I've avoided jumping in on this thread, but I've received a number of private emails asking me to weigh in. So, hear are my opinions, based on 10,000 hours of GA piston experience, as well as looking at close to 2000 RV's.
First, keep in mind that on this forum we are primarily speaking about Lycomings. Mike Bush's experience is primarily on Continentals. Yes, they are different.
First, keep in mind that EVERY ONE of our aricraft is different. Please read that again. I have yet to see 2 aircraft exactly alike, even when constructed by the same builder. I point that out because it seems when someone asks for help everyone wants to point out that their airplane runs differently. Yep, it probably does, and until one closely looks at it, we may not understand why. I still get a kick when someone tries to point out that their particular airplane has been "flying this way for over
200 hours with no problems." Zeesh, we still issue Bi-weekly AD's on a certified fleet that has trillions of hours on it. Our RV fleet is extremely young by any standards.
So, please keep an open mind here, as I do not intend to get into an argument with anyone.
Yes, I did explain to the genleman at OSH that adding some tape or other paraphenalia to cylinders 2&4 as shown in Dan's picture, will in fact help to increase those temps. That is based on experience. It usually does nothing to the other 4 cylinders.
Second, everyone is trying way too hard to keep cylinders below 400 degrees in the climb! Remember I pointed out that Lycomings are different than Continentals. Quit trying to apply the same constraints across both engines. Lycomings will run all day to TBO using 435 in the climb. When Lycoming introduced their LASAR ignition system, it had a CHT probe that would KEEP the CHT's at 435 by advancing the timing in the climb. My RV-6 had that system and went 1800 hours with it. It was clean as a whistle when torn down due to a prop strike, and burned hardly any oil. I've been to the Lycoming factory and spent time with them. They are annoyed that we all keep trying to run them so cool. BTW, for certification purposes they have to run the engine NONSTOP at full throttle with EVERY temp maxed out for 150 hours. We aren't even getting close.
The first advice I give everyone on hot CHT's is to check ignition timing. It's the number one culprit, following by proper airflow. We had an RV-7 come to us this week complaining about high CHT's in the climb, with number 3 cylinder hitting 471 degrees! Yep, that's hot, and need to be corrected. So, first thing we do is check the timing on the O-360. It is at 28 to 28.5 degrees!!! We timed it correctly at 25 DBTDC, and added the washer to cylinder 3 baffling between the rear screw and the baffling, and further opened up the baffling on number 3, as it was tight against the rear of the cylinder. They reported that on the way home all temps were normal, and they are very happy. They also had a big 2" hole in the front baflling pointed at the alternator. We closed that up by more than half. It is important to keep holes into the bottom part of the cowling to a minimum so that the high pressure is on top and allows for good air flow from the top of hte engine to the bottom of the engine.
Next subject---leaning. Before we had all of our fancy gauges, once we reached cruise flight and set power, we pulled the mixture back until it ran rough, and then forward a little until it smoothed out (kind of the way Scott mentioned his wife does it). That pretty much kept us right at PEAK. It worked, and that's the way I've always ran my engines. My current Thunderbolt has 870 hours on it and burns about 1 qt every 12-15 hours. Pretty excellent for an IO-540.
The first thing I do after it starts is to pull the mixture WAY back. It's so far back that if I add any power to taxi I usually have to enrichen it a little. You can't hurt the engine with the mixture control below 75% power. Keeping it lean on the ground stops the lead fouling the spark plugs. Someone already mentioned that lead won't vaporize until about a 1000 degrees. If you look at your EGT's they are more around 900 or less at idle. So keep the mixture leaned ont he ground.
As for approach and landing, I do leave the mixture leaned for descent. Sometimes it requires enrichment during the descent if I've been up in the teens for cruise, and then I do enrichen quite a bit on final, but not full rich. I know it will go to full power easily if I need it, as I've tested it.
That's a hint--- you should test yours, as they are all different.
So in summary, just like we are all different "people", our airplanes are all different. You need to take a hard look at yours to look for differences. Get another set of eyes on it if possible.
In the end, when it comes to cooling, ignition timing and proper airflow on our STOCK engines are the
two primary causes. After that, there are some other things to check for, such as proper fuel flow, especially on injected engines.
Here's a quick test for those of you who are wondering about that one. Set power at 24 squared, cruise flight and FULL RICH, and make a note of the EGT value. Pull mixture back slowly until the engine stumbles. You should see an increase of 175-250 degrees on the EGT. IF not, then it is set up too lean, which could be the injectors or the main nozzles. It's too much to go into detail here.
Other contributing factors can be plenums that are too tight, poor baffling seals around the top of the baffling, poor sealing of the baffling to the nose area and motor mounts, etc.
Actually this whole discussion probably warrants a webinar so we can discuss things better.
One last point--- climbing at 75 knots on a new engine is dumb. Our RV's cool best between 100-110 in the climb. We are redoing the EAA flight test manual to recommend breaking in the engine prior to doing some of the flight testing.
So, there's my .02.
Vic