Ok, having been tweaking my WI kit for a while now, I have come to some observations that I would like to share based on my findings with different pressure sensors mounted in varies places.
1. Boost on the srt builds really really fast compared to most cars.
2. The boost pressure in the intake pipe will build before the pressure in the water injection nozzle.
This causes some problems... I will elaborate the best I can...
The hose from the pump to the injector take a second or 2 to build up enough pressure and begin to spray water. This is due to 2 reasons...
1. Under vacuum all of the pressure in that line stops as the injector is always open. A good amount of water is pulled out as well.
2. The boost pressure fills the output hose up to the check valve or solenoid because its reacts first. (intake boost travels right up the injector and into the system)
Now what happens it the output line is already pressurize by boost, this increases the time need for water to start injecting as it has to partially refill the line and build up pressure again. This takes anywhere from .5 to 2 seconds depending on how long the car has sat, and when the last time the pump was activated.
The problem I see with this scenario on srt-4's is that the turbo spools up very quickly and the nature of the turbo spikes boost up very high initially, and that is where knock occurs, in the big initial spike. However, no water has reached the combustion chamber yet.
On a dyno you have time to let the injector prime the system as you are making several passes and are in the gears longer, but out on the road, the situation is different. Lets say I do a 3rd gear pull on the highway from 3000 rpms to 6000 rpms. It takes about 4 seconds in my car, the water injection wont start spraying until about 4500 rpms. Some initial knock has already occured and some timing gets pulled, then it gets added back as rpms increase but the window is small in third gear.
Now seconds gear is a whole different story, sometimes I can hit near redline before pressure in the output hose even gets high enough to spray water.
These observations are backed up by the fact that I just put some octane booster in my car to help with detonation, and it pulled noticable harder on initiall boost with the octane booster in the tank. While the Water Injection cannot react that fast. Another thing I noticed is the systems with Check valves instead of electric solenoids seem to make the system react even slower as you need to exceed 45psi of the check valve first, where as the electric solenoid opens as soon as the system is active.
It would seem the solution would be to use an electronic injector like a cold start fuel injector, this way pressure is always present in the system after an initial prime, intake boost pressure will never go back up into the system, and also you have almost instant response when the system activates. The nature of WI is to fight detonation, and unfortuntely when you need it most (initial boost spike when going to WOT) is isnt there. For 4th and 5th gear you will be ok, as your in the boost longer and rpms climb slower.. But still the inital boost spike will happen without water doing its job... The boost on this car rises way too fast...
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Good read. Couldn't you adjust your spray to start/full earlier to compensate for the lag?
Thats the problem, there is no lag. My water injection is triggered at 4psi. When you nail the throttle in an srt-4, it gets to 15psi almost instantly, faster than the WI system can react.
I thought about adding a manual override switch to prime the system right before hitting the throttle...
I was referring to the lag in the W/I: "The hose from the pump to the injector take a second or 2 to build up enough pressure and begin to spray water".
I guess if you have yours set to start at 4 psi, you're about as low as you can go.
I was referring to the lag in the W/I: "The hose from the pump to the injector take a second or 2 to build up enough pressure and begin to spray water".
I guess if you have yours set to start at 4 psi, you're about as low as you can go.
They have WOT switches for Nitrous, I wonder if they have let's say 3/4 throttle switches or an adjustable WOT switch...Trigger the jets for that...Mmmmm...
They have WOT switches for Nitrous, I wonder if they have let's say 3/4 throttle switches or an adjustable WOT switch...Trigger the jets for that...Mmmmm...
The only problem with a wide open throttle switch is you could potential hit WOT at say 2000rpms and you probably wouldnt want water spraying then.
But that is a good idea, I could make a contact switch that mounts to the throttle plate, although I still think that will be slow tho, the turbo reacts very quickly over 3000rpms.
I still think an electronic injector is the way to go... hmmm... I had a fifth injector on my last car, no reason that wouldnt work with water...
