is the 7.4 really bad on gas consumption?

Oliver378

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looking at buying a 1993 21' Crownline and am a little leary about it as it has the 7.4 .With gas so expensive here in Canada I'm a nervous that the fuel bill will bring some regrets? any input would be great...cheers
 

H20Rat

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Fuel consumption has far more to do with how you drive than the engine behind you. In many cases, a small engine at WOT will burn more than a larger engine at the exact same speed. It takes x amount of HP to drive a certain speed, and a certain amount of gasoline to produce x HP. How you produce that HP doesn't affect it as much as you would think.

Of course, if you push that throttle level all the way forward, prepare to open your wallet!
 
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MarkSee

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YES ! Quite bad so if you have to think about it now, look for a boat with a more fuel efficient engine so you'll enjoy the boat more without worrying about the fuel costs or limiting what you want to do.

Mark
 

bruceb58

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My boat in my signature has a 7.4L. I have spoken to people that have the 5.7 in the identical boat and we get very similar mileage numbers.
 

UncleWillie

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The amount of fuel burned is proportional to the power produced.
The size on the motor has little impact on the fuel usage at the same speed.
That 7.4 can probably suck down more than 25 gallons an hour at wide open.
Just because you have it, doesn't mean you have to use it.
The same boat with a smaller engine will burn close to the same amount of fuel at the same speed.
You will find that ~40Kph will be a comfortable cruising speed.
The boat may be able to go 100Kph+ . It will be exciting but not pleasant.
It is fun to do when the water permits, then slow down to a speed where you don't have to hang on and conversations are possible again.

I have a 4.3. It Burns ~16gph wide open. I average ~4gph over the season.
That was ~50 hours and 200 Gal. or about $1000 of gas for the year.
That doesn't count the many hours drifting with the engine off watching Sunsets and listening to the water on the hull.
I value my time on the water by how long I can make the day last, Not how far or fast I can go.
The slower you go the longer the fuel lasts. You can idle along at no wake speed and barely burn 1 gallon an hour.

Search BoatTest.Com for a boat your size with a similar engine.
Click on "Test Results" to get an idea of the fuel usage.
 

HT32BSX115

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looking at buying a 1993 21' Crownline and am a little leary about it as it has the 7.4 .With gas so expensive here in Canada I'm a nervous that the fuel bill will bring some regrets? any input would be great...cheers

Howdy,

Welcome aboard!


I have one of those (+ Bravo III) in a 21ft Four Winns.

I was so worried about it that I installed a Lowrance fuel flow gage.

Running at around 30 mph, (and at 3000 RPM) I burn about 10 GPH.................... I would be willing to bet that if I had a smaller 5.7L engine in the boat, to operate it at the same load and speed, it would likely burn approx the same fuel (per hour)

All automotive gasoline engines exhibit roughly the same specific fuel consumption regardless of displacement. That is, they produce HP at roughly the same LB/HP-HR fuel flow (lbs of fuel per horsepower-hour) for a given (same) power output.

You can make some boats a little more efficient by either making them lighter (less people and gear) and by decreasing the propeller "Slip".

Decreasing slip increases (propeller) thrust for a given power output.

You can decrease slip by increasing the number of blades in the water. (there is a limit here though, because more blades also increases hydrodynamic drag on the prop) .................going from a 3 blade to a 4blade will help as will going to a contra-rotating (Bravo III / Volvo Duo-Prop) type drive.........yada yada................

But the real bottom line is your right hand. If you have more power, it's tempting to use it......... so if you are "hot-rodding" around a LOT, you'll use more fuel than if you had a smaller engine and didn't the same "hot-rodding"

A 23' Crownline is a pretty big boat. Mine is 21ft long and I absolutely wouldn't want it with a smaller engine.

IMHO, a 23' boat with a 5.7L engine would be fairly anemic performance-wise.........I would want either a built up "Small block" (stroked/383 etc) OR a 454/496 engine.


Regards,


Rick
 

Scott Danforth

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if your worried about fuel economy in a boat, get one with oars, paddles, or a sail. As indicated prior, fuel consumption has less to do with the motor, and most to do with the operator.

As Rick pointed out, most SI engines have the same BSFC (Brake Specific Fuel Consuption).
 

tpenfield

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Two points.

The 7.4 will not consume all that much more than a smaller V8 to power the same boat. Power works that way in high load applications. It does not compare to a car, which is a low load application.

