Scotty my uncle wants to build a sleeper project car. I suggested an old manual Corolla. Another person suggested an older Miata. Which would be better and what’s the most powerful engine either could sustain.
There isnt really an easy answer to your question. You can do pretty much whatever you want to a car, it basically comes down to what you want to spend. There's a video on YouTube of a Prius with a Hellcat engine in it. https://youtu.be/POSKNO7z5Sw
Cars are engineered for a certain range of power and torque. Take my Ford Ranger, for example. The 4.0 V6 has more power than my 3.0, and it requires a sturdier transmission. Engine swaps with everything else being stock are going to be limiting. Putting in a different transmission will help, assuming it bolts up, but then you also need to consider will things actually fit in the available space. Everything is electronic nowadays as well. That Prius needed quite a few mods to work, for example. Modern cars aren't easy or cheap to make into "sleepers." My '79 Catalina would make an excellent sleeper, there is tons of room under the hood, tons of old GM transmissions to bolt up to bigger, old GM engines, and there are absolutely no computers. My friend and I joke about dropping a 383 Stroker V8 in it if the stock motor ever breaks.
The sky (and your wallet) is the limit.
How about a Nash Metropolitan with a blown big-block? (Well, maybe a bit too conspicuous to be a sleeper...)
If I was looking for performance with off-the-shelf, affordable parts, I'd go with a Honda Civic or a Mazda3. Just leave the body stock, with no spoiler. If I was just looking for something that was fun to drive, you can't go too far wrong with a Miata.
