With the addition of a Cold Air Kit...Headers...High flow Cat...and aftermarket exhaust (borla...flowmaster)...how much HP and MPG difference should I expect from the 3.0 V6 auto 4Runner with 265 tires
Prolly less cuz your foot is going to get heavier!!!
Seriously, there is no number value, but I would guess that you would see a little increase (assuming that you drive like you did before you did the mods).
when adding those parts to your truck, it's def. going to breath better. in theory you should get better gas mileage. at the same time if you have a lead foot it or even drive about avg. speeds there is really no advantage. you may even loose mpg.
