Those were outboards that Merc ran. It was a PR move to prove that Mercs were reliable.

20 hours 3000 rpm should not be a problem for any Mercury stock engine or any other engine for that matter. Heavy truck engines (gasoline) run that rpm all the time. My Ford pulled my boat at that rpm for 24 hours across the country. I do not even think twice about that rpm. My question to you is why do you ask? Most boat engines are that rpm or higher often times for hours, maybe not 20 in a row.

Anybody know what GM's durability testing is? This is off the cuff, but wasn't it 75 hours WFO and not allowed to reach operating temps? I believe they only stop to change the plugs and oil.

Yeah, I remember now, "Their Fast But They Dont Last"

I have been in the GM dyno rooms in Tonawanda, NY. Motors are pulled randomly from the assembly line and placed on the dyno. They are run at idle until they reach operating temperature, then they run at maximum RPM for the particular engine for 55 minutes. They then idle for 5 minutes, run at maximum RPM for 55 minutes and so on. This cycle is repeated for 24 hours. They are then removed from the dyno and tore down and inspected for potential problems!

GM's durability test is 300 hours at WOT and it alternates between max torque and max horse power.
Now that's a test.

the old style compressors used in refining and on natural gas piplines are V10's, turbocharged, spark plugs, ignition coil on each cylinder, 2000 hp monsters. they run for 3000 to 4000 hours before being shut down for tune ups. they use a jet cell to shield the spark plug though. the spark plug ignites a pilot and it shoots a flame into the cylinder instead of direct spark plug exposure. the difference is they run on natural gas and turn at slower RPM's.

we pretty much run all day @ 3200-3600, 502 mag, often 4+ hours at a time, I don't see why it can't run for 20, maybe might want to stop check oil level at 6-8 hour intervals, some 502's would use 2 quarts in 20 hours, some only 1/2 - 1

For the 300 WOT test the engine run to top rpm for engine then a load cell brings rpm down to approx 2,000 . cycle is run in about 2 min. for 300 hours. pretty tough!