As you can see below the relationship between rich / lean mixtures and power output is not a simple one.
If they had used different ignition timing they would have gotten much different curve shapes. My guess is the dip in power under WI in the lean mixture area is due to the (inappropriate) fixed 30 deg BTC ignition timing for the injection rate/AFR.
When they went lean enough they got enormous power output nearly 2x the non-WI max power.
NACA report 812 ( Feb 1944) They ran tests on several "internal coolants" and charted their imep vs Fuel Air ratio ( .08 FAR = 12.5:1 AFR )
Code:
Figure 6 inlet air temp 250 deg F
With no WI (smoothed values read off chart)
Knock limited imep........ FAR .................. AFR
260 ----------------------- 0.12 -------------- 8.33
265 (peak)----------------- 0.11 -------------- 9.09
240 ----------------------- 0.10 -------------- 10.0
233 ----------------------- 0.09 -------------- 11.1
210 ----------------------- 0.08 -------------- 12.5
190 ----------------------- 0.07 -------------- 14.28
175 (min) ---------------- 0.063 ------------- 15.87
180 ----------------------- 0.06 -------------- 16.66
218 ----------------------- 0.05 -------------- 20.0
WI at .5 lb/lb fuel 70% methanol 30% water
408 (rich mixture peak)---- 0.10 --------------- 10.0
408 ----------------------- 0.09 --------------- 11.1
375 ----------------------- 0.08 --------------- 12.5
320 ----------------------- 0.07 --------------- 14.28
285 ----------------------- 0.06 --------------- 16.66
280 (min) ----------------- 0.059 -------------- 16.95
325 ----------------------- 0.05 --------------- 20.0
455 (lean mixture peak)---- 0.04 --------------- 25.0
One obvious lesson from these curves is there may be significant power available if the tuner is willing to explore the limits of the tune into areas that are normally considered unreasonable to even approach. Obviously proper test equipment is needed to prevent destructive knock during testing.
All these power outputs were limited by either presence of knock, they had reached max possible fuel flow, or the had reached max manifold pressure of 150 in/hg ( 75 psi boost) or preignition.
Larry