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Old 04-04-2005, 11:32 AM   #1
omahasubaru
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Default N/A Water Injection

I hate to post this, but the search function still isn't working for me.

I'm curious to know if anyone is running water injection on their N/A subaru.

If any guru's can reply with concrete info to the advantages to a WI system for a N/A car feel free to post up.

Just reviewing the Street Prepared Solo II rules and trying to see what options there are for an N/A subaru to get some power gains. Obviously intake mainfold & heads are a place to start within the rules.. but water injection is an allowable mod and I can see it's beneifit... mainly on turbo cars where intake temps are much higher, but non the less, would be curious to see what kind of gains it would off to a N/A car. If it's advantages offset the cost.

Thanks for your time.
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Old 04-04-2005, 12:06 PM   #2
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Im not sure about cars but I do know that back in WWII Many fighters were equiped with water injection because of the expanding properties of flashing water to steam (something like 15,000 x) I also have been interested in such an idea
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Old 04-04-2005, 12:31 PM   #3
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Water expands around 600x when it flashes into steam, but there is very little heat and time available for a lot of water to expand in your cylinder during the power stroke. The general consensus is that WI is not worthwhile on a non turbo engine since most of its gains come from lowering intake manifold temperature, which is already low (ambient temp versus 200degrees + for a high boost engine) on a N/A engine.
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Old 04-04-2005, 12:51 PM   #4
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the only possible advantage I could see in water injection for N/A would be if you are running some crazy CR (13:1 or higher) and are limited by class rules to use 93 octane. Water injection slows down the combustion event, similar to the slow burn of higher octane fuel. This will help to reduce detonation, but, i don't think it would be useful in real world situations.
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Old 04-04-2005, 12:59 PM   #5
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Quote:
Originally Posted by Boost-Free Subee
the only possible advantage I could see in water injection for N/A would be if you are running some crazy CR (13:1 or higher) and are limited by class rules to use 93 octane. Water injection slows down the combustion event, similar to the slow burn of higher octane fuel. This will help to reduce detonation, but, i don't think it would be useful in real world situations.
I don't think so; water is non compressible so injecting it into the combustion chamber would rise the compression ratio even more and make it more likely to detonate, I believe.
The reason why water injection allows turbo engines to run high boost with lower octane is because, again, it cools down the intake charge. Lower temperature air is less likely to pre-ignite fuel.
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Old 04-04-2005, 01:37 PM   #6
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true, it does cool down the intake charge, as the majority of the water introduced into the intake will evaporate, but it will also slow down the combustion cycle and raise the apparent octane of the fuel, similar to the effect of nitrous, although I have never seen W.I. used in a normally aspirated setup.
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Old 04-05-2005, 12:02 PM   #7
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Thanks for the replies.

Anyone else have more info?
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Old 04-06-2005, 09:21 PM   #8
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The only time you ever pick up any power with WI is when you are running up against the detonation limit of the fuel you are running. If you had really silly high compression (and a very good programmable timing control system) you might pick up A FEW hp. The reason turbo guys pick up so much power with WI is because any tiny little thing that is done to an FI motor to increase thermal efficiency (like advancing the timing) reaps huge rewards because of the large volume of fuel/air you are burning compared to an NA motor.

As for WI raising your compression.... there isn't nearly enough volume of water being injected to make any difference. Maybe .05 points... if that.
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Old 04-07-2005, 11:02 AM   #9
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Quote:
Originally Posted by no-coast-punk
The only time you ever pick up any power with WI is when you are running up against the detonation limit of the fuel you are running.
Jon -

Matt speaks the truth. I ran water injection on my turbo'd RS for a bit. It was simply a mechanism that enabled me to make more power by increasing the boost. (7psi with vs. 5psi without) By itself, it is not a power adder.


Matt - I have a question about this statement:

"...increase thermal efficiency (like advancing the timing)"

I'm assuming that you're speaking of valve timing. I'm not too sure how advancing the spark would increase thermal effeciency. I'm not challenging the statement. I'm just trying to make sure I have grasp of the concept. Thanks.

-paul
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Old 05-01-2005, 02:22 PM   #10
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I think your talking about Ignition timing. Valve timing has to do with the cams.
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Old 05-01-2005, 04:00 PM   #11
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I started a thread about this a couple months back.

http://forums.nasioc.com/forums/showthread.php?t=732918

Some good info in there too, FYI.

-James
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