i checked my exhaust manifold temperatures with a lazer thermometer and between the 3&5 and 4&6 are the highest temps. on the driver side at idle it went up to 790 and on the passenger side it went up to about 690-700. the idle mixture screws are set pretty good i think, they might be a little off, i havn't checked them with a vac guage yet. why would the temps be different in the same place on the manifolds besides the carb adjustments? i leaned the idle out some on the cool side and it didn't do anything much but go up a little. the spark plugs might not be in perfect condition but it idles smooth and runs good with them. thats the only other thing i can think of if the spark is a little weak.

 

Viper,

You might have a vacuum leak on the hot side, a thicker manifold casting on one side, a leaking main metering well plug on the colder side (rendering the idle mixture adjustments almost pointless), incomplete combustion (from many possible causes), worn throttle plates or a bent throttle shaft, low compression on the hot cylinders, a worn distributor (changing timing between different cylinders), a head gasket leak on the cold side, leaky exhaust valves on teh hot side, and probably a hundred other things that I'm not thinking about.

An oscilloscope would be pretty useful in comparing the spark enrgy on each cylinder, and if you have a really nice one, you can perform a power balance test to check the maechanical condition of the suspect cylinders.

 

the compression is fairly good on all of the cylinders, 155 being the lowest on 4 and the other 4 are 165. it has all new cap, rotor, and wires. what i think it is is the spark plugs, it probably has a few weak ones on that side. it might be a vacume leak but i don't think it is, and head gaskets are new. i'm going to lean the carb out a little too since its running a little rich and see if that does anything.

 

The manifold temp will depend as much on the individual manifold's ability to shed heat, as it does on the exhaust gas temp. You really can't tune an engine that way, too many variables. Any number of things could be different about the manifolds on the 2 sides, from their thickness, to the amount of rust built up on them, etc. etc., all of which just contribute to measurement uncertainty.

The places you mention being the hottest, are of course going to be the hottest... there's 2 cylinders cast together there.

It's very doubtful that the ignition system would noticeably affedt manifold temp, unless one cyl is outright missing part of the time.

Header tube temps are much more consistent as an indicator of exhaust gas temp, and therefore are actually useful. Another argument in favor of getting rid of those power-robbing things ASAP.

Also, keep in mind that each side of the carb feeds 2 cyls on each side of the motor if it's a dual-plane intake; not the left side of the carb feeds the left bank or something like that.

 

Stock water pumps will flow more on the pass side, allowing that side to run cooler. (Stewert pumps address that issue)

The combination of what RB83L69 said abt the clys being cast together plus the water flow deal, makes the spot between cyls 3 & 5 the hottest on SBC eng.

 

i was just messing around with it realy and just noticed a difference. guess its nothing to wory about. i have headers, i just need to have a y-pipe made.