357 Mag Bravo 4V Reman, Just Installed, 325HP, WORSE then old engine @ 260HP!!! ??

[sub2010ss]

And this is why I like doing my own work.

 

[Fun Times]

So yup, your OE 350 EFI motor had 260 propshaft HP, so it had around 300 at the flywheel. The reman 357 carb is rated LESS. It's 275 at the flywheel. So there's maybe 235 getting to the propeller. Not 325. See the link. https://www.mercurymarine.com/en/us/...a-sterndrives/
You were sold a smaller output engine unless there's something we don't know about it.
Scream bloody murder.

Correction!
You found/linked the 357 Alpha engine rated for 275, Orbitter (Says he?) bought the 357 Bravo engine rated for 325 at the flywheel.

Knowing the gear ratio may help plus check the basics such as is the throttle cable opening up the carb all the way, did the celery stick at the trim ram pin get installed in the correct position affecting the drive height while trimmed down for take off, dual props are timed correctly, dose the service shop have a propeller shaft dyno and a spare bravo one drive to test engine output power to see if the engine is in range of engines of similar power, pull some spark plugs to ensure the engine seems to be running correctly, fuel pressure, timing is advancing.

https://www.mercurymarine.com/en/us/...ive/compare/?e[]=1255&e[]=1256

275 / 205 Alpha

325 / 242 Bravo

 

[Orbitter]

I will go out and look at my drive here shortly.

 

[Orbitter]

Not positive but, it says "Serial Number 2.20R 0L********"
I'm guessing that means 2.20:1
It's stamped in the drive right near the top on the port side.


And you are correct, it is a 357 Mag Bravo 4V from Mercury Remanufacturing.
It's got a identification plate on the starboard side of the engine block confirming the same, with serial#, part# etc...

 

[Bondo]

Ayuh,..... Before ya throw away the baby with the bath water, do the test I mention in post # 19,....

 

[HT32BSX115]

Not positive but, it says "Serial Number 2.20R 0L********"
I'm guessing that means 2.20:1
It's stamped in the drive right near the top on the port side.


And you are correct, it is a 357 Mag Bravo 4V from Mercury Remanufacturing.
It's got a identification plate on the starboard side of the engine block confirming the same, with serial#, part# etc...

Do you remember what your full throttle RPM and speed (on plane, trimmed for max speed) was with the previous engine installed?

 

[Orbitter]

Well I always thought the 350 efi motors were rated 300 crank horse power. Was your 260 rating at the prop, I bet it was. So if the 357 is 325 crankshaft horse that makes a little more sense.
I bet you need to use the shorter props to allow it to run and not get hot from lugging, also it will make more power at higher rpm, and it will holeshot better. You stated that it started doing the same thing as before when you had the 24's on. Was it weak, or overheating?
That motor can run to 5000 rpm, won't hurt a thing, but over propping it will over work it and shorten it's life.
I will take a browse through the Merc reman catalog and read up on the Merc spec cam if I can find it. I'll come back and bore you all with some tech gobbledygook if I can figure it out.

Has any one checked the fuel supply? Timing? Carburetor setup? Boat weight? Are you certain the boat isn't heavier than it used to be?

I personally have not but the dealer "said" they did. As far as boat weight, it is most certainly lighter then before because I have removed everything. Kitchen stuff, blankets, cleaners, oils etc... It's empty now.

You stated that it started doing the same thing as before when you had the 24's on. Was it weak, or overheating?

Loosing power while trying to plane if throttle advanced past 3/4.

 

[Orbitter]

Do you remember what your full throttle RPM and speed (on plane, trimmed for max speed) was with the previous engine installed?

Unfortunately I don't remember exactly. I know we would cruise around at 35-3800 and that was at about the same throttle position as what I am refering to now on the new engine as being 3/4.
What I mean is, the throttle handle is at 12 o'clock off, 11-11:15 in gear at idle and 9 o'clock WOT.
I have it at around 9:45 to 10 o'clock when I'm referring to 3/4 throttle. So it may actually be closer to 2/3 throttle. If that helps.

It does have more power then before once up on plane. Just to clarify, but getting there (on plane) is certainly more labor intensive!

 

[Orbitter]

Ayuh,..... Before ya throw away the baby with the bath water, do the test I mention in post # 19,....

I will try and do that today (Try).

 

[NHGuy]

glad I got the wrong info for your sake!

 

[JustJason]

Just out of curiosity has the dealer done a compression test or done a cylinder drop test? Misadjusted valves on reman motors happens all the time, and it only takes 1 tight rocker on an exhaust valve to give you a low/no compression scenario. You wouldn't have any other symptoms other than the engine feels a little wimpy. The same thing if you have 1 bad plug wire, or 1 bad plug and a cylinder isn't firing. A V8 will still run very well on 7 cylinders, and still have lots of power.... But it won't have "all" the power it should have, and feel a little wimpy.

