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TOPIC: 2556 - Alpha Drive Owners, please confirm RPM VS. Speed

2556 - Alpha Drive Owners, please confirm RPM VS. Speed 01 Sep 2017 17:57 #1

  • Landin
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Hello BOC Members,

I am having some performance issues with my 1991 - 2556 Bayliner.

Over the past year, I have installed a new Mercruiser 357 MAG Engine along with a new Alpha Drive GEN 1 (waiting on confirmation of drive ratio).

Currently, I am only reaching speeds of 10 - 11 MPH @ 2800 - 3200 RPM. When doing an open throttle test, I am only reaching a max RPM of 3800 - 4200 RPM and reaching a maximum speed of 13 MPH. (SOG)

My prop size is 15 1/2" 15P (is this prop size the same as what other 2556 owners are using with an alpha drive?)

I have electric trim tabs and even without those, the boat has no issued getting up on plain... lots of torque.

I have installed a hydrofoil as of yesterday to be tested this weekend for any improvements. ...

Any comments back confirming you own speeds and specs would be greatly appreciated! My gut is telling me perhaps the shop that ordered me the drive either ordered the wrong ration drive or received the incorrect ratio drive..... hmmmm and so goes on the mystery....

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BOAT: 1991 - Bayliner 2556 Ciera Flybridge
ENGINE: 357 Alpha 4V (275HP)
OUTDRIVE: Alpha Gen 1
RATIO: (to be updated)
PROP: 15 1/2" X 15P
NAME: "Knotty Oar"

Marine Search and Rescue Crew - rcmsar.com/rescue-stations/southern-region/north-vancouver/

2556 - Alpha Drive Owners, please confirm RPM VS. Speed 01 Sep 2017 18:19 #2

  • Ruffryder
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Your 91 MY boat should've had a GEN2 to start with...
Positive they ordered a GEN 1? sounds like your gear ratio is wrong also ;)

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Joon, Kathy, Jaden & Tristan
93 3058
92 2855
91 Fourwinns 205
Longbranch WA
Life is Good

2556 - Alpha Drive Owners, please confirm RPM VS. Speed 01 Sep 2017 18:55 #3

  • builderdude
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Joon, can you confirm what the final drive ratio should be on a 2556 with SBC engine and Alpha? I don't have a clue as a run the Bravo. I'd thinks he should be cruising easily at 20-22 mph.

Landin, is there a maximum recomended RPM on the flame arrestor cover? I'd think at least 4600 for WOT on that 357 MAG

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Dave
Edmonds, WA
"THE FIX"
'93 2556 5.7 Bravo II 2.0:1 18 1/4x19 P
.030 over-Vortec top end-part closed cooled
***The rebuild of my 2556***
www.baylinerownersclub.org/index.php/for...ansom-repair-my-2556
Last Edit: by builderdude.

2556 - Alpha Drive Owners, please confirm RPM VS. Speed 01 Sep 2017 19:11 #4

  • Landin
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Hi Dave, Merc. indicated 4400-4800 RPM

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BOAT: 1991 - Bayliner 2556 Ciera Flybridge
ENGINE: 357 Alpha 4V (275HP)
OUTDRIVE: Alpha Gen 1
RATIO: (to be updated)
PROP: 15 1/2" X 15P
NAME: "Knotty Oar"

Marine Search and Rescue Crew - rcmsar.com/rescue-stations/southern-region/north-vancouver/

2556 - Alpha Drive Owners, please confirm RPM VS. Speed 01 Sep 2017 19:11 #5

  • Landin
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I'll double check the GEN 1 VS. GEN 2 with the shop... Thx!

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BOAT: 1991 - Bayliner 2556 Ciera Flybridge
ENGINE: 357 Alpha 4V (275HP)
OUTDRIVE: Alpha Gen 1
RATIO: (to be updated)
PROP: 15 1/2" X 15P
NAME: "Knotty Oar"

Marine Search and Rescue Crew - rcmsar.com/rescue-stations/southern-region/north-vancouver/

2556 - Alpha Drive Owners, please confirm RPM VS. Speed 01 Sep 2017 19:13 #6

  • Ruffryder
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recommended WOT RPM on a 357 4V Alpha is 4400-4800.
mated Alpha final ratio should be 1.47:1 or HIGH ALTITUDE 1.81:1

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Joon, Kathy, Jaden & Tristan
93 3058
92 2855
91 Fourwinns 205
Longbranch WA
Life is Good

2556 - Alpha Drive Owners, please confirm RPM VS. Speed 01 Sep 2017 19:23 #7

  • Landin
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Thank-you Joon!

