Didn't find anything 40DA specific (that don't mean it ain't here though).

But I would perceive an '05 390 would be close enough to help.
Here is a similar question: (post 657 toward the bottom of the page)
http://www.clubsearay.com/index.php?threads/official-390da-thread.41984/page-33
Jus Cruisin is around here regular, he will comment when he sees this, I'm sure.

Being under powered can be pretty subjective, depending on your point of reference.
I wouldn't think it would be, based on what I know about those engines. However, I do
readily admit to having no experience with that specific boat either.

The difference between those and the HOs is just short of 15%. I don't think that difference would be a deal breaker for me, if the boat is otherwise what I was looking for. But then again, your intent, use and expectations may well be different than mine.

 

Didn't find anything 40DA specific (that don't mean it ain't here though).

But I would perceive an '05 390 would be close enough to help.
Here is a similar question: (post 657 toward the bottom of the page)
http://www.clubsearay.com/index.php?threads/official-390da-thread.41984/page-33
Jus Cruisin is around here regular, he will comment when he sees this, I'm sure.

Being under powered can be pretty subjective, depending on your point of reference.
I wouldn't think it would be, based on what I know about those engines. However, I do
readily admit to having no experience with that specific boat either.

The difference between those and the HOs is just short of 15%. I don't think that difference would be a deal breaker for me, if the boat is otherwise what I was looking for. But then again, your intent, use and expectations may well be different than mine.

Here I am. I bought the boat not wanting or needing a speed demon. The 390 is comfortable boat. Good looks and like @Great Lakes indicated mine uses about 32 gallons per hour at 30 mph. The boat is happy at 3200 rpm.

There was a full right up on the 390 in one of the magazines. They tested the boat with the gassers and were happy with the performance. There was also a diesel being tested at the same time and they did an informal drag race. They said it was surprisingly a dead heat.

If the boat checks out, I wouldn't be afraid of the engines.

 

Where/How will you use the boat. Defining that will help you decide what is the right engine.

HP isn't the only issue' torque is also a big factor hence the reason diesels are aventageous. 3126s are typically 350 to 385 Hp but put out gobs of torque

https://www.clubsearay.com/index.php?threads/8-1l-merc-vs-8-1l-ho-merc.67350/

 

Where/How will you use the boat. Defining that will help you decide what is the right engine.

HP isn't the only issue' torque is also a big factor hence the reason diesels are aventageous. 3126s are typically 350 to 385 Hp but put out gobs of torque

https://www.clubsearay.com/index.php?threads/8-1l-merc-vs-8-1l-ho-merc.67350/

Most likely about 70% local cruises on Detroit River and Lake Erie. Several day trips to put in bay and such approximately 30 mile cruises one way and 2-3 long distance trips a year.

 

In your case, I would focus on overall condition of the boat. The 8.1s would probably be functional. A diesel would be a definite plus, but not if it's a POS.

 

I had a 05 390 with 8.1. She was a bit thirsty but a great boat nonetheless. My boat neighbor has the same boat with HO’s. Runs 1-2 mph quicker and cruises slightly better.

 

An honest opinion is that anything beyond a SR 370 needs diesels unless you spend most of your time below cruise. Just do the math and determine how much of your use will be at cruise or below cruise speeds. It's not that the boats can't maintain a cruise speed but they are really expensive on gas.

The HO option doesn't make much of a difference because the physics of moving weight thru water translates into fuel. Increasing horsepower in a gas boat engine means burning more fuel to get to the horsepower.

 

I think that boat is going to be about 4,000lbs lighter than my vintage 400 (assuming the hull is the same as the 38?). I'm very pleased with performance with my smaller 7.4's. The are quite thirsty, as mentioned above...

