reasons not to use high-performance diesels

CDK, the intercooler I am running is from frozenboost and the outer housing is all 1/4" plate. Can't say for sure what that thickness is on the core tubes. With 3 seasons and 1100+ hours I have had no corrosion issues but then again my boat doesn't see much salt water. I typically make 2 or 3 trips a year to the saltchuck usually just 1 overnight each time. The rest of the time my boat is on glacial rivers, heavily silted but fresh water.

Phil, I did have condensation issues initially with my setup. My boat is mostly on glacial rivers so very cold water going through the intercooler. I have never seen my intake air temperature go above single digits Celsius even under extended heavy loads with 30lbs of boost. This is great for power and helping to keep egt's down but does drop quite a bit of moisture out of the air especially on warm humid days. Had a couple of times initially when on applying full throttle after steady cruising for some time the water built up in the inlet tank was blown through the intercooler into the engine and was enough to put the fire out. Fortunately it wasn't enough to hydrolock the engine and bend a rod. What I did was mount my intercooler with the inlet tank on the bottom and the tubes the air passes through vertical, and drill a .070" hole in the lowest point of the lower(inlet) tank. Any water condensing now seems to run down the tubes into the lower tank and get blown out the hole in the lower tank. It is a small enough hole that the slight boost leak doesn't seem to be a problem. Not very high tech but it works.

 

I love these threads but find it difficult to grasp how an automotive diesel (I don't care about gasoline) which burns 1gph at 1900 rpm is not going to burn the same at the same rpm if installed in a boat. I have an early 1.9l vw tdi which I have driven for 4 1/2 years and documented every gallon that has passed through that engine so im not guessing at the fuel burn. At 58 mph on cruise control on a 55mph speed limit highway I get 57.75mpg so near enough to 1 gph, at that speed im doing about 1900 rpm which is where it gets its best torque. If I were to install that engine in a boat and prop it to get, say, a speed length ratio of 1.1 or 1.2 at 1900 rpm would I not use about the same 1gph? I would love to install a pair of these same 90hp 1z vw engines in a powercat. I assume that the calculations of 180 -190 gr/hp/hr are at wot.

Steve

 

shakescreek: a small drain to let any accumulated condensation out is a good idea.

Steve W: agreed, an engine doesn't know if it is in a boat or a car. But you do have to consider both rpm and load and since most boats don't have gears, you may not be able to operate at the same rpm/load point. If not, efficiency will be effected.

 

Fuel consumption depends on the power being produced as well as the engine speed. At a given engine speed the power will be different between the car and the boat. In fact it will be different as the load on the car changes, will be different depending on the boat, propeller used, etc.

Thought experiment: Find a relatively flat and straight east-west road. On a day with a strong prevailing wind from the west, drive your VW from the west to the east at a constant speed and check the fuel consumption. Next hitch a large box trailer to your VW and drive from east to west at the same speed as before and check the fuel consumption. There will be a significant difference.

 

Yes,i keep a Yakima rack in the trunk for when I need to carry long stuff because if I leave it on it consumes 2-3 mpg, an extra person costs about the same, towing a 19ft beach cat across country with 2 people knocked the mileage down to 30mpg.

Steve.

 

As pointed out by others already, actual consumption depends on load alone. You dictate 1900 rpm with your right foot and the injection circuit tries to obey. One of my cars has a little display showing the amount of fuel injected: at a fixed rpm of 2000, the value is between 2 (steep downhill) and 50 (climbing), while normal values are 8-12 on level roads in 6th gear.

Specific consumption is ruled by rpm and engine design, showing that your VW does far better than most road vehicles. For me the conversion from Mercruisers to VW diesels meant filling the tank once or twice a season instead of almost every week. They each use approx. 0.9 gph at hull speed, running on one engine takes over 2 gph because of more prop slip and rudder drag.

 

" which burns 1gph at 1900 rpm is not going to burn the same at the same rpm if installed in a boat. "

IF the load is the same , the fuel burn will match.

1 GPH is probably 15-20hp, is that what your boat uses to cruise?

 

I suggest that almost nobody has the ability to measure HP output of the small engine in their boat.

 

Fuel flow is just a gauge , and a guesstimate on HP/gal..

A scale and a tow line can create a resistance curve for a towed hull.
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Then the guesstimate plotting fuel burn and thrust required can be more accurate.

 

High performance Diesels, I have owned, 212 Steyers, 240 Steyers, and now 256 Steyers. What do you want to known??? ( Lost engine )

 

jonr wrote "I suggest that almost nobody has the ability to measure HP output of the small engine in their boat."

I think it can be done if you know how much the engine burns at full throttle (wide open). If you have a 100hp engine that develops 100 hp at 2400rpm and at full load at 2400rpm the engine burns 4 gph. If you run that engine in a boat and it burns 2gph your'e making just about exactly 50hp. Diesel engines are heat engines and you burn X amount of fuel and produce X amount of heat you will make X amount of HP within the limits of the variables that are fairly obvious. With the above engine if you were to run it at half speed (1200rpm) you would be making far less than 50hp because the hull load curve is so non-leanear and fairly steep.

An engine is more and less efficient at different rpms and boat hulls have non-leanear resistance but I think fairly close approximations can be made.

 

That gives you a rough idea, but isn't a measurement and isn't accurate enough for some uses. To do it right, you need to know rpm and torque on the prop shaft. Doable, but not a setup that small boats typically have.

 

jonr,
What will rpm and torque tell you to this end?

 

Power = Rotational Speed X Torque (with appropriate conversion factor which is dependent on units used)

 

DCockey yes but take the "rotational speed" out and no work will be done.

One hp lifts 3300lbs 1 foot in one min. I think that's correct. HP is an expression of how much work can be done in a given amount of time.

Torque is a static force and does no work. Horsepower is what pushes boats. But torque applied at speed can do work.