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Over the past few decades, General Motors’ third- and fourth-generation small-block V8s have found their way into everything from Miatas to monster trucks. With literally millions of LS powerplants out in the wild, getting your hands on one is just a matter of a quick online search, a visit to a junkyard, or a call to a crate motor supplier.
Regardless of one’s brand allegiances, it’s hard to deny the fact that the LS is one of the biggest game changers in the history of automotive performance. Offering proven, reliable horsepower in a compact, lightweight package with a stunning amount of strength even in factory production form, the LS platform has also benefited from incredibly robust aftermarket support. Combine all that with the availability of surprisingly low-cost examples, and it’s no wonder these engines have become the darling of engine swappers everywhere.
LS engines have been swapped into just about anything with wheels at this point. But putting one in GM's pony car rival, the Mustang, often evokes fierce brand loyalties and intense reactions. Regardless, the LS platform arguably offers a better performance foundation than many Ford engines, and LS swapped Mustangs have become a common sight at Holley LS Fest.
The Fox-body Ford Mustang’s engine bay is one spot where the presence of an LS might be a controversial sight, though. Built from 1979 to 2004 – with the heavily updated 1994 to 2004 models denoted by the SN-95 moniker – the Blue Oval’s iconic pony car was offered with Ford’s own small-block V8 right from the outset. But while these engines offered respectable performance and a lovely V8 roar right out of the box, enthusiasts quickly found the limitations of this powerplant.
“The factory-produced traditional small-block Ford that was introduced in the Fox-body can’t handle much more than 500 horsepower,” notes Logan Duvall, Project Engineer and Drivetrain Systems Lead for Holley Performance Products. “If you go much further than that with them, the block will split right down the cam tunnel. To get power significantly beyond that, you’d have to go with an aftermarket block.”
Although many Ford loyalists might prefer to stick with Blue Oval power under the hood of their Mustang, LS motors have some compelling benefits, including a strong block that can withstand hefty power increases. "The factory-produced traditional small-block Ford that was introduced in the Fox-body can’t handle much more than 500 horsepower,” says Logan Duvall of Holley. “If you go much further than that with them, the block will split right down the cam tunnel."
While SN-95 Mustangs could be had with the more technically advanced Modular 4.6-liter overhead cam V8, only the less common four-valve Cobra version of that motor came from the factory with more than 300hp. Most of the Modular engines in Mustangs were the less potent two-valve version found in the GT model, which peaked in the mid-200hp range. To go beyond those lackluster power ratings requires significant internal work, which led those seeking serious grunt to look for alternatives.
“On the drag racing side, we started seeing LS stuff in these cars as early as the 2000s,” Duvall says. “And swaps really picked up a lot after we started doing LS Fest back in 2010. The LS is just a much more efficient engine, and it’s much easier to tune. Even if you keep the factory computer, the LS is way ahead of what was available from the factory in the Fox-body platform as far as tunability goes. And if you go with a Terminator X engine management system, that takes things much, much further.”
And with decades of aftermarket development now backing the platform, swapping an LS into a Fox-body Mustang is easier than ever. That said, it’s still a project that you should go into with a battle plan and a solid understanding of what lies ahead.
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Dylan Cato's '89 Mustang is proof of the LS's stout construction. Although his engine is fortified with hefty aftermarket internal pieces, the block on the 2000hp motor is a stock GM piece. With this combination, Cato set the unofficial record for a stock LS block, running a 4.209 at 175.52 mph 1/8 mile at LS Fest 2023.
The dimensions of an LS don’t differ dramatically from a traditional small-block Ford, and these pushrod engines are also significantly narrower than any Ford Modular V8, so packaging is generally less of a concern compared to other popular LS swap platforms. There are, however, some other factors that would-be swappers should be aware of.
“Keep in mind that you’ll also have to swap the transmission, of course,” Duvall points out. “The factory T-5 and AOD bellhousings for the transmissions that those Mustangs were outfitted with won’t bolt up to an LS. And you’ll need a driveshaft to accommodate that switch as well.”
The 1994-2004 SN-95 Mustangs look considerably different than Fox-body 'Stangs, but they're essentially the same under the sheet metal. Because of that, swapping an LS into these later Mustangs is pretty much the same too.
Duvall also tells us that if you’re looking to get the Mustang’s factory gauge cluster to work with the GM powertrain, you’ll need a few items to get the two to talk to one another.
“You can keep your factory wiring for the gauges – it just requires some retrofitting to make it work. You can use an adapter to get the factory small-block Ford oil pressure sending unit into the LS motor, and you’ll need two coolant temperature sensors – one for the EFI system, and another one that will run the factory gauge. And for the tachometer, you’ll splice into the EFI system’s tach output.” The speedometer, meanwhile, will require the correct gear and adapter for the gearbox that you’re using. “But be aware that if you’re using an electronically controlled transmission, you’ll need a converter box to change your VSS to run a cable drive.”
A full tube chassis makes swapping an LS into a Mustang somewhat easier, of course, but the difference isn't as big as you might think. There's plenty of room in the stock engine bay for an LS, and Holley's mounts, accessory drives, and adaptors make the swap a straightforward bolt-in.