There could be a whole slue of things that could be causing the delay in activation. Lets say you make 20psi of boost how is that enough to stop a pump spraying at 60psi of pressure. Things like how your activating your system, the I.D of the hose your using all play a role in how quickly your pump will react. And are you using a pressure gauge vs a activation light to show this?
Boost pressure switches have a accuaracy tolerace of + or - 20% but I doubt that's why. Plus the smaller the I.D of hose you use the harder your pump has to work to get the initial spary going this is a issue. Rembember these were designed for 3/8" I.D hose.
There should be no way vac should effect the pumps ability to spray nor boost pressure in the line especially if a solenoid or check valve with a pressure higher than the vehicles boost capability or vac. Now being a pulling force (there is almost no vac before the throttle body blade) A 1psi check valve would do the job in that spot on any car and it won't pull fluid in. Most grand nationals do not even run a check valve because it's really not needed if the nozzle is mounted before the throttle body blade.
If a pump can go from 0 to 180 psi in under a second there should be no reason for a 2 second spray delay in any boosted enviroment with full voltage to the pump. The only pressure it needs to overcome is the boost going past it so even at the minimum 60psi there should be no delay.
Say a 25psi check valve was 4 inches from the nozzle it will always have 25psi of pressure behind it. Water is only pulled under vac not under boost air is being pushed into the motor under boost. At 0 vac no water would be pulled.
If your using say 1/8" ID hose it's going to take the pump a second or two to reach pressure because it has to build up some pressure before the fluid is going to move. But even with that the delay should be less than 1 second.
I'm doing a SRT-4 install on one of the forum members from Canada at my house today and I will give you guys the whole skinny on it. All I know people running larger ID hose don't have this issue.
People with pressure gauges will also tell you it's pretty much instant at least with 1/4" ID hose.
I'll try to find the video from about 2 years ago with a Turbod Civic with a clear intake tube with water injection on the dyno. He was using a older SMC kit but as soon as the light was on the spray started. And this car was making 28psi of boost
I'll have some results for you later on today. I'm on pacific time so it will be up late today.
I would think the smaller hose would fill up faster, not slower?
In either case, the output hose is the issue, the hose between the check valve and pump is always full and waiting, the output hose however is not.. So it need to be refilled somewhat. My injector is on the bottom of my motor, the fluid will leak out to some degree. A larger hose will need more volume refilled before sparying.
I would think the smaller hose would fill up faster, not slower?
In either case, the output hose is the issue, the hose between the check valve and pump is always full and waiting, the output hose however is not.. So it need to be refilled somewhat. My injector is on the bottom of my motor, the fluid will leak out to some degree. A larger hose will need more volume refilled before sparying.
A larger hose between the check valve and the pump will hold pressure and more of it. It will act like a tank until the pump is at full power. Plus its all physics with diameter and resistance. It is easier to have water flow through a certain size pipe than a smaller one.
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Hmmm, ya know, the Toys sprayer is designed to "lead" the intake temp rise through algorthims that predict the rise before it occurs. So it dones't really cool off the intercooler, but prevents it from getting hot.
I had played with using that signal to trigger W/I, but figured the lag would be too great. You would be spraying too early, since the
spray-mist-heat transfer from intercooler to mist-heat transfer from charger air to intercooler cycle
takes way longer than
the spray-heat transfer from charge air to mist cycle
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I used to own one of the first SRT-4s sold, bought it new in Feb 2003, sold it Nov 2006 with 75K and Stage 3. Now I drive a 2006 SRT-8 Charger.
A larger hose between the check valve and the pump will hold pressure and more of it. It will act like a tank until the pump is at full power. Plus its all physics with diameter and resistance. It is easier to have water flow through a certain size pipe than a smaller one.
The hose from pump to check valve on my car is about 8 inches long, hmmmm. Now that I have a check valve and not an electrical solenoid, I should move the check valve right down near the injector, like 6 inches away, I bet that will help some...
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WI and SRT's - My observations - Good Read
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