running extremely lean HELP!!!!!

[bonestocksr20]

well about a week ago my downpipe broke so while i waited for my new one to come in i drove my car with out a down pipe on it. i just got my new one hooked it up and drove it. car ran like a top, but when i got out of my car i smelled something burning, opened the hood and the exhaust manifold was glowing orange. super f*****g hot. i dont have a a/f gauge but that is the only thing i could think would make it that hot. any ideas i need help dont want to hurt my motor but this is my dd and i need it to run. please help!!!!!

[srdub-t]

you could be running lean or your timing could be retarded. Id check your timing.