Head temp differences, How big is too big? Options

[lapuwali]

I recently fit a CHT gauge, and originally put the sender under the #4 plug. Readings were in line with what I've read here: idled at 300dF, cruised at 325-350dF, touched 400dF under heavy load (lots of long uphill grades here).

I moved the sender to the #1 plug yesterday, and the temps are as much as 50dF lower across the board. Idles at 250dF, cruise about 300dF, never exceeds 350dF even pulling up a long hill.

I expected a difference, but not 50dF (20%!) between heads. I'm running Webers, so it's possible I have completely different mixtures for each cylinder. I presume cooler head temps would usually mean richer? This would be in line with plug colors (blacker on the 1/2 head, tanner on the 3/4 head). Hmmm....

[dmenche914]

yes, all the correct seals on the holes are important to prevent loss of cooling air, and seals in the engine bay (big seal around engine, the two covers over the alternator adjustment holes) prevent heated air from getting in to the fan.

(i dropped 50F just by adding a fire wall in a type I powered kit car)

Beware of tapes to seal holes, many tapes do not last long in the engine bay enviroment (even duct tape) and when they come loose, they often get sucked into the fan, and get trapped on the cylinder fins, hurting cooling)