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BOAT: 1991 - Bayliner 2556 Ciera Flybridge
ENGINE: 357 Alpha 4V (275HP)
OUTDRIVE: Alpha Gen 1
RATIO: (to be updated)
PROP: 15 1/2" X 15P
NAME: "Knotty Oar"

Marine Search and Rescue Crew - rcmsar.com/rescue-stations/southern-region/north-vancouver/

2556 - Alpha Drive Owners, please confirm RPM VS. Speed 02 Sep 2017 06:44 #8

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Ruffryder wrote: recommended WOT RPM on a 357 4V Alpha is 4400-4800.
mated Alpha final ratio should be 1.47:1 or HIGH ALTITUDE 1.81:1


Landin, Sounds like you go for some extended trips and could be heavily loaded with fuel, water, gear, & crew. If you determine the drive ratio is correct it's gotta be to much prop. reduce the prop pitch to achieve your maximum recommended RPM range of 4800 (IMO your mechanic should have tested this)
Also, have you done any testing with the boat lightly loaded? Say half tank of fuel, no water, and no gear?

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Dave
Edmonds, WA
"THE FIX"
'93 2556 5.7 Bravo II 2.0:1 18 1/4x19 P
.030 over-Vortec top end-part closed cooled
***The rebuild of my 2556***
www.baylinerownersclub.org/index.php/for...ansom-repair-my-2556

2556 - Alpha Drive Owners, please confirm RPM VS. Speed 04 Sep 2017 22:05 #9

  • Landin
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Hi Dave,

I have noticed maybe (max) 500 extra RPM with min. Fuel/water and gear... giving me a maximum throttle of 3800 RPM. And still never exceeding 14mph.

I just got back from testing the newly installed hydrofoil... no improvement.
I came up with the following results -
At 3000 Rpm. Boat speed was around 12 mph... Max throttle today was 3400 RPM... I had some gear on board (not much) full fuel tank and no water.

Joon, may I ask what prop specs you're running?

Dave, I understand prop sizing is more of an art than a science... but; Is changing my prop size , say from a 15pitch to a 13pitch - Could it really improve my overall speed 10 - 15 mph...this seems like a huge jump?

Nother big question is how do I test a 13 pitch prop without having to buy one... I heard mercury use to lend out props for prop sizing but don't think that sort of stuff happened anymore... :/

Cheers°°°

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BOAT: 1991 - Bayliner 2556 Ciera Flybridge
ENGINE: 357 Alpha 4V (275HP)
OUTDRIVE: Alpha Gen 1
RATIO: (to be updated)
PROP: 15 1/2" X 15P
NAME: "Knotty Oar"

Marine Search and Rescue Crew - rcmsar.com/rescue-stations/southern-region/north-vancouver/

2556 - Alpha Drive Owners, please confirm RPM VS. Speed 04 Sep 2017 22:41 #10

  • builderdude
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Landin, take a look through the 2556 owners thread. Mojo25 !has a similar set up (5.7 Alpha gen 1) maybe send him a pm asking what prop he's running & drive ratio. There are also many 2556 members running OMC drives, maybe it's a simalar prop as far as diameter goes and such.

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Dave
Edmonds, WA
"THE FIX"
'93 2556 5.7 Bravo II 2.0:1 18 1/4x19 P
.030 over-Vortec top end-part closed cooled
***The rebuild of my 2556***
www.baylinerownersclub.org/index.php/for...ansom-repair-my-2556

2556 - Alpha Drive Owners, please confirm RPM VS. Speed 09 Sep 2017 04:53 #11

  • Vanisle boater
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My '92 2556 with carbureted 350 was a dog. Motor had 200hrs after rebuild. Receipts that came with it showed the carb had be rebuilt recently.
I was quite disappointed that it would not go more than 13-14 mph. Wouldn't rev right up under load.
I replaced the carb with a brand new one. And bingo, 24 MPH (18-21 mph fully loaded with water fuel kids and overnight gear).
The prop is a 15x15. I wouldn't change it.

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2556 - Alpha Drive Owners, please confirm RPM VS. Speed 09 Sep 2017 06:13 #12

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Vanisle boater wrote: My '92 2556 with carbureted 350 was a dog. Motor had 200hrs after rebuild. Receipts that came with it showed the carb had be rebuilt recently.
I was quite disappointed that it would not go more than 13-14 mph. Wouldn't rev right up under load.
I replaced the carb with a brand new one. And bingo, 24 MPH (18-21 mph fully loaded with water fuel kids and overnight gear).
The prop is a 15x15. I wouldn't change it.


