If i were to switch my car from 305tbi to 350 tbi. Why is it neccessary to change spark control module and knock sensor? First what does the spark control module do exactlyand why wouldnt it do what its supposed to with a bigger engine? Any help would be appreciated thanks.

 

Knock sensorso are tuned to a very specific resonance range, the resonance it hears is the ringing of the cylinder wall when you encounter detonation. Since 305's and 350's different size cylinder walls they "ring" at a different pitch. You can run a 305 sensor and module in your 350, but it may pick up false knock or even worse it may not hear real knock. If you budget is real tight I would spring for the sensor and hold out on the module.