The Internet is Wrong About Engine Swaps

If you’ve been following our DriverMod Facebook page, you might have noticed that recently, we’ve spent far more time wrenching on my 1999 Mazda Miata and far less time writing. I took a week off work to swap a GM 2.4L Ecotec engine into my Mazda Miata; a week which I promise you has been documented in complete detail. During that week spent tearing apart my perfectly running car to swap in a Chevy Cobalt engine, I learnt a lot of things, but mainly this; everything the internet has told you about engine swaps is wrong.

Car culture and the internet are infinitely intertwined, and that’s resulted in a culture where everyone is trying to out-crazy each other. One person will boost a Mitsubishi Evo to 1200 bhp, which leads someone else to 2JZ-swap an Evo to 2000 bhp, followed by someone attempting to Lamborghini V12 swap an Evo to a billion horsepower. This isn’t necessarily a bad thing. The internet has allowed this sort of rapid progress to happen, by allowing us all to share ideas and methods. The downside is that it’s created a culture of “go big or go home.” You see this every single time someone does a “simple” engine swap, like LS swapping a 240SX, there’s a barrage of mockery that follows, insisting that the inclusion of the Chevy V8 is “too simple,” and “boring.” The truth is that engine swaps, all engine swaps, are very difficult.

Here’s the thing: a car’s engine bay is not a neat box. You can’t just measure it’s length and width, measure the length and width of a 2JZ and drop it right in. When engineers design an engine bay, the engine bay and the engine are design to fit in perfect harmony. The engine has to stay clear of the power steering rack, the sub frame, the fire wall, any hoses or clamps it could vibrate against; all while leaving room for accessories and an exhaust system. When you look at how the Mazda BP motor fit’s in a Miata’s engine bay, the oil pan is essentially molded around the sub-frame to position it as low as possible.  You’ve now thrown away that engine and are trying to fit an engine in that was designed on a different continent. That usually means a custom oil pan that’s been designed to stay clear of the foreign sub frame, while having sufficient baffling to handle track time. This means custom engine mounts, cutting and re-welding sections of body, relocating front sway bars and in some cases (such as the Miata v8 swap), engineering a completely custom sub-frame to accommodate the new motor. In short, you’ve become an engineer, who knows how to weld and CNC their own parts.

LS Miata custom tubular sub-frame. Source.
LS Miata custom tubular sub-frame. Source.

Now you have the issue of actually getting power from the engine to the wheels. If you’re using a non-factory transmission, you’ll need a custom driveshaft, custom transmission mounts and possibly further chassis modifications to make it fit. If that transmission’s shifter doesn’t end up in the same spot as the factory shifter, you’ll need more creativity. If you’re using a factory transmission, you’ll need a custom bell-housing adapter and flywheel adapter. Then, once you’ve spent countless hours welding, machining, test fitting, and doing it all over again when things don’t line up, you’ll have to deal with wiring, fuel, and exhaust fitment.

When talking about engine swaps, it’s important to remember that you are replacing the heart of a car. Wiring, fuel lines, power steering lines, air conditioning refrigerant lines – everything needs to be adapted, resulting in a million teeny-tiny engineering problems. My intention here is not to dissuade someone from doing an engine swap, but I get frustrated when internet-experts knock someone’s build for being “typical” or “easy.” That’s a bit like booing an Olympic bronze-medalist because they didn’t come home with gold. If you don’t have the skill to completely reengineer a car, manufacture your own parts, do all your own wiring and exhaust work, there’s no shame in doing a well-documented engine swap using a prefabricated swap kit. Chances are that that’ll be more than challenging enough for an amateur mechanic.

ANNOUNCEMENT: We’ve partnered with car-culture website Speed Academy to produce our complete Ecotec Miata swap guide. Follow Speed Academy on Facebook and keep an eye on their website for “Part 1” of our guide coming out this week!