320 Searay - Engine upgrade

GloryOfTheSky

New Member
Jul 3, 2014
6
Florida
Boat Info
Searay 320
Engines
Mercruiser 359 MAG twin
Hi, I currently have twin Mercrusier 350 mag mpi stern boards, I was looking to upgrade then to twin Mercruiser 8.2L H.O 430HP

I do need the extra fuel efficiently as I like to go to the Bahamas and other island a lot.


Would it it be hard to swap out the engines?

The engines are 20k a piece, but how much would it cost to install them?

Would they be able to fit with out a issue?
 
Re: 320 Searay - Engine upgrade to 8.2L H.O Mag engines

Cheaper to buy a new boat than upgrade?

I got the 320 for 50k in great condition with no work needed.

50k + 45k is like 95k, so I guess your right
 
Re: 320 Searay - Engine upgrade to 8.2L H.O Mag engines

Yep, buy a different boat. Not worth the cost to swap.
 
Re: 320 Searay - Engine upgrade to 8.2L H.O Mag engines

Also not sure if they'd fit in there. To my knowledge the 320 was never fitted with big blocks. Might be a reason for that (?)
 
Re: 320 Searay - Engine upgrade to 8.2L H.O Mag engines

The 320 was available with outdrives and big blocks.
 
Re: 320 Searay - Engine upgrade to 8.2L H.O Mag engines

Cheaper and more productive to put in small block 383 strokers. Same size, much more HP and Torque. Boat would be a screamer.
 
Re: 320 Searay - Engine upgrade to 8.2L H.O Mag engines

IMO, it makes no sense to do the project. Why break what's working just fine? I totally agree with RollerCoastr. Since your boating needs have changed it's time to upgrade. And in order to achieve fuel economy you need to get diesel powered express style cruiser. Anything like 400DA, 410DA and alike will do the trick.
 
Re: 320 Searay - Engine upgrade to 8.2L H.O Mag engines

If you want more power, that's one thing. But I can't see how going from small blocks to big blocks is going to be more efficient. Even if they were (and they're not) 10% more efficient - do the math on how L--O--N--G it would take to recoup the money you spent on the swap. It will probably be a few lifetimes. If you're happy with the boat, even just buying a new one is going to, again, take a long, long time to recoup your outlay. You could just carry some extra gas.

Scott... :grin:
 
Re: 320 Searay - Engine upgrade to 8.2L H.O Mag engines

So what engine would be the most efficient/less work, I'm looking for more horsepower and better fuel efficentcy.

I thought a 8.2L would be more efficient looking at tests, as they are later models and with twin 420HP vs 300HP you will run it at less RPM's than the 300HP resulting in better fuel economy.

Also, how much work would it be to replace the inboards with sterndrives?
 
Hi, I own a 2003, 320 Searay with twin 350 MAG MPI, at 300HP. So 600HP in total.

I'm looking for more power and better fuel efficentcy, I asked about 8.2L and they told me not to, so what engine should I go with?

They are inboards, would I get better performance by switching to sterndrives?

I was told to go with diesel, but for it to fit its the same horsepower.

If I got a big block how much would it cost to expand the engine compartment for it to fit?
 
I just saw this same question on another forum. Most say get another boat and it's hard to dissagree. If this is "the boat" then a pair 33 strokers is the way to go. They would be bolt in but would require new props and maybe shafts as well.
 
Actually, I believe all of your questions were answered in the other post, with the exception of the sterndrive question. You will not get more performance and more efficiency by changing engines - regardless of diesel, strokers, etc. The only thing that has even a chance of doing both is converting to stern drives. But then you're back to the same thing most of us recommended in the other post - trade boats.

The only real way you're going to get NOTICEABLE gains in performance AND efficiency is to sell your boat and buy two boats - a go-fast boat and a diesel trawler. Strokers will get you some performance gains, although minimal given the hull type, and will likely be approximately the same in efficiency... maybe a bit better, maybe a bit worse. But, again, look at the cost and the HUGE amount of hours it will take you to recoup the money savings -- IF there is any.
 
Last edited:
sell the 320, buy a boat with either the pods or diesels for more fuel efficiency..
 
If you put bigger engines in that boat you're going to need to hire a tiny female gymnast to work on it. IMHO: Sell the boat. Take the profits and the 50k you have burning a hole in your pocket and buy a diesel boat.
 

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