You only need the high Ef. level, when you need a high speed. It won't help at normal cruising speeds. I didn't realize the higher engine settings use more fuel, even when the Ef. limits the speed increase... interesting, that.

.....

I know you didn't ask about this directly, but people seem to not understand this: The relative fuel consumption at various speeds are hard coded; I have no control over them. If the S-18 has a range in the *.sim file of 6,000 nm @ 6 kn. and I change it to 6,000 nm @ 8 kn., this is effectively giving it a bigger fuel tank. It does NOT alter the most fuel efficient speed. The fleets should get best mileage at ~9 kn. Of course, it is the actual engine speeds, not the telegraph settings which determine this.

I made it for RFB + RSRDC.

It *may* work with RFB alone, but you'll have to try it and see.

I'd try v2.8.

If it doesn't work, then the others probably would not either.