teamstealth

hey every1,
The idea of a DIY water injection kit has been floating around in my mind for quite some time...so i figure i might as well start bouncing ideas off ya and see if i can come up with some numbers and start making something

I got my inspiration from the kit and writeup ZeroBanger ( jimlab, hush ) did a while back but i see some flaws with the design. While it obviously served its purpose, it could have been improved. For those who didn't catch that thread, the way he did it was he had a small nozzle come on at 1psi, and a 2nd larger nozzle come on at 8psi to regulate the water/air ratio. While this is a lot better than one large unregulated nozzle, it could be tuned much finer than that.. (think of a curve graph representing the boost, and then two straight lines for the water...it JUMPS ratios instead of flowing smoothly with the increasing amount of air)

I dont want to reveal all the details of how im going to build mine yet....but i would like to hear your opinions on the ideal amount of water per psi off the STOCK TWINS. ZeroBangers setup IIRC had 7.63 GPH at 8+ psi.
This translates to a 1:1 ratio of water/psi at 8psi, and 1:1.5 at 12psi. Thats the problem i have with that setup...the ratio isnt constant and therefore not totally ideal (****, but thats the best way to design things, ) I'm in search of a constant ratio across the entire boost range....so what do you all think it should be?

Also, if anyone could translate the stock twins flow from 10,11,12,13,14,15,16PSI into CFM and make a ratio like that, that would be MOST helpful

-Zach

teamstealth

Also, the idea of re-vamping the kit's water flow to work with a single turbo has been brought up as well. Basically the way i look at it, single's do flow much more air, but they also have cooler temperatures to begin with, so in my mind I wouldn't have to change the kit very much at all, as the difference in heat and airflow between a single and the twins would be pretty much traded off (that is after deciding the ideal CFM or PSI/water ratio). If im wrong, feel free to correct me!

Kento

Trying to fine tune the ratio of water injection as boost rises isn't nearly as important as tuning to compensate for the drop in combustion chamber temps. Sorry, don't mean to sound so negative, but you will be doing a lot of work for little to no payoff performance-wise. As long as you have the correct ratio of water at the 8 psi level on up (which is debatable in itself), that is really all that matters for the water injection. You will be helping reliability and widening your safety envelope for your engine at that point, but from there it's taking advantage of the cooler combustion chamber temps where your real work should be concentrated.

teamstealth

Exactly. What is the ratio of water to CFM or PSI that i should try to attain? Also, isnt the goal of water injection to maximize the cooling affect but not to the point of adverse performance from too much water?

Kento

You missed my point. If you're only interested in dropping intake temps for reliability reasons, then a system similar to an Aquamist unit will work fine, and you will gain no tangible benefits by spending a lot of money and time trying to fine-tune the water injection ratio.

The goal of water injection is to cool combustion chamber temps so that you can increase boost/fuel/ignition curves for more performance. Which is where the real work should be done.

scotty305

iTrader: (2)

To expand a little on what Kento is saying, the reason to fun water injection is because in stock form, your car is running rich, using excess fuel to cool the combustion chamber and prevent detonation. This wastes fuel. Also, water is more efficient than fuel when it comes to absorbing energy (heat), so the combined volume of water + fuel will be lower than the volume of fuel only required to keep combustion temps under control. This allows you to add more air and fuel, and make more power, because your volumetric efficiency is increased (assuming your ratio of water is in the proper range). Or you can use slightly more water, and add more boost, or more ignition advance. In order to accomplish this, I would implement some sort of full engine management (motec, haltech, apex'i PFC, etc...) before trying to add water injection.



there's a forum re: water injection, I'll post the link a little later, right now it's time for dinner.


-s-

teamstealth

I know how WI works and that i wont gain any performance gains by installing it. The whole reason ive wanted to is for a bigger safety cushion/reliability mod/etc. But truth of the matter is i dont have the money to buy an aquamist kit and tune it, so im going to do it myself since my time is technically free.

And the purpose of this thread was to see what all of you guys thought the ideal water/air ratio was. To get back on topic, from what ive gathered, Zerobanger used to have a 1:1 ratio of water/air, and the car felt like it was breaking up and sluggish in the higher RPMS...he then changed to around a 1:1.5 ratio of water/air and said the car pulled MUCH harder with no breakup.

What do you think the optimal ratio of water/air is for an FD with all boltons and the stock twin turbos?

scotty305

iTrader: (2)

I think it's safe to say that 90% of the people on this board have no experience with water injection. You might be better off searching google or something. A LOT of the musclecar guys have used water injection for a while, I can imagine that you'll find some useful information from their camp.

-s-

scotty305

iTrader: (2)

http://www.waterinjection.info/


http://www.waterinjection.info/phpBB2/


should find some helpful info there...
-s-

jhillyer

I've been lazy and have not tried water injection. For turbo I was considering a bypass pressure much like the fuel system, as a boost-follower using something like an aquamist pump and a pressure regulator plumbed into manifold pressure, and the pump powered after a small boost threshold.

This would allow me to spare water during low throttle/demand, and maintain water injection pressure under extreme boost.

ZeroBanger

Its cool to see what I have missed when I wasnt on the forum for those 3 months. In my thread that you are referring to you saw my first attempt at water injection. Its been just over 1 year now and I have made significant improvements. Also, that 7.63 GPH was found to be too much water at that PSI. As that thread progressed you would see that I eventually changed that.