Getting an LS to work in a platform that it wasn’t originally designed for obviously requires some hardware for the transplant, but the process is surprisingly straightforward these days thanks to a wide roster of purpose-built parts that are now available. Here, we’ll take a closer look at the components you’ll need to get an LS up and running in your Fox-body or SN-95 Mustang.
Motor Mounts
Fox-body and SN-95 owners have several different options when it comes to engine mounts, but it’s important to note that one size does not fit all. “It comes down to what K-member you have in the car,” says Duvall. “We have mounts for the factory K-member, and we have mounts for the K-members from AJE, Team Z, and Maximum Motorsports as well.” Tubular aftermarket K-members like these offer advantages in both weight and packaging, the latter of which can provide more room for exhaust systems, turbo setups, and other performance hardware that you might want to bring into the mix.
Transmission Mounts
You’ll also need a crossmember to get a GM automatic or manual transmission to play nice with your Fox-body or SN-95 Mustang, and Holley offers an adapter if you plan to use a 4L60E or 4L80E automatic as well. “If you use our mounts and crossmember, it makes this a bolt-in solution,” Duvall says.
See Holley's engine and transmission mounts for Fox-body and SN-95 LS swaps now!
Hooker BlackHeart's LS swap kits offer all the mounts and fasteners you need to put an LS motor into your Fox-body or SN-95 Mustang. The kits are offered in several different versions, and the parts are available individually too, allowing you to get precisely the right combination you need for your application.
Accessory Drives
While an OE-style accessory drive can work in some applications, many builders prefer Holley’s LS accessory drive systems in swap projects like these. “Ours use more of a traditional configuration in terms of where the alternator, power steering pump, and other components are located,” Duvall tells us. “And that gives you a layout more like an older car. In the newer Chevrolet trucks and other GM applications, the alternator is mounted really high, which can detract from the visual appeal of the engine bay in general. And the layout just isn’t ideal for an older car. The configuration we use makes it a lot simpler to hook up things like air conditioning and power steering. It puts everything where it needs to be for an application like this.”
Holley also offers alternators that have been designed with LS swaps in mind. “With some of the newer LS stuff, the alternator is PWM-controlled at the voltage regulator, so they won’t charge at full capacity all the time. But some folks will put a carburetor on an LS engine, and if you do that, you won’t have a computer system to manage that alternator. This alternator goes back to a more traditional style – one wire with a resistor in it that goes to 12-volt switch, so when you key-on, that alternator is charging. You won’t need an external regulator, or anything like that.”
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Although it's not absolutely necessary to replace the accessory drive when swapping an LS into a Mustang, it can make the job easier and give you a cleaner looking installation. Holley LS accessory drive kits are available in high-, mid-, and low-mount versions, so you can get the setup that works best for your particular combination.
Exhaust
Holley offers a variety of LS-swap exhaust manifolds that are purpose-built to work within the tight confines of the Fox-body and SN-95 engine bay and chassis. Hooker BlackHeart cat-back systems in both turn-down and rear-exit configurations are available as well.
Fuel System
Duvall says that while you may be able to get away with using the existing Mustang fuel pump on an unmodified 5.3-liter LS, most of these engines will require more flow than the Mustang’s factory unit can provide. “If you’re going with an LS3, an LS7, or something along those lines to really make some power, you’re going to want to take a look at one of our drop-in fuel pump modules,” Duvall says. “These literally drop right into your factory fuel cell, and until you outgrow the factory fuel line size, you can just tie right into the existing stuff.”
See Hooker Blackheart's exhaust systems for Fox-body and SN-95 LS swaps now!
Holley offers these LS motor Ford-style valve covers, for those who want to downplay that they're running a GM engine in a Mustang, or want to retain the classic small-block-Ford look underhood. These covers don't need any adapters, and they hide the LS coil packs under a cleanly shaped shield that mimics the original 5.0 engine's valve covers. You can find them at Holley.com under part number 241-185
Click Here Now to see Holley's Ford-style valve covers for LS engines!
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While it’s not mandatory in most applications, an LS swap radiator can make life easier in the long run. “What’s nice about these is that they’re dual pass, so the coolant is going through the radiator twice before it comes out, which provides better cooling,” Duvall explains. “These radiators are also equipped with inlet and outlet sizes that match the LS engine. That means you don’t have to hunt for radiator hoses that jump sizes from one end to the other, and you don’t have that bottleneck in the system.”
And if you’re using an LS from a truck or SUV application, you may also need an LS swap oil pan due to the clearance issues that can arise from the low-hanging factory pan.
It’s worth noting that Holley also offers an online overview of the LS swap components you’ll need for 1979 through 1993 and 1994 through 2004 Mustangs (along with many other platforms), which can help ensure that you haven’t overlooked anything. “The key to success with a project like this is to avoid over-complicating it,” Duvall adds. “Take it one step at a time, and try not to get overwhelmed with the big picture. If you buy these parts, the new engine will bolt in the same way as the one you took out.”
