How fast is a v12 engine?

There's no single answer to how fast a V12 engine is. The speed (in terms of RPM) and power output of a V12 engine depend entirely on its design and application. V12s are built for a wide range of uses, from high-performance supercars to large luxury vehicles and even some marine applications.

* High-performance V12s in supercars might rev to 8,000 RPM or even higher, producing hundreds, even over 800 horsepower.

* Larger displacement V12s in luxury vehicles might have a lower redline (perhaps 6,000 RPM) but still produce significant power (500-600 horsepower) with more torque at lower RPMs.

* Marine V12s will typically have a different power band altogether, optimized for torque at lower RPMs for moving heavy vessels.

So, without knowing the specific V12 engine you're asking about, it's impossible to give a definitive answer on its speed (RPM) or power output.