This question has the same answer as how long is a piece of string.
With out knowing what engine you have, what exhaust system and what cam you are adding there is no way to know.
Both Magna flo and Comp cams provide "gains" as an advertising tool be careful because depending on how your car is tuned and how good the mechanic is will really affect the results.
Headers, with free flow exhaust system will help.
Does increasing the diameter of your exhaust pipe leading from the engine increase exhaust flow and therefore lessen engine burden causing an increase in horsepower? The answer for that is yes, but is negligible. Maybe 3-15 horsepower at best.
Several things can add horsepower to your truck. A free flow air filter, different exhaust, or computer chip change can all help get more horsepower.
Answertake it to Midas is a good answer, but i was hoping that someone with some knowledge with Titan's could give me a performance exhaust that will not jeopardize the warranty.I have an 05 Nissan Titan, I installed a set of JBA Shorty Headers, Magna Flow Highflow Catalytic Converters, Magna Flow True dual Exhaust and a K&N cold air intake system. Didn't help much with the bottom end but at about the middle of each gear all the way to the top you can feel major horsepower gain. this entire system with installation cost me about $1,500.00 but it sounds great and was amazing at the horsepower increase. you will not be dissapointed. I did put an H pipe in the exhaust because it was to loud without it (couldn't idle through parking lots without setting off alarms) but you may want the extreme sound.
Get a K&N cold air inflow system and Magna flow exhaust. That will get you more HP!
Add a free flow exhaust and a cold air intake free flow air filter. This will give you slightly more h.p. To get some real horsepower you can install a turbo charger or supercharger but they are expensive.
Whether you want to upgrade your Subaru for horsepower and performance or you just want to replace your exhaust, the manufacturers for Subaru exhausts are Exedy, Flow Master, and Takeda.
If you're talking about an RT, a cold air intake, programmer, headers, high-flow cats, and free-flowing exhaust will get you about 60-70. You can get the other 40 with a camshaft designed for vehicles with MDS. Stage 2 should be sufficient. That would get you around 430-450 at the crank.
put a K&N air filter on it, a set of headers and a good high flow exhaust is a good start.
Magna Flows are not as loud as fuel masters. Though most people have a personal preference, some liking the deep tone of the magna flow and saying the fuel master is too unbalanced sounding.
free flow exhaust with reducing bends
God, where to start? there are a LOT of things you can do to add horsepower. How much money are you looking to spend? here's a list of things you can do: cold air intake, swapping exhaust manifolds to headers, changing to a high flow exhaust system, turbo/supercharger, nitrous, aftermarket computer chips, lightweight camshaft gears, bigger camshafts, bigger engine, aftermarket clutch, aftermarket torque converter, etc.etc.etc.etc. There's a helluva lot you can do. It's all in how much money you wanna spend. Agreed. LT headers/cold air intake/catback/tune REALLY wake these bad boys up though