Street Rod Life

Carb vs. EFI: A Look at LS Engine Induction Options

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EFI-01 (800x1200)

There are advantages and disadvantages to both carburetors and EFI. The decision can often come down to what you can afford. EFI is always more expensive, but there are options that can keep the cost down.

Clearing the Air On What is Really Required When Making an LS Induction Swap

Words and Photos By Jeff Smith

The classic tussle of carburetors versus EFI has been brewing now for 30 years. It calls out old versus new and tradition versus technology, and it’s been the perennial question since performance EFI became headline news in the late 1980s.

For our version of this scuffle, we’re going to place our attention on the LS engine. But, instead of focusing on horsepower like everybody else, we will aim our guns on the cost of street engine systems, because unless your name is Bill Gates or Mark Zuckerberg, the cost of all this mechanical wizardry is an overriding consideration.

So here’s the pitch: The LS engine family — from birth — has enjoyed the benefits and performance of sequential EFI. So why take a giant technological step backwards? The answer is simple — an old Holley carburetor is cheaper than a box of electronics. Within the narrow confines of the muscle car engine swap arena, converting to a carburetor is less expensive than retaining the EFI. If you know how to work on carburetors, those antique fuel mixers do a pretty good job and do it for pennies.

To keep this story simple, we are going to assume our LS engine swapper has purchased a used LS engine and is planning a bolt it into a ’60s, ‘70s or ‘80s machine. For the sake of brevity, let’s assume we have just purchased a used LS 6.0L LQ4 truck engine. As it sits on that engine stand, it has a complete front accessory drive, intake manifold, injectors, and fuel rail. Let’s also assume it came with a factory EFI harness and computer.

We’ll start with the carbureted LS conversion and then tackle the more complex possibilities with regard to both factory and aftermarket EFI conversions.

Carb Conversion

Converting an LS engine to a carburetor is actually pretty easy. Unbolt the factory intake, bolt on an intake like this Edelbrock Performer RPM and a Holley 3310 vacuum secondary carburetor and you’re halfway there. This will also require ignition control.

Converting an LS engine to a carburetor is actually pretty easy. Unbolt the factory intake, bolt on an intake like this Edelbrock Performer RPM and a Holley 3310 vacuum secondary carburetor and you’re halfway there. This will also require ignition control.

Carburetors are the epitome of cheap and easy. With our 6.0L truck engine, we’ll first need a carbureted intake manifold. For the street, a dual plane is the best way to go. We’ll assemble a list of parts for the carbureted conversion and offer multiple selections, but unless you’re building some kind of absurdly fast street car, a dual plane like the Edelbrock Performer RPM or Holley’s version is the best choice.

For a carburetor, we’ll use the classic 750 cfm vacuum secondary as our fuel mixer of choice. We’ve chosen the new price of the silver version of that Holley at roughly $350, which is also almost exactly the same price as Edelbrock’s version. For examples, we’ve listed two: a Holley vacuum secondary 750 and an Edelbrock – both retail for around $350. If you know your way around a Holley, then you also know there are about a billion used 3310 carbs floating around that could easily be refurbished, which could save even more.

MSD makes converting to a carburetor really easy with this 6010 box for the early 24x LS engines and the 58x engines, as well. The free MSD software allows you to set your ignition curve — or simply plug a two-pin piece in the side of the box that has a pre-determined ignition curve. It doesn’t get much easier.

MSD makes converting to a carburetor really easy with this 6010 box for the early 24x LS engines and the 58x engines, as well. The free MSD software allows you to set your ignition curve — or simply plug a two-pin piece in the side of the box that has a pre-determined ignition curve. It doesn’t get much easier.

When the factory ECU is removed, this also eliminates ignition control. But MSD can fill that void with its MSD-LS6 control box that plugs right into the existing coil pack wiring harnesses and is simple to use. With a minimal number of electrical connections, this system is easy to install. If you want to create your own custom ignition curve, MSD’s free Pro Data+ software on a laptop makes it easy to get that done. Or, if you’re laptop averse, you can plug is one of six modules that are pre-configured with various ignition curves.

