273 power? HOW?

To maintain reasonble cost effect street driveability use 1 HP per Cubic inch.

You can go more but you'll run into alot of compromises along the way with drive line traction and just plain tearing sh*t up.

273 = 275 HP
360 = 360HP
440 = 440 HP

Just sensible and cost efficient number to guide you in your project.