well looks like i might be getting a Hooker Header Max Flow muffler. and i also have a high-flow cat. would that free the exhaust too much? since all i have is the ATX tb and a 3.0L intake?

 

http://www.ntpog.org/articles/noloss...ssexhaust1.jpg

http://www.ntpog.org/articles/noloss...ssexhaust2.jpg

http://www.ntpog.org/articles/noloss...ssexhaust3.jpg

http://www.ntpog.org/articles/noloss...ssexhaust4.jpg

http://www.ntpog.org/articles/noloss...ssexhaust5.jpg

5 pages of reading but worth it, its almost exactly one of the lessons my dads professor at FSU lectured on when he ws getting his masters in physics, his teacher was a car nut and used cars to explain physics a lot

in short, dont worry about backpressure, its not need for anything but to keep the power down

exhaust diameter, merge collector shape and length, and exhaust length are what changes your torque curve, backpressure just restricts your engine

 

what about MPG though? cause i know when i completely got rid of my cat. on my other car it went down from 35ish MPG down to 25MPG.

 

I'm not a physicist but from experience I know that you can loose low end torque by lowering back pressure (good for high end though)

 

if your losing low end torque, its not from a loss of backpressure, its coming from somewhere else

try upsizing your piping one size

2 examples - 95 fullsize chevy truck 4.3L v-6

cut off the muffler and made killer power until i got a ticket for being too loud, put on a flowmaster single chamber, lost some low end and lots of top end, got frustrated, cut that off and put a 24" glasspack the same diameter as the exhaust piping, got a lot of power back and was as quiet as the flowmaster

2nd example -2 '97 Dodge Neon SOHC Autos, my friends had only a magnaflow put on, when i first got it, i cut my muffler off, and was able to beat him pretty bad in identical cars with only a muffler change, i got ticketed (again) and put a 12" glasspack on, didnt make a noticible reduction in torque, quieted it down a little, and still could beat my friends car easily

if you dont want to take my dads professor or mr. vizards word for it, do some research on racing websites and such, like this one

autospeed.com

they have some very good methods to cheaply gain horsepower by reducing exhaust backpressure and increasing intake flow and lowering intake temps

 

other way
to gain torque, you actually need to go down a size, this is where the misconception comes in

most people hear to go down a size and the only reason they can think of is because the motor needs backpressure, no, the motor needs flow speed for torque, how fast the air is moving through the motor and piping

if you go up a size, you will lose LOW END torque, unless your pipes were too small to begin with which is doubtful

the reason is the air coming out of the exhaust valves will come out with good speed and then slow down, which then means the exhaust coming out of the engine next has to push this exhaust out, and so on and so on