Any performance tips anyone can provide?

Hello everyone,

I own a 1992 Suzuki Swift, 4 cyl 1.3L single overhead cam.

I do the regular maintenance provided by the vehicle booklet that came with the car but now that the vehicle is a little older I know that the performance of the vehicle will not be like new but I would like to know the difference in the performance now and when it was like new. Since I did not create a baseline performance data when the car was new what can I do to make sure my car is performing at peak performance? If I do buy another vehicle and start to create a baseline performance data sheet what would I need to record?

I heard that there is a engine analysis device that connects to the onboard computer on the car but I'm not sure what this is called and if it's available for my vehicle.

I've also heard about performance modifications kits but can't find any for my vehicle. I'm also concerned the car might not be able to handle some performance modifications since it was not engineered and tested to take the extra load or stress on the car's factory built components

Thanks to all who reply!

Ismael