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Old 09-02-2008, 07:59 PM   #1
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High compression + water injection

It's been shown that in boosted engines water injection cools and slows the combustion process enough to prevent destructive knock, thus allowing further increased boost. Has anyone tried using water injection on a high compression n/a? I see there are pistons available for D series hondas that offer 12.5:1 compression (stock on a natural gas powered civic). Normally, this would probably knock pretty bad even on 93 octane gasoline, but what about with water injection? The extra power from the compression would increase fuel economy (more power for the same fuel = less fuel.)


Anyone got a real high compression engine they want to try some lower octane gas in?
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Old 09-03-2008, 09:39 AM   #2
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I've always thought the same thing. Higher compression = more efficiency and power. So you could be cruising at 55MPH and be using less throttle than the same car with a lower compression ratio. Less throttle = higher MPGs as long as you keep your RPMs down as well. I've never had the opportunity to try it, but it'd be nice if someone out there who has tried it could share their experience.
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Old 09-03-2008, 01:38 PM   #3
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Edlebrock used to make a unit called varajection or varijection. It's a water/alky injection kit for NA engines and I know that they're still available used. I've got one on the shelf for another vehicle of mine, and while I was growing up my father used one on our old chevy van after he added a few other minor power adders and ran into detonation issues. I'm sure that there are other similar units still available, and I know for a fact that many aftermarket ECUs like MS, Haltech, Motec, etc have extra driver circuits designed for water/alky injection (among other things).

Water injection is an excellent way of stopping preignition/detonation issues, plus it acts a bit like a steam cleaner and it will keep carbon deposits in the combustion chamber and on the backs of the valves to a minimum.
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Old 09-03-2008, 06:19 PM   #4
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My turboed car is 8 to 1, na's run 10 to 1 in the same non turbo engine. This is because under hi boost i can keep making power under higher temps. The only reason we cool the air is to create higher density air to go with upgraded fuel, fuel pumps, altering the maps to the computer to account for all this. We push it to the edge of acceptable knock before detonation is reached. We don't want to kill our engines but it happens. Meth/water/nitrous are all ways to keep the knock down. In na cars these conditions are not reached unless something is really wrong with the car. na cars should use gearing to reach lower rpms with higher compression without adding the risk of detonation in my opinion.
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Old 09-04-2008, 07:07 PM   #5
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While water injection may reduce intake charge temperatures to a limited degree, that is not it's primary purpose. Water injection reduces combustion chamber temperatures as a result of absorbing heat energy when changing states (liquid to steam) during the combustion process, as the original poster stated. Water injection should work on an N/A engine, though finding and implementing the best delivery rates for various operating conditions will likely be a complicated task.
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Old 09-05-2008, 06:59 AM   #6
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Wouldn't the injected water, in the process of becoming steam, also increase pressure in the combustion chamber?
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Old 09-05-2008, 09:12 AM   #7
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Probably, yes. Since the air/fuel mixture would already be burning at that point, higher pressure couldn't cause pre-ignition. If it did in fact improve the efficiency of converting heat to pressure, it would simply yield additional torque.
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Old 09-05-2008, 09:52 AM   #8
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I would think (or hope) that the water would reduce the load on the cooling system, converting some of that waste heat into torque. Ideally it would be possible to inject so much water that no circulating coolant is required, so converting most of the heat into torque...instead of wasting heat as we do now, having to use a radiator to dispose of it.

There would, of course, be a million reasons why that's a totally ridiculous idea.
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Old 09-06-2008, 11:02 PM   #9
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Guys, you're overthinking this...

Water injection was used on NA cars long before turbuchargers became common on anything other than commercial diesel trucks and airplanes. It has benefits and it works, but it's not an end all solution.

Basically, you have a very archaic computer that controls a small pump. The computer reads engine rpm and vacuum and it responds with a set voltage to the pump. The pump speed and volume of water injected are adjustable through one or two potentiometers or through a simple computer adjustment (for more advanced systems or ECU based systems). You tune the system to add just enough water to stop knocking at the target rpm or rpm range so that you can run increased compression, increased combustion chamber temps, more timing advance, or a leaner mixture. Any benefit detriment of the water beyond that is negligible compared to the benefits of allowing better tuning of the engine.

The edlebrock system that I have sitting on the shelf was purchased from Lopers in 1979, and it wasn't a new system then. This is all old school stuff for the performance crowd... You can run water/alchohol or straight alchohol if you need the extra octane (like the turbo guys do), but for a NA car, its' really not needed.

If you have a turbo car, the solution is even easier. You get a non-expanding tank, route a small line from the pressure side of the turbo to the top. and a small delivery line from the bottom into the intake. You meter the amount of water with a carburetor jet and when the turbo is on boost, the tank pressurizes and water is forced into the intake. The more boost, the more dynamic compression, and the more water needed (and delivered)... Simple, elegant, well tested and proven to work.
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Old 09-07-2008, 02:15 AM   #10
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For high compression, I think that water injection would be a good idea. I actually have a kit waiting for some parts to arrive for my boosted engine. All the water or methanol does is reduce your octane requirements. Yes, it's better for boosted applications, but the water. alcohol will absorb extra intake heat, not so much needed for NA, and reduce temp while increasing combustions pressure(water to steam transition increase volume, and therefore pressure). I suggest you check here

http://www.aquamist.co.uk/phpBB2/viewforum.php?f=14

for more info. If you want to know in theory how it works, hook up a hose off of a vacuum port, and let it suck in some water. Even just want, not at all atomized(meaning hose and plastic bottle), will cool my intake manifold on a 28C day. Only problem you will run into is too much used, and either putting out the flame, or if you go REALLY oveboard, hydrolock. There are failsafes in all real kits to prevent hydrolock.
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