My son also owns a Turbo-Saratoga SP. His is a 1981 model with the intercooler and LoPresti speed mods on it.
I think you will enjoy reading my email to him and his answer.
I am looking at my Saratoga Cruise Performance chart in the POH. One thing that doesn't make any sense
is how they have a line for 55, 65, and 75% power based on 100 degrees rich of peak and one at peak EGT or TIT.
As an example 75% power should be 225 HP. How can they then show two different 75% power speeds?
If the engine is producing 225 HP then the speeds should be the same. Do they really mean the engine is
developing 225 HP at best power mixture and less than 225 HP at peak TIT mixture? I know that is what the
engine is doing but they don't express it that way in the charts. It looks like they are basing their % power
numbers on RPM and Manifold Pressure settings only and not taking into consideration the fuel flow. There
is another table that shows 75% best power fuel flow to be approx 18.7 GPH and another table shows
75% best economy fuel flow to be 16.5 GPH. I wonder which one of these is really producing 225 HP which
is 75% of 300 HP? When running 50 degrees lean of peak TIT at say 16.5 GPH is that producing the same HP as
peak TIT at 16.5 GPH?
If you study what Insight says about the new G3 and all of the variables in displaying % HP it makes you
wonder about these engine analyzers that show % power and are they very accurate.
I did a lot of reading about intercoolers and how one of the companies developed new power charts when their
intercooler was installed. They actually measured the HP or torque with a gauge in flight. They claim that
their method is more accurate than the differential cooling and calculation method that yours uses. The best
way to determine which one is producing more HP is to measure true airspeed at the altitude your are flying.
The best power fuel flow is probably wasting fuel to produce more HP. Stoichiometric ratio refers to the optimum theoretical mix of fuel and air to achieve complete combustion of that fuel. Sometimes called stoichiometric air ratio.
This occurs at peak TIT mixture settings.
Here is his reply!
You are going through the same thoughts that I had been going through when I first got my plane.
I decided to hell with it, and just run 2400 RPM, some manifold pressure, peak EGT as long as the TIT is below red line and then it is what it is.
He gets 180 knots true airspeed at 16,000 feet on 17 GPH.