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

[Orbitter]

Ok, so we just bought a Mercruiser Remanufactured 357 Mag Bravo 4V Complete Engine from our local Mercury Dealer.
The old engine was the stock engine for our boat, a 350 EFI @ 260HP, Chaparral Signature 240 with a Bravo 3 drive & 26" pitch props.

First time out we had the same problems that made us buy a new engine to begin with. Not enough power to get out of the hole quickly
and overheating!
Would barely get up on plane, and once up overheated within 1 minute! Before, with the old engine it would jump out of the water when I was
on it solo, and would then overheat about 10min later.

Took it back to the dealer, they discovered the fresh water intake passage (Tapered Plastic Insert) collapsed (Or so they surmised) so installed a bypass cooling system. Also discovered the carb (Fresh from Mercury Remanufacturing) was flooding the starboard side intake manifold. So they did warranty exchange and got another carb.

At this point they ALSO installed 20" pitch props. We took it out and yes, it certainly gets up faster then with 26's but way under propped. Took it back and had 24" pitch props put on and took it out and it is better but now it's starting to act as before.

Put our original 26" pitch props back on and took it out yesterday evening. Lack of power getting on plane is back. Tried with various trim settings/angles and no improvement, trim up at all and it just got worse. Though at top speed it would pick up about 200 rpm and about 1-2 mph with just slight trim up from full down.

So, ever since getting the new engine, when taking off, power will increase up to about 3/4 throttle. Once pushed past 3/4, power/propulsion & RPM decrease.
RPM's go down about 300 to 2200-2300 rpm vs the 2400-2600 rpm when @ 3/4 throttle. As soon as it gets up then rpm improves greatly and can push 5000 @ full throttle.

So, they are trying to tell us that we need to install trim tabs (Which wouldn't be a bad idea but) and we need to DOWN PROP to 22.5" pitch props.
And that is why I am here.

KEY NOTES:
This is a 99 Chaparral Sig 240, Bravo 3 Drive, 26" pitch props, Bone Dry with just myself & 1/2 tank of fuel on board.
Stock engine 350 EFI (Not the MAG MPI Engine) @ 260HP would push right up on plane NO PROBLEM and quickly.
New engine is 357 Mag Bravo 4V @ 325HP and gets up but SLOWLY, and with 3 adults and 5 kids about 10 yrs old would BARELY GET UP!
Took about 100 yards to get up on plane. With just myself it will get up but is most certainly SLOWER then before with the old engine.

And of course any throttle past 3/4 and it gets worse.

What's going on here? How is it that with an extra 60HP it is harder to get up. The old engine would get us up even when FULLY loaded and actually we were slightly overloaded a few times and with everyone going to the front of the cabin (The big people) it actually would still get up. Had 10 adults, 5 kids AND camping gear.

I have set an appt to get it looked at by the other Mercury dealer here in town but that is 2 weeks out on the 29th.
In talking with the other dealer they seem to think that something is NOT setup correctly and I tend to agree with them.

Again, the dealer that installed the new (Factory Reman Engine) is telling us that the problem is because we are OVER propped and we need to down prop to 22.5" props and THAT is what our problem is! My response to that is (What the hell are they smoking!)

That's all I can think of mentioning at the moment. If you need any more details I can provide them if asked.

Thanks for any help that you may have to offer.

p.s. They also have not submitted the warranty paper work to Mercury yet (I called Mercury) and they also did NOT do the Pre Delivery Inspection Checklist form and give that to me at time of delivery. I have the checklist but it is Totally Empty!

 

[Bt Doctur]

big block power out of a small block motor?????????????????????????????? 26 pitch IS WAY TOO BIG
What is you gear ratio now?
compatable drive are listed as
Bravo One 1.50:1
Bravo One 1.65:1
Bravo Two 2.00:1
Bravo Two 2.20:1
Bravo Two 2.43:1
Bravo Three 2.00:1
Bravo Three 2.20:1
Bravo Three 2.43:1

 

[81 Checkmate]

Is the boat waterloged? Has it always done this?

 

[Tail_Gunner]

big block power out of a small block motor?????????????????????????????? 26 pitch IS WAY TOO BIG
What is you gear ratio now?
compatable drive are listed as
Bravo One 1.50:1
Bravo One 1.65:1
Bravo Two 2.00:1
Bravo Two 2.20:1
Bravo Two 2.43:1
Bravo Three 2.00:1
Bravo Three 2.20:1
Bravo Three 2.43:1

As the Doctor ordered...you need to down pitch to about a 18/maybe 20...Or add about 500hp and that aint cheap ya know what i mean...:laugh:

 

[Bondo]

First time out we had the same problems that made us buy a new engine to begin with. Not enough power to get out of the hole quickly
and overheating!

Ayuh,..... Welcome Aboard,..... Has the boat Ever performed the way you expect it too,..??..??

How long have ya owned it,..?? need some back-story,...

The over heatin' shoulda been takin' care of before, or durin' the motor swap,.....

 

[HT32BSX115]

Ok, so we just bought a Mercruiser Remanufactured 357 Mag Bravo 4V Complete Engine from our local Mercury Dealer.
The old engine was the stock engine for our boat, a 350 EFI @ 260HP, Chaparral Signature 240 with a Bravo 3 drive & 26" pitch props.

Did you recently buy that boat? Did you operate it with the above drive/props and engine?

RPM's go down about 300 to 2200-2300 rpm vs the 2400-2600 rpm when @ 3/4 throttle. As soon as it gets up then rpm improves greatly and can push 5000 @ full throttle.

What is your drive ratio?

