What I built up is fairly stock.
I did polish and radius the intake spider and elbows. Smoothing them with a dremel and brake cylinder hone was easy but time consuming. When I first started, there was a noticeable lib between the intake pipes the the smaller diameter of the castings. Smoothing out the transitions certainly helped the engine breath better. One of the big tricks Don uses, is creating a venturi in the throat of the spider. He actually will use an A-65 spider, because it has more meat in the throat, and machines it to profile. I did the same with a standard C85 spider and created a slight venturi, but was more interested in getting the matting faces matched. Mass balanced the rotating parts to within .4 grams, by swapping parts around. It dyno'd at Don's right at 99hp, so I was happy. When I sent the case off, the plan was to go with a standard C85, but it came back with the machined lifter housings for C90/O-200 lifters as well as the slinger ring. So I guess they do that mod standard now.
We're running a new McCauley 1b90CM7146 which is a lot of prop, but the motor soaks it up nicely. On the Cub (25" Goodyears, no VG's) it will get airborne around 200'-250' but can cruise at 95-100mph. Understand, this is a Champ prop and I didn't want it re-pitched. We tried several other props; CM7445 and a Sensenich 7242, but neither pulled as hard or cruised as fast. I like it that way personally because it will pace with any other aircraft in the class. We flew to Ohio with 3 other Champs (65hp, 75hp, and 85hp.) The Cub was faster, and climbed harder, then any of them.
With the CM7146:
static: 2250-2300rpm
WOT: 2550rpm
Cruise @ 2150 = 80mph 4gph
Cruise @ 2300 = 90mph 4.5-5gph
Cruise @ 2500 = 100mph 5.5-6gph
I've got another C85 were building up soon for a 'project' and it will be for max power. I've got both LyCon, moly coated 10/1 O-200 pistons, and a set of C85 rods/pistons; when we figure out which makes better power I'll let you know. I'll probably change the cam timing by a couple teeth. I'd use the 35* C-90 cam, except it only shows an advantage with an open exhaust; and we will probably be running a system similar to a J-3's. Plus I've got a C85 cam and lifters already. It would be nice to custom profile a cam, but thats above my pay grade. We will dynamically balance the crank this time though. And maybe bump the timing to 30/30. I'll clean the intake system again, but also have the jugs flow balanced. Then maybe get a new CM7642. I don't want the shortest takeoff possible; thats not practical for us. I would rather see the power be put to use in both climb and cruise.
nkh