The Trailblazer SS intake makes more horsepower than an LS6 and more torque than the truck intakes. It also requires a factory fuel rail specific to this intake. A Holley LS1 fuel rail will fit, but we had to make simple custom aluminum Z-brackets. This arrangement will also need a fuel regulator.

The Trailblazer SS intake makes more horsepower than an LS6 and more torque than the truck intakes. It also requires a factory fuel rail specific to this intake. A Holley LS1 fuel rail will fit, but we had to make simple custom aluminum Z-brackets. This arrangement will also need a fuel regulator.

We’ve also included the price of a set of Fel-Pro intake gaskets, and both Edelbrock and Holley intelligently include new intake bolts with their manifolds. Obviously, there are other details that will be needed to complete this carbureted conversion, like an air cleaner, throttle linkage, and a dual-inlet fuel line and filter, but for this story, we’ll assume you can handle those. Just know they will also impact the overall conversion cost.

Carb Conversion Parts List

Description PN Source Price
Edelbrock Performer RPM, LS1 port 71187 Summit Racing $316.84
Edelbrock Performer RPM, LS3 port 71197 Summit Racing $345.94
Holley Dual Plane LS1 port 300-130 Summit Racing $263.96*
Holley 750 cfm Vac. Sec. Carburetor 0-80508-S Summit Racing $344.95
Edelbrock 750 cfm Man. Choke Carb. 1407 Summit Racing $343.50*
MSD 6LS1 ignition box for 24x Gen III 6010 Summit Racing $364.95*
MSD 6LS2 ignition box for 58x Gen IV 6012 Summit Racing $364.95
Fel-Pro intake manifold gaskets 13123 Summit Racing $25.97*
Total Price $998.38
  • Indicates the parts we used for the total

EFI Exemplified

Now we can drop into the slightly more complex world of digital fuel injection. The simplest conversion is to retain the stock intake manifold, injectors, and even the factory wiring harness. If the engine is bone stock, just attaching all the harness connections, adding power and grounds, and finding a home for the ECU will get the job done. The biggest issue then will be supplying the 58 psi fuel pressure to the regulator, along with a return line. We’ll deal with that in an accompanying sidebar.

This approach virtually minimizes the cost. The only significant investment will be for a pair of AN fuel line adapters like those from Aeromotive, Earl’s, or Russell to adapt the factory quick-disconnect connectors to a -6 AN fitting. The only limitation on this idea is the truck manifolds are fairly tall and may not clear the hood line on your car. If you have a ’69 Camaro, it won’t clear; but if you’re swapping into a ’55 Chevy, you are good to go.

EFI Plan A

Description PN Source Price
Stock EFI manifold and injectors N.A. Summit Racing $0
Aeromotive QD 3/8 to -6 ORB 15118 Summit Racing $38.97
Aeromotive QD 5/16 to -6 ORB 15117 Summit Racing $35.11
Aeromotive -6 ORB to -6 AN male 15606 Summit Racing $15.97
Aeromotive -8 ORB to -6 AN male 15605 Summit Racing $18.97
Earl’s 3/8 QD to -6 male 991966ERL Summit Racing $34.25
Earl’s 5/16 QD to -6 AN male 991965ERL Summit Racing $34.55
Russell 3/8 QD to -6 male 644123 Summit Racing $17.97*
Russell 5/16 QD to -6 male 644113 Summit Racing $17.97*
Total $34.94
  • Indicates the parts we used for the total
If you plan on using a stock computer, an aftermarket wiring harness is a wise investment, as the factory harness is cumbersome. This is a Painless harness for a 2000 LQ4 iron truck 6.0L engine and computer.

If you plan on using a stock computer, an aftermarket wiring harness is a wise investment, as the factory harness is cumbersome. This is a Painless harness for a 2000 LQ4 iron truck 6.0L engine and computer.

