2003 182 BR? 3.0L big enough???

keokie said:
In full disclousre, I used to believe as you did, and I remained unconvinced the first time I saw a boat get the same economy with a larger engine. I made a number of excuses, but I have seen it so many times now, and listened to those who build engines and test them in boats and on dynos for a living to have accepted a reality that is obvious after it is understood.
Click to expand...


Me too.

In all reality how much fuel the 18 footer uses does not matter that much because it will be around 3mpg. Also, you don't know how much your old boat used compared to the new one unless you documented long cruising trips. "An afternoon of tubing" is what most of these boats are used for and that cannot be metered close enough to really know.
 
We need to agree to disagree. In the interests of complete disclosure, I am a licensed engineer. I have taken three college courses in thermodynamics, four college courses in fluid dynamics, and one college course in IC engines. I have made fuel measurements on engine dynomometers, which load engines no differently than a planing boat. I studied under a professor who designed engines for GM - who make the auto-derivative marine engines that most of us use.

You name people who have "built engines" to support your qualifications. Builders seldom understand the science behind the engines they build. They think they do, and will tell you they do, but they do not. It is a very complicated subject that the hobbiests and the general public tend to trivialize. Designers must understand the science or they will have problems.

I believe your examples are valid, but for reasons already discussed you are misguided and you trivialize the importance of the science behind energy conversion. Believe as you wish. I was simply attempting to shine the light of truth where there was darkness. At equal power settings, and with all other factors equal, a small engine is going to be more efficient at loads where the small engine is properly engineered and applied. I simply cannot be otherwise, or the world of science has to do a lot of work to catch up with your theory.
 
Last edited:
Back to the original question: the 3.0 is fine for the boat. I have it in my 175BR and it is a competent power plant for the boat. However, the real question might be: is the boat right for you and how you plan to use it? I bought the BR because I was looking for a small boat for mostly day-tripping and the 3.0 does that splendidly. A High-Five prop added pulling torque and I kept it for cruising to get on plane quicker. I find the combination a good compromise for lack of displacement in my usage. If you plan on pulling with the boat most of the time or hauling a ton of stuff like coolers and such, I can see where the extra torque of the 6 or 8 is going to be a better fit. If you're hauling, you might as well get a larger chassis to go with the larger engine as it can get very cramped in the smaller boats. So, a little segue from the debate: will the 175BR chassis handle the weight and torque of a V8? More curious than anything as I am not planning a transplant right now. However, I couldn't help but notice the abundance of 8 cylinder 'replacements' available relative to I-4s around here.
 
Last edited:
The engine builders I refer to have earned their reputations in their own right. Some of them have educations far beyond the handful of classes you refer to, along with decades of daily applied experience. They are certainly not hobbyists.

I appreciate that this has been a polite exchange, and would love to finish the conversation over a beer. This format is less inviting. I value the courteous interaction, though, so I'll continue.

A big block Chevy is capable of providing the same force at a lower RPM than a small block Chevy. In planing boats depending on hull design, weight, etc., the difference is typically about 700 rpm. So, extending the example, a boat that requires 3000 rpm to travel at 25mph with a big block, will require 3700 rpm from the small block. The fuel required to turn the big block 3000 rpm under heavy load will be extremely close to the fuel required to turn the small block to 3700 under heavy load. The differences in the efficiency of the 8 smaller combustion chambers that will fill and fire many more times in the small block are not significant enough to have a noticeable impact on fuel consumption.

In the example of planing boats, a high percentage of the fuel consumed is used for propulsion (as opposed to higher percentages simply generating heat or keeping the motor spinning in autos). Technically, engines do not create energy. They release the energy stored in the fuel. There is a finite amount of energy in a gallon of gasoline. There is not a big enough difference in the efficiency of releasing that energy between small blocks and big blocks under heavy load to matter in planing boats.

As a side note, that is why diesels are more fuel efficient than gasoline engines. There is more energy in the fuel.
 
I also appreciate the civil debate, but I am compelled to challenge the myth that is being perpetuated. I think I said a couple of posts ago that we need to disagree. I would not enjoy discussing this with you over a beer. You are stubborn and will not consider that you could be wrong.

