I had good luck with WMI on the EB Mustang, so decided to go the same route for the Fiesta. My plan is to go with the upgraded turbo, ported manifold, downpipe, and pro-tune in the near future, but decided to run some experiment with the Cobb OTS tunes.
Baseline:
Snow Performance Stage 3 (set to using boost only) with a small 2.5gph/157cc nozzle (will use a bigger nozzle for the turbo upgrade and pro-tune)
70% methanol / 30% distilled water mix
Whoosh V1 IC
Whoosh hot and cold side charge pipes
Whoosh crossover pipe
Mountune induction hose
Cobb drop in filter
Cobb OTS 93 OCT Stage 3 tune
AZ has 91 OCT gas (heard it's worse than 91 OCT from other parts of country)
Ambient temperature over 100 degrees
With WMI off:
Saw negative ignition corrections as much as -2 to -3 degrees when I got on the throttle. OAR got as low as around -0.80
With WMI on:
Only saw one instance of negative ignition correction and it was very low, like -0.06. OAR stayed at -1.00.
STFT at WOT and max boost stayed around -5% and the AFR did not fall below 11. There were no popping noses when lifting off the throttle. These findings suggests that Cobb OTS tune (and likely stock tune) can handle a small nozzle without issues. I heard that the ECU can handle up to around 20-25% fuel adjustment without issues and saw the same for the Mustang.
After using up some fluid, I added more water to get the ratio to around 50/50. No negative ignition correction observed so far. I will keep increasing the ratio of water until I see negative results. I also have 1.5 and 2.0 gph nozzles so I can try them out if I don't see any issues at 100% water.
One thing I noticed is that I didn't see reported charge temp drop during the injection like I did with the Mustang. EB Mustangs have the charge temp sensor in the manifold MAP sensor so it must not be the case for the Fiesta ST.
I used the windshield waster fluid reservoir on the Mustang and decided to do the same. I overestimated the space in front of the bottle and couldn't mount the pump at the lowest point, but at least it's below the largest part of the bottle. I'll revisit later about making a custom mounting bracket to get the pump lower. The bottle holds about three quarts, same as the bottle that came with the Snow kit.
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