A carburetor that's too large can lead to poor throttle response, poor fuel economy, and a generally less efficient engine. It will struggle to meter fuel properly at lower RPMs, resulting in a lean condition.
A more appropriate carburetor size would likely be in the 600-650 CFM range for a mildly modified 400 small block. However, the best carburetor size depends on many factors, including:
* Camshaft: The cam's duration and lift significantly impact airflow requirements.
* Compression ratio: Higher compression needs more fuel.
* Intake manifold: The design and size of the intake manifold influence airflow.
* Head flow: The ability of the cylinder heads to flow air.
If your 400 is heavily modified, a 750 CFM might be suitable, but for a stock or moderately modified engine, it's probably oversized. You'll likely see better performance with a smaller carburetor. Consider consulting a performance shop or using online carburetor sizing calculators to determine the optimal size based on your specific engine modifications.
