Three words, Cooling, Cooling, and Cooling. For all the reasons Lynn talks about above.
Actually, I am not really pusing it very often. At 17.5k' it only took 28" MAP to go 207 KTAS. My real limit is 40" but I have occasionally been not paying attention and looked over and seen 45". But I normally fly around with MAPS in the 20's and climb-out in the low 30's.
BTW, I took a picture of my engine monitor, so here is the data for anyone interested:
altitude 17600
IAS 153 kts
TAS 207 kts
GS 257 kts (nice tailwind)
MAP 28.0
RPM 6560
Oil temp (at the end of continuous climb to 17.5k) 71C (160F)
Coolant temp (normal cruise temps usually even cooler) 80C (176F)
I forgot to look at the screen for manifold temp and fuel flow... that would have been nice.
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