[daveb7577]

Hi All,
I picked up an 05' sti a week ago, my first Subaru, and I love it. I was wondering if anyone has thought about water injection on our cars? I've read about the 2.5 wanting to ping even with 91 octane fuel. Only mods that have been done is a CAI and later a 3" TBE. After adding the CAI I could hear it quickly ping and then stop as the ecu backed off the timing. Granted the ecu is probably still learning after adding the CAI, would adding water injection be worth while or would another route be more effective.

Thanks, Dave .B

05' Sti (daily driver)
02' M5 (weekend toy)
71' Celica (project)
89' 535i (wife's car)

[RemlapaN]

take the CAI off the car. Most of the CAI's that actually add power do so by leaning out the A/F ratio. Also, on the STi, intakes actually do more harm than good until you get to the point of turbo upgrades. You would find, that on a dyno, the stock intake will provide more HP than most aftermarket intakes, with the exception being some that play tricks with the diameter of the MAF housing to lean the car out (dangerous).

Also, if 93 octane is available, run that instead. The owners manual specifically states that 93 octane is the minimum grade fuel that can be run in the car, but if nothing exists, 91 can be used but there will be reduced power output.

[Datadatum]

WI has been done on many WRX's, and a few STi's. There are even some kits out there just for Subaru's. You will need EM to make the best use of it. Post back if you are interested, and I'll point you towards some of the key threads on NASIOC.

Also - M5 as a weekend toy?

[crashsti]

water injection was brought up awhile back. it ended up sounding like a worthwhile mod on a vehicle with lots of mods that ran on the ragged edge of blowing itself up. otherwise it just made more sense to run the specified fuel requirements 93 octane. my car was bought in June 2003 and i have never had audible detonation.

[daveb7577]

I'll pop the stock intake back on maybe with a k&n drop in? There's a 76 station here in fullerton that sells 100 octane but that would get pricy gassing up everytime with that, so 91 is really all I got. It seems to run good with 91, I never heard it ping before with the stock intake.

Would a FMIC be effective in preventing detonation. My goal with this car is a nice daily driver, nothing huge or wild, but just to improve effiency.

---Dave .B

[Datadatum]

K&N has not dyno'ed as an improvement either. Kind of counterintuitive, but true.

With the TBE, you should look at engine management. AccesPort, UTEC, or ECUTek. At the very least, a boost gauge and A/F meter to ensure that the stock ECU isn't taking you into dangerous territory.

[hirevn]

im installing a alcohol injection system,much better than water.uses 100% pure denatured alcohol with the recommended klotz lube.we only have 90 octane available so with this setup at full boost over 100 octane to low boost around 94 octane.

[crashsti]

Originally Posted by daveb7577

I'll pop the stock intake back on maybe with a k&n drop in? There's a 76 station here in fullerton that sells 100 octane but that would get pricy gassing up everytime with that, so 91 is really all I got. It seems to run good with 91, I never heard it ping before with the stock intake.

Would a FMIC be effective in preventing detonation. My goal with this car is a nice daily driver, nothing huge or wild, but just to improve effiency.

---Dave .B

if you have 91 and 100 Octane available why don't you just mix them? as for the K&N Filter, its reusable so even it does'nt give you power it'll sdave you $$$ in the long term.

[donmei]

Dave,

Based on your stated goals: My goal with this car is a nice daily driver, nothing huge or wild, but just to improve effiency.

I'd say do an access port or some other type of plug and play software upgrade. I'd combine that with a catless midpipe if you didn't want much noise, or a compelte turbo back exhaust if you're looking for some noise.

I'm guessing you want to keep your Warranty in place?? If thats the case, I'd say leave it stock.

A bigger Intercooler and water injection are both VERY effective means of reducing the risk of detonation, but if you aren't planning on tuning to take advantage of that, then you aren't getting anything.

Don

[jlcool007]

Originally Posted by RemlapaN

take the CAI off the car. Most of the CAI's that actually add power do so by leaning out the A/F ratio. Also, on the STi, intakes actually do more harm than good until you get to the point of turbo upgrades. You would find, that on a dyno, the stock intake will provide more HP than most aftermarket intakes, with the exception being some that play tricks with the diameter of the MAF housing to lean the car out (dangerous).

so, will doing a intake silencer mod mess up the a/f ratio like you did in your sig?


-spyder

[b_boy]

Let me first say the engine mangagement (EM) is must for modification of your car if you want to do things safely and get the most out of your mods. If you are looking for ~35 more HP, more low end torque, and more responive throttle. EM is all you need.

I'm doing water injection on my STI. I'm also waiting for the Element Hydra. I bought an Aquamist system and it's pretty simple to plumb and wire. The Aquamist system offers a great number of conveniences that other systems don't offer, but you can do things more cheaply by building your own system. It has "quick fit tubing" connections and the ability to run diagnostics and fuel cut in the event of a failure that would otherwise not be part of a homemade system.

