OK thanks for all the info.on the mufflers, I'm going with the SUMMIT TURBO MUFFLERS. now i have good soild 2.5 exhaust pipes that came on the car when i got it .but the guy befor me had a sb
and i have 454 . my headers are hookers with 3.5" collectors so do i use the header pipes that i have or do i go to a 3.00" ??? this a street car I will not be on the track , but i don't want to lose any hp if i can help it . I will be running 2.5" tail pipe just to keep it looking stock out the back .i read on this site that it shoud not hurt anything seeing that after the mufflers its
all about sound control and venting the exhaust away from the car???

Personally I'd go 3" or more but if your looking for quieter sound. 3.5" collectors with reducers to 2.5" then on out the back will work just fine, it'll be even quieter with a cross over between the two pipes after the headers, picking up a little torque to boot.

I would maintain the 3.5" pipe all the way to my x-pipe, then reduce down to the mufflers. Use a 3" muffler then neck down to 2-1/2" pipe. The practice of using a huge collector and then necking it down after the flange really screws up the scavenging intensity and range.