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

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.

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.

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

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.

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.

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

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

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

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