05-04-2009, 01:03 PM
The rule of thumb for pipe size (bigger is not always better) is this,
2.0" pipe for 100 - 150 cubic inches per pipe and 100 Bhp per pipe
2.25" pipe for 150 - 175 cubic inches per pipe and 160 Bhp per pipe
2.5" pipe for 175 - 230 cubic inches per pipe and 200 Bhp per pipe
3.0" pipe for 230 + cubic inches per pipe and 300 Bhp per pipe
Most important is the pipe diameter from collector to tail pipe needs to be the same so you dont "confuse" the exhaust and create turbulence. In other words don't neck the pipe down to fit muffler inlet and outlets.
Bigger pipes flow more volume but the velocity goes way down which does more harm than good. You need some back pressure to create velocity and scavage the system. So for a 302 = 151 cubic inches per pipe (assuming you have dual exaust) you are right in between a 2.0" and 2.25" pipe diameter. I would think for your application 2.25" would be a good choice because that gives you a little wiggle room to add more HP upgrades without out growing your exaust system. I think 2.5" pipes might be too big for your 302 and you will loose a little HP and torque due to not enough back pressure and low exhaust velocity.
Just my .02, hope it helps.
Bill
2.0" pipe for 100 - 150 cubic inches per pipe and 100 Bhp per pipe
2.25" pipe for 150 - 175 cubic inches per pipe and 160 Bhp per pipe
2.5" pipe for 175 - 230 cubic inches per pipe and 200 Bhp per pipe
3.0" pipe for 230 + cubic inches per pipe and 300 Bhp per pipe
Most important is the pipe diameter from collector to tail pipe needs to be the same so you dont "confuse" the exhaust and create turbulence. In other words don't neck the pipe down to fit muffler inlet and outlets.
Bigger pipes flow more volume but the velocity goes way down which does more harm than good. You need some back pressure to create velocity and scavage the system. So for a 302 = 151 cubic inches per pipe (assuming you have dual exaust) you are right in between a 2.0" and 2.25" pipe diameter. I would think for your application 2.25" would be a good choice because that gives you a little wiggle room to add more HP upgrades without out growing your exaust system. I think 2.5" pipes might be too big for your 302 and you will loose a little HP and torque due to not enough back pressure and low exhaust velocity.
Just my .02, hope it helps.
Bill