5.7LX rebuild question

[AKJohne]

The 325 is a mercruiser crate engine intended for bravo drives. The silver package is a partial engine MM puts together from a new base engine. If you have an alpha drive the 325 hp one wont work due to lack of shift interrupt with the bravo TBV ignition module. I think merc makes a 300 hp version for the alphas

I will be using all my accessories, including my existing shift plate with shift interrupt. The base 5700 is the same to my understanding. As you ssid MM builds them for different applications. The only real difference is the 750 vs the 600 cfm carb, as I doubt the delco vs TB offers any increased hp. I am ok with the 10 more hp and I think the drive can handle it ok.
Rereading the description makes me think one is a gm and the other is a merc?

 

[Scott06]

I will be using all my accessories, including my existing shift plate with shift interrupt. The base 5700 is the same to my understanding. As you ssid MM builds them for different applications. The only real difference is the 750 vs the 600 cfm carb, as I doubt the delco vs TB offers any increased hp. I am ok with the 10 more hp and I think the drive can handle it ok.
Rereading the description makes me think one is a gm and the other is a merc?

You can use your shift plate, but unless you swap a alpha ignition module for the bravo ignition module the shift interrupt wont work.
if you look into it they (Merc) make these Gen + crate engines in both alpha and bravo configurations with different hp ratings . Same with the alpha bravo 357 rebuilt bobtail engines. alpha is 275 hp, i think the bravo is 325 hp.
i think the cams have different part numbers as seen on part #11 of this page http://www.marineengine.com/parts/m...000-up/cylinder-block-camshaft-and-crankshaft

carbs also have diff part numbers between the alpha and bravo as well, both 750 cfm webbers (same as edlebrock) but probably different jetting and step up rod sizes. I suspect between cam, carb, and ignition curve you get the difference in power between alpha and bravo se ups.

will an alpha handle a few more ponies, likely if you don’t hammer it or get the prop out of the water. You just need an alpha ignition module or to use the delco set up.

 

[AKJohne]

You can use your shift plate, but unless you swap a alpha ignition module for the bravo ignition module the shift interrupt wont work.
if you look into it they (Merc) make these Gen + crate engines in both alpha and bravo configurations with different hp ratings . Same with the alpha bravo 357 rebuilt bobtail engines. alpha is 275 hp, i think the bravo is 325 hp.
i think the cams have different part numbers as seen on part #11 of this page http://www.marineengine.com/parts/m...000-up/cylinder-block-camshaft-and-crankshaft

carbs also have diff part numbers between the alpha and bravo as well, both 750 cfm webbers (same as edlebrock) but probably different jetting and step up rod sizes. I suspect between cam, carb, and ignition curve you get the difference in power between alpha and bravo se ups.

will an alpha handle a few more ponies, likely if you don’t hammer it or get the prop out of the water. You just need an alpha ignition module or to use the delco set up.

Scott,
My Mistake as I thought the 325 HP Merc was based on a GM 5700, however I see now it is Merc product. I plan to order the 5700 next week and will use my accessories, including the 750 Weber and TB V.
Actual HP..... who knows.... maybe MM knows. I assume it will at least 315 as that is how MM rates it with the Delco and 600 CFM carb. The cam in my existing motor was also used in some Bravos and here is 325 Merc for a Alpha....
https://www.michiganmotorz.com/mercruiser-350-mpi-alpha-complete-engine. I understand now what you are saying about the diffs in the dist (module)between A & B.
W/O getting cam specs I will never know the exact difference, and doesn't really matter as I am only interested in having the same or (hopefully) slightly more (HP) than my existing 5.7 LX. And assuming the Vortec heads will accomplish that. My Motor was not original, it was a pieced together by the PO. and made decent power. I will plan on doing some plug readings once I get it back in the water and may even spring for a O2 sensor..

 

[AKJohne]

I ordered a new 5.7 long block from Michigan Motorz today, I considered the 6,2, however they did not have any in stock and did not have any rebuildable blocks as I considered a reman.
The 5.7 has the 062 heads and the 6200 has 906 heads with Iconel seats. I debated long and hard on that one as I think heads are the weak point and as Chris pointed out, propping is critical. Supposed to shop in the 22nd and plan on 2 weeks to Alaska maybe more, will plan to do over the holidays as I usually take some time off and can get the boat ion the shop.
MM did not have much a of a selction on intakes and I spoke Edelbrock and they suggested a 2716 https://www.edelbrock.com/performer-eps-vortec-intake-manifold-27163.html.
They said it would be better out of the hole and more midrange than the 2516 which is more of a top end intake.... what say you fellahs...?

