Re: Carburetor

Posted by longjohn On 2024/2/9 12:23:25

Ah, the mysterious carburetor. What a "rube goldberg" contraption.

The problem with carburetors is that the carburetor you need at idle is completely different than the one you need for acceleration and different again from the one you need at high constant speed. Trying to satisfy these various conflicting demands led to many complicated solutions, some of which worked better than others.

At idle, the engine requires a small amount of a rich fuel/air mixture. On acceleration, the engine requires a large amount of a rich fuel/air mixture. At high speed, the engine requires a moderate amount of a lean fuel/air mixture.

At high speed, a two barrel carb is pulling air/fuel through both barrels. These barrels are much larger than the engine needs because they must satisfy the acceleration phase so they are not as efficient as they could be. At high speed, a four barrel carburetor is only operating on two barrels. These two are smaller than the two barrels on a two barrel carb and more in line with what the engine needs. So this phase is more efficient resulting in better fuel economy in highway driving.

While driving around town where acceleration is required, the four barrel is operating on all four barrels, increasing the air/fuel mixture. The four barrel carb allows more air/fuel flow than the two barrel leading to better acceleration. However, this results in worse fuel consumption in stop & go driving.

If you look at different carburetors, you can see how different manufacturers tried to satisfy the various engine requirements. The hard part is getting this to happen automatically. It really took the advent of small computers to truly automate the fuel system.

Why did Packard (and other manufacturers) offer both a two barrel and a four barrel? Money, it is more expensive to manufacture the more complicated four barrel. Not only the cost of the carburetor need to be considered but other changes to the intake and exhaust systems need to be made in order to take advantage of the four barrels greater efficiency.