What horsepower was the 3970126 heads?

The casting number 3970126 refers to a cylinder head used on several big-block Chevrolet engines. There's no single horsepower rating associated with the heads themselves. The horsepower of the *entire engine* depends on many factors *in addition* to the cylinder heads, including:

* The engine's displacement (cubic inches): The 3970126 heads were used on various sizes of big-block Chevys.

* Camshaft: The camshaft profile significantly impacts horsepower and torque.

* Intake manifold: Different manifolds offer different airflow characteristics.

* Carburetor: Carb size and type affect airflow.

* Exhaust system: Restrictions in the exhaust system rob horsepower.

* Compression ratio: Higher compression generally means more power, but requires higher-octane fuel.

Therefore, you can't determine the horsepower from just the casting number of the cylinder heads. You need the complete engine specifications.