Fuel is such a small part of the overall cost of boat ownership, that you could raise it by 25-50% and hardly notice it.
 

thumpar

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The fuel usage is proportional to how far you push your right hand forward. I can burn up 40 gallons in a day with my 5.7l if I wanted to.
 
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philipp10

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Smokingcrater is correct that it takes "X" amount of energy to push the boat, no matter the engine size. But he is wrong (and many people make this mistake) as there is much more to the story. If you are looking at comparing say a 3.0 L to a 7.4 at wide open thottle (for the 3.0), the 7.4 would probably be a 2/3rds throttle you would get similar mpg. The 7.4 at this speed would use somewhat more due to the extra weight it is pushing as the motor is much heavier, but in general, they would be close. However, you don't boat all day at high speeds. You do way more idling than you realize (no wake zones, just wanting to go slow etc). It is at these speeds where the 7.4 will burn way more fuel than the smaller motor. Same thing happens in a car. The V8 stuck in traffic idling uses probably 1.5 times the 4 cyl.
 

Tail_Gunner

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All of this sounds good and is pretty much spot on if that is the carb or Fi is tuned properly. I have a buddy who burns fuel in a 454 in 21' boat at rates that would stagger your mind..however the carb is a original carb 1989 vintage it appears to have never been opened up the paint on the carb is pristine. I have tried with no avail to get get a new carb on that boat but it still runs decent so he refuse's to even think about a new carb....how he can think it can still meter fuel right at that age and how it is still running stagger's my mind...Dont be one of those guys that assumes if it run's thing's are ok...:D I dont have the heart to tell him the fuel consumption rate he is going thourgh now could easliy pay for a new carb and i would no longer pass his old tub in my 4.3..:faint2:
 

philipp10

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All of this sounds good and is pretty much spot on if that is the carb or Fi is tuned properly. I have a buddy who burns fuel in a 454 in 21' boat at rates that would stagger your mind..however the carb is a original carb 1989 vintage it appears to have never been opened up the paint on the carb is pristine. I have tried with no avail to get get a new carb on that boat but it still runs decent so he refuse's to even think about a new carb....how he can think it can still meter fuel right at that age and how it is still running stagger's my mind...Dont be one of those guys that assumes if it run's thing's are ok...:D I dont have the heart to tell him the fuel consumption rate he is going thourgh now could easliy pay for a new carb and i would no longer pass his old tub in my 4.3..:faint2:

if it's running well its doubtful you would save much in gas getting in that carb. If your wasting so much fuel you would see poor running performance.
 

Tail_Gunner

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Well Phil we shall find out it does not take much to get a idle circut to run smooth but metering at rpm is another thing along with throttle response. I will say this however for a old rochester to survive 20 yrs with the same float and needle's and seat's is saying something.
 

HT32BSX115

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you don't boat all day at high speeds. You do way more idling than you realize (no wake zones, just wanting to go slow etc). It is at these speeds where the 7.4 will burn way more fuel than the smaller motor. Same thing happens in a car. The V8 stuck in traffic idling uses probably 1.5 times the 4 cyl.

You may be right about the idle fuel flow being more for a 7.4L engine vs a 3.0L engine..........but to operate a 21ft boat at "no wake" with a 3.0L engine would probably be using similar fuel flow because it would need to be operated at "OFF-idle" throttle settings to get the same "no-wake" speed.

Also, I don't think the OP is talking about getting that 21ft Crownline with a 3.0L engine (if one even exists.....I don't think Crownline offered ANY 21' boat with a 3.0L engine....it appears that the 4.3L V-6 is the smallest )

He's likely referring to the difference between a 7.4L engine and maybe a 5.7L V-8.

I suspect the difference running at idle between the two, is minor.
I would be willing to bet if (2) identical 21' Crownline boats (5.7L, 7.4L) were operated similarly for a day, the 7.4L boat would likely use less than 10 gallons more and possibly less than 5 gallons(more)

If you ran them around at WOT a LOT and did a lot of FULL-throttle launches, then the 7.4L powered boat would of course use considerably more.

When I go to the lake for a day of wake-boarding, I NEVER need full throttle launches.

Because of the Bravo III, it's just not necessary. Even pulling a skier, full throttle is not required (out of the hole) OTOH, It probably would be if I had the same boat with a 5.7L engine...............and full throttle absolutely would be needed with a 4.3.......
 

tpenfield

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In general, the bigger engines will use more fuel at idling speeds and at the higher throttle ranges (because they can). In terms of the OP's question, it will not be 'bad' versus what may be perceived, due to the power usage factors discussed in the previous posts.

