Posted for "George Braly" <gwbraly@gami.com>:

 Colyn
 
 The PRIMARY reason for using  8.5:1 CR on the  550 with turbo’s is to manage
the  TIT.   Not Hp.  They also do get a bit more efficient.
 
 The gain in fundamental  Carnot efficiency from going from 8.5 to 10:1
 compressions is really pretty small.   This is an area with a rapidly
declining rate of return.

 It is worth doing in normally aspirated engines - - because they get some Hp
with the change to higher CR.
 
 But in turbo’d engines,  you can get the same Hp increase by adding boost
which is much easier and keeps more options available.
 
 So, there is very little reason to go much past 8.5 : 1 compression ratio in
turbo’d engines - - since the goal of managing the  EGTs and TIT limits at the
turbine are fully realized by going from 7.5:1 up to 8.5:1.
 
 Regards,  George

 PS:    REMEMBER,  sometimes the enemy of good - - - is an attempt at better.
""""
 Okay -make me ask:  Let's suppose I crank my FF to 46 gph WOT full rich for
climb and LOP for cruise and have a prism system. (all help manage CHT), and
let's say I manage to keep CHT's below 350 at all times.  how far can I push
the CR on a TSIO-550 without having a detonation problem?
"""