Here's why:
* Computer Calibration: The 1995 truck's computer (ECM) is specifically programmed for the 305's fuel injection, ignition timing, and other parameters. A 350, even if it's a very similar year and model, will have different fuel delivery requirements, and the timing curves will likely be different. Using the wrong calibration will result in poor performance, drivability issues, and potentially engine damage.
* Sensors: While some sensors might be interchangeable, others may have different specifications or locations. The computer might not recognize the signals from the 350's sensors correctly.
* Wiring Harness: The wiring harness might need modifications to accommodate the different sensors and outputs of the 350.
To successfully perform this swap, you would need to either:
* Get a 350-specific ECM: This is the most straightforward approach. Find a computer from a similar-year Chevy truck with a 350. Even then, you might need some minor wiring adjustments.
* Use a standalone engine management system (EMS): This is a more expensive but more flexible solution. A standalone EMS allows you to completely customize the engine's fueling and timing parameters regardless of the engine or the original truck's system.
* Use a custom-tuned ECM: A professional tuner can modify the existing ECM or program a new one to work with the 350. This is likely the most expensive option.
In short, while the engines are similar, the supporting systems are not directly compatible. You'll need a new computer or a significant amount of custom tuning work to make the swap function correctly.
