Usually a lean condition creates higher combustion temps. In a rich condition the extra fuel usualy acts as a heat absorber. Possiibly in your case, the fuel was still burning in the headers. Do you have a decent overlap cam grind? I could see this causing what you described. Or possibly it has to do with the forced induction. Im not well educated in that field.

 

Actually this is a misconception??? The extra fuel does NOT act as a heat absorber.
Think about it? A extra small amount of fuel and it doesn't take much to go from a good mix to a over rich mix. This extra fuel is suppose to absorb all this extra heat??? No way simply adding a small amount of extra fuel is going to pull more heat out of the combustion chamber.



Someone give me the answer? If not I will get back to this in a few hours.
Hint. A motor makes it's most power around 13.2 to one but for safety they run about 12.5 and with forced induction can drop into the 10 to be extra safe. Why???

 

 

late timing can cause a red glow

 

Well, carb or timing it may be. But why would they both no glow then?

 

It really does not matter what material the headers are made of, if you wrap them they will eventually "cook out". Now, if you do not mind replacing the headers with new ones every so often, then this is the way to go to cut down on the heat. If not, you may want to look into one of the available coatings in conjunction with a heat barrier at the firewall and floorpans.

 

I had a set wrapped and sealed that rusted out in 1-2 years as well. Not going to ever use the stuff again frankly.

 

carbs are notorious for awful uneven fuel distribution.

 

FWIW... I don't know about lean conditions, but I have experienced a rich condition causing the manifolds and pipes to glow red. That was because the AIR pump was "after-burning" the excess fuel in the exhaust system instead of in the combustion chambers.

The rich condition was caused by a bad choke pull-off diaphragm on a Q-jet (big block Chevy).

I don't think a rich condition would cause excess heat any other way than if you have an AIR pump adding O2 downstream. The fuel doesn't absorb the heat, it just doesn't burn as hot due to O2 starvation.

 

Yep, I concider pipes to be expendable. In a few yrs I'll be happy to build annother set if it keeps the cabin cool, cheap investment

 

On the too rich / too lean debate, I've been thinking about this one for a bit and have come up with examples where either can raise exhaust temps.

First, in aviation, after take-off and climb-out with mixture full rich, the A/F ratio is leaned out as altitude is gained due to thinning air. EGT is monitored to assure proper tuning. If the mix is leaned out too much the temp rises, which is corrected by richening it back up a tick. Fail to do so, and you run the risk of "burning a valve".

In a diesel engine, if eroded injectors aren't replaced in a timely manner, the increasingly rich delivery of fuel will eventually raise EGT to a point where turbo bearings can fail. This is due to the additional heat generated in the combustion chamber (or exhaust pipe) from burning off the extra fuel. However, in gasoline engines, except for those equiped with AIR systems, I'm not certain this effect would be quite so pronounced before you foul a cylinder.

Other than when mixture is too lean, any cooling effect from an overly rich A/F ratio is likely limited to that on the intake charge going into the cylinder, as it should stand to reason that once combustion begins, burning the denser charge is going to create more thermal energy. That said, cooling the intake charge by richening the mixture can sometimes crutch pre-ignition problems, and may explain part of why you'd need to be rich with a blower. (Thoughts, Norval??)

Bottom line is, whether I've got it exactly right or not, it's important to get the A/F ratio within the correct range. But if you're going to miss, it's probably best to err just on the rich side of "optimum" for our purposes.

Now, anyone else wishing for an EGT gauge in their Vette??

 

Well thats something we can all agree with!