Originally Posted by semtex

Just dyno your car after you get all your mods in. As part of the dynoing process, they measure your AFR. (Not all places do it automatically, so you might have to ask for it.) If your AFR is in the acceptable range, then you're good to go. If it's out of whack, then you know you need a tune. There's no sense in guessing on whether or not you'll need a tune when you can actually go get your AFR measured and find out for sure. It's like trying to figure out if you need blood pressure medication without getting your BP reading checked first.