i have a 1970 monte carlo with a 400 small block how much is the horspower

The 400 small block with the standard 2-barrel carburetor had an advertised "gross" horsepower rating of 265 at 4400 rpms until 1972, when the rating system changed to the more realistic SAE "net" method. There was virtually no difference between the 400 small-block engines of this period in terms of stock horsepower and torque. This would just be my personal opinion, but I would suspect that the actual flywheel horsepower of this engine, in stock form, would be about 215 at a lower engine speed of 4,000 rpms. This would likely give your Monte Carlo a wheel horsepower of 165-170, or enough to make a quarter-mile run to about 85 mph.