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OK, I
started this discussion, so I will attempt to summarize with my opinion based on
input I have received. Stated as opinion because I suspect the information
I have received does not fall into the "laboratory data"
category.
1. Do
8.5 CR engines go faster than 7.5 CR engines at the same fuel flow rate and
LOP? To close to call, this is sorting the fly shit out of the
pepper.
2. Will 8.5 CR reduce TIT when LOP and at the same fuel flow
rate? Yes. Around 100 deg F. You then have two choices. Run
lower TIT's or increase the fuel rate and go faster. The actual
IAS seems to be more airplane or possibly instrument related than
CR.
3. When TIT limited, 8.5 CR will allow fuel rate increases to
produce approximately a 30 to 50 HP increase over 7.5 CR for identical
TIT. These power increase numbers are a calculation based on .40
BSFC. At FL230 and up the many 7.5 CR engines have to run very LOP to
control TIT, particularly if 1650 deg F is the limit. At these altitudes,
some drivers choose ROP and this does affect the $'s per mile. There does
seem to be a significant variance in TIT from airplane to airplane with the same
CR. I wonder if this can be traced back to the intercoolers. If the
manifold air temp goes up due to intercooler efficiency then the fuel rate must
go down to maintain TIT.
Your
mileage may vary.
Craig
Berland
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