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Nothing noticeable. Change the exhaust if you want to affect the sound. That's about it. Tune is the only way to go for bumping up horsepower.
Exhaust and intake make zero hp on a tuned truck.
I feel like this should read, "Exhaust and intake make zero hp on a[n] [un]tuned truck."
A tune will increase your horsepower. You can benefit from the potential gains of increased airflow and exhaust with tuning. I don't think adding a pretty cai, or a catback will do much for you, especially if it is without tuning. Now, increase the size of downpipes, headers with bigger primaries and collector, better breathing cold air intake (big ones with increased CFM, not just pretty painted plastic), bigger exhausts with restrictions like catalytics removed, can definitely increase horsepower if properly tuned for. This is all especially true on forced induction applications. I don't know that this stuff exists in its best form for the Raptor yet. I am just saying, getting the air to the charge side of the turbo, and getting the exhaust into and out of the turbo faster makes for more power... when properly tuned.
The stock exhaust does not have any restrictions for the amount of air the stock turbos can flow. The downpipes are a diffrent story and aftermarket ones DO make power.
A few shops have claimed changing the intake makes power on a stock truck. The stock intake with the silencers removed can flow more air then the stock turbos and is not a restriction.
Some shops are claiming a small hp increase back to back with stock because larger diameter screws up the airflow scaling in a stock tune and makes it run lean until the fuel trims adjust. Thus making more power for a small period of time on an UNTUNED truck until it adjusts itself. This happens on alot of newer cars and the intake companies love changing pipe diameter to screw with maf and iat calibrations to fool people.
But a tuned stock truck (with intake silencers removed) and a tuned truck with a cai and a catback will make within the dynos margin of error of eachother.
Now downpipes on the other hand make power.
Tl/dr: pull the intake silencers, buy downpipes and get a tune. Leave the rest alone unless you play in the sand. Then get an intercooler.