Re: How long at WOT?
I am pretty sure most engine makers recommend pulling back to about 4/5 throttle, but this info is just general recollection and anecdotal at best.
Running at full throttle merely offers potential for more issues. It depends on the engine, the design and the margin of error at WOT.
In some engines, WOT running at redline* can introduce new wear and tear. At WOT and redlined, there might be moments of valve float, small hot spots developing, minor coking and less-than-best intake and exhaust scavenging. If running at redline for long periods, just coming down a wave can momentarily break redline, even in rev-limiter engines.
If someone said they wanted to run WOT in a 2-stroker @ 5800 RPMs when the redline was 6000, I would probably yawn and tell them, "That's nice." Now, if you want to run some 4-stroke modern O/B at absolute redline for a long time, I think I'd be a little more hesitant. This is based more of an amalgamation of stuff stuck into the various parts of my head. High-performance engine builders dyno engines and pay very, very close attention to what happens at redline. Based on their instinct and experience, when they push over to redline, everyone listens a little harder and watches things more closely. And these are engines with over-the-top-quality parts built for stress. Don't care if it is Ferrari or Chevy; the builders all feel the same tension and react the same way.
It's hard to make a blanket statement about running at WOT redline. But, lacking finger-tip accessible information based on controlled studies, I am willing to lean on anecdotal evidence and common sense.
Because my input is anecdotal, I won't posit any argument against someone who has years of experience running their specific engine at WOT.
*Clarification: Redline is the absolute upper RPM limit spec'd by the engine builder. If a marine engine has WOT max RPM range of 4800-5200 RPM, then 5200 is the 'redline', wherein the term 'redline' is borrowed from car tachometers that display, literally, red lines marking excessive RPM so one's eye can catch it when shifting in a hustle w/time only to glance. It's also the speed at which a rev limiter would kick in, if so equipped. You can blow past the limit on any engine not equipped w/ a rev limiter. A marine engine propped properly can still exceed the absolute max RPM if the load is light and conditions are right. Smart marine engine manufacturers will set a rev limiter about 50-100 RPMs below the theoretical limit. How important is this theoretical wall? On some engines, valve float can cause serious shortening of the engine's life. Not all engine are protected by electronics.