Now, let’s move to Plan B. This entails using a custom wiring harness in place of the clunky production version. Several companies offer custom harnesses — as examples, we’ll use Painless and PSI. These harnesses can be paired with the stock computer with no other changes. The only disadvantage with these first two approaches is they do not easily accommodate significant power changes to the engine. These first two approaches are for the guy who doesn’t plan on changing anything on the engine more than perhaps a set of headers.

With factory multipoint, injector sizing is an issue. Stock LS injector sizes for normally aspirated engines range from 22 to 41 lb/hr A 26 lb/hr injector is good for 400 hp. AN LS3 41 lb/hr version will deliver 600 hp. A stock 6.0L with a cam and headers will need at least 30 lb/hr injectors to supply sufficient fuel. LS engines also use two different styles of injectors with different connectors.

With factory multipoint, injector sizing is an issue. Stock LS injector sizes for normally aspirated engines range from 22 to 41 lb/hr A 26 lb/hr injector is good for 400 hp. AN LS3 41 lb/hr version will deliver 600 hp. A stock 6.0L with a cam and headers will need at least 30 lb/hr injectors to supply sufficient fuel. LS engines also use two different styles of injectors with different connectors.

The limitation here will be the size of the stock injectors. According to Jim Hall at TPIS in Minnesota, the stock injectors in the Gen III 6.0L LS truck engines are capable of moving enough fuel to support up to 450 hp. A stock LQ4 will make around 410 hp with headers and no other changes. If you really want to add power, many enthusiasts recommend replacing the truck manifold with an LS6 factory manifold. But our fellow Xceleration Media tech writer and dyno guru Richard Holdener discovered the factory Trailblazer SS manifold is a pretty good piece. You can buy a new Dorman version of this manifold from RockAuto for a mere $142 and it will make more torque than the stock LQ4 intake and more horsepower than an LS6. This could push the power to perhaps 425 or more when combined with headers. This will require investing in a set of aftermarket Holley fuel rails and custom mounts, but the conversion is easy. Again, this is a tall manifold, so there are many hood lines it won’t fit beneath.

Larger injectors will require reconfiguring the stock EFI computer. This is a screen shot of spark advance vs. load vs. rpm from the JET Dynamic Spectrum Tuning software that allows making changes to the stock computer.

Larger injectors will require reconfiguring the stock EFI computer. This is a screen shot of spark advance vs. load vs. rpm from the JET Dynamic Spectrum Tuning software that allows making changes to the stock computer.

Before we move on, let’s touch on tweaking the stock GM ECU with a tuner like HP Tuner, EFILive, or the new software from JET Performance. All of these software companies offer easy access to the factory tuning parameters — especially fuel and spark. For example, the factory generally sets the truck engines to run rich at wide-open throttle (WOT) to prevent overheating the catalytic converters. Combining the headers with leaning, the fuel at WOT can potentially be worth 10 to 15 hp.

If embarking on this kind of tuning is intimidating, you also have the option of sending your computer to a tuner. The performance is often worth the investment. Of course, return trips may be required with later changes to heads, cam, or larger injectors.

EFI Plan B

Description PN Source Price
PSI 24x truck harness cable throttle HAR-1018 PSI Conversion $549.00*
Painless 24x harness, cable throttle 60218 Summit Racing $724.99
Previous cost of AN hose connectors            —           $34.94*
Total $583.94
HP Tuner VCM Suite HPTuner $499.00
JET Dynamic Spectrum Tuner 14007 Summit Racing $399.99
TrailBlazer SS intake – Dorman 12580420 RockAuto $141.79
Holley fuel rail LS1 cathedral port 534-209 Summit Racing $144.95
  • Indicates the parts we used for the total
One alternative to using a factory ECU is to retain the factory injection manifold and throttle body, but convert to aftermarket control. FAST offers an EZ-EFI conversion that applies its self-learning capabilities to the LS engine family. This also requires a XFI ignition box to control the spark.

One alternative to using a factory ECU is to retain the factory injection manifold and throttle body, but convert to aftermarket control. FAST offers an EZ-EFI conversion that applies its self-learning capabilities to the LS engine family. This also requires a XFI ignition box to control the spark.

