* Year of manufacture: Older 350s produced significantly less horsepower than newer ones. Early small-block Chevys might only put out 150-200 horsepower, while later, performance-tuned versions could exceed 300 or even 400 horsepower.
* Engine modifications: Modifications like different camshafts, carburetors, cylinder heads, intake manifolds, and exhaust systems dramatically impact horsepower. A heavily modified 350 could produce far more than a stock one.
* Engine condition: Worn-out parts, improper tuning, and poor maintenance will significantly reduce horsepower.
* Application: The intended use (truck, car, boat) also influences the engine's horsepower rating.
In short, there's no single answer. You need more specifics to even begin to estimate the horsepower. If you can provide the year, make, model of the vehicle it's in, and any modifications, a more accurate estimate might be possible.
