Car will not overheat when it's idling, but when I take it out of the drive way and down the road it takes less than minute to climb up near 260 degrees. It only seems to overheat under power. Everything seems to be working fine. I can't think of anything that has went wrong. Timing appears to be on, new 160 thermostat, radiator is filled and holds pressure, fan works and blows in the correct direction. The plugs seem to be fouled though and it seems to run a bit different (maybe a bit more "rough").

I had the motor in and it ran perfect. Never came close to 220 with the fan on. We had to pull the motor to seal up the timing cover and now it wont run for ****. I'm stumped.

Any ideas?

Motor specs:
400, vortec heads, holley 750 cfm 3310 vacc secondary carb, air gap intake, gear drive, lunati 0010 cam, hooker headers, aluminum radiator, single electric fan ran by manual switch, holley red inline fuel pump.

 

Check the air dam.

 

It's there and fine.

EDIT: It's fixed. Thanks for looking.