Breaking Down Carbureted LS vs EFI

“I tried it when I was scared to learn EFI. I won’t do it again.”

Did you ever think you would see the day when people would opt to put a carburetor in place of a fuel injection system? Did you ever think you’d see the day when it would be more complex to do so? Are you one of these crazy souls?

When it comes to V8 freaks, most of us got our start turning wrenches on old carbureted V8 engines. Why? Because, based on what we have access to, it’s generally cheaper and easier to learn. It also serves as pretty much the perfect way to learn the fundamentals of an engine’s operating system.

Carb vs EFI

“Contrary to what some might lead you to believe, let us assure you, there’s no increased risk in killing your motor if you run a carb over a fuel injected system,” explain the folks over at LSX Magazine. “The reasons why a carb on an LS makes sense are pretty simple. In LS swaps or street/strip/race cars, a carbureted LS is simple, cheaper, and often can make more top-end power than EFI.”

While LSX works to reassure builders, a carbureted LS is something that tends to bring some controversy. Essentially, setting up an LS with a carburetor isn’t something many self-proclaimed sane individuals would recommend. Even as a carb tends to produce more peak power, the reliability and efficiency of an EFI system isn’t exactly worth sacrificing simply to put a carburetor on top. As Pro Stock racer Warren Johnson told HotRod damn near twenty years ago, “There’s no excuse for [sanctioning bodies] not moving to EFI.”

“Properly tuned, carburetors make more peak power than EFI in a Pro Stock engine,” Johnson continued. “A carb’s pressure differential atomizes the gas a lot better than spraying fuel through an orifice. But EFI has a broader power band and superior cylinder-to-cylinder fuel distribution. The 1,100- to 1,300-cfm dual carbs are good only over a narrow range, about 1,500 rpm at most. EFI performs well over 2,000 rpm or more. On average, if optimized, both systems perform about the same as far as how fast you get down the track. However, the EFI system is much easier to tune than a carburetor.”

Basically, more peak power isn’t everything. While it does give you an edge, a healthier power band is much more important for performance. So, in all reality, the answer to “How much more power can you see with a carburetor?” is relative. It honestly boils down to the person.

So, let’s see if we can’t break down the who, what, and why-in-the-world would you want a carbureted LS?

The Case for EFI

As always, we turned to our good friend and resident LS-wizard John Potucek of Keystone Automotive for some guidance on the matter.

“I used to think a carb on an LS was a good idea,” says Potucek. “I thought this way for multiple reasons: I thought it would be cheaper and I’ve always been good at tuning a carb, so it’s what I was familiar with. Plus, I hated wiring and knew nothing about EFI. Seemed like an easy decision, right?”

It’s a valid argument. Knowing the ins and outs of one system and not the other is a deciding factor for a lot of people. There’s also the “wow” factor. While the tone will vary, a carb will certainly carry a presence when you pop your hood to show off.

It’s important to remember that this does come with some potential pitfalls. In fact, while Potucek originally went with a carbureted LS, he eventually converted back to EFI. “At the track one day, I saw just how much I was missing out on,” he says. “Friends being able to monitor every single thing the engine is doing. Adding more fuel to certain cylinders, adjusting timing by cylinder—yes, I know some timing controls for LS engines now allow this—being able to adjust the tune basically any way you can imagine. I wanted these things!”

“I dove past all my fears of EFI and made it happen. And I can honestly say, it was one of the best things I’ve ever done to my car. It’s really not much different in price then converting to a carb—deals are out there for either set-up. But now, with the Holley Terminator X systems, you can get the ECU and a dummy-proof wiring harness for under $1,000. That is a steal for everything it has to offer,” says Potucek.

Now, this isn’t to say you can’t get a carbureted engine running reliably and consistently at the track. It’s just that EFI offers an edge in terms of tunability. And because it monitors and adjusts itself, you don’t have to spend much time tinkering with it once it’s installed.

“My car runs and drives just like my daily driver—with the exception of making 800+hp,” continues Potucek. “It’ll start without a hiccup whether its 15° or 95°. I can monitor and adjust more than I ever dreamed of when I was carbureted. It was an easy learning curve for me to be able to tune my setup and partly because Holley made it easy. I use to think my car drove great with the carb—and it did drive well—but it doesn’t compare to how it drives now, being EFI. It’s just more fun on the street and at the track. I honestly can’t think of one downfall to making the switch.”

