What is the best mod for the Money

SouthArk370Z

CAI is a great start. Pretty safe. Reasonable bang for the buck. If you have much experience working on cars, it's an easy DIY (in most cases; some require body mods). If that's the only mod you make, you may not need to re-tune.

Exhaust is another good one. Can get pricey and you need a lift or good ramps to install. If you get CAI and exhaust together, will probably require a re-tune.

A supercharger is expensive to install. Since your asking, it's probably not a job you could DIY. Will definitely need a re-tune. Not really unsafe, but you will be putting a lot of extra stress on the drivetrain, so things will break more often. May also require other mods/upgrades, eg, exhaust and injectors. The cost gets high quickly, but probably your best bet for horsepower if you have deep pockets.

A short shifter will only help if you know how to use it. For most DDs the only benefit is bragging rights. If you plan on needing faster shifts, maybe you should jump straight to a supercharger and hipo exhaust.

YMMV

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