I've had the opportunity to play with several Stearmans with W-670's, R-755's and R-985's. It really depends on what you want out of the airplane. My favorite combination option is the R-985. I have never flown behind either of the Lycoming options (225 or 300) but I have worked a little on a 225 Lyc.
If you are going stock, I'd run a 220 Continental with a McCauley steel prop. The AD on the prop is a pain but I've never found another prop that performs as well as the McCauley. I've flow behind and in formation with Sensenich and MT wood props as well as Ham Std 5404's. The Hamilton Standard is typically smoother than a McCauley, but it won't perform as well. The MT is the better performer of the wood options.
The 275 Jacobs is a pretty sweet setup. Air Repair and Radial Engines have really refined the R-755-B2 and it is a good fit for the Stearman. It retains the stock look and does help with performance. The 2B20 is a natoriously poor performing prop, so I don't think you ever get to see the full potential of the Jacobs on a Stearman but, oh well. I'd lean towards the Jacobs if you want stock, live or operate at higher elevations and have money to spend. I personally think the conversion price of a Jacobs with the STC and all is way over priced.
I've never gotten to fly behind either of the Lycoming options. I think reason they don't get the love & admiration that the other options get is that it is a bit of a dated design and maybe not as refined as the 220 or the 450 specifically. I've been told many people that they are smooth (as they should be with 9 cylinders and a relatively small displacement) and I think they are fine engines. I'm biased, but they'll never be as reliable as a 220 or a Pratt. I've flown a bit with 300 Stearmans in a 450 and to match the speeds the 450 will burn less fuel than the Lyc airplane every time.
Like i said, the 450 is my favorite combo. It fits the airplane well and performs excellent. I love the 985 in general, but it's a perfect fit for a Stearman IMHO. You can cruise around at low power or bump it up to cruise fast, climb or do acro. You do get my cockpit wind and at the higher speeds you'll feel the controls get heavier for sure.
My general thought is all or nothing. I'd do a bone-stock 220 Stearman, or a 450 with 4-ailerons and all the mods (just keep it light). That's my two cents.
Ryan
_________________ Ryan Pemberton www.pembertonandsons.com
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