Many Small Cars Have Been "Squirreled"... (long, w/rants)
In the 60's and early 1970's General Motors brought to the US a product manufactured in Germany called an Opel. The last year they imported them was 1975. Several GM cars have carried the "Opel" name after that and Opels are still made in Germany by GM.
The 1975 models were port-fuel injected had disk breaks, coil over shock front ends and coil spring, drag-link rear suspensions. Producing stock power of 118 HP from their 1875cc 4 cylinder engines (with a smaller engine available on special order) these cars were "hot" right out of the box. (they weighed-in at 2300 pounds with driver and a tank of fuel)
The first thing we did to all of our Opels (we used them for off-road racing and "rat" street racing) was to put a skid plate under them and replace the stock alternator with a heaver unit. We moved the battery from it's (stupid) location under the hood to a location in the trunk and did some re-wiring to reinforce the power distribution system. We put roll bars in all our cars and still do. Then we went after the suspension, adding gas shocks, sway bars, track rods, and cables to limit the extension of the swing arms. We replaced the stock break pads with copper "loaded" pads and replaced the clutches with heaver 2700 pound-pressure plates and "loaded" clutch disks. Then we went in after the engine. First, the stock cast-iron exhaust header was replaced with a tuned-length unit with a 2-1/2 inch collector. Two, that's right, 2 mufflers in series went after that and then after the "hump" to get the pipe (now at 3 inches in diameter) past the rear axle, a "glass pack" muffler was added to bring the noise level down to something you could speed down a neighborhood street in without alerting anyone that you were there. In the "good old days" we gave a damn about not pissing-off everyone with noisy cars... not like today where it's "cool" to have a car that sounds like it's got an open pipe directly from a 2-stroke lawn mower engine.
After the exhaust was under control, we would begin re-curving the fuel injection. No computers here, just analog electronics which you modified using skill, a soldering iron, and a real understanding of how an engine works... no attaching your laptop and running some program you bought at the store.
A set of good mud/snow type tires and we were off to the races.
If I had to give a single piece of advice to someone who is just starting-out working with cars as a hobby, it would be this:
Leave The Car As It Is.
People with real skills designed it to do what it does. If you mess with it, you will make it less reliable and if it's your only car (the one you drive to work) then you just don't want to screw it up on the weekend and have to beg for a ride on Monday. If it's a second car, a "toy" then have fun, but keep a cell phone in your pocket and be sure you have the number to a friend who will come pick you up when your "bitchen mods" turn your car to a piece of junk on the roadside.
(And what ever you do, do not think for a single moment that stickers make anything go faster, and stay away from spray paint when you have been drinking... it's easy to spot fools with red break rotors or gold bumpers or yellow dashboards.)