I've been battling with higher than desired CHTs (>400). At the time I only had two cowl flaps in the same location as the default RV-10 louvers. Typically my hot cylinders were 1,2,5,6. At times a few of these would push towards 440 on my earlier flights. Here were some of the steps I took which incrementally improved things.
- Ensured baffling material was flat, especially in the rear corners.
- RTV'd obvious openings.
- Did the 'washer trick' behind #5.
- Trimmed 1 & 2 baffle dams.
The above along with pulling power out faster, managing climb speed (125 knots) helped but I was still seeing 1,2 & 6 get into the 430s (5 was good) and I didn't really like reducing power so fast and it started to get hotter out which started to drive the temps back up. So next I-
- Went through a ton of RTV, putting it on every gap, between the cylinders, all over my hands, floor... it was a mess but hey it has to be sealed at this point right?
- I also replaced the outboard lower baffle rods with some ends I fabricated out of bolts and used hose covered safety wire to pull them in nice and tight.
- I shimmed the space behind #6 to ensure there was an adequate gap.
- A major improvement was fiber-glassing in the top cowl inlets especially around the prop governor.
This got me able to full power climb in about 80 OAT with 1&2 just a bit over 420... still high but easily manageable.
The latest, and the reasoning for me posting here, was the installation of stock louvers in the not stock area. I'm post paint so the idea of installing something that would botch that up didn't set well with me. I noticed Vans now sells a louver kit for the 7&9 which looked as if they could be replicated on the 10. So that's what I did, I installed two louvers in the bottom area on the most outboard part of the lower cowling.
Here are some pictures but all in all it took me maybe 10 hours, most of that being the fiberglass work. These louvers in conjunction with my cowl flaps open seemed to really improve airflow. Today 91 OAT, full power climb at 95 knots (was doing this on purpose) and the hottest cylinder was 410. My intent was to push it hard and see the results. I'm really happy with the results of the louvers. I look forward to sub 400 climb outs!