Engine Swaps

At one time or another almost everyone who has ever owned a car has thought it would be nice to change something about it. Be it the stereo, color, wheels, drive-train, etcetera, etcetera. Most of the things a person can change about their vehicle tend to be simple and straight-forward.

When it comes to the drive-train however, you get into an area that people with engineering degrees hanging on their walls last tread. It is no big secret that a light car with a lot of power under the hood will go fast. It's a little thing called Power-to Weight Ratio. The trick is in keeping that car safe, streetable and practical.

Planning and experience are keys to the whole thing. You have to ask yourself some questions first off. Things like: "What am I trying to accomplish?" and, "What am I going to use this car for?", "Daily driver, racing, cruising or some combination of those?" You wouldn't want to drive a car in traffic every day that got 8 miles to the gallon, idled (rather roughly) at 1200 RPM, and sounded like 10 Harley's going after the guy who knocked over the 11th when you get rolling.

Time, money, equipment and skill are all things that need to be taken into account as well. A lot of swaps never get finished due to poor planning. Many reasons could be given for this, but the initial plan is almost certainly the main fault.

Hopefully the following sections will give you a better understanding of what it takes to pull this sort of thing off.

Types of Swaps

In order of difficulty, I see four basic kinds of engine swaps:

1) The "bolt-in" swap:

Installing a similar, but usually larger (internally), engine into a like-brand car (such as a 350 or 400 Chevy small-block in place of a 305) using the same mounts and accessories. These are swaps that were:

(a) once produced by the factory, or
(b) involve engines with identical mounts or bosses.

2) The "family" swap:

Mating products from the same company that more or less fit together but weren't original factory combinations Examples would be swap such as putting a Chevy small-block in a Buick Regal or a 460 Ford big-block into somthing like a '79 Ranchero. You can usually bolt together these combinations using factory parts, if you know the right pieces.

3) The "kit" swap:

A non-related engine/vehicle combination for which an aftermarket company has developed a bolt-in or weld-in swap kit. They're not as numerous as they once were, and some kits are much more complete than others. The most basic is a set of engine/trans mounts and possibly a set of headers. You know you need a lot more than that to complete a swap.

4) The "custom" swap:

Comprises several levels of involvement. In the simplest, you position your chosen engine/trans in the chosen vehicle, then fabricate brackets, tabs, or crossmembers to attach to the mounts. In increasing order of complexity, custom swaps might require the reshaping of the firewall or fender panels, modifying or replacing crossmembers or frame rails, altering steering or suspension, installing a new subframe, or fabricating a whole new chassis.

In any of the above cases, you are going to have to deal with some or all of the following considerations.

Engine swap checklist

- Mounts
- Driveline
- Frame Clearance
- Steering Clearance
- Body Clearance
- Exhaust System
- Cooling System
- Electrical System
- Linkage

The best overall advice I can give you toward a successful engine swap is to plan ahead.

Mounts

The primary step in any engine/trans transplant is to physically locate and attach the new powertrain in the chassis. This requires mounts, usually two near the middle of the block (called "sidemounts"), and one at the rear of the transmission. This is the preferred setup. Using front block mounts (or a motor plate) with a rear trans mount is a no-no, because this places too much stress at the bellhousing (use bellhousing mounts with front mounts).

Any street-driven vehicle should have cushioned mounts. In general, I strongly recommend using the factory rubber mounts designed for the engine you are installing. That is, attach the factory brackets and rubber mounts to the engine and trans, position the assembly in the new chassis, then fabricate new brackets and/or crossmembers to mate with the mounts. If you want to use a motor plate or other solid block mount, sandwich a rubber biscuit, or at least a polyurethane bushing, between the mount and the frame. If you don't, all engine vibration and torque will be transmitted to the chassis, which is not only uncomfortable for passengers but also leads to frame tweaking and cracking.

Where do you mount the engine? Clearance, the location of the prior powerplant, and common sense should guide you. You want it high enough to clear the ground, low enough to clear the hood, basically centered between the frame rails (though offsetting it one or two inches to the right to clear steering is admissible), and far enough back so that it doesn't shift too much weight to the front of the car (no more than 60 percent of vehicle weight on the front wheels). If your chosen powertrain won't fit within these confines, maybe you need to select a more compact engine. When the car is finished, the engine should be level with the ground so that oil, gasoline, and trans fluids will sit (and measure) properly in their respective reservoirs (especially the carb float bowls).