The question was about the 3 liter GM auto-derivitive marine engine. It is well engineered, and everyone that has owned one, me included, marvels at its low fuel usage compared to larger engines. You tried to claim no advantage exists. You are dead wrong, and I have tried to show why.

I have agreed with your examples. Yours are examples of poorly engineered engines or poorly engineered applications where the larger engine pulls the same load more efficiently. However, your theory is wrong, and your proof shows only that the small engine lacks engineering refinement. You have disputed my examples, even though mine are valid and are supported by the science.

The correct theory is the science of energy conversion, which predicts that what I am saying is correct. The proof of the theory is the engine dynometer test were engines are run at constant and accurately-measured loads while fuel consumption is also measured accurately. If the engineering is equal, the small engine wins every time because it has inherently lower pumping loss, lower internal friction, and higher thermal efficiency due to operation at a higher percentage of its capacity.

Run the equally-engineered engines at the same percent of full power, and both the theory and the dynometer say their efficiency is equal. Run the equally-engineered engines against equal loads, and the smaller engine is always more efficient.

You are only partly correct about diesel efficiency. There is more energy in the fuel, but also the diesel has two thermodynamic advantages: lower part-throttle pumping loss and higher thermal efficiency.
 
springer3 said:
I also appreciate the civil debate, but I am compelled to challenge the myth that is being perpetuated. I think I said a couple of posts ago that we need to disagree. I would not enjoy discussing this with you over a beer. You are stubborn and will not consider that you could be wrong.
Click to expand...

Ut oh... it's getting ramped up:lol:

We will consider that we COULD BE wrong, but you should consider that you ARE wrong:grin:
 
WOW! this is a fun thread. Don't know too much about the fuel economy for this application, and the original poster probably doesn't care. He just wanted to know if the engine was too small. So...as to that point, it really depends on the design and weight of the 182. I had an Ebbtide 182 ('95) with the 3.0 A1, and it was great. Pulled as many as 4 teenage kids on seperate tubes with 2 adults on board with no problem. That boat was about 2300 lbs. My 220 SD with the 5.0 A1 will not do nearly as good, but it is much more comfortable. (except to my wallet)
 
What is this debate all about? It all depends on what metric you are using to define efficiency. If it is purely based on fuel consumption per stroke, then the 3.0l wins by pure volume (or lack thereof) versus the 4.3 or 5.0. It should be fairly common sense that an engine that sucks in 3 liter of air/fuel volume per stroke is going to consume less gas than one that draws in 4.3 or 5.0 liter per cycle. Bare block to bare block, the 3.0 is going be more 'fuel efficient', i.e. drink less gas per revolution, than the V6 or V8 when all are doing zero work other than overcoming the parasitic drag of the reciprocating mass and compression. The gray area that you can debate until you are breathless is how that energy is put to use. You would have to accept that hull design, chassis weight, gearing, prop pitch, blade size...etc. are going to factor. Then, you would need to consider how the user wants to use that boat and power plant. It really isn't going to benefit a bass fisherman on a lake in an aluminum boat to have the same V8 engine that a salt water center console owner has. And that 3hp kicker on the aluminum boat is undoubtedly 'less efficient' trying to push a sea going craft with primary twin diesel power plants. There's a good chance you wouldn't budge an inch GPS wise relative to the current. If you have that 'need for speed' or have to haul a lot of dead weight, get yourself a big V8 (a larger boat too if you are hauling) because it is more 'efficient' at producing the the kind of thrust (or torque) you want, though a 1000rr motor revving at 15000rpm in my 175BR is more appealing to me (but that's just me because I like the weight savings as I only weigh 145lbs and like to launch and recover by myself...which is why I got the smallest 'boat' before they are called speedsters or dinghys). However, if boating for you is trolling along at a leisurely pace, a 3.0 will keep you on the waters for a longer period of time with 20 gallons of gas than a 4.3 or 5.0.
 
berth control said:
Ut oh... it's getting ramped up:lol:

We will consider that we COULD BE wrong, but you should consider that you ARE wrong:grin:
Click to expand...
I have said we need to agree to disagree. I have not disputed your examples, but tried to explain the science behind both opinions.

