RE: 250° F - is that too hot?
I have a sort of a similar setup as branwell on my 88" EF Yak. The pipe tunnel entrance is open but the tunnel is empty. The tunnel exit opening has the covering removed on the bottom. Question: Does my oil pan create that negative pressure like the modification you guys were talking about doing? If not I was thinking of cutting the trailing edge of the oil pan on both bottom corners and curving the FG down to create that lip needed to draw air out of the cowling. I also wonder if doing this at the pipe tunnel exit would help. I have no temp readings to share. The engine runs great but more cooling is more power.