OK, I am looking for help, especially from some of you who push the 4 cylinder envelope.

Built the 2056 and calculated 8.5 CR. It is a webcam and I have managed to get the MPS and ECU to play nice. I like the power I get, but not the heat. I have a pair of Dakota Digital CHTs wired up. One on #2 and the other on #3. We don't really have hills in Wisconsin, but on a pleasant day running at the speed limit of say 65 mph the #3 gauge will drift above 400 and then stay there. If I drive it like I want to it will go over 450 (and I won't get a speeding ticket) .

So I stopped driving it. The #2 cylinder is happy at maybe 320 at the same time.

What I have done:
set fuel so I am running at about 13:1. The car runs slightly better leaner, but the plugs look like a nice piece of toast in color, so I am OK with that. Actually, adding more fuel did not help much. It is 92 octane.

Changed timing. I found that the lowest temperature roughly coincides with stock advance.

Switched around and calibrated instruments - I think they are accurate.

I suspected that I might have gotten the deck height wrong with one cylinder bank, so I checked the compression. I get numbers between 125 and 135 psi, but 3# is in the middle. I suppose the numbers are related to compression ration, but don't really tell.

Final information is that the system heats up and cools down within seconds of changing the load. Something is cooling the cylinder off, but not well enough.

Before you say pull the engine out, can you tell me what I would be looking for? Are there things that I can check for so I have a target?

For example, can the cooling system fail in a known way? The fan is still on the crank and all of the tin is in place. I have a bellows new from Awesome Powder Coat, and it seems to function.

Thanks. Sorry this is so long, but thought more info would be better than less.

#3 is your hottest running cylinder. Is that temp taken from plug or head. Get the other 2 channels so you can watch 1 & 4. They'll be close to #1 but not the same. That's the problem with multi channel CHT's on air cooled engines. I wish you had EGT readings for those 2 cylinders.

And if I get the data, how do I steer forward? I can tap for EGT, and I can get 4 channels for cht. I am a scientist, so I love data. But what you do with it is where the skill comes in. Can you send a bit more help? I know #3 is farthest away, and I am measuring something arbitrary, the plug seal.
Anyone else? I really really want to drive this car!

If poor plug seal is the root cause of your extreme readouts, then how about a customized plug gasket with relief for the ring terminal?