Hi Old Akro
It's been a few years since I've flown a Seneca and I can't remember fuel flows, power settings etc., but I currently get to fly between a couple of intercooled, twin turbo'd IO-540's every now and then.
The aeroplane has it's stock engine instrumentation, but there are no EGT gauges. Just a couple of TIT and fuel flow gauges.
Takeoff power shows up as 42" and 2500RPM with the fuel flow sitting on 175l/h per side. The TIT hovers around 1250°F or a bit more. I normally set climb power at 38" and 2400RPM. If the mixture is left full rich the TIT drops back to a bit over 1200°F and the fuel flow settles on 160l/h per engine.
However, I find that some times if the mixture is left full rich in the climb (the POH states full rich anytime you're above 75%), the aeroplane leaves long trails of black smoke everywhere it goes. It was enough for someone who knows the aeroplane to give me a call one day as I climbed out, suggesting that I had an engine fire!
For me, that indicates that the engines are running far too rich. With climb power dialled up I'll pull the mixtures back slightly, looking for 1350°F on the TIT's. The fuel flow comes back to a more reasonable 150l/h (although at 300l/h total, some might say that's still very unreasonable). I never have a problem with CHT's at any of the above power settings. The CHT sits rock solid on 320° in the climb all the way to FL200. It's only when the aeroplane gets above this altitude and the wastegates are fully closed, that the CHT might drift up to and nudge 340°F. That's still way below 400°F and I feel comfortable with that CHT at high altitude.
I realise I'm not talking TCM IO-360's here, but you were mentioning TIT's so I thought I'd compare notes.GB.