 12-30-2008, 06:35 AM   #4
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It's still more of a PITA than it's worth. You gain 4% efficiency for every full point of CR you add, but the difference between a low-boost 11:1 motor and a high-boost 9:1 motor is bigger than just 8%. Mark had to use a huge turbo to keep heat out of that 11:1 motor. The idea is that it's easy to remove heat from a pressurized intake charge (water, intercooling, etc), and very hard to remove it from the cylinder (really the only way to do this is excess fuel, which we already use).

I would probably do 9.5:1 or 10:1 if you wanted to do a high-CR turbo motor. 11:1 is excessive. Once I finally build a motor, it's getting 9.5:1 pistons.
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Old 12-30-2008, 06:40 AM   #5
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Quote:
Originally Posted by N3v View Post
awesome! This kinda solves my whole dilemma of high compression or turbo.
while it certainly helps it is still not a replacement for lower compression. you can raise boost/inject more water into a high compression engine to a certain point, after which the engine will blow.

I think water/meth injection is absolutely awesome/amazing and am surprised people are just now starting to really use it/implement it in turbocharged applications. Just have to know the limits

Quote:
Originally Posted by Savington View Post
It's still more of a PITA than it's worth. You gain 4% efficiency for every full point of CR you add, but the difference between a low-boost 11:1 motor and a high-boost 9:1 motor is bigger than just 8%. Mark had to use a huge turbo to keep heat out of that 11:1 motor. The idea is that it's easy to remove heat from a pressurized intake charge (water, intercooling, etc), and very hard to remove it from the cylinder (really the only way to do this is excess fuel, which we already use).

I would probably do 9.5:1 or 10:1 if you wanted to do a high-CR turbo motor. 11:1 is excessive. Once I finally build a motor, it's getting 9.5:1 pistons.
I know a crap load of rsx-s and s2000 owners that boost up to 12psi on their 11:1+ engines safely. with the right tuning its not a problem. start to go higher in boost and yes you need lower compression for sure.
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Old 12-30-2008, 03:16 PM   #6
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well, I think this suits my needs, as I'm probably going to finish my engine pretty soon with and run it 11:1 NA for one or two seasons, then turbo it. Its just nice to know I've got that option available.
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Old 12-30-2008, 07:32 PM   #7
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I run Water/methanol injection on my Subaru. It kicks on at 7psi, and hits full duty cycle at 11psi. Just make sure you have the car properly tuned. Its cheap and effective, my Devilsown kit cost $330, and i pay about $20 per month on a 50/50 Water/methanol premix supplied by the same company.
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Old 12-30-2008, 08:39 PM   #8
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has anyone ever rigged up some sort of sensor inside their water tank that reads out to an E-----F gauge? Could you just put a fuel pump assembly into a water tank?
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Old 12-30-2008, 09:01 PM   #9
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The real benefit of WI is not evaporation cooling but in-cylinder cooling and knock suppression.

All are pretty tightly link as generally speaking the cooler the intake charge the less chance of knock (for the same boost CR etc).

It's also not really useful to talk about compression ratio's without also mentioning MBT and timing in general.

As an example you could fit 12:1 CR pistons bang 14psi through them and it you run enough retard the motor will still run (be it with high EGT's).


I was pretty adamant that i wasn't going to run a IC, as i'm using a SC i was worried about throttle volume.
I managed to get up to 11psi but then reached a point where if i added more water the car started feeling sluggish so i had to retard the timing.
This then gave EGT's over 950c.

I then fitted a IC, i can now together with the IC and WI run 13psi (it dropped around 2psi when the IC was fitted) at 14 BTDC base timing without having to pull any timing at all from the stock ECU's timing curve.

The car also runs a lot more predictable and consistent with the IC as a lot of the intake heat is being dissipated out under the motor instead of being pumped through it.

On the ITB WI idea there are a few guys in the UK running that type of system and few non Miata mates over here (Greece) tried it.

The theory is that is reduces the lag/delay in getting the water in the cylinders.

In practice it does work, the biggest problem though is blocked jets.

On my system with 1 jet/nozzle if it blocks then my knocklite flashes straight away and i know theres a problem.
I've also got a flow meter/gauge installed and can see straight away i have no flow.

From what i've seen on ITB WI installs though if you (or when) get a block jet it's virtually impossible to spot.
The flow meter still detects flow and because 1 nozzle is blocked it then increases the pressure and therefore flow to the other 3 cylinders.
It's not the same amount of flow but it's close enough to make it difficult to notice.

Another thing we saw was that because we were only getting knock on 1 cylinder the knock sensor was not picking this up all the time.
So we think the car was being driven and raced for around 4 weeks with a blocked jet till the piston popped.

The thing is though the advantage of ITB WI is the reduction of lag.
If you fit something like the AM HSV then you have such fine control over the quantity of water you pump that you can set it to start pumping a very small amount at 0psi so when you do hit boost there is already water in the system, so no lag.

Biggest disadvantages with WI are running out and blocked jets.
I have a 17 go-kart fuel tank and fill it up once a month or so and have never run out.
With the flow meter and knocklite it's pretty obvious if the jets blocked, but if i could get me **** into gear i have a idea of rigging up the SC valve so if the flow meter detects a flow problem it cuts the boost, damn site easier with a tubby and EBC though.

So my advice is fit a IC and if you still feel you need more timing advance fit WI.


Cheers
Mark
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