V8 Engine Swaps for Classic Mustangs

Classic Mustangs are hard to find, and if you find one that’s in great shape but with a six-cylinder where a V8 should be, you may end up scratching your head trying to figure out if it’s worth the energy and wrench time it’ll require to give that vintage Mustang the growl it deserves.

The answer is a resounding “Yes.” You can swap a V8 into a six cylinder, and though it’s not trivial, it’s also not the world’s most difficult install.

The Donor Car Method

One easy way to do a basic V8 swap is to purchase a donor car at the same time as you purchase your six-cylindered Mustang. A donor car could be one that has a V8 engine, or had a V8 engine, and then was involved in an accident and was salvaged.

If the two cars are the same year, you can do an almost piece for piece swap out, replacing only which pieces are too damaged to be worthwhile. This is a frequently used strategy, even for things like automatic to manual transmission swaps.

Even though this may seem more expensive at the onset, having a donor car you can pick nuts and bolts off of, and rely on for your bushings and suspension components, can give you the authentic vintage look you’re after.

This only really works if you’re happy with the components that were available at the time though, if you’re thinking this is a good time to upgrade to a modern V8 engine, add a transmission with overdrive, or convert to disc brakes, we absolutely agree. But using a donor car is a great strategy and one to consider as you narrow down what it really is that you’re hoping to get out of the swap, whether that’s period-correct or resto-mod.

Restoring and Improving

If you’re looking for some more specific boxes to tick off, then you may end up needing to piecemeal a solution together from multiple avenues. Even though this isn’t the most straight-forward option, it does tend to produce the most unique results, and that usually ends up making a Mustang that’s perfectly suited to you.

Obviously, you’ll need a Mustang that’s going to be worth all of the work. There’s a lot of good advice for buying a classic Mustang, but you’ll want to keep in mind the other parts that you’ll need. It’s easiest to think of these parts in terms of large groups, but keep in mind that with every part comes all of its associated connections and components.

Engine Swap Options

You’ll need a V8 to swap into your Mustang. Whether you want a modern engine, like an LS or a Coyote, or a V8 from the same era, you’ll also need motor mounts, accessory brackets, a flywheel (or flexplate if you’re doing a V8 conversion but also want an automatic transmission) and motor mount frame brackets.

If you choose to get a modern engine you’ll also need a variety of tools to make the computer talk to the analog systems. Though there are countless potential engine swaps, a few have pushed their way to the forefront as popular choices. Each of these has its own set of pros and cons that should be weighed against your end goals.

Small Block Windsor V8

The small-block Windsor V8 is going to be the optimal engine for this swap. This isn’t so much because of its power, which obviously might look lackluster in comparison to some more modern engines, but rather because of its availability, size, and compatibility.

Ford introduced the Windsor back in the ‘60s, before the first Mustang even existed, and then continued to produce variations of this engine till 2000. There are a lot of reasons for why this engine’s architecture was used for so long. It’s dependable, it’s easy to work on, and it has a lot of aftermarket support. It remains popular because it was used for so long and great Windsors can be found in nearly every junkyard in America.

Modern Ford Small Block V8s

If you love vintage cars but want to make have a lot more power than was available at the time, Ford Performance, Edelbrock, and other aftermarket providers have created resto-mod styled small-block V8s that churn out a lot of power and are brand new, without any of the issues that can plague junkyard engines. Though you pay more upfront, there is more standardization with what you’re getting with these, and they produce significantly more horsepower.

Coyote Engine

This one needs to be mentioned, just because so many people think it’s a good idea. We absolutely love Coyote swaps, but in this case, it is a lot of work for not a lot of performance benefits. A lot of what gives the Coyote power relies on modern wiring and capabilities. By the time you got it up and running, you would have swapped out every single component of the classic Mustang, and you’ll still have a pretty hefty pony that it’s got to lug around.

The big difference between pony cars and muscle cars in the ‘60s was the engine size, and pony cars were designed with a relatively small engine compartment because it was assumed if you wanted something bigger you would probably be getting a muscle car.

The Fox Body makes for a more interesting Coyote swap because of its lightweight frame. New Edge and SN95 Mustangs have enough modern components that they can be made to work with the Coyote relatively easily. But vintage Mustangs? It’s a poor fit and you’ll be doing a lot of fabricating. If you have your heart set on it, it can be made to work but it’s not a great first-engine swap.

LS Engines

There’s a reason people throw LS engines in just about everything. The LS engine is tiny compared to its other eight-cylindered peers. It’s a more modern engine than the Windsor, or at least has the potential to be since there are versions still being manufactured today, and it’s just as abundant at your local junkyard.

You can also find information about how to LS swap the engine into anything from the engine’s many advocates, who border on the evangelical with regards to extolling the virtues of their preferred V8. The LS’ main issue with regards to swapping it into the Ford Mustang is a lack of brand compatibility, but that can be overcome.

Additional Components

Naturally, the engine isn’t the only part you’ll end up swapping during the course of an engine swap. The rest of the mechanical components of your classic Mustang will need to be compatible with the new engine, and that requires a few extra parts. From the transmission, which will need to be able to handle as much power as the engine produces, to the cooling system that will be necessary to remove the additional heat that’s created when you add horsepower under your hood.

Ultimately, we can divide these mechanical components up into a few loose categories:

Transmission, driveshaft and rear axle, suspension, cooling, intake and exhaust, and fuel system.

