In your opinion, will a 5.0 get more power with a 3 inch SI/SO then dual 2.5's with a mostly stock (k&n air, bbk headers) motor?

 

I do not know that motor too well. If I were to guess, single 3". I know a lot of 302 Mustang owners use dual 2.5", but they are going more for the upper engien speed power, not the 1500-3000rpm range most trucks see. The cross sectional area of a single 2.5" pipe is 4.9 sq in. 3" is 7.1 and obviously dual 2.5" is 9.8". Cross sectional area is important because the goal is to have the exhaust exit quickly. Volume of air is fixed coming out of the engine. The smaller the diameter, the faster the air come out which provides more torque. But, don't go too small or you will affect the volume of air out of the motor. There is no such thing as backpressure. There is no air that goes back into the engine. There are just exhaust restrictions that can provide higher exhaust speeds than if you open it up too much.

Gosh, imagine what I would know if I studied mechanical engineering instead of computer engineering.

 

Thanks for your input. I talked to a guy today at the muffler shop who said he thought they would be about the same, but of course he didn't give me as much info as you. This forum is great, it's nice for us rookies to be able to pick some knowledge from your brains.