Repower from 5.7 to 8.1 engines

I had a 1988 Dancer. You may want to check the height of the engine. But this may be a problem: the engine is heavier and if you put a heavier outdrive on also you will lower the transom in the water a few inches. Usually not a problem but it will affect getting on plane. Its not just about power. But another serious consideration: That with the added weight and transom lower in water, you will have to watch the height of your risers relative to the waterline to prevent water entering under a quick stop or stall. Also it can be a problem with boat just sitting in water and next thing you know you have water in cylinder #1. The standard risers on a 8.1L are high and under the above noted conditions you may not have the clearance to the underside of the engine hatch. Somethign to explore.
Several people on this Forum site have noted they used a repower of the 383 Stroker. Its a good match for the existing Alphas or Bravo series; has pleanty of torque for your size boat and will be pretty fuel efficient. Best to luck to you
 
BadaBingII said:
Smart move on underpropping the alpha. On my 268, mine was propped out to max out at 4600 rpm. I don't remember the prop dimensions. The drive failed at 200 hrs, and 400 hrs. First was covered under warranty. Paid for the second one and I'd had it. It was right around then that merc mechanics admitted the alpha wasn't enough drive for the 454.
Click to expand...
My next step is installing the Corsa captain's call and Gil muffled tips I picked up cheap on Ebay. The goal isn't so much the maybe 10% power increase but the cooler engine temps and better efficiency from less exhaust restriction along with a cooler alpha drive without the big block exhaust volume running through it's narrow passages.

I'm still always looking for a deal on a B3 and transom assembly too...
 
chollyjohn said:
I had a 1988 Dancer. You may want to check the height of the engine. But this may be a problem: the engine is heavier and if you put a heavier outdrive on also you will lower the transom in the water a few inches. Usually not a problem but it will affect getting on plane. Its not just about power. But another serious consideration: That with the added weight and transom lower in water, you will have to watch the height of your risers relative to the waterline to prevent water entering under a quick stop or stall. Also it can be a problem with boat just sitting in water and next thing you know you have water in cylinder #1. The standard risers on a 8.1L are high and under the above noted conditions you may not have the clearance to the underside of the engine hatch. Somethign to explore.
Several people on this Forum site have noted they used a repower of the 383 Stroker. Its a good match for the existing Alphas or Bravo series; has pleanty of torque for your size boat and will be pretty fuel efficient. Best to luck to you
Click to expand...

Thanks for the input.
keokie has done three early/mid 80's 26' Sundancers.
A 454ci Mag, 496 ci, and a 502ci.
Tight fit put they work real good.

I checked the specs on different engines
The 5.7 engine is 31.7" high
The 8.1 engine is 31.5" high

5.7 engine with Bravo 3 weighs 1070 lbs
Probably a little more. 383ci Fresh water cooling?
390 ft lbs tq. Should work nice.
8.1 engine with Bravo 3 weighs 1271 lbs
That wt is with fresh water cooling.
500 ft lbs of tq (I think) No doubt. works nice.

Cost is 4 k more for the 8.1
You get 100 more ft lbs of tq.
Thats good for 4" more prop pitch.
And dropping the cruise RPM down about 800 rpm for the same cruise speed.

Adding 200 lbs of wt to the stern hurts a bit.

I would like to find the post where members did the 383ci repower.
 
berth control said:
Thanks for the compliments -

About your new favorite boat - sounds good! Sign me up when you find a used one that someone put that motor and drive in! I'm not picky though, it could be a perkins, yanmar, or stehr diesel:grin: That would make docking a lot tougher though without twins....:smt009 Maybe two small diesels:smt038
Click to expand...

I found this website......
BOE Marine Docking School
After giving there twin screw class a shot.
I found I'm not very good with twin screws.
I'm all over the place :lol:
 
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Tail Chaser 661 said:
I'm not very good with twins.
I found this website......
BOE Marine Docking School
I'm all over the place :lol:
Click to expand...

Here's the thing about twins - they make docking easier because the boat will pivot on it's bow and swing the stern around when you put one in foreword and the other in reverse:smt043
Couldn't resist. Made for a funny youtube video though
 
Tail Chaser 661 said:
Thanks for the input.
keokie has done three early/mid 80's 26' Sundancers.
A 454ci Mag, 496 ci, and a 502ci.
Tight fit put they work real good.

I checked the specs on different engines
The 5.7 engine is 31.7" high
The 8.1 engine is 31.5" high

5.7 engine with Bravo 3 weighs 1070 lbs
Probably a little more. 383ci Fresh water cooling?
390 ft lbs tq. Should work nice.
8.1 engine with Bravo 3 weighs 1271 lbs
That wt is with fresh water cooling.
500 ft lbs of tq (I think) No doubt. works nice.

Cost is 4 k more for the 8.1
You get 100 more ft lbs of tq.
Thats good for 4" more prop pitch.
And dropping the cruise RPM down about 800 rpm for the same cruise speed.

