: I am upgrading the engine in my N-35 bonanza from a io470 to a IO-550.
 : Does anyone have any experence with this change.  I am interested in
 : what kind of performance improvments I can expect, fuel burn, climb rate,
 : speed, etc....
 : Also I will have to put on a new 3blade prop, and have to decide between the
 : Hartzell or Black-Mac.  Anyone have any comments pro/con on these props???
 
         1.  Your airplane will be blindingly fast.  It will be 5-8 K faster
             on equal fuel flows than it is now.   Being light and of high
             HP, it will also be among the better climbers.  And very smooth.
              = Big smile...
 
         2.  You must suffer the gear-driven alternator; therefore extensive
             nose and baffling work is required.  Also air induction system
             is changed (=larger).  I'd get Beryl D'Shannon or someone who has
             done it before to do the work.  They are much higher on the
             learning curve.  Their STC is pretty marginal, so let them sign
             it off!
 
         3.  You may have problems keeping the engine cool.  Contrary to the
             location of the CHT probe in cyl #3, the hottest by far is #2.
             The only proven solution is the Pagosa Springs outfit mods to
             baffling and air vents.  As much as $2K more.
                 aside: Why should an engine that is obviously  more
                 efficient have MORE trouble cooling?   The 520s run much
                 cooler.
 
         4.  If cost is an objective, upgrading to a 520 would be much cheaper;
             you can find 'em in large #s from those who just *have* to have
             the 550.  Pick a -BB with the VAR crank and new style case.
 
         5.  Find out whether the Hartzell is covered by the 5yr AD.  =OH in
             5 calender years, independent of hours. = $$.  I'd not cheat
             on the hours for OH, but hangered in a reasonably dry place makes
             the /5yrs excessive.  The black mac is a McCauley with a 3rd
             party STC and I don't believe it has such a requirement.  Hartzell
             is a good outfit, tho.  Also check on the relative weights; on the
             older props, the Hartzell 3-blade was MUCH heavier than the
             76NB McCauley.
 
         6.  With either engine, expect an expensive top at ~400hrs if they
             have the Nitralloy valve guides.  Continental forgot that one
             can't make a bearing out of two hard materials, no matter how
             hard.  Use one hard and one soft (Bronze, Ni-Resist=Cast Iron).
             Shipped in a lot of engines in late eighties/early nineties.
             Also, the engine should be in compliance with the Continental
             SB on ++ fuel flows.  Early ones were way too lean and didn't
             live.  Newer ones are shipped in compliance.
 
 	 Regards, Bill Hale;  hale@fc.hp.com
         Instructor,  ABS BPPP program
         Personally installed IO-520 in my C33 using BDS STC.