new exhaust, doing this one right need help

[95offroadx]

well im tired of my 2.5" catback flowmaster 40series exhaust and hollowed cats, i had it custom made at my local exhaust shop, i noticed little performance inprovement, well i got tired of the look, soo now i want to do a side pipe type exhaust kind of like the ford lightnings, with magnaflow highflow cats, and a flowmaster super 40's muffler single in/dual out and dual 2.5" tips

i dont want to loose any backpressure or anything i just want to gain power, what size in should i use? what size out?

either 2.5" in and 2.25" out
or
2.25 and 2.5" out

 

[triplexplorer]

When you get it done can you post pics i was looking @ doing side exhaust but i wanna see what it looks like before i throw the bills at it.

 

[mikehawk]

I have a straight 2 1/2" pipe off the y-pipe to a 50 series flowmaster, then the pre-bent 2 1/4" pipe from the FM force II kit goes from the muffler to the tail pipe. I didn't choose this exact exhaust set-up, after I hung my FM catback I brought it to an exhaust shop to weld it up, and they came up with the 2 1/2" before the muffler idea. I think it kind of makes sense because the further the exhaust travels from the motor, the more it cools down and the more it condenses so it doesn't really need big pipe all the way back. Sounds awesome, too.