V6 vs V8 for the 20-21ft boat Efficiency vs power?

[gtochris]

I know this could be a very vague topic with many variables, especially hull and weight.

I had a 4.3L in a 1990 Regal 19ft (175hp I believe back then). For the time, I recall it having better pickup and such then many of our friends similar boats with the 5.0L and 5.7L (pre MPI). Maybe it was the lighter weight/ improved power/ weight ratio?

My partner and I are really torn on our needs vs wants for the next boat. The 19ft Stingray is "adequate" and a bit surprising how capable it is at times, BUT it comes at the expense of a rough ride being so light. It also is not a slomn skiing boat, just doesn’t have the torque. I love power, but am inherently cheep- so I question if my ideal power train: a 5.0L MPI or a 350 MAG would suck down fuel more so then a 4.3L MPI? I look at brands such as Regal and they advertise that their Fast-Trac hull is more efficient and can run comparable speeds with the V6 rather the competitions V8... I like boats like the Crownline 21ss or the Larson Senza 20ft and have seen both advertised with everything from the 4.3L MPI to 350MAG. I like the low profile sporty look.

With the auto industry going toward smaller power plants, *(and the marine industry being 20+ years behind) Is it reasonable to believe such desire for improved efficiency will be one day upon the marine industry? Or should one just buy the engine they want as the amount of driving on a boat is minimal compared to a car?

 

[A/C Guy]

Re: V6 vs V8 for the 20-21ft boat Efficiency vs power?

I have a new 5.7L, 330 HP, and we use 3 GPH skiing, tubing, and wakeboarding with 2000lbs of ballast and 6 passengers. Fuel costs are such a small fraction of the cost of boat ownership that I consider it a non issue. WHat does it cost if you burn 4 GPH, an extra $4? By the time I trailer the boat to the lake, buy the snacks and drinks, amortize the cost of the truck, boat, trailer, insurance, does an extra $4 per hour factor in? No.

 

[Monterey10]

Re: V6 vs V8 for the 20-21ft boat Efficiency vs power?

I've run a 21 with a 4 cylinder and the V8. The 4 was barely adequate for fishing. The V8 was too much. I would imagine the V6 would be ideal

 

[The Rooster]

Re: V6 vs V8 for the 20-21ft boat Efficiency vs power?

I know this could be a very vague topic with many variables, especially hull and weight.

I had a 4.3L in a 1990 Regal 19ft (175hp I believe back then). For the time, I recall it having better pickup and such then many of our friends similar boats with the 5.0L and 5.7L (pre MPI). Maybe it was the lighter weight/ improved power/ weight ratio?

My partner and I are really torn on our needs vs wants for the next boat. The 19ft Stingray is "adequate" and a bit surprising how capable it is at times, BUT it comes at the expense of a rough ride being so light. It also is not a slomn skiing boat, just doesn’t have the torque. I love power, but am inherently cheep- so I question if my ideal power train: a 5.0L MPI or a 350 MAG would suck down fuel more so then a 4.3L MPI? I look at brands such as Regal and they advertise that their Fast-Trac hull is more efficient and can run comparable speeds with the V6 rather the competitions V8... I like boats like the Crownline 21ss or the Larson Senza 20ft and have seen both advertised with everything from the 4.3L MPI to 350MAG. I like the low profile sporty look.

With the auto industry going toward smaller power plants, *(and the marine industry being 20+ years behind) Is it reasonable to believe such desire for improved efficiency will be one day upon the marine industry? Or should one just buy the engine they want as the amount of driving on a boat is minimal compared to a car?

I think you've hit the nail on the head there, Chris. I'd agree w/ "A/C Guy". A fellow member recently stated that if fuel cost was a major concern, then don't buy a boat. A day spent on the water w/ family and friends is worth every penny it costs for fuel. Having said that, I don't look for gas to go back to $2.00 a gallon in the next 10-20 years. Good luck !!!

 

[Charlie in TX]

Re: V6 vs V8 for the 20-21ft boat Efficiency vs power?

I believe fuel efficiency is based on hull design, weight and engine efficiency. The 4.3l and the 5.7l are about the same efficiency. They will burn about the same fuel in the same hull.

 

[drrpm]

Re: V6 vs V8 for the 20-21ft boat Efficiency vs power?

Those engines will convert fuel into power at essentially the same rate of efficiency. The 4.3 L MPI has a peak rating of 220 HP. The 5.0 and 5.7 L MPI engines will burn about the same amount of fuel at 220 HP as well. The bigger engines give you a chance to turn even more fuel into power. I have a 5.0 L MPI in my 20 foot bowrider and it has plenty of power.

 

[H20Rat]

Re: V6 vs V8 for the 20-21ft boat Efficiency vs power?