Driveline

Whether or not you need to change the rear axle depends on how weak the rearend is, how strong the engine is, and what sort of driving you intend to do. Some cases are obvious. In many, however, I'd say try the stock rear (assuming the gear ratio is adequate); if it breaks, install something stronger. Cars with parallel leaf springs are the easiest to swap a new rearend into using a universal U-bolt and axle pad kit available from most rod shops.

Nearly every engine swap will require a modified or custom driveshaft. Accept this as part of the deal. It's not that expensive, and it should definitely be left to a professional driveline shop. They can install the U-joints you need to match the trans and rear, phase them, balance the shaft, and make it the proper length.

You've undoubtedly heard about driveline "phasing". Simply put, you want the engine/trans parallel to the chassis centerline, and the rearend perpendicular to it, as viewed from the top; the centerline of the engine/trans parallel to the centerline of the differential pinion shaft, as viewed from the side; and the "U's" for the U-joints aligned on the driveshaft. That is, don't install the engine/trans so it "points" to the rearend; and don't angle the differential so it "points" to the trans. Why? The U-joints need to be phased on the driveshaft because they are not constant-velocity joints; if they aren't aligned, the driveshaft will try to twist on each revolution. The trans and rearend need to be parallel for the same reason, but also to make the rollers in the U-joints rotate so they don't wear flat.

Frame Clearance

If the engine and chassis weren't designed for each other, you'll probably discover some basic incompatibilities. One of the most common is interference between the engine's oil pan and the chassis' front crossmember and/or steering linkage. Some engines (i.e., most Fords) have the oil pan sump in the front, others (most Chevies) have a rear sump. Trying to fit a front-sump engine into a chassis designed for a rear-sump block is difficult. In many cases a rear-sump pan, oil-pump pick-up, and dipstick can be found in factory parts books (i.e., a Bronco pan for a small-block Ford). In extreme cases the pan can be cut and modified to fit. But the best case is to select an engine that fits in the first place.

Things that protrude from the engine block also cause clearance problems: the starter, fuel pump, oil filter, and so on. Most modern engines mount the starter on the right side, where it won't interfere with the steering. If the oil filter sticks out in the wrong place, it can be replaced with a remote-mount unit. If the fuel pump hits the frame, it can be replaced with an electric one. The small-block Chevy V8 is by far the "cleanest" power package with the fewest annoying protrusions; that's why it is the ubiquitous engine-swap favorite.

Notching or modifying the frame is usually a poor alternative but can be done in moderation. The primary concern is not to weaken or alter the alignment of the frame. If you carve a notch out of a frame rail, "box in" the section, or add a fishplate to the outside, to strengthen it. Rather than cutting a crossmember, perhaps you should make a new one to fit.

Steering Clearance

Steering always seems to get in the way of swapped-in engines. If it's just the steering shaft or column, the simple solution is to install a couple of high-quality U-joints in the shaft to route it around the problem. If the steering box itself is in the way, you might be able to move it, or replace it with a better, more compact type. This is common in street rod swaps.

In many cases a simple, compact solution to steering box and linkage interference is a rack-and-pinion assembly. They come in manual or power types that mount ahead of, or behind, the front crossmember (choose the right one for your application; they turn opposite ways).

Moving or modifying steering components, especially on newer vehicles with independent front suspensions, is serious business. It must be done properly (both in terms of engineering and fabrication) if you want it to be safe and function correctly. If you're not an expert in either of these fields-engineering or fabrication-don't mess with your car's steering.

Body Clearance

The first area of sheetmetal-to-engine concern is the firewall. Sometimes it's more practical to move, modify, or build a brand-new firewall than it is to fit the engine in front of it. But in most cases you want to leave the original firewall intact. Engines with rear-mounted distributors (i.e., Chevies) need clearance to allow distributor/manifold removal. A firewall-mounted master cylinder should not preclude valve cover/head removal. If it does, move it.

Other common engine room interference's include the heater and the battery. Rather than removing the heater or air conditioner, look for smaller units, such as those from foreign cars or those made for street rods. The battery can be relocated to the trunk or elsewhere. Make sure it is firmly mounted, vented, and has good connections and adequate-size cables.

In many swaps, hood clearance is another problem. Since it is easier to deal with-by adding a bubble or scoop or even a hole in the hood-it is usually of less concern than is engine-to-ground or engine-to-frame clearance. But plan how to deal with it.

