"In the TSIO 550 a common problem is overheating of #2 cylinder and a common fix is to build a little scoop in the forward wall of the oil cooler box to create more air flow down the back side of this cylinder."
Yes. This is because on cylinder 2, the back side of the cylinder has no fins over a portion of the cylinder head circumference. The fins are cut very short (like there is a zone with NO fins) to fit against the next cylinder as with cylinders 4 and 6. See oversimplified sketch attached showing the fin arrangement on the cylinder heads where most of the engine heat not in the exhaust is rejected. Cylinders must be round, but the layout of fins is a modified square to get maximum fin area into the available area.
But there is a rub. The fins on one side are zero height, but air flows through down and through the fin passages on the adjacent head. Except in two cases: cylinders 2 and 5. Two has a piece of sheet metal on the back side ducting air to the oil cooler, but blocking the airflow through the fins. The fix is to add a blister (you called it a scoop) on the sheet metal to let the air go around the choke zone as shown. My blister is shown in an attached photo. No surprise, it works well. No flow before, flow afterwards, and like magic, cooling!
Same thing on cylinder 5, right front. The sheet metal baffle blocks airflow down the fins for the same reason and the same fix works. Or in the case of the Cirrus, the GAMI folks advocate putting a slot in the sheet metal and a deflector to guide the air flowing up locally into this slot. Again, magic: it works.
Cylinder 1 has lots of fins and fin passages on the back side because the cylinder is turned around compared to cylinder 2. It should cool just fine. But..... It is really yard to see that on the Lancair-provided sheet metal, there is a huge hole around the back side and it is also difficult to get the sheet metal to wrap around the head tightly to confine the flow inside the fin passages. If it is hot, it is probably because of hidden leaks that are very hard to spot. Use lights, mirrors, and persistence until you can see every bit of the area. Fix what leaks.
"Although I've only been to 12K in my IVP so far, I was impressed by the low CHTs in general, but true to form #2 was the hot one. I installed this mod and also modified the tops of the cowl air inlets on both sides to remove the factory lip and create a tear drop shape in X section to result in what I hoped was more laminar flow of the air entering the cowls."
A photo of the inlet mods would be helpful.
"So now, #1 cylinder is the hot one and I wonder why no one is talking about a scoop here in the aft baffle wall similar to the one advised for #2 cylinder.
From the fin layout, you can see no such mod is necessary because there are adequate fin passages on that side of the cylinder head. See comments and sketch referenced above. Cylinder 1 should cool fine due to layout of fins and baffles, but only if potential large leaks are fixed. Like the area under the crankshaft at the front of the engine where another huge hole exists in Lancair baffling, it is a common leakage area because it is very hard to see.
Fred Moreno