Repower from 5.7 to 8.1 engines

[Tail Chaser 661]

Repower from 5.7 to 8.1 engine

I'm concerned with clearance issues

My 1985 26' dancer has approx 5" clearance from the front of the 5.7 engine to the 100 gal gas tank.

The overall length of a 5.7 is 36.8"
The length of the 8.1 is 40.1"

Ive heard a 8.1 with the 100 gal tank will have like 2' clearance in front of the engine.

I don't know how long a waterpump last in a big block.
But it seems to me you would have to pull the engine for a waterpump replacement?

The other options are the 6.2 or the 383ci efi Merc.
The 383 has 390 ft lbs of tq from 2800 rpm to 3500. 5k redline.

The Volvo D4 260 hp@ 3500rpm is sweet. 453 ft lbs of tq.
Length is 36.7 That beast weighs 1455 lbs with a duo prop compared to 1271 lbs for the 8.1 with a bravo 3.

The Volvo cost an extra 15k also.
I think the 8.1 TQ is near 500 ft lbs?

So it looks like the big block gets the most bang for the buck.
But maybe not being able to get a wrench anywhere near the front of the engine may be a very stupid upgrade.

What do you guys think?
As you can see from the pic. There's plenty of room everywhere, except the front of the engine.

 

[Nehalennia]

Are you replacing the drive too?

 

[dpmulvey]

What drive do you have? What are you trying to accomplish? What are you willing to spend?

 

[Vince_nj1]

Another issue to consider is the addtional weight of a big block. That boat is already heavy in the stern. (I had 79 260 dancer) It may seem like an attractive idea, but I think after doing the research, you will find that its not practical. By the time you change the transom plate, outdrive, controls etc you would have been better off selling your boat and buying a 28 footer.

 

[Tail Chaser 661]

Im changing out the drives also. Going from Alpha to Bravo is only drilling two more holes for the bravo transom plate.

Buying the engine and drive as a brand new complete package. They come with a new transom plate, belows, etc.

I would replace/upgrade the shifter.
Buy all new shift, throttle, steering cables.

Cost of complete engine and drive packages are....
#1- 12k for Merc 383 325 hp efi Raw water cooled with bravo 3 drive.

#2- 15k For Merc 6.2 320hp efi Raw water cooled with bravo 3 drive.

#3- 17k For Merc 8.1 375 hp Fresh water cooled with bravo 3 drive

#4 30k for a Volvo D4 260hp diesel with a duopro
That engine package gets 3.1 mpg in a 26' flybridge Skipjack. Much more labor involved. New gauges, bigger cutout for drive etc.

I'm looking for better MPG and faster cruise speed. Im at 1.5 mpg now. Usually cruising at 3000/3200 rpm@17kts.
The boats not really on plane till 20 kts.
That's with a 16"Dx14"P 3 blade prop and a 1.47 Ratio Alpha 1 drive.
I'm usually in wht cap seas with a 3'/5'swell (Pacific Ocean)
A local prop guy said that a new 5.7 with the BRAVO 2 with the really big prop works really nice with a 26' Dancer in rough seas.
I personally think with a single screw. That application will have a nasty list condition?
I need to run 10/20% on the port trimtabs under power even with my current setup.
Seems almost everyone always upgrades with bravo 3.

Goal is 20kts@3000rpm and 2 MPG
So Calif waters Lots of the time. Over 18kts, you can start beating your boat up.

So basically,
I need a stronger drive. And the power/tq to push a prop with at least 3" more of pitch dropping my RPM down another 600rpm.
I ve read that every 50ft lbs of tq is good for about 2" increase in prop pitch.
My 260hp Merc when new. Was suppose to put out 350 ft lbs of tq at 3500 rpm.

 

[MAKC]

Have you considered that the repower you are talking about might be worth more than the boat itself? If you are talking on average 15K for everything, you will never be able to recover any of your costs.

That being said, i would rebuild your current engine and convert to a fuel injection system versus your carbed setup right now. With a mild cam, higher-compression valve springs, a performance intake, and EFI, you could probably get a lot more power and torque for maybe 3K when all i said and done. That would be the best bang for the buck IMHO.

 

[Tail Chaser 661]

I don't plan on ever selling her.
So over the next 15 yrs or more.
Spending 15k/17k seems worth it.

A new 26'/28' boat would cost me min. 80k to 150k
It probably would not have that 7' long aft cabin bunk this boat does. If I bought a fishing boat anyway. I'm 6' 6" tall.