This is good info for the OP, not sure if his new engine came equiped with a new carburator or not but it's possible a fuel delivery issue is causing the poor performance.

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Dave
Edmonds, WA
"THE FIX"
'93 2556 5.7 Bravo II 2.0:1 18 1/4x19 P
.030 over-Vortec top end-part closed cooled
***The rebuild of my 2556***
www.baylinerownersclub.org/index.php/for...ansom-repair-my-2556

2556 - Alpha Drive Owners, please confirm RPM VS. Speed 09 Sep 2017 20:51 #13

  • Landin
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Yup... brand new carb.

I'm having a mechanic sea trial it this upcoming week.....some interesting info... boat mechanics boss said the matched ratio drive for my engine is a 1:67 and currently my drive is a 1:47...

....a bit of history on the boat - approx.14 months ago the engine and engine components were replaced new.... then about 1 week later the drive seized....so the shop ordered and installed a new drive ( 1:47 ratio, alpha gen 1).... now I am assuming the shop whom ordered the new drive (same shop purchased and installed the engine) should have spec'd the correct drive for the engine they installed, right!?????

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BOAT: 1991 - Bayliner 2556 Ciera Flybridge
ENGINE: 357 Alpha 4V (275HP)
OUTDRIVE: Alpha Gen 1
RATIO: (to be updated)
PROP: 15 1/2" X 15P
NAME: "Knotty Oar"

Marine Search and Rescue Crew - rcmsar.com/rescue-stations/southern-region/north-vancouver/
Last Edit: by Landin.

2556 - Alpha Drive Owners, please confirm RPM VS. Speed 09 Sep 2017 21:07 #14

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What speeds were you getting before the original new drive seized? Or did you purchase the boat after?
Yes shop should have replaced it with the same ratio unless they were instructed to do different :S . So you thinking it's a ratio issue then? I hope you get it figured out, I made a run today at 3700 RPM @ 28 MPH

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Dave
Edmonds, WA
"THE FIX"
'93 2556 5.7 Bravo II 2.0:1 18 1/4x19 P
.030 over-Vortec top end-part closed cooled
***The rebuild of my 2556***
www.baylinerownersclub.org/index.php/for...ansom-repair-my-2556
Last Edit: by builderdude.

2556 - Alpha Drive Owners, please confirm RPM VS. Speed 10 Sep 2017 00:09 #15

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your boat mechanic's boss has been smoking tough... 1.67 gear ratio doesn't even exist.
correct gear ratio 1.65 GEN 1 OR 1.62 GEN 2 IS NOT for your engine, this gear ratio is for lower HP 5.0.
Once again you stated that you have a GEN 1 1.47 on her... 1.47 not even available on GEN 1.

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Joon, Kathy, Jaden & Tristan
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92 2855
91 Fourwinns 205
Longbranch WA
Life is Good

2556 - Alpha Drive Owners, please confirm RPM VS. Speed 10 Sep 2017 03:15 #16

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How is the gen 1 or 2 identified? Are they visually different somehow?

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Dave
Edmonds, WA
"THE FIX"
'93 2556 5.7 Bravo II 2.0:1 18 1/4x19 P
.030 over-Vortec top end-part closed cooled
***The rebuild of my 2556***
www.baylinerownersclub.org/index.php/for...ansom-repair-my-2556

2556 - Alpha Drive Owners, please confirm RPM VS. Speed 10 Sep 2017 04:03 #17

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yes
The following user(s) said Thank You: builderdude

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Joon, Kathy, Jaden & Tristan
93 3058
92 2855
91 Fourwinns 205
Longbranch WA
Life is Good

2556 - Alpha Drive Owners, please confirm RPM VS. Speed 10 Sep 2017 08:58 #18

  • MadWill
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At 275 HP I wouldnt be surprised they would use a 1.47 ratio.

My boat was a 5.7 250 with a 1.62 ratio. The engine was upgraded to 350 mpi 300. HP, however left the original ratio of 1.62. It took less than 3 hours to self destruct the upper box.

Replaced under warranty with the stipulation from Mercruiser they would only use the 1.47 ratio. The 1.62 ratio cant handle the torque and are known to have small teeth etc. That is they will self destruct.

I had to drop 2 inches of pitch to compensate for the ratio change.

This is an alpha gen 2.

