How much difference would I see (Power wise) with a complete exhaust replacement after the manifolds?
I have an '03 Scab 4x4 4.6L, stock exhaust.
I have 1 unpackaged box magnaflow 17549 SI/DO cat back exhaust system.
I plan to buy Magnaflow's direct fit catalytic converter system (driver and passenger side) hi flow, as told from magnaflow customer support.
I do have K&N CAI kit in place now.
There is 102K on the motor.
I'd expect to buy a tuner (SCT?) from a local place who can dial in the truck once the exhaust is installed.
Exhaust investment would be approx. $1020.
Once I install the cat system and cat back exhaust system, how much power difference would I really see?
Describe in HP, or other ways?
Thanks.

 

Unless your OEM cats are slowly clogging, you would barely notice a power change, maybe a slight increase on avg mpg. Until you replace the manifolds with longtube headers ( for a 4.6L Pacesetter is the only option ), and run universal catalytic hi-flow cats ( not direct fits ), you won't have a performance improvement.

You could save a tremendous amount of money by using universal cats and not using direct fits, having an exhaust shop fab everything together.

 

^x2
Lts, high flow cats, single 3" or dual 2.5" straight thru design muffler.

 

Very little. I can't give you a HP figure, but less than 10 for sure. And whatever little gain there will be, will be almost entirely unnoticeable. The programmer with custom tunes (I wouldn't get tunes from a local place - too expensive and they have to really know what they're doing, and most don't. Plus there's no reason for an individual custom tune for a simple exhaust change) on the other hand, should provide something noticeable. I have longtube headers (no cats), along with full exhaust after it, along with an SCT with custom tunes. With both combined I barely noticed anything. But when I just had a catback, I didn't notice a thing.

Dang, the two of y'all posted while I was writing mine haha. But the universal Magnaflow cats are fine, especially if cheaper than direct fits

 

Thanks, everyone, for your replies and comments.

 

I didn't notice any power difference really, just a little better throttle response, but that was about it. Oh, and the enjoyment of that sound when I romp on it a little.

 

you might see three or four rear wheel horsepower....



so look into investing a grand for mods that will allow you some enjoyment besides sound

 

$1k+ for nothing more than noise my man. Sorry to disappoint you, but you will have minimal HP gains that you won't be able to feel.

 

You can do what you want for less than $1,000, should be less anyway. Mine has cost 1,300 in parts + a lot of my labor + $350 for some shop labor. And that's for the headers and everything. So $1k without headers doesn't make a lot of sense to me, even when having someone else do the labor. People have done what you want for less, probably closer to $800. Wish I could reference someone specific.