Old Acro:
**I'm going to set about the CMI KB " full Rich" flow (70 litres/hr), then check the TIT and lean further to 1250 degF TIT - 1300 degF TIT (with the caveat's about CHT). **
That should give you plenty of "head room" on the Red Box, ROP. Should work fine.
**I have never been able to achieve the CMI fuel flows. I have a deep suspicion that despite their "prohibition" on fuel flows leaner than 25 degF ROP TIT that in fact the economy fuel flows that they publish are maybe 25 degF LOP TIT.**
The POH Best Economy FFs will probably be either AT peak TIT or at 40dF LOP. If they are interested in TRUE Best Economy, it will be at 40dF LOP where the engineering graphs say it is. If they are hedging their bet about balanced F:A ratios and rough running, the number will likely be at peak. It will be interesting to find that out.
**This would explain why I can't get there, because I stop at 1650 degF TIT. Getting to LOP requires going though the 1650 TIT limit. **
The TIT limit is often misunderstood -- it is not an instantaneous limit. It is a limit for continuous ops at max rotor speed at 1650dF, which would likely only occur at critical altitude. This seldom the case, so there is a buffer built in. You can safely exceed the limit for the time it takes to find peak and reset the mixture either ROP or LOP. Most POHs list this a five-minute period.