Exhaust System

Nearly any engine swap will require a custom exhaust system. If your car is intended for street driving, cast manifolds are the best bet. They're quiet, non-corrosive, compact, and often flow as well as headers through a full exhaust system. If you can't find factory variations that fit, a competent muffler shop can even cut and weld cast manifolds to suit your needs.

Several companies offer tube headers to fit popular engine/chassis swap combinations. Check to see if something is ready-made for your concoction. Another excellent source is the street rod market, which offers many "block-hugging" headers to fit popular engines in tight chassis.

Your final options are to find headers that come close and modify them, or to make a set of custom headers to fit your specific application. And don't forget to finish the exhaust system; it's part of doing the job right.

Cooling System

A bigger engine that makes more power also makes more heat. It needs a bigger radiator. Inadequate cooling is probably the biggest bugaboo of all engine swaps. A hot rod that overheats is no fun.

You basically have three choices:

1. Find a good-size radiator that will fit in the car.

2. Have a radiator shop fit the largest (thickest) core they can to the existing tanks.

3. Have a custom radiator made to fit the application.

Don't cut corners on cooling. In most cases you'll need to change water outlets anyway, which means spending money at the radiator shop. You might as well step up and get a radiator that will do the job. It's the wisest money you can spend on an engine swap.

A radiator alone won't do the job, however. Cool air must be ducted to it, and hot air must be ducted out of the engine compartment. If not, the radiator cannot function properly, regardless of its size. Louvering the hood is one traditional solution; better yet is to provide adequate venting around the engine and out the fender panels.

For stop-and-go cruising you also need a fan. The stock engine fan and shrouding is a hassle to fit in most swap situations. Radiator-mounted electric fans are the simple solution.

Electrical System

The general rule for swaps is to retain the electricals that come on the engine (alternator, starter, solenoid, coil, distributor) and add a voltage regulator to match, along with a ballast resistor or distributor electronic module, as necessary. Wiring the components is straightforward. Of course the complexity or thoroughness of the swap will dictate the degree to which you will rewire the car.

An all-new problem, however, is the swap into a computer controlled vehicle.

Again you have three basic choices:

1. Choose a similar-to-original engine and swap all the computer hardware onto it.

2. Adapt the computer sensors in appropriate locations on a "non-similar" engine you have installed.

3. Chuck the computer, either partially or entirely.

I don't want to get into a debate the feasibility or legality of these options here, but I will say that more and more fully computerized swaps are being accomplished, even into cars that weren't computerized in the first place, by typical hot rodders who have figured it out by reading the factory wiring diagrams.

Linkage

Hey, we're getting close. Now that everything's in place, all we need to do is hook up the throttle and trans linkage and we're ready to boogie.

Cable throttles greatly simplify carburetor linkage these days. If the parent car didn't come with a cable, check the wrecking yard, car dealer, speedshop, or street rod catalog. The beauty of cable throttles is that length and alignment are not critical, and they seal where they pass through the firewall. (Sealing and insulating the firewall and floor is something many engine swappers forget and regret.)

Automatic transmission linkage hookup is straightforward, since the "PRNDL" pattern has been standardized. If you prefer a floor shift, as most rodders do, you can choose an after- market unit or an easily adaptable factory unit, such as the Mustang. If you want solid-rod linkage, a shifter that mounts directly to the transmission housing is best; if the shifter mounts to the floorboard, a cable-actuated type is preferable. In any case, install a neutral safety switch so the vehicle cannot be started in gear. Hear that?

What about a stick shift? If the car didn't originally come with a clutch, the automatic is by far the easier way to go. If you want a standard trans, be advised that hanging a clutch pedal, designing the linkage, and getting it to work smoothly and properly could be a major challenge. Options include mechanical, cable, or hydraulic linkage with a floor or firewall-mounted pedal. Plan it thoroughly ahead of time. Maybe you'll opt for the automatic.

Oh yes, don't forget the speedometer hookup. Fortunately, most cables are interchangeable. If you need a longer one, or if the calibration is off, visit your local speedometer shop (they're everywhere). They can give you the proper trans speedo' gear for your combination, or a gear-reduction unit that fits between the trans and the cable.

No swap is truly simple, and no matter how well you plan, you'll find dozens of kinks to fix and loose ends to tie up at the end. But that's hot rodding; if you do it right, it's always worth it.