Plan C brings in aftermarket EFI. Holley, FAST, and MSD’s Atomic offer retro-fit EFI control that will bolt directly to the existing LS engine and control both the fuel and spark. All three systems require only simple inputs like engine displacement and injector sizing, and then they create their own spark and fuel maps that generate instant results at the touch of the key. Then the self-learning software tunes the system to match your air-fuel ratio and ignition timing inputs. These stand-alone EFI systems are more expensive than using a factory-based ECU, but don’t require the complex tuning and navigation knowledge demanded by the OE computers.

EFI Plan C

Description PN Source Price
FAST-EZ-EFI GM LS Transplant kit 302002 Summit Racing $1,360.97
Holley Dominator LS ECU 550-602 Summit Racing $1,766.97
MSD Atomic LS EFI 2950 Summit Racing $2,164.95
It’s also possible to use a carbureted intake with any number of different stand-alone EFI systems, such as Edelbrock’s E-Street EFI. This system will not be compatible with the ignition, which will require a separate ignition control box like the MSD-6010 for the 24x engines.

It’s also possible to use a carbureted intake with any number of different stand-alone EFI systems, such as Edelbrock’s E-Street EFI. This system will not be compatible with the ignition, which will require a separate ignition control box like the MSD-6010 for the 24x engines.

The next, Plan D is a hybrid that blends the nostalgic look of a carbureted intake with EFI. Let’s say you have a carbureted LS engine but have decided it would be nice to upgrade to EFI. This approach allows you to retain the carburetor and ignition control and just go with one of the many stand-alone EFI throttle body systems. These operate just like the multi-point self-learning control systems. Because you already have ignition control, that part is already done. This is a spinoff creating a traditional looking induction system while enjoying the fruits of digital control over both fuel and spark.

EFI Plan D

Description PN Source Price
Edelbrock E-Street-2 EFI, no fuel pump 36649 Summit Racing $1,699.95
FAST EZ-EFI 2.0, no fuel pump 30400-KIT Summit Racing $2,296.97
MSD Atomic EFI 2910 Summit Racing $2,212.95
FiTech 600HP  EFI 30002 Summit Racing $995.00*
Holley Sniper 600 hp EFI 550-510 Summit Racing $995.95
QuickFuel QFI EFI 500S Summit Racing $2,012.95
Professional Products EFI 70054 Summit Racing $2,194.97
MSD 6LS1 ignition box for 24x Gen III 6010 Summit Racing $364.95*
Fel-Pro intake manifold gaskets 13123 Summit Racing $25.97*
Total $1,385.92
  • Indicates the parts we used for the total
A well-designed in-tank fuel pump assembly is essential when using any EFI system regardless of engine. One of the better ideas is Aeromotive Phantom system that allows you to retro-fit one of the Stealth 340 pumps inside your stock tank. This kit creates a reservoir inside the stock tank to prevent fuel slosh from causing the fuel pressure to drop during hard braking or acceleration.

A well-designed in-tank fuel pump assembly is essential when using any EFI system regardless of engine. One of the better ideas is Aeromotive Phantom system that allows you to retro-fit one of the Stealth 340 pumps inside your stock tank. This kit creates a reservoir inside the stock tank to prevent fuel slosh from causing the fuel pressure to drop during hard braking or acceleration.

There’s quite a bit to digest, and hopefully we’ve given you some ideas and options. Simplicity and carburetion have a lot going for them, but the sophistication of EFI and the control it offers is also enticing. Either way, it will be hard to make a bad decision.

Sources: Aeromotive, Aeromotiveinc.com; Edelbrock (Russell), Edelbrock.com; Federal-Mogul (Fel-Pro), federal-mogul.com; FiTech Fuel Injection, Fitechefi.com;

Holley Performance Products (Earl’s), Holley.com; MSD, MSDignition.com; McRobb Performance Products, Robbmcperformance.com; Painless Wiring, Painlessperformance.com; Professional Products, professional-products.com; PSI, PSIconversion.com; Quick Fuel Technology; Quickfueltechnology.com.