47-55.1 Exhaust manifold temp

[1project2many]

SBC dual plane intakes feed cylinders 1,4,6,7 from the left carb bore and 2,3,5,8 from the right bore. When the readings are colored to match the bores of a dual plane intake, it appears that the problem may not be bad mixture from one side of the carb.

L cylinder # 	intake	exhaust 	R cylinder # 	intake	exhaust
1		170	370			2	185 	460
3			760			4		763
5		165	715			6	170	575
7			495			8		290

With a ram's horn manifolds I would expect the four corner ports to be cooler and the four center ports to be warmer due to the direction of exhaust flow. The temperature chart shows the corner ports (#'s 1,2,7, and 8) are definitely cooler while the center ports are warmer. Generally speaking I'd say the engine is operating normally. When you look at the temperature readings for the center ports, and subtract the temp readings from each port's neighbor, the center port temperature readings seem reasonable as well.

It can be tough to determine why there are such large temperature differences between individual ports. There are so many variables to work out. Combustion rate is affected by the combustion chamber temperature and by the actual compression ratio. Is coolant circulating properly inside the heads? Is carbon buildup causing higher compression ratio in some cylinders? Exhaust port temperature is a reflection of how the mixture has reacted before the exhaust valves have opened. Is the ignition system triggering spark at the same time on every cylinder? Is the cam ground so each cylinder's valve events happen at the same relative time? Is something slowing the speed of combustion for some cylinders? Many of these questions are very tough for us average guys to answer.

I think you're on the right track with a valve adjustment. I personally try to adjust valves with the engine warm and running on SBC with hydraulic lifters. I would also double check ignition timing and see if vacuum and mechanical advance are causing timing variations at idle speed. Oil temperature is a good indicator of upcoming issues so I migh install an oil temperature gauge. Id' probably work the idle mixture screws a bit until I was satisfied the engine is idling as well as it can. Then I would put it on the road and monitor the gauges for issues.