We can fine-tune your car
To modify your car for better performance costs money, time, and requires extensive experience and knowledge
If you are planning to go N/A (natural aspiration) rather than the turbo route, your best bet is changing the bore, stroke or compression ratio, for example a Nissan skyline GT-S R33 has a compression ratio of about 9.5 to 1, the 9.5 represents the air/fuel mixture in the cylinder before compression, the 1 represents what its being compressed to, so in this case raising it to 10.5 to 1 would give a nice increase of power over the low end of the RPM band.
If you go with a turbo you don’t need a very high compression ratio because you already have forced induction. But be wary of changes of more than 2.5 over factory settings, too high compression ratio could send your spark plugs through the hood.(Not literally but you get the point) You could use a small car with a large engine installed. For example a Ford Mustang V8 forced into the body of a little Ford Focus. Keep in mind that a heavier engine will likely change the front-rear weight ratio. This change could significantly affect handling, traction and braking.
Consider a common conversion like a Chevy LS-1 and Ford 302 (5.0L) powered Mazda Miata’s. It’s a pretty easy swap and pretty cheap too for the performance these motors can be made to deliver.