I've recently seen a few newer 44's with the 8.1's. If they can do it, anyone can do it

 

Go for it if it's a clean boat do it

 

the 8.1,s and the 8.1Ho are virtually the same power output until you get to 3800 rpm , that’s when the extra horses kick in .
8.1L tops out at 46-4800 rpm
The 8.1ho pulls 5000 rpm thus the top speed difference!
My 06-40 DA with 8.1L burning 32GPH and cruised comfortably between 32-3600 rpm

My 05-340DA cruised/burned the same with 8.1L

 

the 8.1,s and the 8.1Ho are virtually the same power output until you get to 3800 rpm , that’s when the extra horses kick in .
8.1L tops out at 46-4800 rpm
The 8.1ho pulls 5000 rpm thus the top speed difference!
My 06-40 DA with 8.1L burning 32GPH and cruised comfortably between 32-3600 rpm

My 05-340DA cruised/burned the same with 8.1L

your 40 was getting 32gph from 3200-3600??? The same as your 340? Sorry have to say no. I don't mean to question you, but I captain boats of all kinds and that gallon burn sounds way off.

 

I have a 2004 340 with 8.1. I think it's powered perfect. I went on my friends 2002 38 foot Sundancer and a huge difference in power and fuel. His cruise was only like 23mph and was burning 42-44 gph. I cruise at 30mph burning 31gph. With 8 people on his it he was really pushing it and felt like it was really working. Putting those behind a 40, I would say no. I wouldn't do it. Way under powered in my opinion.

 

When we got our boat it would easily do 22 knots. We loaded it up and it did 18 knots. Bigger more powerful engines would probably solve our problem. Load the boat up with all your friends, full of water and fuel and see what it does.

 

I think you're out of gas

 

As a rule of thumb, a gas engine will burn about 10% of the rated HP at WOT in GPH. Ex: 350 HP gasser with burn abou5 35 gal/hr at WOT regardless if the boat it’s installed in. You could estimate a cruise burn from there and be pretty close. Not exact but it’ll get you in the ballpark.

The difference between a 340 and a 380/400 will be how fast it will cruise. The heavier/longer/wider boat will cruise slower as it would take more HP to move the bigger boat, but the engine still put out the same power and burn the same amount of gas. And you won’t have gone as far a distance for the same fuel burn.

 

Well put. The difference from the 340/40 at 3500rpm is the mph. But the fuel burn will be more overall because it takes much more to get them on plane also. 36gph I’m at 31mph in my boat. The 40 will cruise at 23-24 at 3500-3600. I still feel the 8.1 is really working all the time in that 40. Just my opinion.

 

Also keep in mind the larger boat has a lot more hull planing area, and the mechanicals are further forward so they are not as tail heavy as the 340. They actually plane faster, run more level and stay in plane longer at slower speeds, regardless of number of passengers or gear. That eases the load on the engines, so it’s not an apples to apples comparison.
I run around 25mph, at 3300 and have never had a moment I felt I needed more. It’s thirsty, but only boating for four months out of the year you’ll never make up the cost in fuel savings. I say just do it!

 

Also keep in mind the larger boat has a lot more hull planing area, and the mechanicals are further forward so they are not as tail heavy as the 340. They actually plane faster, run more level and stay in plane longer at slower speeds, regardless of number of passengers or gear. That eases the load on the engines, so it’s not an apples to apples comparison.
I run around 25mph, at 3300 and have never had a moment I felt I needed more. It’s thirsty, but only boating for four months out of the year you’ll never make up the cost in fuel savings. I say just do it!

This is something I don't think anyone will ever believe! I went from a 99 340 to a 97 400, both gas 7.4's. The overall performance and handling (on plane) of my 400 is worlds better than my 340 ever was. Planes faster, stays on plane slower, less tab required, all of it. I was shocked when I sea trialed the 400.

What I do miss is the slow speed handling of the 340. With 4 blade props that 340 would turn on a dime. You gotta get used to how the gas 400's move when docking. They can be...stubborn.

 

I get the best Mpg at 3450rpm/ 29mph, Standard 8.1's. My friends HO's like 3500-3600. Any lower they feel like they want a little more.

 

Previous boat of ours was a 2000 410 Sundancer with the 454’s in her, some said it would be underpowered but I never had any issues with it at all.
Multiple trips that were in the 80 mile range and yes the fuel burn was higher but if it’s the boat you like and want then go for it.
Everyone has something negative to say no matter what you choose but in the end you have to be happy.