No Turning Back

But maybe you just have your heart set on a carbureted LS. Alright then, you mad scientist, we warned you. Just know that’s it’s not quite as simple as ripping off an intake and throwing on one to handle a carb in its place.

Well, wait a minute, it pretty much is that simple. Edelbrock makes the intakes, and with these you will have the option of running pretty much any carburetor you could ever want. (Though, most people stick to Holley 4150 carbs or something very similar.)

Other than that, you’ll need an ignition controller. In this case, MSD LS Series (PN 6014) is an excellent system that will run it for you. Installation is simple, thanks to a mostly a plug-and-play system and will only take a few minutes to run.

Fuel delivery can pose some issues, though, and here’s why: If you’re running a vehicle that was designed to run EFI, you’re going to have an in-tank pump that’s pumping a lot of pressure. You hook that up to a carburetor and you’re going to have a big mess on your hands.

So what do you do? Well, you can grab a fuel pressure regulator from Aeromotive.

If you’ve come this far, you might as well install a regulator from the best in the business, right? Plus all Aeromotive products are all made in the USA and you’re looking at a pretty simple installation.

First, you will want to have the regulator close to the carburetor. While many feel it’s best to have it after the fuel filter, it won’t hurt to run the regulator where it’s out of sight. For peace of mind, it also won’t hurt to run another filter before the regulator. (This can also be sourced from Aeromotive.)

If you’re not running a vehicle originally equipped with EFI, you will still have the issue of feeding fuel to that engine in the first place. There’s no place on an LS for a mechanical pump, which means you’ll need to install an electric pump between the tank and the carburetor. Luckily, Aeromotive has a variety of in-line fuel pumps for carbureted applications that you can get your hands on for this swap. The company’s SS Fuel Pump (PN: 11203) is a perfect choice for a naturally-aspirated, carb-fed engine running in the neighborhood of 450-hp and is but one example of their offerings.

So, maybe it’s not as simple as tearing off the intake and popping a carb on, eh?

Also—all in—prepare to throw affordability out the window. All of the above-mentioned product necessary to make this carbureted LS swap will total up a price tag north of $1,000. And, as Potucek pointed out, an aftermarket EFI set-up that more easily hits all your performance needs runs for right around the same amount.

Finicky Fixes

In our research, we also found that a lot of people have some issues with getting their carbureted system to run properly. If you’re on the fence about swapping to a carburetor, this can be discouraging and may be enough to drive you away. But, if you’re a true gearhead, you’ve already decided this won’t stand in your way. Here we go, then.

“Grounds, grounds, grounds. I have seen many just not start, start sometimes, or start but run like garbage,” says ZONES89RS, a member of the online forum LS1tech.com who was kind enough to literally post an entire thread on everything you need to know to get one of these systems up and running. (It’s an absolute must-read if you’re making this leap.)

“You will need a solid ground for the ignition. I ground mine to the intake, since the connector that comes with it is just long enough to do so. BUT, I also have a ground from the battery negative to the engine, a ground from the battery negative to the chassis, and usually two grounds from the engine to the chassis.”

Other small hiccups and issues will be present with an analog system like this. Some guys have trouble with the ignition, which is typically an easy fix, while others will have some issues tuning the carb. Though, when stepping into this territory, you’ll likely know your way around a carburetor and tinkering will be easy enough.

Is a Carbureted LS Worth the Trouble?

Keep in mind, you already have EFI. Making this swap is going to cost as much as an upgraded EFI system and, honestly, you’ll be spending more time tuning and dialing the system in—as it is a routine process with a carburetor. But don’t forget that a big reason to ditch the EFI is to ditch the wiring trouble that comes with LS swaps.

“One thing that still gives some trepidation about performing an LS swap into an older vehicle is fuel injection,” says SuperChevy. “All the wiring, fuel line plumbing, mounting a computer, etc., is still a daunting task for many when compared to bolting on a simple carburetor that you only need a screwdriver and vacuum gauge to tune. Many enthusiasts tend to stick with what they know. And a lot of guys know carbs better than they know their own cell number.”

And that’s what it comes down to. A lot of people are going to tell you that you’re nuts to do this. (And you are.) But that’s not a bad thing! If you feel a carb is the tool you need to perform based on your experiences, well, then it is. Just don’t say we didn’t warn you.