Ten steps to installing a diesel engine in virtually any vehicle
Diesels are no longer the pokey-slow powerplants that clog up the left lane of the freeway. We’re starting to see diesel swaps everywhere, and they’re in everything from show vehicles to rat rods to race cars and trucks. Frequently the diesel engine’s power and torque are highlighted, as diesels are often able to compete with or surpass their gas-powered counterparts of similar displacement. Re-powering your vehicle with a diesel engine isn’t always easy, as there are weight and size constraints to contend with, as well as difficult electronics and transmission decisions. In this piece we’ll be looking at a number of vehicles that have made the transition and some of the hurdles they’ve stumbled into along the way. Once it’s running, however, there’s nothing quite like a diesel-swapped ride.
Step One: Selecting Your Ride & Fitting the Engine
With enough work, a diesel engine can fit into just about anything, and the Cummins-swapped RX-8 sports car that’s rounding the Internet seems to prove our point. There are some swaps that are easier than others however, with pickups and SUVs being a popular choice thanks to their parts availability and engine bay space. The most common truck swaps usually involve Cummins engines, as kits and parts are available to swap the Cummins inline six into Chevy and Ford trucks, both old and new, two-wheel and four-wheel-drive. Swapping Duramax and Power Stroke engines can be slightly more difficult, as they’re both large engines that place the turbo in the valley, which can lead to hood clearance and firewall issues. There also aren’t many ready-made kits for these engines, although swap-specific items like dry sump oil systems, engine mounts, flex plates and engine-to-transmission adapters are all still available. Also, be honest with yourself and your skill level before you begin your swap, and decide if you’re more of a Cummins-in-a-pickup kind of guy or if you can really tackle that Duramax-powered Mini Cooper project.
Step Two: Selecting a Transmission
Another major decision in starting a diesel swap is the selection of a transmission. There are literally dozens of choices out there, both manual and automatic, overdrive and non-overdrive. Perhaps the most common swap (and the first thing one should consider) is “whatever transmission came with the engine.” If you’re swapping in a Cummins, pick a Getrag 5-speed, NV4500, NV5600 or G56 (manual), or a 727, 47RH, 47RE, 48RE or 68RFE (automatic). Duramax engines have 4L-based transmissions at their disposal (4L85Es came in vans) as well as five- and six-speed Allison 1000s. If you’re a manual guy, the stout ZF-6 could be a choice. Finally, if you’re into Fords, there are ZF-5s and ZF-6s (manual) and E4OD, 4R100, 5R110 and 6R140 (automatic) transmissions to choose from. There are also units like TH400s and Powerglides for racing applications that will work for almost any engine and can handle quite a bit of power.
Step Three: How Good Are You at Electrical Work?
After selecting an engine and transmission it’s honesty time again, and this time it’s about electronics. Most newer diesel engines are controlled via complex computer systems, as are their transmissions. Earlier mechanical engines on the other hand are almost completely free of electronics, which is why there has been such a resurgence in early 12-valve Cummins swaps. If you’re not a computer person, your other option is a body swap (an old body on a new frame and powertrain) or buying your way out of the problem with a diesel-swap harness. Duramax harnesses are probably the most popular, but if a $1,000-plus price tag (plus a donor harness) scares you, then it might be time to re-think things. Transmissions like the 4R100, 47RE and Allison 1000 also require quite a bit of electrical work, which is why many folks choose to go with a manual transmission swap or an early non-electronically controlled 47RH Dodge transmission.
Step Four: Sourcing a Donor Engine & Transmission
There are a couple ways to buy an engine and transmission for your diesel swap: the easy way and the hard way. By far the easiest way is to get a complete donor vehicle that’s been wrecked or needs work. You’re not going to use the body (we’re guessing), so a wrecked vehicle is usually the cheapest. The hard way is to try and get an engine and transmission separate from the vehicle, which is usually marketed as some sort of deal. This is by far the harder route to take, as many swaps can require wiring, linkages, pumps, adapters, starters and a wide variety of parts that can all be used from a donor vehicle. Unless you have a big bank account and aren’t worried about a $50,000 swap cost, we’d start with a donor.
Step Five: Time for Reinforcements—Frame, Body & Suspension
Diesels are torque monsters. While a full-blown race car might make 1,000 lb-ft of torque, that number can be accomplished with a stock or near-stock diesel. This twisting force can play havoc on your swap vehicle’s chassis, which can bend or crack under the strain. The same can go for suspension pieces, which will crumple under the weight of most diesels. Even the body can be at risk, as we know of one owner who ended up with a cracked windshield from flex under a full-throttle pull. Since diesel engines are fairly large, a decision is often made to box the frame or strengthen various areas, usually with the body off, except in the case of unibody vehicles. If racing is at all an option, a good roll cage is also a great way to stiffen a chassis for drag racing, rock crawling or sled pulling.
