one bank or exhaust runs hotter?

[grumpyvette]

Just curious why the exhaust temperature on my 1977 van's 350 would be higher on one side than the other.
It's totally stock. I would think that if the idle air mixture screws were adjusted unevenly, that the differences might lead to the temps being hotter on cylinders 1/7/4/6 or 3/5/2/8 because of the stock intake configuration.
Not the case here. Using a non contact IR thermometer on the exhaust manifolds about an inch above the level of the spark plugs, I find that the temperatures are 30 to 60 degrees higher on the passenger side (2/4/6/8) that the drivers side.
The front and back pairs ( 1/2 and 7/8) are each about 30 degrees different. The center ones (3/5 and 2/4) average 60 degrees different.
I can see the center pairs being naturally hotter because the ports are a larger mass since they are paired side by side.
.......so how come the temperatures exiting each head are higher on the passenger side? It's a single exhaust system with a y-pipe configuration.
One note:
I just did a running valve adjustment on the drivers side when replacing the rocker gasket. I set them 1/4 turn like it's recommended. I think they were close to correct before I did the adjustment.
I have yet to replace the gasket on the passenger side. I'll adjust those valves at that time.

[/IMG]

look closely, on many chevy v8 engines theres a Exhaust Manifold Heat Riser Valve designed to route exhaust flow through the intake manifold to speed up the carb base reaching higher temps to help fuel vaporize to lower emissions these can and do occasionally restrict exhaust flow on one bank, thus one bank tends to run a bit hotter.
obviously a worn cam, a bad ignition,like a cracked distributor cap, or worn spark plugs or a vacuum leaks ,a partially clogged muffler or catalytic converter, leaking valve seals,bad rings etc. could contribute to the issue, or be the major cause.

 

[johnnmo]

Back a long time ago, when I had my 69 chevy 427 factory dual exhaust, I had noticed the mpg dropped 3-4. A brother walked around it and asked why one tail pipe was quiet.!!
I found the factory pipes were dual walled and the inside pipe collapsed 3 feet from the manifold! It really sucked it down and was hard to see when we cut the pipe in half because water wouldn't run thru it. Put all new exhaust on it and it was fun again.