I recall reading an article on this very topic in a boating magazine quite a few years ago . . . 7.4 vs. 5.7's . . . same boats, but properly matched gear ratio and prop pitch . . . the 7.4's used about 10-15% more fuel than the 5.7 overall, even though the engines were 30% more displacement.
 
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HT32BSX115

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In general, the bigger engines will use more fuel at idling speeds and at the higher throttle ranges (because they can). In terms of the OP's question, it will not be 'bad' versus what may be perceived, due to the power usage factors discussed in the previous posts.

I recall reading an article on this very topic in a boating magazine quite a few years ago . . . 7.4 vs. 5.7's . . . same boats, but properly matched gear ratio and prop pitch . . . the 7.4's used about 10-15% more fuel than the 5.7 overall, even though the engines were 30% more displacement.

So with my 44 gallon tank, If I used 30 gallons in a day, (I have never used 30 gallons in a day btw.......probably more like 30-35 gallons in a week of skiing, wake-boarding cruising around a couple of times per day......)

10%-15% of 30 gallons would be about 3-5 gallons (more) of fuel burned regardless


I'd get the 7.4L engine over the 5.7 in a medium to large boat (21+ ft) anyday!
 

thumpar

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If it is a 21' Crownline it is probably a 210ccr. Those boats are heavy. I looked at one before I bought the 202br. The 210ccr is much bigger. Go with the 7.4l.
 

philipp10

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You may be right about the idle fuel flow being more for a 7.4L engine vs a 3.0L engine..........but to operate a 21ft boat at "no wake" with a 3.0L engine would probably be using similar fuel flow because it would need to be operated at "OFF-idle" throttle settings to get the same "no-wake" speed.

Also, I don't think the OP is talking about getting that 21ft Crownline with a 3.0L engine (if one even exists.....I don't think Crownline offered ANY 21' boat with a 3.0L engine....it appears that the 4.3L V-6 is the smallest )

He's likely referring to the difference between a 7.4L engine and maybe a 5.7L V-8.

I suspect the difference running at idle between the two, is minor.
I would be willing to bet if (2) identical 21' Crownline boats (5.7L, 7.4L) were operated similarly for a day, the 7.4L boat would likely use less than 10 gallons more and possibly less than 5 gallons(more)

If you ran them around at WOT a LOT and did a lot of FULL-throttle launches, then the 7.4L powered boat would of course use considerably more.

When I go to the lake for a day of wake-boarding, I NEVER need full throttle launches.

Because of the Bravo III, it's just not necessary. Even pulling a skier, full throttle is not required (out of the hole) OTOH, It probably would be if I had the same boat with a 5.7L engine...............and full throttle absolutely would be needed with a 4.3.......

I wasn't trying to say a 21 ft Crownline would run a 3.0 L motor. My point was, a larger motor always uses more fuel at low throttle positions. At idle, it takes a lot more fuel just to overcome engine friction on the larger motor. Thats where you will use more fuel along with the weight penalty of a larger motor over a smaller lighter one. It take lots of fuel to push that extra weight. Why do you see the car makers now using smaller 4 and even 3 cylinder engines in cars? CAFE is forcing that. BTW, take a look at the most efficient boats of all, a sailboat. They run 10 hp OB and get incredible mileage. Running a smaller motor at its rated capacity is always more efficient than running some huge monster at 5% of rated output. Its just a fact of life. That said, like an earlier poster said, the difference between a 5.7 and a 7.4 is not going to break the bank.
 
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thumpar

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I wasn't trying to say a 21 ft Crownline would run a 3.0 L motor. My point was, a larger motor always uses more fuel at low throttle positions. At idle, it takes a lot more fuel just to overcome engine friction on the larger motor. Thats where you will use more fuel along with the weight penalty of a larger motor over a smaller lighter one. It take lots of fuel to push that extra weight. Why do you see the car makers now using smaller 4 and even 3 cylinder engines in cars? CAFE is forcing that. BTW, take a look at the most efficient boats of all, a sailboat. They run 10 hp OB and get incredible mileage. Running a smaller motor at its rated capacity is always more efficient than running some huge monster at 5% of rated output. Its just a fact of life. That said, like an earlier poster said, the difference between a 5.7 and a 7.4 is not going to break the bank.
A 3.0l may use less fuel at idle but it is also doing less work. Car and boat engines have nothing in common when it comes to fuel efficiency.
 
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