The R32's beating and ferocious heart.
Just about every automaker has at least one iconic engine. It's the one that's asked about just as you pop the hood of your Supra, or your Evo, or perhaps your M3. The same question is asked of 240SX owners here in the US. At least with those cars the engines were detuned or completely different, but the chassis still made it overseas. It's a completely different story for the Skyline. The R32 is now legal in the US because it's been 25 years and it's import restriction has lifted. And no, the Skyline was never illegal because it's engine was too powerful.
Skylines at the time of the 1980s and 90s used Nissan's fabled RB series engine, and different variations of it. The most powerful one out of the Nissan factory was the RB26DETT. It was an RB (inline-six) series, 2.6-liter DE (dual cam, electronic fuel injection), twin-turbocharged engine outputting officially 276 horsepower. Due to a "gentlemen's agreement" in Japan, no car was allowed to advertise having more horsepower than 276. However, many years later Honda broke the agreement with a 300-horsepower 3.5-liter V6, which was put into the Acura RL. Other manufacturers followed suit. Some were known to have broken the agreement years beforehand in practice but not on paper.
Subaru's WRX STI, Mitsubishi's Evo and Nissan's 300ZX all at some point broke the gentlemen's agreement. The RB26DETT made 276 horsepower with restrictions, but with those removed the RB could make 320 horsepower on its own.
Some people report gains of up to 600 horsepower on a stock bottom end. Numbers show that the R32 Skyline, released in 1989 and equipped with the RB26DETT, could get to 60 mph in about 4.8 seconds. A 1997 Ferrari 456 GTA stood at 4.9 seconds. It's no wonder the RB26 earns the title of one of the best production engines of all time. This list of possible modifications shows how easy it is to extract power from the RB26. To put things in perspective, all it takes for one bar of boost is to remove a restrictor. That means the RB26 will go from 10psi to around 14, which is a big jump for just removing a restrictor.
It's unfortunate that it didn't make it to America during its heyday. The rigid gentlemen's agreement led to tuners extracting every ounce of power possible out of the RB26. Thank goodness that happened. If it didn't, the RB26 could have been confined to the history books as just another 276 horsepower inline-six, sitting in some junked R32 in a far corner of the world.