* Driving style: Aggressive acceleration and high speeds drastically reduce fuel economy regardless of the engine.
* Vehicle condition: Tire pressure, overall vehicle maintenance (tune-up, etc.), and even axle ratios significantly impact fuel efficiency.
* 700R4 calibration: The 700R4's shift points and overall programming affect fuel usage. A poorly calibrated transmission can waste fuel.
* Carburation: Even with a 2-barrel, the carburetor's condition and tuning significantly impact fuel delivery and efficiency.
* Overall vehicle weight: A heavier car will generally consume more fuel. A '63 Impala four-door is already a relatively heavy vehicle.
General Expectations:
While the 350 cubic inch engine has more power, it generally requires *more* fuel to operate than the smaller 283. However, the difference might not be as dramatic as one would assume, *especially* with a 700R4 overdrive transmission. The overdrive gear allows the engine to run at lower RPMs at highway speeds, offsetting some of the larger engine's thirst.
Hypothetical Comparison:
You might see a difference of perhaps 2-4 miles per gallon (mpg) – with the 283 achieving the higher mileage. However, it's quite possible the difference could be less or even – depending on the variables above – the 350 might show slightly better highway mileage with the overdrive.
Conclusion:
To get a real-world comparison, you'd need to test both setups under identical conditions and driving styles, which is quite difficult. Real-world mpg figures vary greatly. Don't expect a precise numerical answer without extensive testing.
