I HAVE A 1976 CORVETTE AND HAVE BEEN RESTORING IT FOR FIVE LONG YEARS NOW.
EVERYTHING HAS BEEN REBUILT. 350 WITH HEADERS, I LAID HEAT INSULATION FROM FIRE WALL THRU THE VERY BACK OF THE CAR.
BUT SEEM TO BLOW HOT AIR AS THOUGH THE HEATER WERE ON ONCE MOTOR WARMS UP...ROUGHLY FROM THE FOOT WELL AREA
DOES ANY ONE HAVE A CLUE...
THANKS DALE

 

is the floor pan solid?

 

the floor pans have both been replaced (the original two had liscence plates rivited in them for patches).
the hot air usually blows in around 55 mph and up...

 

is it actually heat "blowing up"..or is it more like a radiant heat from the exhaust heating the floor?

 

I also have a 76 and have made extreme attempts to do everything i can for the heat you are speaking of. It seems to be coming out of the vents at the feet of the passenger and driver. Even when they are closed I still get the hot air. So that is not the only place under there it is coming from. I am trying to solve the problem as well.

 

this may sound a bit redneckish...but when i was in college, i had a 83 oilds brougham, and it did the same thing...my father, who is a mechanic, put a closable valve on the hose leading to the heater core, and in the summer, i woudl shut it off to keep the hot water from heating the heater core,.

 

Check this. I had a similar problem on my '81 ... it turned out that, while replacing the headers one time, I poked a hole in the fiberglass box that holds the heater core. Since the hole was out of sight and right next to the headers, I would get a lot of hot air blowing in even when the heater was off. Just a thought