If enough is good…more is better…and too much is just right. Yes the old saying can often get you in trouble whether it's too much Christmas turkey, or too much carburetor on your old Ford. Many have complained that replacing their worn out Holley four-barrel carburetor with the standard Holley 600 CFM (cubic feet per minute), replacement carburetor, turns their Y-block or FE Ford into a gas guzzler. Why?
If we look at the factory carburetor you removed and size it up with the 600 CFM replacement, we see that the barrels or venturis are noticeably smaller than the new carburetor. While going with the larger carburetor on a modified engine will boost power, it does little on the stock engine in your '50s Ford cruiser. Wide-open throttle may feel a bit better, but slower throttle response, a rich idle and poor gas mileage are a lousy trade-off. While that 600 CFM. carburetor should be quite happy on top of a 390 V8, it's just going to cause trouble on a smaller engine. What works is to choose the correct CFM replacement and there's nothing magical about it.