Adding 200 lbs of wt to the stern hurts a bit.

I would like to find the post where members did the 383ci repower.
Click to expand...

You can save a few pounds with aluminum heads & intake, and stainless exhaust. I'm sure this options will up your price tag some. Not sure if this is feasible with the big block put just throwing ideas out there to help.

Good luck.
 
Being a saltwater boat.
I stay away from Aluminum as much as I can.
I spent all day researching engines, Instead of painting my Rod holder bulkheads :smt021
I don't know if its true.
Or the marine industry's pushing small blocks. Mostly 6.2 engines.
Because GM dropped there 7.4 and is dropping there 8.1 engines.

The test were comparing replacement engines over the 7.4
They lowered the gear ratio on the small blocks. 1.8 Gear Ratio. Bravo 3 drive
They also used a 24" pitch prop on the small blocks
26" pitch on the 8.1
Test said, That would even out the RPM and Power difference of BB vs SB engines on a 26' boat
Volvo 280 hp GSI
Volvo 320 hp GSI
Merc 6.2 320 hp
Merc 8.1 375 hp
Outcome was.....
8.1 engine cruise 23kts@2500 rpm Claimed best cruise rpm?
All small blocks cruise 26kts@3500rpm
All engines had same MPG at that speed/rpm
All engines get same MPG at about 30% throttle

Both 320 hp engines got on plane almost as fast as the 8.1
The 8.1 gets a 7 mph faster top speed then all small blocks.
Testers said they would pay extra for 8.1 if most trips boat was loaded heavy with passengers.

For a 3 kt cruise difference.
8.1 chugging along at 2500rpm
6.2 screaming along at 3500 rpm
You could guess which package is more reliable for long term.

You know where these test are bogus for me.
A 5.7 320hp with 360ftlbs of tq at 3500rpm pushing a 24' pitch prop.?

My boat with a 350 mag 355 ft/lbs tq @3500 rpm 1.50 gear ratio alpha drive. Specs with a 16x14 alum prop or 15.75x15 stainless.
Boat came with a 15x19 stainless. Im using a 16x14 alum now
Them new boats must be made out of bolsa wood (LIGHT) No wonder they run for cover every time the wind picks up:lol:
 
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Seems like alot is being covered on this topic. I share the excitement for added power, torque speed and lesser cruising speed; just rememebr that the 200+ pound difference is like a person standing on yoru swim platform. Watch the hatch clearance adn watch the waterline relative to the manifolds with the added weight. Meanwhile, I'll try to find you those 383 Stroker threads. If not on here, it may be on one of the other marine engine forums. Meanwhile try this site : www.boatpoint.com.au/boat-review/1960519.aspx
 
The weight of the big block is not even noticeable. I have added aluminum headers (which saved a little) with IMCO's Sound Advantage and full closed cooling (which put some back). I even put 4 six volt batteries in the bilge at 80 pounds a piece, and it didn't make a difference. Oh, and the risers sit higher than the small blocks as well, so no water intrusion problems.

Another buddy of mine has an '84 260 with twin 350's in it. It handles that weight very well also. Downside is the bilge is very, very tight and it doesn't perform quite as well as a single 502.

The short of it is I (and friends and family) have built and run these boats with countless propulsion options. We all agree the single Big Block is the best way to go. There is no debate among us.

I don't want to ruffle any feathers, but a 383 won't touch a 502.

All this talk is giving me second thoughts about selling mine, which is inconvenient since I have a buyer.
 
Berth Control -- one point of correction. In the 80's models, the 30' had an 11' beam. You don't get 12' until the 340. (11'11")

Tail,

I have been reading this thread with interest and amusement. I have been down this road when I had a partner on an '85 23' Cobalt. Without going into a lot of detail he wanted the boat to be faster and against my arguments made the engine switch. This began a spiral down into a bottomless money pit. One change led to another and to another and the investment very quickly became many, many times what the boat would ever be worth. (I exited the partnership before I lost a lot of money) My partner claimed it was OK, that he loved that boat and would never even consider selling it.

About 3 years later he saw a good deal on a 2-year old 28' Chris Craft Corsair and fell in love. I don't need to continue. Everyone can guess the end of the story.

This was a very open saga as my partner owns a couple of very popular waterfront restaurants in Long Beach, CA and it was discussed a lot by many. During a discussion one day, a very seasoned old boater gave some very sage, if unheeded advice:

"I you have a wife or a woman you are not happy with , trying to change her will never work. You need to just get another one the way you want her in the first place."

Regardless of how much you love this boat or intend to keep it. Things change, life happens....

You sound pretty convinced this swap is what you want to do and I doubt anyone on this forum is going to change your mind. You need to just understand that you WILL lose money on this deal and most likely a pretty good amount. For every one of these swaps that go well the are 50 that are disasters.

Good Luck
 
Norcal -
thanks for the correction, you are right about the beam.