Then if I bought used. I would be back to repairing, replacing, and upgrading to my specs again.

If I get a stronger drive, With longer cruise range.
This boat does pretty much everything I want.
Set up for fishing with good over night multi day sleeping amenity's.

 

[berth control]

Tail Chaser -
you make some good points, but I have to agree with the other advice here, don't put the money into that boat. It looks like a really nice boat, the radar arch and radar look really good, and I'm sure you have it just the way you want it. The problem is when you have kids, move, see a smoking deal on another boat, or any number of reasons you will want a different boat. Maybe not a newer one, but a different one. That being a bowrider, bigger cruiser, trawler, whatever. I would just hate to see you put 30,000 into your boat for a sweet diesel engine, and then sell it two years later for the same as any other 260 with a rebuilt or repowered gaser. Also, like Mike said above, why not just rebuild and do some upgrades to the current engine? Your 350 with a hotter cam and head job, higher compression, and whatever else you want to do will do the same as the other upgrades you are talking about. Especially if you upgrade to tuned port injection, you could get 300+ hp out of that motor easily. About the higher nautical mpg, I don't think you will see any increase no matter what you do, other than a newer turbo diesel. Bigger motor almost never means less fuel. I know it will work less, but not enough to actually improve your mpg. My boat is not much bigger. It has twins, but they are four cylinders, and I get about 1.5mpg at my optimal cruise speed on smooth water, but in rough seas it goes way down. Newer boats of similar size get better mpg out of the newer engines, but I would argue that is because of improvements in hull design and weight savings, not the motors. Our boats are not known for their light weight!

I hate to tell you not to do the project, but I have done what you are planning on with other things, and got burned. bad. It would be a bummer for you to go throught the same. I have got about 14K into my boat, wouldn't you rather sell yours and buy a new boat for 30K? That would be the money you are going to put into the engine plus the sale of yours. Just a thought

 

[comsnark]

He has the disease. There is no cure. Every year he will put in more money than the boat is worth. He will just keep pouring money into the rat hole. . and be happy doing it.

I have a 1972 blowboat. I have the disease.

 

[Jimmy Buoy]

I had a 1989 268 Dancer at one time with a 7.4Ltr (454ci) gasser and a Bravo 2 drive/Stainless Prop. :lol:

There was enough room between the engine and gas tank to replace the water pump. I can't imagine the 8.1 being that much different in total length.

It's not so much the hp difference between marine engines, but the torque that offers more "get up'n go".

On my 268 it seemed to have plenty of power to get up on plane, but still wouldn't cruise below 20Kts. I ended up taking the stock trim tabs that were only about 12" wide and replacing them with 24" wide ones. That made a HUGE difference! With the tabs down, I could stay on plane down to about 13Kts. It didn't help the fuel consuption, but it did allow a soft, stable, and more controllable ride in rougher conditions and I think the additional torque supplied by the 7.4 helped as well. Going 20Kts in rough seas meant some "slamin" that Mamma didn't like.:smt021

Eventually, we got 2footitis again and went to a 32' with more beam - so I'm hearing what others are saying about investing too much in your current boat.:huh:

Good luck with your decisions.

 

[fwebster]

I don't have a dog in this fight, but my view is to see what is out there for sale in the area of what you can get for your boat + the cost you anticipate foe your repower.

Maybe nothing that suits you better than your current 25 year old boat, but my guess is that you can find something like a mid 90's 300WE with inboard power, not outdrives for about the same money. Sea Ray solved a bunch of problems with rotton coring, leaks, unsealed plywood, etc between the mid 80's and mid 90's and I would rather have a later boat with none of those potential problems as a platform to build on for a long term keeper.

 

[BadaBingII]

i hear where you are coming from. You do have the disease. I had a 78 Mako. Rebuilt one engine, and repowered two more times. I had so many memories in that boat and it did exactly what I wanted. I had a hard time parting with

But in my case, life changed. Kids, wife, some physical issues that made standing all day in a center console difficult.

Depending on what your situation is, only you can decide what to do. I know I am probably never going to see another new boat in my life. One kid in college, looking at retirement in 4 years, and slim possibility of dramatically increasing my wages, plus risk of losing employment, I just don't see any way to make it happen.

You are right, a 7' mid berth will be hard to find. I'm curious, have you considered a rebuilt 454? Had one in a 268 with an alpha. You might be able to save a lot of bucks. But stay with the Bravo. The alpha is marginal with a big block. Beam on the 268 is 8' 6". So not sure if stringer work would be needed on your boat.
My mpg with the 7.4 was about 1.5 mpg at cruise. Top speed recorded on loran was 43.5mph. Would cruise easily at 30 mph.