With the auto industry going toward smaller power plants, *(and the marine industry being 20+ years behind) Is it reasonable to believe such desire for improved efficiency will be one day upon the marine industry? Or should one just buy the engine they want as the amount of driving on a boat is minimal compared to a car?

Two comments on that... The auto industry is going towards smaller displacement but substantially higher horsepower engines. I have a 2 liter, 4 cylinder engine in my car. It also puts out over 300 horsepower and 330 or so of torque. Keep in mind that it takes about 40 horsepower for your average car to cruise down the interstate at 75 mph. (so cruising is roughly 13% of max power in my case)

Now in the boating world, its an entirely different animal. 13% of max power is also known as 'trolling'. Cruise power is often 60-75% of max. The engine is asked to put out its rated power for far longer time periods, far more often. The reason this becomes important is that horsepower takes fuel, and in the boating world, it really doesn't much much difference how you are creating that horsepower. Identical hulls cruising at the same speed, a v8 equipped boat is basically going to get the same as a small v6, plus or minus a little. If you run WOT, then the higher horsepower engine will always suck down more fuel, simple rule of physics.

Would my 300hp car engine make a good boat engine? Probably not. I'm pushing 18 psi of boost, if I asked the engine to do that constantly its life expectancy would suffer. (although I have to admit, i have 120k miles on that engine, lots of it driven hard, and lots of towing with extended boost, although I still limit boost pressure while towing to something more reasonable) As a general statement, the less you push an engine, the longer it will last. A v6 running around at WOT all the time will not make it as long as a v8 at half throttle.

 

[cyclops2]

Re: V6 vs V8 for the 20-21ft boat Efficiency vs power?

Have to throw in the most important reason for LARGE engines. Cubic inches & the weight they bring with them.

Safety. Main normal reason.
Power to tow another boat in a storm. Heavier to ride smoother.

towing & carrying near a maximum load are all horsepower.
Acceleration with maximum load & a long trouble free lifespan, is all cubic inches.

Anything that reduces those 2 facts is less than desireable.

5 L V8 220 hp in my 18.5' bow rider is pushing 3500 pounds. no people. I would go about a 5.7 L V 8. Too much ? Do not push the throttle lever so hard.

 

[QC]

Re: V6 vs V8 for the 20-21ft boat Efficiency vs power?

I would agree with cyclops except replace displacement with air . . . Not exactly the same thing since smaller displacement engines often add air for more power i.e. some kind of blower.

Yes, if ALL else is equal, smaller displacement for the same load is more efficient, particularly for Otto cycle engines, not the same discussion for diesels. The reason is throttling losses. However, in the grand scheme, the fuel differences are minimal as drrpm has pointed out. Get the boat you like with the biggest powerplant you can afford. With that said, I would much more like to see a 5.0 MPI than a 5.7 Carb, and I'd much more like a 4.3 MPI than a 5.0 Carb. Other than those swings, no biggee.

 

[PrinceValium]

Re: V6 vs V8 for the 20-21ft boat Efficiency vs power?

I think you've hit the nail on the head there, Chris. I'd agree w/ "A/C Guy". A fellow member recently stated that if fuel cost was a major concern, then don't buy a boat. A day spent on the water w/ family and friends is worth every penny it costs for fuel. Having said that, I don't look for gas to go back to $2.00 a gallon in the next 10-20 years. Good luck !!!

X2!

I do have the newest 4.3 MPI V6 220 hp motor in my Tahoe...and I really love the performance of it. it pulls wake boarders, tubes, and skiers with no problems. I never feel like I don't have enough power and frankly I think it is plenty fast enough for us (indicated 58 mg at WOT) Where I do understand your concern for some fuel economy, like others have said on the water it just isn't the same. My boat has a 45 gallon tank and after a whole day of tubing etc. and running around the big lake out here, I am at about half a tank when we get back to the ramp. I would say that is pretty damn good! For the price I just didn't see the need for a 5.0L motor for the same HP as the V6. The biggest reason we went with the MPI is so we didn't have to worry about retuning at altitude!

 

[cyclops2]

Re: V6 vs V8 for the 20-21ft boat Efficiency vs power?

I am 74.
So I know that I can get any carb to dribble gas into the engine well enough to comfortably limp home. We even held a 6 gallon can in the air with a Vise grip plier squeezing the cut off end of the rubber hose. Piece of cake to run sweetly at a steady rpm.
No can do that stuff with non carbs very easily.

Still... Next boat will be fuel injected.

Rich

 

[gtochris]

Re: V6 vs V8 for the 20-21ft boat Efficiency vs power?

I would much more like to see a 5.0 MPI than a 5.7 Carb, and I'd much more like a 4.3 MPI than a 5.0 Carb. Other than those swings, no biggee.

I can agree with that statement, crazy that carbs are still offered in 2012 when they havent been on cars in 20+ years...

