There is a discussion on a marine board regarding the PSD as used by Mercruiser, rated at 300hp. There is no reference regarding limiting wide open throttle operation. The question is, can the PSD be operated continously at WOT with it loaded down to an RPM of say 2800-3000. Since there is continous fresh water being circulated, cooling capacity is not a real big problem. Maybe The Diesel Dude has some knowlege on this use of the PSD.

 

Under load, I don't see a problem running that rpm range.

Les

 

I'm not sure what Mercruiser's stratigy is for making power. I know that it is rated at 330 HP @ 3800 RPM and 550 ft. lb. of torque @ 2000 RPM so the torque is not all that much different than the Power Stroke's numbers. The Mercruiser uses a different cam (the Power Stroke runs retarded cam timing for exhaust emissions purposes) and different injectors (I don't know what other differences there are). The marine ECM obviously has a higher governor, so, I'm just guessing, if you measured HP at 3000 RPM instead of 3800 RPM it wouldn't be all that much different than the Power Strokes numbers. What they've done is remap the fuel mapping to continue to make power for an extra 800 RPM past the governed engine speed of the Power Stroke engine. If you maintain a degree of torque at a higher RPM, you have automatically created more HP. A truck with 4.11 gears, a .70 overdrive and 33 inch tires will be running just over 100 MPH at 3000 RPM, so there is no reason to run a higher governed engine speed for a truck engine. The marine engine, on the other hand, has no transmission and, I presume, needs the extra RPM to run the boat at the speed the engineers want to run it at. Maybe someone with some experience with marine engine applications can give a better explaination but I think the HP and torque numbers are in line with the 275 HP Power Stroke engine's numbers.

 

I think I answered a question that you didn't ask and failed to answer the question you did ask. If you are asking if the Power Stroke can maintain a full throttle load continuously at 3000 RPM in the 275 HP to 300 HP range, as far as I know, the answer is yes, although I can't imagine what scenario could possibly exist, other than a dyno, where such conditions would be prevalent.

 

Freedom from Emission restrictions and a very low restriction exhaust system can more than make up the extra HP.

As for maintaining WOT ... most planing boats will cruise between 60 to 80% throttle for extended times, anything over 80% may gain a few extra knots but the fuel comsumption goes up exponentially. Displacment hulls on long cruises generally will maintain 30 to 40% throttle.

Robert

 

Thanks to all of you for your replies, you have been most helpful. It would appear the 7.3 PSD is running in most cases, derated. Not a bad thing for reliablility. I wonder if the upcoming 6.0 PSD will be used elsewhere like its predecessor.

 

Navistar has a version of the new 6.0L engine in production now at the Huntsville, Alabama plant. When Ford redesignes the Econoline (in a year or two) they will also make that engine in Huntsville. If Mercruiser doesn't like the new engine for their application, they can get the current 7.3L engine from Brazil.