One of the big advantages of the Chevy LS engine family is a modern electronic fuel injection system (EFI).
Spark timing and air/fuel mixture are controlled by sophisticated computer fed inputs from a variety of sensor inputs. The engine therefore can adapt automatically to changes such as fuel quality, temperature and elevation.
So, why in the world would anyone want to run a carburetor on an LS engine?
Well, there are situations where it might make sense and that means the market is large enough that both Edelbrock and Holley have geared up to make intake manifolds for just that purpose. But it takes more than just an intake manifold and a carburetor. You also have to have a way to provide spark timing through the LS one-coil-per-plug ignition system. And Holley, through their MSD division, can provide such a thing. A second company, Daytona Sensors, also has an ignition box that can do the same thing.
Examples of when someone might want to carb an LS include:
- Horsepower junkies. Lots of dyno tests show that a carbureted LS can edge out EFI in peak horsepower. Maybe at the expense of low-end torque and with no consideration for mid-range drivability but still winning the peak number.
- Old-school hotrodders. Some people are experienced with carb tuning. Some people just like the looks of a carburetor, especially compared to the admittedly ugly LS truck EFI intake manifold.
- Engine swappers who want a quick-and-dirty route to LS power
- Here at Kwik Performance we acquired a 1990 Chevy 1500 test mule just to mock up some of our front drive systems. It came with a 700R4 transmission and originally had a throttle-body-injection (TBI) engine. The most common way to do an LS swap would have been to replace the 700R4 and its troublesome TV cable with an electronically-controlled 4L60e transmission and pull the gas tank to install a high-pressure fuel pump. Instead, the TV cable easily hooked up to our Edelbrock carb and a simple fuel pressure regulator reduced the TBI fuel pressure of around 13 PSI to a carb-friendly 7 PSI.
- Other engine swap examples are where the builder wants to keep an older style transmission such as a TH350 or 400 or perhaps an older manual transmission to avoid new cross-members or driveshaft changes and also doesn't want the complication of a high-pressure fuel system which might require a pump, regulator and new pressure and return fuel lines.
- Expense. A junkyard 5.3L truck engine may have come with an intake manifold, computer and wiring harness and it's fairly simple to modify the harness and find someone to remove the anti-theft function in the ECU. Compare that to a carburetor, manifold and ignition box and EFI may be cheaper. Or, maybe not, if you need all new injectors, your wiring is all chopped up, and you need a new, standalone harness plus the high-pressure fuel system we keep mentioning.
Conclusion? We're big fans of modern EFI and use it in most of our LS swaps. And we now have personal experience with the simplicity of a carbureted LS and know that is an option if needed. We're also pretty sure the internal parts of an LS engine don't know or care how they get their air/fuel mixture.