One of the boats we are considering is 20ft and 5.0L MPI with an Alpha 1, Depending on what we get back for taxes and the pending sale of our house, we might buy that.

 

[PrinceValium]

Re: V6 vs V8 for the 20-21ft boat Efficiency vs power?

I am 74.
So I know that I can get any carb to dribble gas into the engine well enough to comfortably limp home. We even held a 6 gallon can in the air with a Vise grip plier squeezing the cut off end of the rubber hose. Piece of cake to run sweetly at a steady rpm.
No can do that stuff with non carbs very easily.

Still... Next boat will be fuel injected.

Rich

My last boat had a Mercury 1500 inline 6 and it was a pain to have to adjust the 3 carbs at altitude, to which it basically did not want to run well when towing ANYTHING. At sea level it would scream across the lake with no issues at all. I don't have to worry about adjusting anything anymore...I just get in the boat and go have fun in it...which is the way it should be.

 

[cyclops2]

Re: V6 vs V8 for the 20-21ft boat Efficiency vs power?

My 2002 5 L with Alpha has $0 put into either piece. 250 ??? max hours. Family cruises & then I go out alone & WOT the beans off of it.

Rich

 

[H20Rat]

Re: V6 vs V8 for the 20-21ft boat Efficiency vs power?

I would agree with cyclops except replace displacement with air . . . Not exactly the same thing since smaller displacement engines often add air for more power i.e. some kind of blower.

Yes, if ALL else is equal, smaller displacement for the same load is more efficient, particularly for Otto cycle engines, not the same discussion for diesels. The reason is throttling losses. However, in the grand scheme, the fuel differences are minimal as drrpm has pointed out. Get the boat you like with the biggest powerplant you can afford. With that said, I would much more like to see a 5.0 MPI than a 5.7 Carb, and I'd much more like a 4.3 MPI than a 5.0 Carb. Other than those swings, no biggee.

In theory, yes, the less throttling losses you have, the better. In reality, throttling losses end up being minor compared to a couple other things. The closer to WOT an engine runs, the further it needs to be from 14.7:1. This is especially true in small displacement forced induction engines, which use fuel to cool the charge, so they intentionally run a very rich mixture. 10:1 or richer is not uncommon on a higher horsepower FI non-race car.

So in comparison, running a larger engine at 50% throttle, 14.7:1 (or leaner for lean-burn conditions) and dealing with that loss is more better than a small engine at 100% throttle, at 10:1.

 

[cyclops2]

Re: V6 vs V8 for the 20-21ft boat Efficiency vs power?

Not a true, all the time rule, but for valved engines, the best breathing occurs between 2500 rpms ...old USA V8s.
& add 1000 t0 1500 rpms for the camdriven overhead imported engines. so pick what you like for cruising speed.

Then go to Boat Tests US for a boat / engine that is similar. Most deeep Vs same, power/ gear ratio/ weight & prop are the same. Names change but not much else.

I hate breaking new toy bubbles. But comparison shopping does matter.

 

[sbbamafan]

Re: V6 vs V8 for the 20-21ft boat Efficiency vs power?

When was the last time you heard someone complain that they had too much power?

On a serious note, I doubt the fuel usage different is much different at all, unless you are all the way into most of the time.

 

[A/C Guy]

Re: V6 vs V8 for the 20-21ft boat Efficiency vs power?

I am 74.
So I know that I can get any carb to dribble gas into the engine well enough to comfortably limp home. We even held a 6 gallon can in the air with a Vise grip plier squeezing the cut off end of the rubber hose. Piece of cake to run sweetly at a steady rpm.
No can do that stuff with non carbs very easily.

Still... Next boat will be fuel injected.

Rich

My last boat had a Mercury 1500 inline 6 and it was a pain to have to adjust the 3 carbs at altitude, to which it basically did not want to run well when towing ANYTHING. At sea level it would scream across the lake with no issues at all. I don't have to worry about adjusting anything anymore...I just get in the boat and go have fun in it...which is the way it should be.

With Fuel Injection, we no longer worry about the engine backfiring and causing a fire or explosion. We also don't worry about fuel fumes from the carb causing a dangerous situation in the engine compartment. We also don't worry about vapor lock on hot days when a beginner skier or boarder keeps falling and we have to repeatedly stop.

Lots of reasons to not consider a carburated engine

 

[QC]

Re: V6 vs V8 for the 20-21ft boat Efficiency vs power?

MPIs do vapor lock and you do still have to worry about fumes. Trust me, I have vapor locked and set my 6.2 on fire :facepalm:

Edit: wait, check that, the fire was the stupid operator :redface:

 

[cyclops2]

Re: V6 vs V8 for the 20-21ft boat Efficiency vs power?

I can match that one.

" What dirt bag untied my dock lines & let it drift away during lunch ????? "

Me. Forgot to tie the lines while Bull crapping to other people coming in.