Are run-ups required or advisable on multiengine piston aircraft?
...be operated from its crossfeed position during the run-up. The engines should be checked individually and allowed to run at moderate power (1,500 rpm minimum) for at least 1 minute to ensure that fuel flow can be established from the crossfeed source. Upon completion of the check, each engine should be operated for at least 1 minute at moderate power from the main (takeoff) fuel tanks to reconfirm fuel flow prior to takeoff.
Some multiengine airplanes have a ramp weight, which is in excess of the maximum takeoff weight. The ramp weight is an allowance for fuel that would be burned during taxi and run-up, permitting a takeoff at full maximum takeoff weight.
For what its worth a multi-engine piston plane is mechanically double what a single engine plane is, and often carries a similar if not the same engine as a single. The things you are checking in run-up, primarily the ignition system holds true for both single and multi-engine aircraft.
The run-up test is an essential pre-flight test for every piston-powered aircraft. Wether it's single engine, twin engine, or more.
It is important to test if the magnetos work properly and if you have a constant speed propeller, if the governor does what it should and also to renew the oil in the governors system.
You can also see if there are any power problems before you take-off.