Cheers Adam

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2005 Trophy 2352 WA
Mercruiser 350 MPI
Located in Brisbane QLD, Australia

2556 - Alpha Drive Owners, please confirm RPM VS. Speed 10 Sep 2017 17:42 #19

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Alphas in general don't do well with 300+ hp, IMO they should have put a B2 behind it.

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Dave
Edmonds, WA
"THE FIX"
'93 2556 5.7 Bravo II 2.0:1 18 1/4x19 P
.030 over-Vortec top end-part closed cooled
***The rebuild of my 2556***
www.baylinerownersclub.org/index.php/for...ansom-repair-my-2556

2556 - Alpha Drive Owners, please confirm RPM VS. Speed 10 Sep 2017 20:01 #20

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Me too, I would love to have a B2 behind my 300HP. I bought it with the 300HP and Alpha 1 leg though.

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2005 Trophy 2352 WA
Mercruiser 350 MPI
Located in Brisbane QLD, Australia

2556 - Alpha Drive Owners, please confirm RPM VS. Speed 11 Sep 2017 01:54 #21

  • hfxjack
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How are you measuring speed?

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John McLellan White Rock BC
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1999 2855 383 stroker BII
MMSI 316004337

2556 - Alpha Drive Owners, please confirm RPM VS. Speed 05 Oct 2017 20:14 #22

  • Landin
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Navionics - SOG

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BOAT: 1991 - Bayliner 2556 Ciera Flybridge
ENGINE: 357 Alpha 4V (275HP)
OUTDRIVE: Alpha Gen 1
RATIO: (to be updated)
PROP: 15 1/2" X 15P
NAME: "Knotty Oar"

Marine Search and Rescue Crew - rcmsar.com/rescue-stations/southern-region/north-vancouver/

2556 - Alpha Drive Owners, please confirm RPM VS. Speed 05 Oct 2017 20:25 #23

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UPDATE:

The shop that installed the new engine and the new alpha drive indicated they just matched the old drive ratio of 1:47 and installed the new one. The shop has just offered to swap out the 1:47 to a 1:65; I pay for the haul out/in and labour and the shop will cover the 1:65 drive (no warranty). My concern here is the torque of the engine destroying the gears… thoughts?

One corrective action path I would like to try is to buy a 13P prop and see if that offers any improvement.

Also, the current 15P prop does look to be very old and I wonder if the prop is aged and flexing, not giving me the right output?

Really trying to test out some low costs options before hauling the boat….

Thank all!!!

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BOAT: 1991 - Bayliner 2556 Ciera Flybridge
ENGINE: 357 Alpha 4V (275HP)
OUTDRIVE: Alpha Gen 1
RATIO: (to be updated)
PROP: 15 1/2" X 15P
NAME: "Knotty Oar"

Marine Search and Rescue Crew - rcmsar.com/rescue-stations/southern-region/north-vancouver/

2556 - Alpha Drive Owners, please confirm RPM VS. Speed 06 Oct 2017 00:34 #24

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How did the boat perform before the engine/drive replacement? Or did you purchased the boat as a project?
Did you get confirmation on weather this is a gen 1 or gen 2 drive?
It's sounds like the drive ratio of 1.47:1 is correct, personally I'd want to test some different props before anything els. Seems like the shop that Installed the engine/drive combo would help out with this :S

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Dave
Edmonds, WA
"THE FIX"
'93 2556 5.7 Bravo II 2.0:1 18 1/4x19 P
.030 over-Vortec top end-part closed cooled
***The rebuild of my 2556***
www.baylinerownersclub.org/index.php/for...ansom-repair-my-2556

2556 - Alpha Drive Owners, please confirm RPM VS. Speed 06 Oct 2017 05:40 #25

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Hi Dave,

Yes a project, but was operational when I first bought it .. because it was an older engine and this was my first ocean vessel, I never opened it wide open and got such a good deal on it an ocean trial was not required...

What would your first move be ?

A) replace the 15 × 15p prop that's on the boat now to ensure there is no flex/ its a very old prop

B) try a 14 × 14p prop

C) try a 13 x 13p prop

D) new transom assembly and find a good / used bravo drive? $$$$$$$$

On goes the journey...

Next week, I'm gonna reach out to Mercury and see what thay advise.....this just all seems so strange....

THX!!!!

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BOAT: 1991 - Bayliner 2556 Ciera Flybridge
ENGINE: 357 Alpha 4V (275HP)
OUTDRIVE: Alpha Gen 1
RATIO: (to be updated)
PROP: 15 1/2" X 15P
NAME: "Knotty Oar"

Marine Search and Rescue Crew - rcmsar.com/rescue-stations/southern-region/north-vancouver/
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