Straight water, how many % fuel removal

[UCTURBO]

Hi, Im currently running an rb30 ( 6.5:1 compression ) with 35psi boost on 98 ron with 15-18 degrees timing. At the moment the injectors are maxed at 7000rpm which flow 5250cc combined. If I injected 700-750cc straight water how many % of fuel should I pull out of my table? Should I pull a percentage to pull fuel and replace the same amount with water? Cheers

[Richard L]

What is the AFR?

If your are running below 11.5:1, there is scope for removing fuel.

[UCTURBO]

Its around 11.3:1 at the moment. Should I be aiming for around 12.5:1 with straight water? Im thinking of taking around 10% fuel away. Cheers

[Flr Power]

You should also think about using at least some methanol in the mixture has it helps the atomization.

[Richard L]

Based on the calculated diagram below, you can gain 2.5 points by injecting 3% of water and retain the same latent heat's cooling effect of gasoline.

3% of 5250cc of fuel = 157.5cc of water.




But there are other factors involved such as the combustion temperature increase rapidly as you are leaning off the AFR toward 14.7:1. (stoichometric of a perfect burn). Depending on the homogeneous of air and fuel distribution and the spark power, misfire will occur much earlier before 14.7:1 AFR, so 12.5 is about the limit of a non-leanburn combustion chamber design.

In practice, 12.5 is the ideal and injecting 3x the theoretical cooling value of 3% or 472.4cc/min), just to be on the safe side.

You can adjust you ignition to suit always go towards MBT. Adding methanol is good way to bump up the octane of your fuel. As suggested on the previous post

Here are more charts below for you to chew on. So always inject 3x or more as methanol concentration increases. (Latent heat of water is twice as methanol)




Further readings
http://www.aquamist.co.uk/vbulletin/...ead.php?t=2187

[UCTURBO]

I ended up taking 13.5% fuel away and injected the 750cc straight water. It went well with no knock with more timing, although after pulling the plugs one of them is fairly lean. 3/4 base ring is dark tan and 1/4 is a dark white. So Im going to add 7% fuel back into it and through a 50/50 mix in.

It was a guess my previous 11.3 afr going by the plugs ( black approx half way up the porcelain from the bottom) So I honestly dont know how lean it was but I'd feel safer if I richened it a little and added methanol. At least the mix will ignite easier than straight water. Which is the main reason I kept leaning it out with straight water. The mix will be around 15% to fuel volume. With 7% water so still fairly good cooling . Cheers

[Richard L]

Without seeing the entire setup it is difficult to know why the distribution is not good.

Where are the jet placed? The further away from the throttle the better. The best place is at the exit of the intercooler. You might like to consider port injection.

[UCTURBO]

Distribution is pretty good, that 1 cylinder is always a little leaner than the rest anyways.

[Richard L]

Good distribution improves even cooling to all cylinders otherwise you will always tune for the one cylinder and the rest over cooled. Some power will be lost overall.

[stevieturbo]

Originally Posted by UCTURBO

Distribution is pretty good, that 1 cylinder is always a little leaner than the rest anyways.

How are you determining this ?

Where are you injecting, and what sort of inlet manifold are you using ? and wow...thats seriously low CR !