Interesting changes as new technology is applied to old engines

I have been reading articles, and watching YouTube videos, about people putting throttle-body fuel injection on what are now called “Traditional V-8s”. The goal is better fuel economy while maintaining or improving performance. And what they are finding out is that the parts they used to use to get fuel economy with a carburetor don’t work with fuel injection. And also it has been so long since I worked on cars with carburetors that I forgot how to spell it.

Anyway, theory of operation of a carburetor is they suck. Literally, they work by drawing air through a venturi, which creates a lower than atmospheric pressure that pulls fuel from a small chamber inside the carburetor through a metering orifice called a jet, that is then atomized by the airflow and sent to the intake manifold and into the engine. Because of physics explained by Bernoulli’s Law, the faster the air is moving the lower the pressure inside and the stronger it sucks fuel into the manifold, and because our monkey brains won’t stop trying to put 5 pounds of stuff into a one-pound rated container, compromises had to be made in engine design. Since only one cylinder at a time can draw on the carburetor engineers made intake manifolds designed to only use ½ of the carburetor at a time.

dual plane intake manifold

Now we could literally get the same performance with half a carb used all the time, but like I said, monkey brains. Anyway, because of compromises to split the engine in half so that succeeding cylinders draw from opposite halves of the carb, mixture distribution gets moved down in priority by actually having fuel mixed with air. This means that when you use a throttle body fuel injection on the existing dual plane fuel economy manifold, you get an engine that runs like crap because of incompatible fuel delivery methods. You get some cylinders that get too much fuel and some that don’t get enough and maybe one or two that are right but only if you’re lucky.

Now the thing about single plane manifolds is they get all the fuel and air through just one hole in the top, or several holes that are connected inside, so after that they try to get the same mixture of fuel and air distributed to all the cylinders in the same volume of air distributed to each cylinder, so that each cylinder makes the same power and the engine makes as much power as possible for the amount of air it is consuming.

single plane intake manifold

side by side in the wild

The thing is single plane manifolds were generally considered race-only equipment, not suited for street applications and most definitely not for fuel economy on the street, but EFI is changing all the rules. Since fuel delivery is no longer dependent on airflow through a venturi it becomes more important to make sure cylinders all get the same amount of air mixed with the same amount of fuel, to all make the same amount of power so they use less fuel, and don’t just dump it out the tailpipe unburned. And in spite of initially being designed as race-only, with EFI they become the preferred application for street fuel economy. With EFI the Edelbrock Victor Jr. becomes the preferred street performance manifold over their RPM Air Gap dual plane, simply because it’s physically impossible to get equal mixture distribution with EFI from a dual plane manifold. With a carb you could never get decent street performance out of the Victor Jr. manifold because the intake velocity would not pull enough fuel from the carb or atomize it properly. Note in the links the RPM range for the manifolds when used as intended with carburetors, and then realize with EFI that doesn’t apply. That is what modern technology does when used properly. It makes ancient engines run like modern economy engines, almost. And even Edelbrock’s EFI kit comes with a modified Victor Jr. manifold. Notice I have no relationship with Edelbrock other than having installed one of their manifolds on an engine about 35 years ago when I was racing and working on race cars.


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