i put on hooker headers and had to get a custom y-pipe made, as i was driving to the shop my car kept making a loud banging sound and i could feel each bang in the floor boards. I had a friend following me and he said that orange flames were coming out. After the new y-pipe was installed the same problem persisted... so i double checked my spark plug wires and sure enough, the guy who had been helping me had put them on in the wrong order (cool huh). After fixing the order the problem seems to be fixed. Does anyone know what the noise was, and what caused it... also what permanent effects this might have on the engine?

on a side note: i also had the shop grind off a flange that was resting on the transmission, but this was after the spark plug order was fixed and the problem seemed to go away

 

It was just unspent fuel-igniting cause the firing order was wrong so it would fire while the exhaust valve was open. I have done this before once too.

 

I've done it before where the valve timing was such that the exhaust valve was wide open when the cylinder fired. Sounded like someone fired a cannon in my driveway

I learned that lesson pretty quick, and haven't done it since...

Left two big soot marks under my tailpipes (had the frontend jacked up pretty high), I'm just glad I didn't burn the valve or anything...