When choosing an appropriate horsepower (HP) for a street car, there are a few key factors to consider:
Street Legality
Most states have regulations regarding how powerful a street legal production car can be. For example, in California the limit is around 700-800 HP for a street legal car. Going above this may require special registration and inspections to be street legal.
Usability
Very high horsepower may not be usable on public streets. Most city and highway speeds are well below 100 mph. High HP cars with 500+ hp often require going over 100 mph to reach max power. This speed is not legal or safe on public roads.
Driver Skill
An inexperienced driver will not be able to safely control a car with a very high amount of horsepower. As a general guideline, below 400 HP is suitable for beginners, 400-600 HP for experienced enthusiasts, and 600+ HP requires advanced driving skills.
Traction
Putting down high HP to the pavement requires good traction. Race cars use sticky racing slicks and aerodynamics to achieve traction. Street cars have harder commercial tires and no aero which limits traction. Too much power can easily break loose on the street.
torque ratio
Horsepower doesn’t tell the whole story. The torque ratio, or how quickly peak torque is reached compared to peak HP, is also important. High torque available at low RPMs improves street drivability. High horsepower with low torque requires revving the engine high to achieve acceleration.
Weight
Heavier cars can handle more power due to increased traction. Lightweight sports cars require lower power to achieve quick acceleration. As a general guideline:
| Weight | HP Guideline |
| Under 3000 lbs | 300-400 hp |
| 3000-4000 lbs | 400-500 hp |
| Over 4000 lbs | 500+ hp |
Cost
The engine upgrades required to reach high horsepower levels get very expensive. For most buyers, choosing 400-500 hp offers a good compromise of power versus cost.
Reliability
Engine stress increases exponentially with horsepower. The highest output engines require frequent maintenance, upgraded cooling, short rebuild intervals, race fuel, etc. A reliable street car generally keeps horsepower levels more conservative.
Drive Type
Rear-wheel drive cars have an easier time putting power down compared to front-wheel drive, allowing them to use more power effectively. All-wheel drive improves traction further, and enables the highest possible power levels.
Conclusion
For a street driven sports car or muscle car, a good target horsepower level is around 400-600 HP. This offers strong acceleration and speed, while still being drivable on public roads. Fully street legal production cars often cap power around 700-800 HP. Race cars can achieve 1000+ HP, but require special tires, cooling and maintenance. Choosing the right HP comes down to balancing drivability, cost, legality and overall needs for your street driven car.