Normal Engine RPM's

[Nomad Willy]

boatk9,

"Never mind....better*solution is to convert the engines*to NA."

BAD idea.

 

[RickB]

bobofthenorth wrote:And these real time load changes were on just exactly which recreational trawler power train?

*If you honestly believe that there is a separate set of physical laws that apply only to diesel engines when operated for recreational purposes then there really is no point in your being involved in this discussion.

I think you missed jleonard's comment as well.

 

[jleonard]

I also do not believe there is much if any significant fuel savings by loading the engine harder and running a lower rpm. A diesel is a pretty precise machine. It uses fuel to make horsepower, and since it takes X hp for a given boat ot go a certain speed, the fuel consumption will be the same. I will also theorize here that perhaps heavily loading "might" actually use MORE fuel, because the extra loading will certainly raise EGT (still might be within the max spec) and a higher EGT would indicate an energy loss.

As far as noise and vibration levels, in the boats I have run I really have never noticed much difference from 1600 to 1900.

Actually the turbocharged engines I have run are MUCH quieter when cruised over 1800 RPM because the turbo does help*quiet the exhaust noise once it starts producing some boost. (plus there is more water being pumped into the stream).

Anywho, my boats will always be propped within mfg specs based on*my experience and my knowledge. And I hope I can avoid buying a boat that had been overpropped for any significant part of it's life.

By the way one of my (many) winter projects is to replce the exhaust elbow on the FL120 and I will be adding a pyrometer

 

[FF]

"I will also theorize here that perhaps heavily loading "might" actually use MORE fuel, because the extra loading will certainly raise EGT (still might be within the max spec) and a higher EGT would indicate an energy loss."

Got it backwards J, the higher temps are a sign of a more efficient engine.Up to a point.

Higher EGT is better as our engines are all heat pumps of a sort .

Look up Evans Coolant , and you will find many of the class 8 trucks installing 235f thermostats , to increase the operating temps and the efficiency.

Believe me the guys that burn 700 or more gallons a week are willing to try modern concepts to stay afloat.

 

[jleonard]

FF wrote:
"I will also theorize here that perhaps heavily loading "might" actually use MORE fuel, because the extra loading will certainly raise EGT (still might be within the max spec) and a higher EGT would indicate an energy loss."

Got it backwards J, the higher temps are a sign of a more efficient engine.Up to a point.

Higher EGT is better as our engines are all heat pumps of a sort .

Look up Evans Coolant , and you will find many of the class 8 trucks installing 235f thermostats , to increase the operating temps and the efficiency.

Believe me the guys that burn 700 or more gallons a week are willing to try modern concepts to stay afloat.

*Yes up to a point, and that's my point.* And coolant temps are different than exhaust gas temps.

 

[Nomad Willy]

boatk9,

First of all you'd need to pull the head and remove enough metal to raise the compression ratio to NA levels or the engine would be much less efficient. How much to remove??? One may need to shave the block to remove enough. And then the valves may hit the pistons or run too close and too hot. Some of this may not be true but you'd really need to know what your about to be successful. First things first as I see it and that would be to run the turbo until it needed enough attention to objectively consider a conversion. As DAvidM says (usually) take it to BoatDiesel.

 

[sunchaser]

If* you ever intend to sell or buy a boat, one of the basic tests during sea trial is to assess if the engine can achieve full rated RPM without overheating. Obviously an over propped boat will overheat.*This then creates anxiety and the boat remains unsold until a brave soul shows up that believes no damage was done during the many hours of operation the boat was improperly set up with too big a prop.

The long and the short of it, given the little downside associated with proper sized props, ignore the cruising prop stuff if you want to buy or sell a boat.

 

[RickB]

nomadwilly wrote:First of all you'd need to pull the head and remove enough metal to raise the compression ratio to NA levels or the engine would be much less efficient. How much to remove??? One may need to shave the block to remove enough. And then the valves may hit the pistons or run too close and too hot.

*

I'm not advocating converting any engine from turbo to non turbo but it isn't quite that bad. The 3208 mentioned has a c/r of 16.5:1, the n/a version is 18.2:1. Both start as normally aspirated engines and if a diesel has enough compression to start, it has enough to run.

The important differences and major consideration as far as economy goes is the cam, piston style, and injection pump/injectors.

Among those, the cam and fuel injection are biggies, turbo engines use valve overlap for valve cooling, n/a engines don't so volumetric efficiency falls pretty low*and the useful power available will be pretty*small before you start making some serious smoke.

 

[Nomad Willy]

boatk9,

I just thought of another thing that may need to be replaced** .....camshaft. Very likely a turbo'd engine will/would require different valve lift and timing* ...most likely the latter.