I am not sure if there is a length advantage for you with the 454, but if you are looking for torque.......

Just my $.02

Best of luck,

Jeff

 

[keokie]

Okay,

I have done this to an '83. My dad put a 502 in his '81 260. A very close friend put a 454 Mag EFI in an '82 260.

Along the way various forms of small blocks were tried.

What we learned:

Small Blocks don't have enough torque (a new 350 Mag rated at 300 hp at the prop did not perform any better than the original 350 rated at 230hp at the prop).

Alpha's can't hold the big blocks.

The switch is relatively uncomplicated. It is tight in front of the motor, but we all work on them.

You can easily beef up the motor mounts. The stringers (if rot free) are plenty strong.

This hull design responds very well to more power.


Remember, this will be expensive and you will never get it back. Also, remember a newer old boat with twins will absorb ten grand pretty quickly.

If you make this change, (as with most boat decisions) you will lose money in the end.

However, if you like the overall boat, and I do, there is a great advantage to all new propulsion.

Here's mine:

 

[Tail Chaser 661]

He has the disease. There is no cure. Every year he will put in more money than the boat is worth. He will just keep pouring money into the rat hole. . and be happy doing it.

I have a 1972 blowboat. I have the disease.

:grin::grin::grin: But its a nice rat hole.

Boat is actually almost complete.
Boat has a 48" wide bench seat.
It sits on a storage box 12"H x 48"L X 36"D
Going to build a new box. same dimensions.
Make it a insulated fish hold.
Then mount Two helms chair on top the fish hold.
The chairs will rotate 360 degrees. So it will be more comfy facing the rear of the boat while fishing.
I have room for two more rod holders on the arch.

Being such a heavy boat. Doing 100 mile trips offshore. Would like a stronger drive.
Might as well upgrade the engine also.

 

[Tail Chaser 661]

I don't have a dog in this fight, but my view is to see what is out there for sale in the area of what you can get for your boat + the cost you anticipate foe your repower.

Maybe nothing that suits you better than your current 25 year old boat, but my guess is that you can find something like a mid 90's 300WE with inboard power, not outdrives for about the same money. Sea Ray solved a bunch of problems with rotton coring, leaks, unsealed plywood, etc between the mid 80's and mid 90's and I would rather have a later boat with none of those potential problems as a platform to build on for a long term keeper.

30 fters are real nice. But I don't want twins. And I want a trailable boat. Also having a boat in a corrosive environment 24/7 would really bother me. The cost of a slip in one year is equal to a new drive. Having a boat out of sight, is out of mind also.

 

[Tail Chaser 661]

Have you considered that the repower you are talking about might be worth more than the boat itself? If you are talking on average 15K for everything, you will never be able to recover any of your costs.

That being said, i would rebuild your current engine and convert to a fuel injection system versus your carbed setup right now. With a mild cam, higher-compression valve springs, a performance intake, and EFI, you could probably get a lot more power and torque for maybe 3K when all i said and done. That would be the best bang for the buck IMHO.

The cheapest route I would consider.
2800.00 for a 383ci long block. Thats 350 hp/400lbs Tq
Would still need .
300.00 Vortec intake manifold.
New exhaust manifolds $$??
1000.00 for fresh water cooling.
Then all my other stuff bolts on this engine.

The alpha drive has got to go.
So I still need...
3k for a bravo drive
3k for the stern plate. Or whatever its called.
Then I'm not sure about flywheels, couplers, etc
That's whats nice about the complete kits.
No dealing with parts people that sell you the wrong stuff.
Avoiding the run around and headache is probably worth 1K or 2 K.

Ive heard EFI cost 3k
So replacing that alpha drive.
There no way around the 12k price tag.

 

[Tail Chaser 661]

I had a 1989 268 Dancer at one time with a 7.4Ltr (454ci) gasser and a Bravo 2 drive/Stainless Prop. :lol:

There was enough room between the engine and gas tank to replace the water pump. I can't imagine the 8.1 being that much different in total length.

It's not so much the hp difference between marine engines, but the torque that offers more "get up'n go".

