I'm thinking of getting a 2019 manual honda fit sport. Is there any performance mods I can do to increase the HP? Aside from swapping engines.

 

You going big or just talking CAI and exhaust? From what I've read the L15 engines don't like boost very much. Check these guys out here, they have a list of parts that fit the Fit.

 

Cat back exhaust with a Borla Muffler.

Replace the stock air filter with a K&N air filter.

Replace the wheels with stock black sport wheels from a Honda Fit Sport.

 

 

I heard K&N air filters are trash. They don't filter properly compared to a high quality filter.
i do have 16in 2019 honda fit sport black wheel. I also have some 16in sparco assetto gara ET37 that I'm restoring but idk if it'll look good on the fit because of the offset.

 

Go with an axel back muffler then! https://www.kamispeed.com/collections/honda-fit?page=1&rb_snize_facet1=2019&rb_snize_facet2=Ax le-Backs

 

If you go that route, even the most well-built axle back exhaust will make your car noticeably louder.
It's fun around town, but if you do any long duration highway driving, that noise will become bothersome (unless you enjoy the sound of a lawn mower at high RPM's).
I have an HKS axle back and have delegated my FIT to "city only" use. Which is fine, as that's what I purchased the car for.

 

Besides what has been mentioned, I found my Savanni Throttle Body Spacer to provide noticeable benefits while still using ECO on a CVT. No detriment to fuel economy when driven normally.

 

Works great for me.

I also have one on my 2007 Ruckus with a Yoshimura Exhaust.

 

The Fits probably benefit best from grippier tires, lighter rims, lowering springs and weight reduction through lighter exhaust systems than anything. Stock engines don't have too much potential worth modding.