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Greenv8s 09-01-2005 02:01 AM

This may be a silly question, but do any of you have any experience of the in-cylinder cleaning effects of water injection? Several people have mentioned that WI cleans the combustion chamber up nicely but I don't know anyone with first hand experience of it.

I've got a low pressure supercharger on a Rover V8, which hasn't been set up yet. It may be some time before it is set up properly because there's a slight distribution problem at the moment. In the mean time I'm running it massively overfuelled to make sure none of the cylinders lean out. I expect that in time this'll coke up the insides of the engine nicely and could aggravate detonation problems. So I was wondering whether my WI system is going to be any help to control the coke build up?

hotrod 09-01-2005 10:26 AM

cleaning effects
The carbon cleaning effects of WI are well documented. I've never pulled the heads on a WI car but have seen first hand the effects of water on carbon build up.

Many years ago 1950-1970's it was a common tune up "trick" used by many hotrodders to remove carbon buildup on the high power V8's in use at the time. Carburators were jetted quite rich to control high load detonation.

Carbon build up became a problem, especially in the 1970's when the oil crisis hit and folks were trying to run cheaper grades of fuel or high octane fuel simply disappeared from the market.

We would take an engine that was well warmed up, set it at a fast idle and trickle a thin stream of plain old water down the throat of the carburator, gradually opening the throttle until you got to about 3000 rpm or so, then increase the water flow until the engine seemed to have trouble with the excess water (sounded like the engine was strangling). It is truely astounding how much water you can pour down the bores of a large V8's carburator at a high throttle setting.

On an engine that had heavy carbon build up on the spark plugs prior to the "treatment" they would be nearly as clean as new if you pulled them afterward. If the engine was pinging due to carbon build up, it would magically go away after just a few minutes of this process.

Red hot carbon and steam react in a process called the "water gas reaction" --- look it up. It converts the carbon to gaseous CO and hydrogen both of which burn off inside the engine. This was used to by industry for many years to produce combustable "water gas" ( substitute for natural gas ) from coal.

You may need to back off your excess fuel a bit if you add water injection, to avoid a slight power loss caused by the combination of too much fuel and WI, but that would be the only down side I can see.


Greenv8s 09-01-2005 11:16 AM

Thanks, that sounds very encouraging. Do you reckon the effect would still occur with a small WI rate over a longer period, or is it important to add enogh excess water to make the engine bog down? I guess I can just try it and see what happens to the plugs?

hotrod 09-01-2005 03:27 PM

small injection rates
Small injection rates are good enough, it does not require a lot of water unless you want to get the job done in 10 minutes.


mr2turbored 12-03-2006 10:20 PM

is this process only if you've got the jets near the throttle body?

Am i right in believing that in cylinder effects happen when the WI jets are near the throttle body and intercooling effects are far from the throttle body.

Please excuse the stupid questions as i'm new to this and looking whats best for my car etc.


keithmac 20-03-2006 06:43 PM

I`ve always gone with this theory, jet placed further away from inlet valve will have longer to mix with the charge and therefore cool the charge ideal substitute for an intercooler. Jet placed closer to the inlet will have less time to mix with the charge and cool it but more water mist/vapour will be present in the combustion chamber which will better cool the in-cylinder temps and prevent knock.

First time I let rip with the WI the amount of crap that came out of the exhaust made me think I`d blown the engine!, will be pulling the engine to pieces in the summet so I`ll post some pics..

wingzero 17-07-2010 09:37 PM

Re: decoke?
Are there any ill effects this decoking process will have on the O2 sensor down stream?

maxc 20-07-2010 12:43 AM

Re: decoke?
decoking too fast is hard on the cly walls!

Richard L 27-10-2011 10:57 PM

Re: decoke?
This old thread becomes more interesting on direct injection engines such as the audi's FSI, BMW's Piezo electric injector etc. All suffering from carbon build up on the valves.

Dust 30-04-2012 12:29 PM

Re: decoke?
Wanted to post here, since I just finished reading some thread on NAM




here are two more related to mini stuff if you want to read



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