I have tried many different types of setups and have settled to a dual stage setup that I think is the best. In my current setup I have a small nozzel (approx 2 GPH) that comes on at 1 psi located in the throttlebody elbow. Its critical to point out the flow of the nozzel is not aimed toward the engine, but toward the intercooler. In otherwords it goes against the airflow. I believe the water would better evaporate..rather than going directly into the engine.

My 2nd nozzle comes on at 12 PSI and is located in my intercooler exit end tank.

During other tests I found massive hesitation that was caused by too much water at too low of an RPM.

The easiest way to find what you need interms of fuel is to take your power fc and run some WOT tests. Take a look at your injector duty. If your injector duty is .80 and your primary injectors were 550's and secondary injectors were 1200's you would take this formula.

.016 * ((1200 * 2) + (550*2))

the above formula gives you your maximum fuel. Which in this case is 56 GPH. If you are at 80 pct fuel at WOT that gives you about a 45 GPH. To maintain a 10-15 pct water to fuel ratio you would stay between a 4.5 to 6.3 or so GPH nozzle (that is between your 2 nozzels if you have a dual stage).

The way I planed mine is to have around 20 pct at 1 PSI on and as the boost raises it will lower to 10-12 pct...putting me in the range I want to be at redline.

BTW, if you want it to be linear its going to be very complicated and you are better off getting an aquamist system.

Hope that makes sense.

FD_Newb_1974

For the aquamist calculations, add the total of your injectors and then take 10% (or 15%) of that. Aquamist will maintain 10%-15% water to fuel throughout your entire duty cycle. The percentage water to fuel depends on the injection mixture, and ambient temps.

Distilled water will give you the MOST anti-det properties. Methanol will give you the most cooling properties. anything greater than 50% methanol/50% water will start to create heat in the combustion process.

I don't believe there is any measure of water / psi . I think you should be shooting for water/fuel and adjust timing, a/f (or a/f/w) accordingly.

ZeroBanger

You are correct, water to PSI would almost be pointless except with the DIY kit the water injects based on PSI. By looking at the power fc you can find your duty cycle and compare to psi. I find that at 1 psi I am always at 49 pct or so. As I increase boost it it will increase. When I am maxed out at my settings I am around .70-80 depending on how much boost I run, etc.

In otherwords with the DIY kits you have to look at your boost and your given duty cycle at that boost, paying most importance to your duty cycle at full boost/redline.

Aquamist kits are great, I recommend them. Just a little expensive and complicated.

teamstealth

Thanks for the replies Zerobanger and FD_Newb! So basically my design is something better implemented by a $500 Aquamist kit....damn. Also, i'm installing a Pettit Unlimited as my ECU in a few days, any way of finding out the duty cycles w/o calling pettit?

ZeroBanger

In your case just assume 100 pct.
You can click the link in my sig for water injection and I have the formula in more detail and some idea's for different stages of water injection. I'm just putting this site up today so its a little rough.

Link is here

http://www.davidhillsoftware.com/rx7...injection.html

teamstealth

so assume 100% for 14psi which is the maxed its tuned for and 85% for 12psi?

ZeroBanger

I cant say that. I would set the max water injection assuming a 100 pct use of duty cycle. This is to be safe. You can guess 85 pct @ 12, but its your call.

In reality... as long as you dont tune for water injection, assuming 85 pct is ok. You are just a little blind as to actual water to fuel ratio.

peejay

There is a really, really simple way to have water flow boost-dependent. Actually it's how water injection USED to be done.

Just use air pressure from the piping between the turbo outlet and the intake manifold to pressurize the water tank. You will need to have fairly large diameter hose between the two to ensure there isn't any lag time between the pressure in the tank and the pressure the turbo is generating.

The nozzle is placed before the turbo, and a pressure holdoff valve prevents water flow until a certain air (water, now) pressure is reached. Water flow is tuned by the size of the squirter jet.

The beauty of this is, you get water injection when the turbos are generating boost (and heating up the air) but the throttle blades are closed enough that the intake manifold pressure is still below atmospheric.

edit: Before someone poses the argument "But filling the volume of the tank will cause lag!" Um, no. Let's say you have a two gallon water tank (big!) and your happy little 1.3-liters-per-rotation engine is humming along at 3000rpm and you're almost out of water so your 2 gallon tank is mostly air, and the water remaining in the tank represents the volume of air in the connecting pipe. Let's also assume that you get boost INSTANTANOUSLY when you whack the throttle open, and you can whack the throttle open INSTANTANEOUSLY.

2 gallons of air is (3.78x2) 7.56 liters. 7.56 liters is (7.56 / 1.3) 5.8 engine revolutions. 3000rpm is 50 revolutions per second, or 20 milliseconds per revolution. (Can you see where this is going?) 5.8 revolutions therefore is 116 milliseconds... not even an eighth of a second!

Now the REALITY CHECK. There is already air in the tank, at atmospheric (well, slightly higher) pressure, so you won't be filling it up with 2 gallons of air. You will not be able to whack the throttle open instantaneously, even the Top Fuel guys with their special throttle pedals that allow them to use their (faster) leg muscles instead of their ankle muscles have measurable throttle opening time. And your turbo WILL NOT spool instantaneously either, especially at 3000rpm! And finally, most of the time you will have the tank topped up anyway (RIGHT??? ) so it's even more of a non-issue.