Unfortunately for tail chaser, I think you are right about the motor swap too. I have talked to other people that swapped motors, and it seems to always cost more than they thought.

To give credit though Tail Chaser - you seem to have done way more research than most people, and you are planning on changing the drive, which is a spot where others have run into problems. It seems that the people that run into the problem are the "I can get a rebuilt 454 from my buddie's truck and sell mine and it will only cost a hundred bucks" crowd.

Here's a thought though. Your current motor gets the job done, it just has to scream to do it. If you are not rebuilding it anyway - you don't need the block or components - why not just let it scream until it or the drive dies? You may get five seasons out of it as is. If it ain't broke....
 
chollyjohn said:
Seems like alot is being covered on this topic. I share the excitement for added power, torque speed and lesser cruising speed; just rememebr that the 200+ pound difference is like a person standing on yoru swim platform. Watch the hatch clearance adn watch the waterline relative to the manifolds with the added weight. Meanwhile, I'll try to find you those 383 Stroker threads. If not on here, it may be on one of the other marine engine forums. Meanwhile try this site : www.boatpoint.com.au/boat-review/1960519.aspx
Click to expand...

Just doing my homework so I don't make a mistake.
The chart on that website. Does not show comparisons of both engines together?

Whats interesting is...
If my 7500 lb boat can push a 24" pitch prop with a 383/6.2
engine.
That's 26 kts@3500rpm
My goal is 20kts@3000 rpm. Due to rough water I boat in.
Then a the small block will work darn good also.
I just wont have top end speed of the big block.

Now I have to confirm/research what gear ratio and prop size and pitch a 26' 7500lb boat with a 320hp small block bravo 3 uses.

Volvo 320hp Tq was actually 370ft/lbs
Merc 6.2 320hp is 375ft/lbs
390 ft/lbs for a 383 ci
Tq of a 350 Mag is down at 355 ft/lbs
Manufactures make it way to hard to find them #s :smt013
 
Tail Chaser 661 said:
Now I have to confirm/research what gear ratio and prop size and pitch a 26' 7500lb boat with a 320hp small block bravo 3 uses.
Click to expand...

That boat size, weight, and horsepower closely resemble the newer version 260DA's with the Mag350 which many here own. I'm sure someone can provide you with the drive ratio and prop pitch needed.
 
Tail Chaser 661 said:
Just doing my homework so I don't make a mistake.
The chart on that website. Does not show comparisons of both engines together?

Whats interesting is...
If my 7500 lb boat can push a 24" pitch prop with a 383/6.2
engine.
That's 26 kts@3500rpm
My goal is 20kts@3000 rpm. Due to rough water I boat in.
Then a the small block will work darn good also.
I just wont have top end speed of the big block.

Now I have to confirm/research what gear ratio and prop size and pitch a 26' 7500lb boat with a 320hp small block bravo 3 uses.

Volvo 320hp Tq was actually 370ft/lbs
Merc 6.2 320hp is 375ft/lbs
390 ft/lbs for a 383 ci
Tq of a 350 Mag is down at 355 ft/lbs
Manufactures make it way to hard to find them #s :smt013
Click to expand...

TC,

I boated for almost 20 years out of Long Beach and have countless trips offshore mostly to Catalina and The Channel Islands. I had the afore mentioned Cobalt with a 260hp/Alpha and an '87 24' Sea Ray Sorrento with the same engine/drive package. The listed dry weight difference between your boat (5200) and my old 24 (3900) is 1300 lbs. Fairly substantial. My point is this: when I was in rough water going to or coming back from the islands I could not go as fast due to sea conditions. There were very few times I ever run wide open even up here on the glassy smooth waters of the Delta. I'm confused by your need for the additional top end speed. :huh:

Also you say you want to trailer your boat. Everyone has said that until they enjoy the ease and convenience of a slipped boat. Our Cobalt was in Alamitos Bay from the day it was new (1985-its still there by the way) and we had a bottom cleaning service twice a month so the zincs were changed regularly and it had a MerCathode system. That drive did not have a spot on it for 10 years and then the MerCathode system quit. There is nothing wrong with keeping a boat in salt water. Look at all the boats in Marina Del Rey and all the other marinas up and down both coasts.

I know you are getting lots of opinions here and you will make your own decision but to add one more....spend the money on the lady that has all that you need and sell the other one to some one looking for that lady.

One last thing. Our '89 340 has a v-berth that is wider than a king size bed. It comfortably sleeps me at 6'2", my wife and 2, 85lb dogs. The aft cabin berth is slightly narrower than a queen. It is 12' wide has a really great cabin layout and a huge cockpit. YachtWorld currently lists 7 Sundancers or Expresses in Southern Cal and and a total of 12 in California priced from $34,500 to $69,000.
http://www.yachtworld.com/core/list...&spid=104&slim=quick&No=0&Ns=PAll_sortPrice|1
 
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