 

[Scott06]

I ordered a new 5.7 long block from Michigan Motorz today, I considered the 6,2, however they did not have any in stock and did not have any rebuildable blocks as I considered a reman.
The 5.7 has the 062 heads and the 6200 has 906 heads with Iconel seats. I debated long and hard on that one as I think heads are the weak point and as Chris pointed out, propping is critical. Supposed to shop in the 22nd and plan on 2 weeks to Alaska maybe more, will plan to do over the holidays as I usually take some time off and can get the boat ion the shop.
MM did not have much a of a selction on intakes and I spoke Edelbrock and they suggested a 2716 https://www.edelbrock.com/performer-eps-vortec-intake-manifold-27163.html.
They said it would be better out of the hole and more midrange than the 2516 which is more of a top end intake.... what say you fellahs...?

2516 is a performer rpm manifold. The performer rpms are indeed intended for higher rpm applications ( aka not basically stock marine) than the standard dual plane, basically a bridge between historically dual plane and single plan intake rpm ranges.
yes go with the eps manifold, will be better suited to your application.

 

[AKJohne]

I have been on the hunt for a manifold and I think I have one pinned down. Considering comments made about tuning and mostly concerned with a potential lean condition. I am considering a AFR gauge, maybe not a permanent install and maybe just one side. I can read plugs, however I thought this might be helpful. I understand the "ideal" numbers in regards to stoichiometric ratio of 14.7:1.
My question is, is this appropriate for a cruise RPM of ~ 3300? Intuitively I would think it should be slightly rich at those RPMs... I have searched for this on WWW and not finding any answers. What say you guys or should I post this query elsewhere on I BOATS?

 

[nola mike]

I have been on the hunt for a manifold and I think I have one pinned down. Considering comments made about tuning and mostly concerned with a potential lean condition. I am considering a AFR gauge, maybe not a permanent install and maybe just one side. I can read plugs, however I thought this might be helpful. I understand the "ideal" numbers in regards to stoichiometric ratio of 14.7:1.
My question is, is this appropriate for a cruise RPM of ~ 3300? Intuitively I would think it should be slightly rich at those RPMs... I have searched for this on WWW and not finding any answers. What say you guys or should I post this query elsewhere on I BOATS?

That's the right ratio unless you're at WOT. that being said, there aren't any easy options for installing an Afr gauge afaik...

 

[AKJohne]

That's the right ratio unless you're at WOT. that being said, there aren't any easy options for installing an Afr gauge afaik...

I ordered one of these https://www.michiganmotorz.com/o2-spacer-stock-mercury-riser-wet-joint
Will swap out one of my 4" risers for a 3" and the O2 plate. Which side runs hotter on a SBC?

 

[Scott Danforth]

Which side runs hotter on a SBC?

the one that is higher in the boat. if your boat lists to port, uses starboard. if your boat lists to starboard, use port

 

[Scott06]

An excerpt from this page- https://www.innovatemotorsports.com/resources/marine-carb.php

A starting point for air/fuel mixtures for most performance marine engines is:

Idle:�� 14.1-13.4 to 1 air/fuel mixture

Cruise/light loads rpm 14.2 �14.0 to 1 air/fuel mixture

Power mixture and acceleration: 12.5 to 1 is the ideal air/fuel mixture for a �normal� engine, but many marine engine builders prefer a 11 or 11.5 to 1 power mixture; a high performance engine with improved combustion chamber design such as a Pro-Stock or a Winston Cup engine, which are being used in some of the top offshore race boats, can use a slightly leaner power mixture of 13.0 to 1 air/fuel ratio. A supercharged engine can use a power mixture richer than 12 to 1 as a method to help control the detonation that can be caused by the higher cylinder pressures.

Keep in mind in a marine application with wet exhaust- the heated O2 sensors tend to have shorter lives. I recall reading somewhere that they only recommend using them for tuning. You can buy plugs to plug the sensor port or maybe use an dead sensor off a car.

 

[AKJohne]

An excerpt from this page- https://www.innovatemotorsports.com/resources/marine-carb.php

A starting point for air/fuel mixtures for most performance marine engines is:

Idle:�� 14.1-13.4 to 1 air/fuel mixture

Cruise/light loads rpm 14.2 �14.0 to 1 air/fuel mixture

Power mixture and acceleration: 12.5 to 1 is the ideal air/fuel mixture for a �normal� engine, but many marine engine builders prefer a 11 or 11.5 to 1 power mixture; a high performance engine with improved combustion chamber design such as a Pro-Stock or a Winston Cup engine, which are being used in some of the top offshore race boats, can use a slightly leaner power mixture of 13.0 to 1 air/fuel ratio. A supercharged engine can use a power mixture richer than 12 to 1 as a method to help control the detonation that can be caused by the higher cylinder pressures.

