View Full Version : Mercruiser 357 Alpha 4v vs 357 Mag Bravo 4v

07-19-2012, 10:12 PM
Hi Folks,
I'm trying to understand why the Mercruiser 357 Alpha 4v is rated at 275 HP, while the Mercruiser 357 Mag Brave 4v is rated at 325 HP. Does anyone understand this? Can you explain it to me?

They both have the same bore and stroke, and the same compression ratio..... I'm puzzled.

The reason I ask is that I need to replace my engine, and I found a 357 Alpha 4v that I can afford. It was advertised as a 357 Mag (so I assumed it was a bravo setup), and I now realize it is the Alpha setup. Other than an engine coupler and adding the raw water pump, would I actually be losing 50 HP with this engine versus one originally setup for Bravo? I don't see the difference aside from the drive itself, the coupler and the water pump....

Let me know if this 50 HP apparent difference from the specs will really be there if I were to hook this engine up to my bravo drive....

Don Banfield

ps: any of you donzi brethren near Surf City NJ, and willing to look at this supposedly nearly new engine with me on Saturday (July 21, 2012) ~2PM?

07-20-2012, 05:36 AM
For starters, the carb is detuned to keep the alpha under the 300 HP max rating it's designed to handle + there is a differents between the two ignition control modules + the camshaft is different.

There are a few notable differences in part numbers like for example, The carb part number, Primary metering jets, metering rod kit, accelerator pump plunger kit, ignition control modules, Longblock Assembly, Shift Bracket, Standard Cooling System, belt, camshaft, Coupler and related parts, Mercathode Components.:wrench::)

Carburetor, Four Barrel, Bravo found here,

And Carburetor, Four Barrel, Alpha found here,

And the whole engine for everything else listed,

07-20-2012, 07:09 AM
The 275 is a replacement for the older 350 260hp, I can give a little info on these 357's but I am not sure about the HP differences. Probably just cam and carb. The real scoop on the 357 is the blocks are delivered incomplete as 350's Merc bores them out to 357 this is done to beat CARB rulings on catalytic converters. All completed engines delivered to any marine manufacturer must be equipped with a converter, the risers are rumored to cost over $1,000 each and will have a life span. This will be pushing engine prices to the moon overtime. I got the skinny on this last week when I sold a my first 357, at first I thought they were re-mans why else bore a new block.


07-20-2012, 09:06 AM
I think, like MOP said, The only difference is the cam. The carb is listed differently but it's still a 750 weber, I am guessing it's just jetted differently to handle the smaller cam.

The compression, pistons, rockers, intake, exhaust, etc. are all the same. I'm guessing the price difference is actually to handle the Bravo water pump. If you are hooking it to a Bravo you'll need to figure out the water pump, brackets, and longer serpentine belt.

07-20-2012, 11:23 AM
Merc only rates the Alpha for up to 300 hp. So if you have the alpha setup, they probably de-tune the engine accordingly. So, my guess is that you could get the lower hp engine, hook it to an alpha and then bump up the hp through the cam an carb, as stated earlier.


07-20-2012, 11:55 AM
that cam isn't 50 hp :bonk:

07-20-2012, 12:30 PM
The cams used between the two seems to be the same as the standard 350 Mag line over the years.

In a nutshell, the 275 version uses the cam from the old 350 / 260HP; The 325 version uses the same cam as the newer 350 / 300hp.

(the 383 / 350 HP reman uses a cam out of an old 350 inboard designed for ski boats)

Maybe merc is just a bit aggressive in the marketing on the 325 version and it should be 315? I dunno.

07-20-2012, 02:31 PM
Ahhhhh.... of course. the cam.
Seriously, thanks a lot for the insight. With the info you guys gave me, I decided to try renegotiating on the engine, and they said no. So the deal is off. If it really is 45 HP less than I thought, then it simply isn't worth as much to me.

I did finally dig up a link from Mercruiser that indicated the cam difference:

if you scroll down to page 12 of the catalog (page 20 of the PDF), it lists the detailed specs of the 357 Alpha 4V and the 357 MAG Bravo 4V. The key difference is the Alpha version only lists "Roller Camshaft", while the Bravo version lists "High-Lift Roller Camshaft". So I guess that very subtle difference explains the 45 HP?

Thanks again!

Don Banfield
Fingerlakes, NY
22' Classic (1983).... now with a blown 454.

07-20-2012, 10:54 PM
Main differences are the cam, carb jetting, timing and rpm.
The main factor that you MUST address is what drive are you running behind it.
The Bravo 357 WILL NOT have the shift interupter programed in the ICM. So if you plan on using it in front of an alpha you will have to change the ICM to the alpha ICM.