Is this system worth getting? Are there any long term effects on engine or spark plug longevity? Are there noticeable horsepower gains? Looking for pros and cons before purchase for my 2001 SC S2000.

 

Craig,

This is designed for a roots type blower as they run very hot, however the centerfugal type (Comptech and Vortech) don't run as hot. The Comptech system runs very low boost and therefore doesn't really need a cooling method... I don't think that you'd benefit much.

Chris

 

Craig,

I've used the Aquamist system on my SC'd CRX, and tuned some turbo cars with them.

On Roots SC apps, you really need multiple injectors or they don't work very well. H20 distribution in the intake manifold is a real bitch to get right.

Conversely, on turbo apps, even intercooled ones, the water injection systems tend to really help out power, especially if you're running pump gas. I've never seen one used on a system running less than 8-10 psi though. That means that on a Comptech system it might be marginal in terms of benefit. However, there should be no detriment, including spark plug problems, etc. At $500 or so its a pretty small investment (relative to other S2K parts) and can probably be resold easily. I'd be more than happy to lend you what assistance I can if you decide to give it a shot.

UL

 

Chris & UL,

I have noticed significant horsepower drops on these hot Florida afternoons. My quest to look for ways to cool intake charge led me to JR's water injection system. Since water cools approx 4
times better than an air/air IC my feelings are this system would be more efficient. Plus it is probably lighter and certainly less expensive.

 

Yes, well, the '4 times better' is in the JR advertising, right? Its probably true, but doesn't tell the whole story. The JR system is a rebadged Aquamist setup. I'd suggest visiting their site (www.aquamist.co.uk I believe, do a search) for complete information.

The problem with water is that it slows down the combustion process. Thus, it can actually sap power if you use too much. Won't hurt the engine, you'll just be down on power. However under hot running conditions you'll be much safer.

UL

 

I am confused about the benefit of spraying moisture into the intake. I see how it would cool things down, but wouldn't it displace oxygen? Doesn't high humidity reduce power?

 

The water evaporates in a high temperature environment. If it doesn't actually evaporate in the intake manifold, it will in the combustion chamber. The heat of evaporation cools the charge temperature. In return, you do end up with a higher H20 content in the intake charge (like running on a very humid day), but the charge temp reduction will usually more than compensate for the power lost from the increased water content.

For example, going from 0% humidity at 80F to 100% will cost you about 4% in power. Since you're almost never at 0% (more like 30-50% in most areas) the relative difference is closer to 2%. This of course assumes that all the water evaporates properly, which is why sizing the water injector and making it sure it has good atomization is critical (the Aquamist system operates around 150 psi, so atomization is quite good). Now, if you if you have an intake charge temp of, say 200F (my supercharged car would see 200-210F on a 65-70F day - quite a large temp increase!). With proper water injection you could see pretty large decreases in temperature.

For example, it takes about 2300 Joules of energy to evaporate 1 gram of water that starts at 20 C (70F). If we are injecting 300 cc/min (not an unusual rate for an aquamist system), we're injecting 5 cc/sec. This equates to 5 grams of water and would require 11,500 Joules to evaporate it. At the same time, if we're running around 7 psi of boost, we've got an air density in the manifold of about 2.0 kg/m^3 (this is actually high, but its o.k., that means we're being conservative on the temp reduction calculation). At 9000 rpm, the engine is ingesting 150 liters of air/second, or about 300 grams of air/second. Air has a specific heat of around 1 Joule/gram*C - IOW, it takes 1 Joule to raise the temp of 1 gram of air by 1 deg Celsius. If we assume the water we injected is all evaporated (and distributed equally between all cylinders), we will actually be removing 11,500 Joules/sec of energy from the air. A little calculation tells us that we could then lower the temperature of the air in the intake manifold by 38 C! Since we're starting out at nearly 100C, we get the temp down quite a bit, down to 60 C (140 F). If we were starting at a lower temp (say 60 C), then we could get the temp back to nearly ambient.

Such a temperature decrease would improve power production by about 8%, easily offsetting the losses from the increased water content in the intake charge (total gain of perhaps 5% with reduced risk of detonation as well).

Of course, this is all theoretical. In reality, results vary widely since not all the water is evaporated in the intake tract (but in the combustion chamber as well), the effect of water on the combustion process (it slows it down and requires tuning changes) and many other things. I've seen water injection return virtually no gains on some engines, and gains of 12-14% on some mid-high level turbo systems (300+ hp 2.0 liter turbos).

In the end, as with most things, execution matters more than theory. But I do believe some professional motorsports teams (World Rally) are using water injection on their turbo engines.

UL

 

[QUOTE]Originally posted by ultimate lurker
[B]
For example, it takes about 2300 Joules of energy to evaporate 1 gram of water that starts at 20 C (70F).

 

Thanks UL. Your explanation sounded so much like some of the test problems from Engineering Physics.

 

50/50 water/meth would cool better for you and reduce detonation. Search the GNX boards for more info than you could ever want to know about FI (turbo) and water/alcohol injection. A lot of the guys run washer fluid since its cheap and have zero problems. Shouldnt be much different with a super charger.