Step Six: Selecting Parts for the Transformation
So you have your engine, transmission and your swap vehicle ready to go. Now it’s just time to stuff everything in, right? Not so fast. Diesel swaps don’t often have “ready made” parts available and are often at the mercy of the builder for even a simple task like installing an engine and transmission. If you’re using a brand of engine and transmission that never came in the same vehicle (let’s say a Cummins with a 4L80E) make sure you have your engine-to-transmission adapter ready, flexplate, and a converter that is spaced properly. Diesels can also be more difficult than other swaps at this point due to their height, complicated exhaust routing and requiring engine mounting solutions. Engine plates, which are commonly used in gas applications, are usually a no-no in any street-driven diesel, as the vibration from the engine can be horrendous. Keep an eye out for clearance issues, as everything from harmonic balancers to oil pans to the engine itself can be a problem. Keep an eye on your suspension and steering and make sure they can both support the weight of a diesel and clear the engine itself. The lesson here is to keep an eye out for what you might need at this juncture so you’re not stuck for weeks waiting on parts.
Step Seven: Cutting, Trimming & Welding
With an engine and transmission mounted and the chassis and suspension reinforced there’s still a ways to go, and this is often the most time-consuming part. Unless you’re just willing to chop up your entire car (say, a rat rod), it would probably be nice to have things like a dashboard, firewall, inner fenders, trunk and the rest of your sheet metal. Unless you’re shooting for a swap into a similarly large truck, much of the sheet metal on your vehicle will need trimming or massaging. The firewall may need to be moved back, the core support modified, or the hood may need a hole cut into it. On the inside, the pedals and steering column may not line up anymore, or the transmission tunnel could require some rehashing if a large transmission like an Allison 1000 is being used. There’s also gauges and gauge placement to think about, unless you want a lot of stuff zip-tied to other stuff.
Diesels are torque monsters. While a full-blown race car might make 1,000 lb-ft of torque, that number can be accomplished with a stock or near-stock diesel.
Step Eight: Getting Power to the Ground
For vehicles that aren’t heavy-duty in nature, the rear axle can be quite a task if performance is involved. Remember when we said that a diesel makes the torque of a race engine? Well, your rear axle won’t know the difference, so don’t expect a stock truck or car 10-bolt or GM 7.5, or anything else of that nature, to live long behind a diesel powertrain. Custom front and/or rear axles can be required if jumping, off-roading or drag racing is involved. Try to think about your needs and price margins, as light axles usually aren’t cheap, and cheap axles usually aren’t light. If you’re building a truck, you may even be able to grab an axle from your donor vehicle—something heavy duty like a Dana 70 or 80 or AAM 1150.
Step Nine: Cooling & Other Ancillary Systems
We know of one less-than-bright enthusiast who had almost completed his project and decided he didn’t need a transmission cooler just for driving around. Instead of finding and running one, he just looped the lines and fried his transmission. Take a moment here and make sure all your cooling, steering and add-ons (like air conditioning) will work well with your diesel engine. Diesels don’t make much heat at idle, but under load it’s a different story. Both engine and transmission heat are something that must be factored in on a build (especially on a modified engine) and it’s better to be safe than to skimp. Items like NASCAR-style aluminum radiators or oversize transmission coolers are still relatively cheap considering the cost of a new engine or transmission.
Step Ten: The Test Drive!
It’s running! You’ve done the necessary wiring, engine and transmission mounting, and your body and frame look sort of all right. Now the fun and important part begins. Check for all types of leaks (fluid and air), have pressure gauges on everything you can (oil, fuel, even transmission), and most importantly take your time! It’s easy to get in and just blast down the street in a vehicle that will start and run, but we’ve seen more problems arise on test drives than anywhere else. Here it also helps to have a buddy to check everything with you and then follow you around when you hit the road. There’s no worse feeling than having to walk back after your newly completed project breaks down a few blocks from home.
We hope you enjoyed our swap guidelines, and that they at least got you thinking about new and exciting aspects of taking a diesel swap from dream to reality. There will be plenty of awesome examples here on these pages, so don’t be afraid to study in detail each owner’s project and see how well they followed our ten steps to success!