It's been a few weeks since I got my KR back into the air and got started on Engine break-in and evaluating the changes in the perfromance of the plane. ?I have roughly 10 hours on the new top end now, so temps and performance are finally starting to settle in.
In February, as part of the annual I installed new Superior cylinders on my O-200 with the 8.5:1 O-200-D pistons. ?I removed my Slick magnetos and sold them, then replaced them with 2 new P-mags. ?During break-in, I have been running the P-mags with the conservative timing curve limiting the spark advance to 34 degrees. ?Now that the engine temps have settled down, I'll be changing to the aggressive timing curve that will allow the spark advance up to 39 degress. As of this writing, I have not tried the aggressive timing curve yet. Additionally, I cut down the exit area on the cowling and extended the lower cowl back to match up with the front of the firewall. ?I then added a servo actuated cowl flap. ?Other changes included removal of the spring biasing trim I installed several years ago and the addition of a servo actuated trim tab in the right elevator. ?I added intersection fairings to the wheel pants to clean up the air flow and cover the flat gussets that were still sticking out in the wind. ?I also corrected some wiring issues with the plane, built a new instrument panel replaced the fuses with breakers, replaced all of the switches, added a Dynon pocket panel and added all LED illumination to light the panel better for night flight. ?I also pulled the graphics off the plane, repainted some sections of the plane and am waiting for delivery of new graphics with a new scheme for it. ?All of this work is documents with lots of photos at <http://jeffsplanes.com>. First flights: ?The first thing I discovered was that #2 CHT was running pretty warm and my oil temps were running much warmer than normal. ?Of course that was kind of expected since I was breaking in a new top end with new cylinders. ?My experience with overhauling cylinders is that a good quality hone job usually takes a couple of hours for the temps to settle in. ?Same with chrome cylinders. ?With new nitrided cylinders, I have 10 hours on it so far, but the temps are still coming down a bit with every flight. ?Right now under summer conditions, my oil temps are running at 205 - 210. ?My hottest CHT runs at 390 during climb out, then settles with all the CHTs even at 325 in cruise. I had convinced myself that I had somehow created a dog out of my nice flying KR. ?However, all of my flying since completion has been in hot, rough air with density altitudes between 11,500 and 14,000'. ?It's really difficult to establish any kind of usable numbers from those conditions. ?I had pretty much convinced myself that I had created a dog from my nice flying KR. Today I was able to spend some time in smooth air doing some one on one flying vs a Cirrus SR-20. ?The reason that was important to me is that the numbers on the Cirrus are well established and this particular Cirrus flies the book to the numbers very nicely. ?Additionally, this Cirrus is owned by a friend and he and I have many, many hours flying side by side and racing each other. ?I have always been able to smoke the Cirrus in a big way in climb performance, but once we reached altitude, he would gradually creep up on me and walk away at abou 2 - 3 knots faster than my KR. ?If we were going to fly together, I always needed for him to reduce throttle just a little. ?Today's comparison was an eye opener. ?As usual, I let him take off first, and went smoking by during climb out. ?Then I throttled back enroute to our destination cruising at 10,500'. ?After 30 minutes, I finally turned a wide 360 to let him catch up. ?I then dropped into formation with him, throttle up and passed him. ?Ok, well, I had just descended from above him, so I throttled back and let him pass me at the same altitude, then throttled back up and passed him again, with the KR steadily moving away at 1 - 2 knots faster than the Cirrus. ?The Cirrus has well established numbers showing that it flies at 155 kts under those conditions. ?My conclusion is that at full throttle level flight, my KR now tops out at roughly 156+ kts, which is right at 180 mph. ?My normal cruise is more in the range of 140 kts (160 mph). ?My goal when I started on these mods was to reach 155 kts at full throttle level flight. ?I really thought I had failed as previous flights had only shown a top speed of 151 kts. ?However, I had only got one other chance to actually run the plane in smooth air at the engine was still very early in the break-in at that time. ?But from today's flight I found that I was indeed successful at reaching my quest for speed. My impression of the P-mag performance: ?So far, I haven't seen anything great in the way of performance or fuel savings flying the Pmags. ?However, a caveat to that is that I have always ran my mags at 30*BTDC (since I am always at high altitudes) and my Pmags are currently limited to 34*BTDC, so I shouldn't expect to see anything special until I put in the more aggressive timing curve. ?However, I have noted that the P-mags significantly retard the timing for start up and idle, which makes for a much smoother idle. ?Additionally, the Pmags have a much hotter spark which will light less than ideal mixtures that weren't firing reliably with the magnetos. ?This makes for an instant startup whether hot or cold. ?Additionally, it seems to have reslved the following problem. ?Ever since I built the 4 header pipe exhaust system, my engine has always loved to run at full throttle. ?It ran very smooth at full throttle. ?However, when I would start dialing back the throttle, then engine would get decidedly unhappy. ?It just didn't run smoothly until I reduced the throttle at least 2 inches of manifold pressure. ?I had concluded that the carb was simply going too lean under those conditions thanks to the header pipes creating better flow with the valve overlap. ?So I had to either run WOT or do more of an economy cruise. ?In between I had to enrichen the mixture and the engine was still not running smooth like it did before the exhaust change, but was acceptable. ?With the installation of the Pmags, the roughness simply went away. ?The engine still loves to run at WOT in level flight, but now any other throttle setting works equally as well. ?The CHTs definitely run a bit warmer with the additional advance, but the EGTs now run significantly cooler. ?EGT on #2 cylinder now runs 300 degrees cooler than it did previously, although the CHT on #2 is now bumping up against 400*F during climb out. ?This is an indication that a lot more of the fuel is burning in the cylinder and not burning in the exhaust. ?The cooler EGTs should also contribute to longer exhaust valve and exhaust valve guide life. I will do another round of evaluations once I put the aggressive timing curve in on the P-mags and will report back if I find anything significant. -Jeff Scott Los Alamos, NM
