The key is to choose the correct kit for a given application; i.e., 4 cyl. engines normally allow an extra 40- 60 HP, 6 cyl. engines usually work great between 75-100 extra HP, small block V8’s (302/350/400cid) can typically accept up to 140 extra HP, and big block V8’s (427-454) might accept from 125-200 extra HP. Jul 09, 2020 · If you have decided to add nitrous to your car, you may want to know how much speed it can increase. This gas indeed brings amazing results. For example, you can add 100 to 200 horsepower to your engine by spending less than $500. However, you have to follow some rules to get the desired result.