Transmission

No matter how much power your engine produces, you’re not getting anywhere without a new transmission. It’s fair to say that a transmission made for a V6 engine in the 1960s is not going to withstand a great deal of horsepower, and presumably that’s what you’re after since you’re V8 swapping.

Your engine selection is going to inform your transmission choice significantly, but a few good ones to consider are Tremec’s newer T5 styled transmissions. These are good, dependable transmissions that preserved everything people really liked about the T5 while simultaneously increasing the maximum torque capacity significantly. There are T5 conversion kits available for classic Mustangs to make the swap easier.

If you’re more interested in automatic transmissions, then it would be worthwhile to consider a more modern one. We’ve come a long way from the slushboxes of yore. If you’re thinking something simple then you should at least look at some of the automatic transmissions that come with overdrive, like the AODE or 470RW.

Along with the transmission, you’ll need the transmission related components, like the clutch and flywheel.

Driveshaft and Rear Axle

In order to get the power from the transmission to the rear axle, you’ll need a driveshaft of an appropriate length. Unfortunately, you’ll also probably want to consider changing out your entire rear axle. A V8 engine puts out a lot of torque, and if you want to enjoy all of that torque-y goodness without feeling your rear axle break at an inopportune moment you’ll want a more substantial one.

If you already have to replace your rear axle, then it’s a great idea to also get one that’s capable of accepting five-lug wheels as well. Not only will this open up a lot of wheel options, but you’ll also be able to install disc brakes, a great upgrade that you can either do now or down the road.

Suspension Changes

Depending on the age of your vintage Mustang and the engine you choose to upgrade it to, you may end up needing to change out a lot of your front suspension components to handle the V8.

The front spindles, coil springs, shocks, and upper and lower control arms all will need to be evaluated based on your unique combination of engine, transmission, and Mustang. You may also want to consider changing out for a five lug front axle as well so that you can have the same wheels on your front and rear wheels.

You can always decide you want to go completely modern, whether that be simply improving the suspension components, adding lowering springs, or even an air ride suspension setup.

Cooling Considerations

More engine power means more heat is being created. Heat causes a large number of problems under the hood, so you should upgrade your car’s cooling system to meet the needs of your new engine.

Depending on what radiator you select, you’ll also probably want to get a new water pump.

Intake and Exhaust

This, like most of the components, is going to depend on your unique combination of components, but it’s good to be aware of. A bigger engine will likely need better exhaust and intake parts. If a V6 is a jogger, then a V8 is a competitive runner, and it is used to having a greater lung capacity. In order to increase your car’s ability to breathe, you’ll need to increase the capability of your intake and exhaust system.

These improvements can take a lot of different forms. Whether you’re interested in going all out and installing a new cold air intake, or just want to try out a set of long tube or shorty headers, you’ll improve your car’s breathing capability.

Fuel System

Depending on which engine you select, you’ll have a lot of options with regards to a fuel system. Whether you want to go with electronically injected or carbureted, you’ll need some way of getting more fuel for the two additional cylinders you added.

Not getting enough fuel to the engine can lead to vapor lock, a condition caused by an overly lean fuel-air mixture. Vapor lock can wreck an engine, undoing all of your hard work. So, make sure that your fuel system is designed to work with your new engine.

Cost

Most people estimate the cost for an engine conversion to come in around $5,000 if you stick to era-appropriate components. Upgrading to modern functionality will increase the cost a little, but can also make your Mustang an even better daily driver if that’s what you’re looking for.

If you’re trying to make a serious performance car that’s modern in every way except for its vintage frame, then that’s going to cost significantly more.

A lot of this cost also depends on how much of the mechanical work you expect to do, or are capable of doing. Engine swaps are a lot of hard work and require a fair amount of skill and automotive know-how.

Other Considerations

There aren’t a lot of problems associated with upgrading an older Mustang to a V8. It’s a conversion that has been done countless times and considering the relatively low cost of six-cylinder vintage Mustangs in great shape, it will continue to be popular.

The cost difference between six-cylinder and eight-cylinder Mustangs from the same year with the same options is astonishing, and even after paying for the engine upgrade, in many cases the six-cylinder is a better buy. Fewer six-cylinder Mustangs have been driven hard as well, meaning they tend to be in better shape.

Unfortunately, installing a new V8 isn’t quite the same as having one installed straight from the factory, and it’s nearly impossible to win any period-correct style shows, even if you paint your Mustang’s engine just right and find the exact first generation Mustang wheels to go with it.

It’s also possible that while installing your new V8 you’ll find or create some additional mechanical gremlins that will need to be addressed either during this process or else in the future, which can add to the cost and frustration level pretty quickly.

Finding Your Perfect Solution

Ultimately, it’s about what’s best for you, and if you’re on the fence it may make sense to drive your Mustang as it is for the time being. You can always choose to embark on an engine swap later, but abandoning one midway through is why you can find so many engine-less Mustangs inexpensively. No one wants to pick up someone else’s project car after they’ve already made a mess of it.

Though some purists claim that it isn’t truly a Mustang until it has eight cylinders, we love all of the vintage pony cars and depending on how you’re driving it a six-cylinder might be the perfect fit.

Image Credit: Hemmings, Hot Rod Network, Mustang Evolution, Ford Muscle