Im experiencing a very odd issue with a friends 69 z28. Its got a 302 in it still that we just rebuilt. It has high compression forged pistons from sealed power and moly rings. We used a new set of AFR aluminum heads, Victor Junior intake and a used Holley 750 double. After starting the engine for the first time, and getting into about 15 minutes of the cam break in process we noticed that the headers on 6 and 8 were beginning to get red hot. Engine coolant temp was about 230 so we shut it down. We richened up the carb the next day, we put a large fan in front of the car to help cool the radiator. Coolant temps while running are still right around 190-200 so that seemed to help but the headers are still getting HOT. The passenger side bank is almost 100-200 degrees hotter than the drivers side. (With 6 and 8 glowing).

So far we've checked:

Plugs appear to be normal. They are not white, they have a nice dry tan color. After we richened up the carb, they are actually starting to foul.

Weve checked the intake manifold for air leaks and none are apparent.

Coolant seems to be flowing, so I dont _THINK_ theres an air pocket in the head.

What are we missing ?? It seems like its running pretty good. But that header worries me. Its already killed the ceramic coating on the headers.

 

Have you run the car from cold to operating temp w/ the rad. cap off? What kind of fan or fans are on the car?

Usually an air pocket makes the temp go up and down aside from gettin pretty hot.

Wierd problem man,get back to us we'll get it straightened out.

 

Headers will glow red while breaking in a cam due to the higher rpm and lack of airflow across the tubes sitting still in the driveway. Lean the carb back out and advance the timing some temporarily. This will reduce the amount of fuel buring in the exhaust and cool things off some. You don't want to wash the cylinders off with fuel.

 

What i'd look at is; if it's backfiring, you may have overtightened the lifters and be holding the exhaust valves open on those cylinders.

otherwise, air pockets are easy to get rid of, just jack the front end up a bit and run it for awhile pouring in antifreeze,

could check and make sure that those plugs are in good shape and burning all the fuel, could check and make sure that the antifreeze has enough antifreeze in it, sometimes water doesnt move the heat out as well as a 50/50 mix of coolant does, and thus it leaves hotspots...

just some stuff to look at

 

This is the first thing I thought of too. It may not even be enough to make it backfire but you might want to back off the valve adjustment just a touch.

 

First i'd figure that you have aa air bubble in the cooling system. Fix that first.

 

Are you running an exhaust system or just open headers?

I had a bank run hot after an engine swap on a 72 camaro..the exhaust sytem was in OK shape, but old...during the swap we apparanetly got some header gasket material into the exhaust system on that side and it clogged up the muffler..

What temp thermostat are your running?...

1971 Camaro, roller cam 454 LS6, tremec TKO 600, 2.56 gears, berlineta t-top, New Mexico plate "RAT454"