I hope nobody goes out and buys a larger engine than needed based on the myth that they can expect equal or better fuel consumption. You spend extra thousands of $$$ over the life of the boat if you have more engine than you really need. That is the reason I challenged the unfounded, but evidently well-established myth.

This debate reminds me of the perpetual motion crowd - poor understanding of science combined with a belief system too strong to be pursuaded by scientific fact.
 
Springer,

We have clearly agreed to disagree. We are just continuing the conversation which is okay by me.

As a few points of order... In our brief exchange, I have made no assumptions about your intelligence, personality, or associations. You have determined you have enough information about me to conclude I am stubborn, trivialize science and associate with engine builders who are ignorant, and I am similar to the perpetual motion crowd (whoever they are). At the same time, you indicate I am the one who is not thorough enough in information gathering before reaching a conclusion.

Another point of order is my comment on diesel engines. My statement was not partly correct, it was mostly correct. The primary reason for greater efficiency of diesel engines is the fuel. There are other less impactful contributing factors.

To state that diesels have lower part throttle pumping loss is not correct. Diesel engines do not have throttles. That's not how they operate. Gas engines can be burdened with part throttle pumping loss as the restriction in airflow caused by the throttle creates resistance to reciprocation. Still, even when both engines are running at full power (no part throttle loss on the gas engine) the diesel is very significantly more efficient.

You also stated my examples involve very inefficient engines or examples of improper application. The engines I refer to are of the very most common inboards on the marine market. And in application, the most common offered by manufacturers. As far as technology goes, small blocks and big blocks are very nearly identical with exception to size.

As Smartcraft and similar technology is offered on more vessels, the myth about the smaller engine in planing hulls will show. I would encourage those looking at new boats with Smartcraft to sea trial boats with different motors. Measure the fuel flow at given planing speeds and report back to the rest of us.
 
Your points of order are well-taken. You are correct. I hope you will take equally-well my points about engine efficiency. You do a disservice to encourage someone to buy more engine than they need. Extra power is more expensive up front, more expensive at service time, and the fuel is more expensive even if you never use the extra power.

You made my point about diesels. They have lower part-throttle pumping loss exactly because they do not need a restriction in the throttle, and run at the most efficient WOT all the time. All air breathing engines including diesels have pumping losses. Diesels get better fuel economy because that loss is lower except at full power. I do not recall the exact numbers, but the energy difference in the fuel is a small factor compared to the thermal efficiency advantages of the diesel cycle.

Try this exercise and see it if can lead you to the truth about gas engine efficiency:

1) Design the best single-cylinder 50 cc gas engine you know how. Remember fuel is expensive, so no bad engineering like that found in the small engines you use for examples. Remember power is important, so use the best components for that as well. Keep it a basic engine like a marine engine for a sport boat.

2) Build a 4-cylinder, 2-liter gas engine using four identical single-cylinder engines. Keep the independent fuel systems, cooling systems, etc just to avoid confusion. Add controls that make each single-cylinder engine pull 1/4 of the total engine load.

3) Build an 8-cylinder, 4-liter gas engine using eight single-cylinder engines identical to the four you used in the four cylinder engine. Again, the controls make sure each cylinder pulls exactly 1/8 of the total load.

Put the two engines on two identical dynomometers, and measure the fuel flow for the following engine conditions:

Idle in neutral (zero shaft hp)
"No wake" idle (about 5 hp out the shaft)
Low-speed cruise (off plane, about 25 hp out the shaft)
High-speed cruise (on plane, about 120 hp out the shaft)
Maximum speed (150 hp)

We will finally compare apples to apples in regards to fuel consumption. Describe the following engine parameters for each condition for the 4-cylinder and the 8-cylinder:

1) Internal friction loss
2) Pumping loss
3) Thermal efficiency loss
4) Power out the shaft.
5) Total fuel consumption (the sum of the factors above).

Both engines are designed to drive the same boat, so HP output is identical until the smaller engine reaches maximum power. This exercise will show for certain that we pay dearly for the ability to go fast. The Ferrari vs Civic example have similar engine differences as the exercise. Ferrari understands this, and so does Honda. People still buy both cars, but nobody gets told the Ferrari burns the same amount of fuel at idle or any speed where the Civic can keep up. If you work the exercise, you will see it is not even close.
 