On my 268 it seemed to have plenty of power to get up on plane, but still wouldn't cruise below 20Kts. I ended up taking the stock trim tabs that were only about 12" wide and replacing them with 24" wide ones. That made a HUGE difference! With the tabs down, I could stay on plane down to about 13Kts. It didn't help the fuel consuption, but it did allow a soft, stable, and more controllable ride in rougher conditions and I think the additional torque supplied by the 7.4 helped as well. Going 20Kts in rough seas meant some "slamin" that Mamma didn't like.:smt021

Eventually, we got 2footitis again and went to a 32' with more beam - so I'm hearing what others are saying about investing too much in your current boat.:huh:

Good luck with your decisions.

In pu truck applications ive heard the 454 can run hot.
Dont know if thats a problem with the marine engine.

I asked a good marine mechanic about the 454ci.
He said they suck exhaust valves? So I had not looked into them any further. They do put out 440 ft lbs of tq at low rpm. With a strong drive. I could increase pitch in my prop 4" to 6" over what I have now. Problem would be solved.

My local saltwater prop guy. Says he has done a lot 26 Sundancers. Repower with Merc 350 mag and Bravo 2 with a huge prop. The bravo 2 is geared down to push the big prop.
Lower gearing also increases output tq. That drive is designed for displacement hulls

The 454 with the Bravo 2.
Did that have a very bad List condition. (Boat leans badly) under power?

Very cool getting info on the same or similar boats.

 

[Tail Chaser 661]

i hear where you are coming from. You do have the disease. I had a 78 Mako. Rebuilt one engine, and repowered two more times. I had so many memories in that boat and it did exactly what I wanted. I had a hard time parting with

But in my case, life changed. Kids, wife, some physical issues that made standing all day in a center console difficult.

Depending on what your situation is, only you can decide what to do. I know I am probably never going to see another new boat in my life. One kid in college, looking at retirement in 4 years, and slim possibility of dramatically increasing my wages, plus risk of losing employment, I just don't see any way to make it happen.

You are right, a 7' mid berth will be hard to find. I'm curious, have you considered a rebuilt 454? Had one in a 268 with an alpha. You might be able to save a lot of bucks. But stay with the Bravo. The alpha is marginal with a big block. Beam on the 268 is 8' 6". So not sure if stringer work would be needed on your boat.
My mpg with the 7.4 was about 1.5 mpg at cruise. Top speed recorded on loran was 43.5mph. Would cruise easily at 30 mph.

I am not sure if there is a length advantage for you with the 454, but if you are looking for torque.......

Just my $.02

Best of luck,

Jeff

Its interesting about the 454 mated with the Alpha drive.
I had found a good website on picking the right prop for different engine drive combos.

The 454ci alpha drive speced out the same as the 5.7 any HP with the same prop.
That was stating a 7500 lb 26' boat.
Obvious you cant put much Tq into the alpha drive.
I expected to see at least a 4" increase in prop pitch with the high Tq 454 engine. So a 454 with a Alpha will always be way under propped on a heavy boat if you don't want to break the drive.

I bet the 26' Sea Rays that that came with 454 alpha combo were 800 to 1000 rpm underproped hurting the mpg badly.

 

[Tail Chaser 661]

Okay,

I have done this to an '83. My dad put a 502 in his '81 260. A very close friend put a 454 Mag EFI in an '82 260.

Along the way various forms of small blocks were tried.

What we learned:

Small Blocks don't have enough torque (a new 350 Mag rated at 300 hp at the prop did not perform any better than the original 350 rated at 230hp at the prop).

Alpha's can't hold the big blocks.

The switch is relatively uncomplicated. It is tight in front of the motor, but we all work on them.

You can easily beef up the motor mounts. The stringers (if rot free) are plenty strong.

This hull design responds very well to more power.


Remember, this will be expensive and you will never get it back. Also, remember a newer old boat with twins will absorb ten grand pretty quickly.

If you make this change, (as with most boat decisions) you will lose money in the end.

However, if you like the overall boat, and I do, there is a great advantage to all new propulsion.

Here's mine:

You have a really clean boat there.
I was just assuming a SBC and a BBC motor mounts line up.
I have not got around to thinking of the small details yet.:lol:

 

[Tail Chaser 661]

I really appreciate everyone's info and opinions.
Ive learned a lot.
Kind of a bummer most of you think I should not repower this boat.
I'm way ahead of the money game. Knowing I needed atleast a 25' boat. This is my first boat. Bought in 04
That's really about the Minimum size boat for consistently hitting the offshore islands off So Calif. Then returning in nasty windy conditions.

I personally cant see selling a nice boat that is set up for what I want to do. And it does have the range (Barely) to go as far as I want to go.

My main issue with this boat.
That radar dome is 13' 6" high. When the boat is on the trl.