I have searched many places and can not find a straight answer, not even on this forumn.

My engine is a FD 13B-REW with all the supporting mods for power and reliability. Intial safe tune without any WI was 11.1 AFR at 16 psi boost which has been run for a few years without mishap.

For safety I added 350 cc / minute water only injection back in late 2010. With this, AFRs richen up some and I lose a little power.

I want to now tune to gain that power back or increase power a little. What is a good way to do this? Should I reduce fuel enough to lean out the AFR back to where it was before adding water?

IN THEORY: If I want to maximise power, would I:
(1) calulate and adjust fuel by: (11.1/12.2) * fuel which would give an AFR of 12.2.
(2) add enough water so that with the above fuel my new measured AFRS would be again 11.1?

 

let's assume you are making 400 SAE RWHP at 16 psi.

400 X 1.92 = 768 CFM /14.471 = 53.07 pounds of air per minute

assume you are at 11.0 AFR

53.07/ 11= 4.82 pounds of fuel per minute or/6.35 = .759 Gallons per minute

.759 X 116,090 = 88201 BTUs from fuel to make 400 at 11 AFR

350 CC/Min water = .0924 Gallons per minute X 8087 = 747 BTUs of cooling

747/88201 = .84 of one percent negative (cooling) BTUs in relation to energy BTUs

so the amount of water works out to be less than one percent of your positive energy...

it should be looked at as a non factor as it relates to power loss.

disregard it and tune your motor to whatever AFR you wish based on the usual factors of risk and return. feel free to up your water if you wish to around 500 CC.

while the water appears insignificant, it takes the edge off the CCP/CCH and greatly lowers the autoignition level while cleaning the motor.

just retune your motor as if it wasn't part of the equation.

regards,

howard

 

I'll share my thoughts and experiences tuning with just WI. Power is significantly better with a AFR of 11.5 - 12 compared to something like 11.1, with water injection, and PFC knock readings via datalogit can actually be lower with a leaner afr. When I was on the dyno I gained 26 hp on back to back pulls by leaning out my tune a little and getting the AFRs from 11.3 up to around 11.8.

when I was drag racing this past year I accidentally had a couple passes where my AFR's were logged between 12.5 to 12.8 and with the one run I did my best ever trap speed of 133.5. The motor ran great, sounded great, and again pfc knock readings stayed low. While there I figured out that I was tuning at night when my ait's would stay low the whole time, but when I was at the drag strip the ait's would be much higher especially after the burnout and they stay higher during the run down the track, the problem was my Inj vs Air temp fuel table needed adjusted so I added some fuel to the 30c and 50c setting to get my afr back down in the 11s.

My point is the WI may have saved my motor. I don't suggest running afr in the 12's, but it's good to see the motor will be okay if it accidentally happens. So after these experiences I try to keep my AFR between 11.5 and 11.8 for the best tune for the track and dyno. The richer you go below 11.5 the more power you loose, and I don't feel it's necessary if using WI, but that's just my opinion based on my experiences.

 

Depending on your ECU, it appears that your Air Temp vs. Injector settings are off.
Mine keeps the AFRs constant between seasons for boost. I also use the fast reacting Triumph air temp sensor.

 

Ya my settings needed adjusted in the power fc (also using the fraits) to get my afr where I wanted them while drag racing with the ait's higher than they were when tuning in colder temps ..

 

I found the most info about WI and WAI on the Aquamist site forumns.

http://www.aquamist.co.uk/vbulletin/