In general water injection reduces intake air temp (increasing the density of the air per unit volume) and the ability to run leaner fuel ratios that will increase power output, increased fuel economy (no fuel dumping), and the ability to run higher boost (and other stuff like cylinder cooling, lower EGT, and slower fuel burn rate). In addition, by injecting water pre-turbo one can extend the compressor map toward the right. This last function is a new one to me. By injecting water in the air intake prior to the turbo (not huge amounts of H2O) one can cause the turbo to work more efficiently, using the heat of evaporation to reduce the wasted energy of compressor that goes into heat. Unlike a huge intercooler, WI offers a regulatable cooling of the intake's air with very little pressure drop. The main criticism of WI is that if the water stops flowing you are in danger of blowing up the engine via denotation. While true, that criticism could be had for many mechanical engine components as well (fuel injectors, thermostats, wiring, MAF failure, etc). You have to add fuel to your car and to the WI tank. Plus lot's of people just don't know their chemistry well enough see how WI works, and it does work wonders). With no other modificaitons you will not realize huge power increases with WI alone, but leaning from our STI's typical 10:1 AFR at WOT to 12.5 will yield you about 20 hp and 25% less fuel just going out the tail pipe.

My plan is to run water injection post-turbo starting at a boost of 3 psi on up to maximum boost (for the VF39 about 18 psi) at 5000 RPM with boost at >= 15 psi, I will inject water pre-turbo, increasing the efficiency of the turbo compressor. With increase compression efficiency (a possibly slowing the compressor wheel slightly via viscosity) I hope to extend the stock turbo's boost level all the way to redline at 15 psi or higher, something that has not been done without FMIC (where you lose 2 psi in pressure drop).

Combined with the Element Hydra all sorts of options become available for programming. You can cycle the Aquamist high speed valve at any frequency you would like, plus add in a new site of spray in a different location when you need it most. Other engine management systems can be configured to do the same thing with a little more hardware (I can elaborate if you want).

The basics of water injection is a tank of water or water/methanol (of whatever miscible fuilds you wish) hooked up to a very high pressure pump. Aquamist's can run continously at 10 Bar, that's 147 psi. The pressurized water is injected by pulsing a high speed valve with intermittant voltage, the frequency and pressure dictating how much water is released through the valve. "Jets" at the termini of the system are usually placed just ahead of the throttle body in the silicone tubing that connects the intercooler to the intake manifold. The size of the jets restrict or permit water/methanol flow according to the speed of the valve (upstream) and the size of the jet opening (0.3 mm, 0.4, 0.5.....1.0 mm). With the high pressure, small apeture, and slight bevel you get a very fine conical mist with very small droplet size. The heat of evaporation (energy needed to change liquid to gas) is very high for water (higher than any other liquid I know of). So in a higher temp atomsphere like after turbo compression, the water's evaporation removes tons of heat--just like sweating makes you cooler.

http://www.waterinjection.info/phpBB2/ offer's more insight and info than you could ever absorb. Ed Haney of ChargedPerformance.com is a vendor on this site and is very helpful and knowledgeable.

[donmei]

Bboy,

Very nicely said.

[donmei]

Bboy,

Very nicely said.

[VV]

Careful. Injecting water before the compressor will lead to erosion of the compressor blades. Over time the compressor will lose efficiency, and you boost will go down. The best theoretical location to inject water or an alcohol/water mixture is at the throttle body. The higher temperatures entering the IC will allow it to maximize its cooling duty, and then you quench it even further before it goes to the cylinders. It will also provide the best det resistance due to the entrained liquid particles entering the cylinder, where they slow the burn rate, prevent hot spots, and flashing to a vapor, increasing peak cylinder pressures and producing more power. If all of the water is completely evaporated before it reaches the cylinder, your det protection is greatly reduced.

[b_boy]

BTW, in my salesman-jaded opinion air intakes don't make power, more air (oxygen) makes power, but unless you are willing to run no filter at all, or a poor air filter (i.e. SUS intakes), you just do not waste much HP sucking air in through the stock intake (use a good high flow filter, there are tons of brands). That said, if you have a 1000 hp drag engine 1) you don't care if dust get's in the engine and wears parts for 1/4 mile, and 2) you probably won't have a filter at all, then, yes then you will take a hit with a stock intake.

If you are in the 400 whp or less range, the additional <10 HP you'll pick up over a good filter is just not worth the incredible wear on your engine (in fact if you could screen out all particles at the intake, you'd probably only have to change your oil every 25-50,000 miles--if that, with at good synthetic).

It's nice for the bling factor, but your engine will thank you everyday with good air flitration for very little sacrifice.