Engine swapping is often used as a way to repair a major mechanical problem if your vehicle is no longer under warranty. Installing a used engine is normally less expensive than costly mechanical repairs.
Swapping is also a form of vehicle modification as a motor with a similar size may have higher horsepower.
GM Gen III / IV small-blocks, Ford Modular motors, and new Chrysler Hemis have rejuvenated production cars, and now they're poised to revolutionize hot-rodding.
Overhead cams, forced induction, aluminum heads, and even aluminum blocks are no longer exotic rarities. Engine life is now measured in hundreds of thousands of miles. Fast-burn combustion chambers and heads that flow on a par with old-school big-blocks offer growth potential old-school small-block owners could only dream of. Combine the new engine designs with an overdrive trans, and you can have your cake and eat it too-economical highway cruising with big horsepower. A whole new industry has arisen for hopping them up, supplying them, and even installing them in classic musclecars-that bundle of snakes under the hood notwithstanding. No doubt, traditionalists shy away from the high-tech marvels because of their seeming technical complexity. And while the electronic component of a modern swap is at least as complex as the physical aspect, aftermarket solutions are appearing almost daily.
Many rodders prefer to swap in the late-model engine along with its corresponding electronic trans, which interfaces correctly with the factory computer and eliminates adapter issues, but it's also possible to bolt up classic transmissions using available aftermarket parts. Remember that any high-pressure EFI retrofit requires EFI-compatible fuel-tank baffling, fuel lines, and fuel-pump configuration (Rock Valley is one source for retrofit fuel tanks).
The Ford and GM engines have been available for more than 10 years; even the new Hemi is now five years old. Standard-perf versions of these engines are fairly common and affordable in the wrecking yards.