Just a FWIW, for anyone contemplating an engine swap for a 170 or 172, while I'm happy with my 180hp Avcon conversion, it's not all a bed of roses. After talking with others, mostly experienced mechanics including my IA, the kits of all the STC holders often haven't included all that is necessary, so you'll be sourcing stuff elsewhere. And it's a whole lot of work, with a fair share of McGivering necessary to get the job done, no matter whose STC is used.
If you're dealing with an already converted airplane, it can get pretty interesting at times, when parts need to be replaced, because they were sourced elsewhere--sometimes off of some dusty shelf in the converter's shop because they happened to fit, but not necessarily very well.
Just recently, for instance, my IA replaced my prop control, as the old one was binding and was worn out. The control that was in it was a vernier, and I'm happy with a vernier, so he obtained a new vernier control. I played mechanic assistant, essentially providing an extra hand when he needed it, which is just about the limit of my aviation mechanicking skills. When he pulled out the old one and compared its length to the new one he'd measured for and ordered, there was almost a 2' difference in length! Yet the new one fits perfectly, and is of course much smoother. I'm guessing that some of the old one's stiffness was caused by the circuitous bends it had to make, to fit in a much shorter space than its length.
The end result, though, should be gratifying. I've flown dozens of 172s, many of them stock variants Cessna has made ranging from the 145 hp Continentals through the 150 hp and 160 hp Lycomings and the 195 hp Continental powered XP; the 180 hp Lycoming conversions with a CS prop are IMHO the best for the buck (I'm biased, obviously). They're still relatively economical to operate (I figure 9.8 gph), and they climb very well. They cruise a little faster than stock, although no 172 will be a speed demon just because it has 20 or 30 or 35 extra horses out front. The slight edge that the XP's 195 hp provides over the 180 hp conversions isn't noticeable in the real world. I suspect a 220 hp conversion might be pretty noticeable--although some might argue that it's too much for the airframe.
Well done, a higher powered engine conversion plus a CS prop turns a relatively mundane airplane into a much more capable one.
Cary