Keep in mind in a marine application with wet exhaust- the heated O2 sensors tend to have shorter lives. I recall reading somewhere that they only recommend using them for tuning. You can buy plugs to plug the sensor port or maybe use an dead sensor off a car.

Thanks Scott, thanks the info I have been searching for. I have been debating with myself whether to make a permanent install or just use as a tuning tool as I have also heard sensor's have short lives in marine applications.

 

[AKJohne]

the one that is higher in the boat. if your boat lists to port, uses starboard. if your boat lists to starboard, use port

 

[AKJohne]

Thinking about tuning this carb and Merc did some tricky bizness with 3 step rods and a low step main jet in my Weber ( 9781S 3106). I think I need to buy a assortment of Edlebrock/Carter springs, rods and jets .... but what size to buy?
Mikes Carburetors says they dont have a direct conversion for the Merc rods/jets. I assume any EB 750 CFM marine setup would be a good starting point?

Ideas?

 

[Scott06]

Thinking about tuning this carb and Merc did some tricky bizness with 3 step rods and a low step main jet in my Weber ( 9781S 3106). I think I need to buy a assortment of Edlebrock/Carter springs, rods and jets .... but what size to buy?
Mikes Carburetors says they dont have a direct conversion for the Merc rods/jets. I assume any EB 750 CFM marine setup would be a good starting point?

Ideas?

Edlebrock parts will fit in the weber carb, they are the same carb. https://www.edelbrock.com/pub/media/wysiwyg/documents/carb-owners-manual.pdf

is the edlebrock carb bible you should be able to use calipers to figure out your step up rod sizes and see what edlebrock rod and jet combo will make you richer or leaner As needed.

merc used both two and three step rods so probably one is not superior to the other .

here is a calibration kit for 1410 carbs which is the weber 750 cfm merc used

 

[AKJohne]

Edlebrock parts will fit in the weber carb, they are the same carb. https://www.edelbrock.com/pub/media/wysiwyg/documents/carb-owners-manual.pdf

is the edlebrock carb bible you should be able to use calipers to figure out your step up rod sizes and see what edlebrock rod and jet combo will make you richer or leaner As needed.

merc used both two and three step rods so probably one is not superior to the other .

here is a calibration kit for 1410 carbs which is the weber 750 cfm merc used

I was going to order the 1408 kit, I guess the question is, will the two step rods work with the low step jet? (That's what Mikes C. refereed to it as).
I kinda assume they will, I just need to pay attention to whats going on.
I have the bible and have read through it several times.
I did find the factory rods/jets for a 1410 marine.

 

[nola mike]

I was going to order the 1408 kit, I guess the question is, will the two step rods work with the low step jet? (That's what Mikes C. refereed to it as).
I kinda assume they will, I just need to pay attention to whats going on.
I have the bible and have read through it several times.
I did find the factory rods/jets for a 1410 marine.

What's a low step jet? Afaik, a jet is a fixed orifice...

 

[AKJohne]

What's a low step jet? Afaik, a jet is a fixed orifice...

"low step" is what the guy ate mikes Carb called it last year when I was looking for some replacement rods while rebuilding. I did not ask him what he meant but I will find out. I did find some NOS quicksilver rods/springs/pistons and used those last season.
Maybe overthinking this whole thing winter is here and excited about getting a new motor. Trying to avoid lean condition by learning now and getting what I need to tune it..... heck maybe the Weber will be fine on the new motor... I just dont want to be in a position where I have a trip planned and need parts and have to order them. Where we boat is pretty isolated and we are 375 miles form there as I live in the interior....

I appreciate the help I get here, always seems to be spot on and have learned along the way. I try to pay it back now and then with what I have learned.

 

[nola mike]

I'd call Edelbrock and see what they recommend for a tuning kit (or look at the tubing Bible to get in range). Michigan motorz is another good source; I'm too lazy to Google, but if they offer the Edelbrock on their crate engines, ask what they use for jetting.

 

[AKJohne]

I'd call Edelbrock and see what they recommend for a tuning kit (or look at the tubing Bible to get in range). Michigan motorz is another good source; I'm too lazy to Google, but if they offer the Edelbrock on their crate engines, ask what they use for jetting.

Good idea on MM