1987 white mustang convertible 5.0 EFI. Cobra Upper and Lowers. Ported GT-40 Heads. Bassani headers and x-pipe. Not sure what cam is in the car but it is very aggressive (not stock). Cold Air intake. Mass Air. screaming demon ignition. 8mm plug wires. Not sure what size injectors but they are not stock. frame rails. Lowered 1.5 inches. Custom dugan racing rear shock supports. I bought the car as is and have slowly been learning what is on it. I have blown the enging twice already, first time they told me the "bottom end fell out" had to get a new block, crank, and pistons so they are all stock. the second time i broke a valve spring and dropped a valve, it wasnt too bad though. so they replaced my valve springs with 90 pounders. This morning on my way to work the car is making a really wierd noise out the exhaust, sounds like gurgling. Also lost some power, am afraid to take it over 3000 rpm. I have no idea what could be causing this. I just replace my fuel filter last month and I use only 93 octane. everything under the hood and sounds normal so any help would be nice...