* Year of manufacture: Different years had slightly different specifications and tuning.
* Modifications: Has the engine been modified with performance parts like a camshaft, intake manifold, headers, etc.? These significantly alter horsepower.
* Condition: Is the engine well-maintained? A well-maintained engine will produce more power than a neglected one.
* Specific application: Was it in a truck, car, or boat? The intended application influenced tuning.
Stock, un-modified: A completely stock 350 TBI with centerbolt heads (typically found in some older GM trucks and SUVs) would likely produce somewhere in the range of 170-230 horsepower. This is a broad range, and the actual output would depend on the factors listed above. It's closer to the lower end of that range unless it's exceptionally well-maintained.
Modified: With modifications, the horsepower could easily exceed 300 horsepower or even more, depending on the extent and type of modifications.
In short: You can't give a precise horsepower figure without more information about the specific engine. The range provided above is a reasonable estimate for a stock engine, but any modifications dramatically change the output.
