hi, i have an old 73 el tigre 440. It has been running great until just recently. It runs fine but after fifteen minutes it starts to bog down and won't go above 5000 rpm's. I notice huge amount of exaust collecting under the hood so i took off the pipe when i got home and i found about a 10 inch crack right by the mounting bracket and all so the connection to the y pipe was all cracked and chipped so exhaust was leaking there to. I think that thins is my problem but i'm not sure. I have heard that you need the pressure from the exhaust pipe to make the sled run right. Is this true, and if not what could it be?