Last edited:
Springer, here's the main reason for my reasoning:

Engines do not make power at the same efficiency across their entire power range. If you were to graph an engine's efficiency across it's power output it would look like a shallow bell curve, they do not make a set power output per gallon of gas through the power range, it changes. It is less efficient at the low end and the high end, most efficient in the middle. If you run the 3.0 in a range that is beyond it's peak efficiency range to keep the boat going 40mph and the 4.3 is at it's peak efficiency to run 40mph, the 4.3 will go farther on a gallon of gas. At 30mph, it will likely be the other way around. At no wake, it will almost always be the smaller engine that does better. But the whole idea is that at CERTAIN speeds for CERTAIN engines the economy will be better with the bigger engine. The efficiency curve is like a torque curve and hp curve, they are not straight lines.

This shows up in cruisers more than runabouts, when you run for hours as a set rpm to get to a destination.
 
Last edited:
Uh, no. If you look at a dyno graph of a bare engine, it is not bell shaped. It is a curved incline that plateaus and maybe dips at the top end as the motor hits the limit of the intake system. The bell curve is a product of gearing which is where a powertrain makes its money in efficiency. Higher ratio gearing is going to give you the most 'efficiency' as far as fuel consumption but your 'power' and torque is going to suffer. If you have a heavy load, you can get a bigger power source or get shorter gears. The other way to get more power is to rev the snot out of the motor until you reach the limit of your intake system. One way to relieve that limit is to have valves that open at higher RPMs like Honda's V-tec or get more cylinders. This is because it is the burning of petrol that makes 'power' and you can increase the revs so that more combustion can take place or increase the volume/displacement of the cylinders to achieve the same end. V-tec is geared toward low consumption with extra valves on standby for power on demand at high revs. V8s and some new V6s have gone the other way by offering a system where they shutdown cylinders when the work demand is low to save gas, since they don't need those work units from the burning of fuel. All things being equal, any engine of the same technology and properly geared to handle the same load should consume the same amount of gas to do the same work unit(s) but the time equation will be different for each system. On that basis, your statement that a 4.3 will go farther on a gallon of gas is incorrect.
 
berth control said:
Springer, here's the main reason for my reasoning:

Engines do not make power at the same efficiency across their entire power range. If you were to graph an engine's efficiency across it's power output it would look like a shallow bell curve, they do not make a set power output per gallon of gas through the power range, it changes. It is less efficient at the low end and the high end, most efficient in the middle. If you run the 3.0 in a range that is beyond it's peak efficiency range to keep the boat going 40mph and the 4.3 is at it's peak efficiency to run 40mph, the 4.3 will go farther on a gallon of gas. At 30mph, it will likely be the other way around. At no wake, it will almost always be the smaller engine that does better. But the whole idea is that at CERTAIN speeds for CERTAIN engines the economy will be better with the bigger engine. The efficiency curve is like a torque curve and hp curve, they are not straight lines.

This shows up in cruisers more than runabouts, when you run for hours as a set rpm to get to a destination.
Click to expand...
Several really baffling statements in all of this. The efficiency curve for the single cylinder 50 cc engine is the same as the efficiency curve for the 4 cylinder and 8 cylinder engines built from the single-cylinder engines. The power curve and the torque curve are the same shape, except of course they are in proportion to the number of cylinders.

You are correct on your efficiency curve for engines with poor controls, but for a well-engineered engine, peak thermal efficiency is at maximum power and WOT (please do not confuse this with maximum RPM, or you will get into another misconseption. You say peak efficiency it is at peak torque. That is technically not correct, but only a small error from that misconseption.

Work your way through my word proplem, and that will help me identify where your other misconceptions are.
 
Springer - thanks for shining your light of knowledge on me. Please shine some more and draw me what you think an efficiency curve looks like for a typical gas engine. An efficiency curve, not a dyno curve that biff thinks I am talking about; hp output on the X axis and gallons pr. hour / hp output on the Y axis.
 
Last edited:
Springer,

I think I see the crux of our disagreement. You are talking about engine efficiency, and I am refering to application efficiency.

