454 MAG MPI - Periodically run at WOT?

[Nepenthe]

I have a 400 DB with 454 Mag MPI's (385 hp) and boat on a small inland lake. We usually cruise at cocktail speed (1,200-1800 RPM) as there is typically no reason to run otherwise. Over the years I have had a few mechanics mention that these engines do not like to be run slow and that I am doing them a great disservice if I do not spend some time running at max RPM to "blow out the carbon."

I would appreciate some insight as to whether there any validity to this theory. And, if so, how often and for how long should they be run hard?

Thank you in advance!

 

[sheehyjo]

My mechanic has provided me the same advice. I have 350 Mag MPIs and typically run them at 3400 RPM with a 30 mph cruise. At then end of every other trip or so, I open it up before I get back to the marina, although it is not for more than a minute. He told me that running below planing speeds can put additional stress on the engine/drive too.

 

[Winch1995]

Mixed feelings about this. I was running my 350 at WOT for a very short time and ended up dropping a valve and ruining the engine. I would run WOT for 30 seconds or less.

 

[Strecker25]

Mixed feelings about this. I was running my 350 at WOT for a very short time and ended up dropping a valve and ruining the engine. I would run WOT for 30 seconds or less.

I hate doing it as well. I had to run WOT a few times this year as we were trying new props but it's an uneasy feeling at the top of the rev range on 19 year old engines.

 

[aerobat77]

well , on a fresh and healthy engine its a good thing to cycle it thru the entire load and rpm range - on an old and tired one you may blow it beating the last out of it .

 

[skibum]

I do it once or twice a year just to make sure that there isn't anything wrong. I can't keep it there for long though. My boat will exceed 45mph and the hull wasn't designed to be a speed boat. I give it full throttle and make sure that it hits 5K and will stay there for about 30 seconds. One of these days I'll let her keep going until she stops accelerating.

 

[Nepenthe]

Thank you. I appreciate all of the input!

 

[tdgard]

We always used to refer to that as the Italian Tune-up in cars. Not sure how relevant it is now with all the detergents in gasoline and oil, but it can be fun for a minute. Just change your fuel flow screen to something else.

 

[skibum]

We always used to refer to that as the Italian Tune-up in cars. Not sure how relevant it is now with all the detergents in gasoline and oil, but it can be fun for a minute. Just change your fuel flow screen to something else.

LOL... THIS! Seeing a single engine drink 21+ gal/hr is a bit disconcerting. I think a hole in the bottom of the tank would empty it slower.