EFI versus Carburetors for Classic Cars & Hot Rods
Published on 6/7/2021
A very popular upgrade classic car owners are considering these days is ditching the carburetor for EFI, or Electronic Fuel Injection. There are many good reasons to do so, however carburetors do still have their place. Let's start by discussing the problem with carbs and why to consider EFI in the first place.
Carburetors are an old technology mechanical fuel system - although tried and true - they are not without their issues in the modern world. For decades, carburetors worked just fine. With most carbureted vehicles off the road these for long periods of time between drives AND the heat they can experience during modern traffic patterns, they aren't always optimal. EFI by contrast is a modern technology typically electronically controlled by a computer and is generally very reliable and consistent.
Basic carb operation works by a mechanical fuel pump filling the float bowls on a carburetor at a rate of about 5-6 PSI. The float bowls of the carb are what actually feed the engine when it demands fuel by opening up the needle from the seat to fill up the bowl, then through a power valve, accelerator pump and squirt nozzle into the venturi or the carburetor and into the engine's intake manifold. This worked fine for years - and still works fine for many race engines - but there are problems with carbs for use in today's world. First off, the gasoline is not the same as it used to be. Most fuel has 10% or more Ethanol mixed into it which is not good for rubber, plastic or soft aluminum parts that most carburetors are made of. Second, depending where you live, there is generally much more traffic on the road then there was in the "old day" which means engines are going to run hotter due to sitting in traffic more with not much air flow. Gasoline can boil at as low as 100 degrees and has a max high boiling point of 400 degrees. Underhood temps can easily get up to 250 or more degrees when sitting in traffic which can cause a condition called Vapor Lock. When fuel begins to boil, there are air pockets in the fuel supply in the line to the float bowl or at the extreme end, the fuel in the float bowl boils away before it can be refilled. Sometimes an electric fuel pump helps with this issue as it provides constant pressure to the bowl even when fuel starts boiling.
EFI by contrast uses an electric fuel pump with a much higher pressure (typically around 60 PSI) and fuel injectors that only fire when the computer tells them too. The trick is how the computer knows when to fire the injectors and how to adjust the air fuel mixture based on feedback it receives from the engine sensors. EFI uses a coolant temp sensor, an oxygen sensor in the exhaust, a throttle position sensor, and sometimes a knock sensor, intake air temp sensor and mass air flow sensor. This all depends on the particular EFI system in use. Whiel semi complicated to wire up and install, the results can be increased reliability and consistency in starting, idles, cold starts, hot starts and no vapor lock. Unlike a carburetor, the EFI computer is constantly testing the air/fuel mixture and making enhancements and corrections (known as self-tuning) - carbs must be manually tuned, driven and tuned again if needed for changes in weather and altitude.
There are a few different brands and types of EFI systems available to retrofit onto classic car engines - several options to install them as well. The top brands offering EFI now are Holley and its Sniper system, FiTech, and Edelbrock. There are others as well but we'll just focus on these for now. Holley and FiTech offer what's known as Carburetor Replacement systems or Throttle Body EFI, where Edelbrock offers "multi-port" EFI which includes an intake manifold with fuel rails that incorporate an injector for each cylinder. All companies promise simple installation, and this is generally true for all but the wiring portion, which can can get tricky. The other gotcha the big vendors don't focus on is the need to find a good initial tune. Yes they self tune, but you have to start somewhere. They all ask for a few bits of information such as the engine size, cam specs, etc then start with a base tune from there. Sometimes this works, sometimes it doesn't. EFI is not a fixit tool for a poor running engine. You should do your best to get an engine running well before installing EFI. If there are vacuum leaks, weak cylinders, ignition issues causing the engine to run poorly, adding EFI will only make this worse.
EFI installations require an electric fuel pump and a return line back to the tank. The most desirable way to install this is by using a fuel tank that has an internal pump and return fitting. Sometimes called "EFI Tanks" they are available for some cars by Aeromotive and TANKS, Inc. There are ways to retrofit an electric pump and a return line into a stock tank but this is challenging for more DIYers (and some repair shops). Inline pumps are available and a good alternative sometimes but a return line must still be tapped into the tank somehow - there are some universal return line kits available now that tap into the fuel filler neck hose. Some companies offer the concept of a surge tank that is essentially a small fuel tank that is fed by the car's mechanical fuel pump, has its own electric fuel pump that feeds the EFI unit and also has a return line built in. It's simple to install for the DIYer but it does have some major drawbacks. First off, a 1/3 gallor or raw fuel in in a tank under the hood. Just another firebomb exposed to extreme heat and available to be crushed in the event of a collision. Second, there are multiples points of failure when using these tanks as the mechanical pump is still in play - not to mention vapor lock can still be an issue.
Modern EFI systems offer many advantages and promise fixes for many traditional carburetor "problems" like consistent starts, idle and vapor lock. However, it's important to be sure an engine is running well before installing EFI. It's also important to know that EFI, while self tuning, is not a magic bullet out of the box. It can take significant tuning effort sometimes to get EFI running correctly and reliably. Some say the EFI retrofit technology is not quite there yet - do your research or consult with us to find out more before you make a decision to go EFI.
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