 

[kbsunlovers]

FWIW, I'm inclined to agree with achris here (post #10) the behavior sounds a lot like overcarburation or secondaries opening too soon. 750 cfm may be a bit much in this application. My opinion the 600 cfm carb would deliver a more usable powerband with little or no loss in WOT power.

 

[HT32BSX115]

Unfortunately I don't remember exactly. I know we would cruise around at 35-3800 and that was at about the same throttle position as what I am refering to now on the new engine as being 3/4.

It does have more power then before once up on plane. Just to clarify, but getting there (on plane) is certainly more labor intensive!

Ok,

Well, throttle position is not even relevant before or now really.......

I suspect you were over propped before..............

Once you ensure that the valves, timing (knock sensor) and fuel delivery are correct, do a WOT(wide-open-throttle) run with the boat lightly loaded and adjust the trim for MAX RPM/Speed.

Note your RPM and speed (use a GPS speed, phone, etc)

Once everything is running right, select a prop-set to give you MAX RPM (or close to it) (5000-5200RPM for that engine?)

Just found this @ http://forum.chaparralboats.com

I have been "testing" my new 2004 Sig. 240 and think that my prop needs replacing:
Mercruiser 350 mag with Bravo III, 2:20 gear ratio.

3/4 tank gas, two people

WOT ~ 5400 rpm (manual says it should be 4800-5200)

44 mph at 5400 rpm (WOT)
28 mph at 3600 rpm

Currently have 22p props. I filled out the info at the mercruiser site and it came back with a 24p prop. This sound reasonable? What are all you 240 captains getting out of your boats and with what prop?

I'd say 26p props are a little "tall"


Let me also add that I have 26p Props on the (1.8:1) Bravo III I have in my 21' Four Winns 211 Liberator.

My best WOT (trimmed, lightly loaded) speed is 57mph @ 4600RPM. MAX RPM for a 454 IS 4600RPM.

 

[achris]

FWIW, I'm inclined to agree with achris here (post #10) the behavior sounds a lot like overcarburation or secondaries opening too soon. 750 cfm may be a bit much in this application. My opinion the 600 cfm carb would deliver a more usable powerband with little or no loss in WOT power.

I didn't realise it was running a 750cfm carb. Yeah, way too big. Here's a 'snip' of the Summit racing website carb CFM calculator. Ignore the 'racing' number, but look at the street value. Indicates a 600cfm is more than adequate...

 

[Orbitter]

Oops, copy paste didn't work for the new engines specs...

 

[Tail_Gunner]

I didn't realise it was running a 750cfm carb. Yeah, way too big. Here's a 'snip' of the Summit racing website carb CFM calculator. Ignore the 'racing' number, but look at the street value. Indicates a 600cfm is more than adequate...

Good catch someone has bigger is better. Why would merc dump a 750 on that engine???
And while were at it.. a very accurate tool for speed measurement
http://www.go-fast.com/boat_speed_predictions.htm

 

[Orbitter]

Just out of curiosity has the dealer done a compression test or done a cylinder drop test? Misadjusted valves on reman motors happens all the time, and it only takes 1 tight rocker on an exhaust valve to give you a low/no compression scenario. You wouldn't have any other symptoms other than the engine feels a little wimpy. The same thing if you have 1 bad plug wire, or 1 bad plug and a cylinder isn't firing. A V8 will still run very well on 7 cylinders, and still have lots of power.... But it won't have "all" the power it should have, and feel a little wimpy.

To my knowledge they have not. Or have not mentioned it upon questioning.

 

[Orbitter]

That CFM calc makes me wonder what merc was thinking when they reman'd the engine and put a 750 cfm Weber on it.

Heading to the lake now to run some tests. Will report back this evening.

 

[skippy2235]

What needs to be mentioned is take a temp of each exhust port, should all be equal about 200+ F. Use a cheap harbor frieght infarded thermomentor.
just poit at the manifold near each port.

 

[Orbitter]

Ok, here goes...

Took it out, 4 adults & 5 kids. Struggled to get up on plane at any trim setting/angle. Eventually would plane and as soon as it got up it would take off and you could feal the power kick in but the old engine would get up on plane with more then twice the weight in people and camping gear. Same props as before.

Max RPM @ WOT was 4900 with some slight up trim on the outdrive and just barely 50 MPH according to GPS. Took about 5 min to hit 50 but with just the right trim we hit 50.

Here is a video and I'll post some photos of the spark plugs down below.
I pulled all the plugs mid outing to see what they looked like. All but cylinder 7 looked a tad on the white side imo...
These plugs now have 10 hours on them. (That's how many are on the reman'd engine.
Have not done a compression or leakdown test yet, but will hopefully tomorrow, as well as the temp readings on the manifolds.

Thought I would shoot a video to help show the wimpy power.