I was wondering if it is better to go with a 2.5 or a 3.0 inch exhaust for sound and compression. I want the compression to stay up, but i heard that if you go with to big of a system you would lose compression and power. I don't want that. So what is the best way to go.

You wont loose compression and power will be affected somewhat, depending on the power level. The smaller pipes will be quieter and work well up to say 450 hp but would choke a 500 hp engine. Above 450 hp a 3" system will work better but you'd want to match that with 1 3/4" headers. I have a 2.5" mandral system on my 390 hp 383 with 1 5/8 headers and a 3" system on my 540hp 406 with 1 3/4" headers. Both sound good but the 3" system is quite a bit louder at idle.

It really depends how much street and how much strip. If you drive the car on the street a lot 2.5" will keep the low end torque, but will maybe lose a .1 at the track compare to 3". It also depends on the cam if you have a wide lsa in your cam I believe the wider lsa likes back pressure and a narrower lsa like not a lot of back pressure

If you like your exhaust running over the rear end housing and fully out from under the car (which I highly recommend if you cruise in it much) you will have a much easier time with 2.5 inch. I have had a couple of 3 inch systems and there is little room under an A body if you run past the housing. I see so many people that run 3 inch systems with turndowns under the car which gives me a headache from fumes pretty easily.

I got you Good info.