You state that effficiency of an engine is determined by:

"1) Internal friction loss
2) Pumping loss
3) Thermal efficiency loss
4) Power out the shaft."

Here's where application matters. In cars, much of the running time the engine is actually doing very little work, so internal friction loss, pumping loss, and thermal efficiency loss have a measurable effect on mileage. When trying to push a boat through a highly resistant environment (water) at a high rate of speed, these factors are very, very small compared to the extremely high resistance put on the effort of the crankshaft to spin.

Think of it this way, take two five gallon pails and put a shovel load of dirt in each and weigh them. The percentage difference in weight will be very small. Then add a second shovel full of dirt to one of the pails. Now weigh them. Percentage wise they will appear much different. Now take two wheel barrows and fill them each with 250 shovels full of dirt. Again percentage difference in weight will be very small. Now add the same shovel full of dirt that you added to one of the pails to one of the wheel barrows. Now weigh them again. Percentage wise there will be no practical change.

The pail example represents engines in auto applications, and the wheel barrows represent planing boats.

The point I am trying to make is again in the planing boat application, the differences in the engines' efficiencies will be insignificant when measured in gallons. Where your passengers sit in your boat, how you trim, and type of propeller will impact the MPG of a boat more than the cubic inches of the engine.

Again, there is a set amount of energy in a gallon of gasoline. If you put a very high percentage of that fuel to use producing torque, the other factors will be insignificant.

As I said earlier, I had to be convinced of this. My own hundreds of hours of measurements taken with precise instruments (GPS, radar, and calibrated digital fuel flow meters, etc.) in identical boats with different engines supports this. Many others have done the same.

I probably never would have cared all that much, except our primary boating destination is quite large with very few fueling opportunities. Add the fact that most boats have pretty inaccurate fuel guages. This necessitated a very thorough understanding of what is otherwise a minor percentage of the cost of boating for most.

Get the bigger engine.
 
Please work through the word problem, and you will be forced to face your misceptions. I know all about efficiency curves, and we can talk about efficiency curves when you reach the steps where that matters. I will help you through the problem, but not if you are not willing to try to understand.

You challenged my comment that one would miss the great fuel economy if you switched from the 3.0 to a larger boat engine. That is my experience after 8 years in a 3.0 followed by this year in a 4.3 LX. My study of thermodynamics and IC engines supports my comment, and so does experience in automove engines.

The word problem I am proposing to expose your misconceptions is applicable to boats. Put the motor in a boat instead of the dyno if you like - the answers are the same. Just do it!

I will help you through the first set:

At idle, both the 4-cylinder and the 8-cylinder have identical cylinders running at the same speed. Brake (dyno) efficiency of each is zero (no power out the shaft). Pumping loss and friction loss is identical in each cylinder, but the 8-cylinder has twice as many. Therefore, there is no doubt that the 8-cylinder uses exactly double the fuel at idle.
 
Last edited:
springer3 said:
Please work through the word problem, and you will be forced to face your misceptions. I know all about efficiency curves, and we can talk about efficiency curves when you reach the steps where that matters. I will help you through the problem, but not if you are not willing to try to understand.

You challenged my comment that one would miss the great fuel economy if you switched from the 3.0 to a larger boat engine. That is my experience after 8 years in a 3.0 followed by this year in a 4.3 LX. My study of thermodynamics and IC engines supports my comment, and so does experience in automove engines.

The word problem I am proposing to expose your misconceptions is applicable to boats. Put the motor in a boat instead of the dyno if you like - the answers are the same. Just do it!

I will help you through the first set:

At idle, both the 4-cylinder and the 8-cylinder have identical cylinders running at the same speed. Brake (dyno) efficiency of each is zero (no power out the shaft). Pumping loss and friction loss is identical in each cylinder, but the 8-cylinder has twice as many. Therefore, there is no doubt that the 8-cylinder uses exactly double the fuel at idle.
Click to expand...

I agree with your statement about using twice the fuel at idle, but we are not talking about at idle.
This does not look like an efficiency curve to me...:smt101
 
You must log in or register to reply here.

Forum statistics

Threads
113,172
Messages
1,427,862
Members
61,086
Latest member
MrWebster
Back
Top