I seriously doubt it performed very good even with the "correct" ratio drive, (2.00/2.20:1) and 26p props! Do you have a 2.43:1 drive maybe?(even with a 2.43:1 drive, with 26p props, you would see a WOT [max] speed of about 45mph)

What was your performance with the "old" engine? (WOT RPM, and GPS speed?)

 

[r.j.dawg]

I had a 1997 Chap 240 with a 350 Mag EFI/MP Bravo III that came with the same 26p props that you have. I switched to the Gen II Bravo III props, where the inside prop is a 4 blade and the outside one is a 3 blade, and dropped to a 22.5p and it made all the difference in the world.

 

[achris]

Just a thought to consider. You have (roughly) the same displacement engine, but it's producing 65hp more. In engine terms there is always a trade-off between top-end power and low-end torque. You may well have sacrificed a great hole-shot for that extra 65hp, and because the engine's got nothing at the bottom to push the boat onto the plane, it can't ever rev out to the top-end.... Like a car trying to take off up a hill in top gear. Never going to happen! And as boats don't have gearboxes with different ratios, we need an engine with bags of low-end grunt to push up the hill (of water).... The 'sacrifice' is top-end horsepower. Unfortunately, we can't break the laws of physics. The way around your problem (if this is indeed the problem) is to reduce the prop size, significantly, and just live with the engine not being able to be pushed to Wide Open because it'll over-rev...

Just a thought to consider.

Chris........

 

[Orbitter]

Ayuh,..... Welcome Aboard,..... Has the boat Ever performed the way you expect it too,..??..??

How long have ya owned it,..?? need some back-story,...

The over heatin' shoulda been takin' care of before, or durin' the motor swap,.....

Yea, owned it about 4 yrs now and it performed very well even loaded 3/4 capacity. Only above 3/4 capacity (Camping trips) did it have trouble getting up.
And yea, the over heating "SHOULD" have been taken care of as that is the main reason we took it in for repair. The loss of power was just a side problem as it still had power to get up just NOT when loaded with much more then 4 people. And at this time, it was running on 2 cylinders with low compression/Dead!

I am very inclined to agree with achris, not something I had considered before. But that makes total sense because we have the top end power now (Spinning an extra 600 rpm then before with old engine) but has CRAP for low end torque to get out of the hole!

Seeing as the boat came stock with 26" as r.j.dawg stated, and that is what came on it when we bought it. I don't agree that it is over propped. Doesn't make sense.

If you have X horsepower, and you *Increase* that horsepower... According to what physics laws does that translate to Decrease Prop Pitch?
An increase in power always translates to an increase in speed. Period!

Seeing as our bottom end is not very strong but our top end is better... achris unfortunately is on the right track. At least that makes sense. Unfortunately, there is no replacement, for Displacement

That infuriates me! Cooling issue and lack of ability to get out of the hole was why we took the boat in.
So they sell us an engine with less low end torque, and fail to fix the cooling issue!

Sounds like PURE GREED is behind this transaction! :facepalm:

However, that doesn't really explain the lack of power as you go from 3/4 throttle to full throttle while trying to plane and the RPM's decrease by 200-300.
It has more torque at 3/4 throttle while trying to plane then if at full throttle while trying to get up...
Carburetion does however if it has an old tech carb on it. Which it probably does. No Constant Velocity mech built in I doubt.

fyi: if I haven't made it clear (I don't think I did) but at full throttle it will HARDLY get up on plane with 3 people on board.
empty water tank, 1/2 tank fuel and 5 life jackets. All else totally empty.

So, is that a way to verify that? I would imagine (Unless they are hiding something) that mercruiser would publish the engine performance data (HP & Torque Graphs). I suppose that may not be a question for the forum but something I can call mercruiser about directly.

 

[achris]

However, that doesn't really explain the lack of power as you go from 3/4 throttle to full throttle while trying to plane and the RPM's decrease by 200-300.
It has more torque at 3/4 throttle while trying to plane then if at full throttle while trying to get up...
Carburetion does however if it has an old tech carb on it. Which it probably does. No Constant Velocity mech built in I doubt.

Too much air. What you are doing by having the throttle plate at 3/4 is blocking off the size of the carb. I know that sounds obvious, but it has serious ramifications. Let's say the engine is doing 2500rpm with your 3/4 setting. At that speed the engine is trying to pull about 200 cubic feet per minute. Now, it matters little (to the cylinders) whether that air is pulled though a 1 sq in hole or a 10 sq in hole. What DOES change is the velocity of that air. The higher the velocity, the better chance of the air picking up the right ratio of fuel. (Remember the school science experiment with moving air and balloons). If the velocity of the air slows sufficiently, the volume of fuel will also drop, resulting in a weaker mixture, and less.... power/torque....

Chris.....

 

[NHGuy]

So have them check for poor perfomance at WOT. It's a carburetor engine. You want an old school guy setting it up, perhaps a hot rodder or such.

 

[Orbitter]

I wish I could find the performance data on the two engines. The old one 5.7L EFI @ 260HP and our new 357 Mag Bravo 4V.
I have been searching since yesterday so I could compare HP & Torque curves and see if in fact it is lower power at the rpm we're at while trying to plane.
If so, then the dealer sold us an engine that totally did not address our concerns mentioned when we took the boat in.
Not once did we want more top speed. Just something to get us up when loaded. Low end torque.

Anyone know of how to get a hold of those graphs? I would love to go into the dealer prepared with proof cause right now they just think we're crazy and the lack of ability to get on plane is all in our heads! Infuriating!

Talked to them yesterday after reinstalling and testing our original 26" pitch props after trying some 24's and he said the same BS about how I must be delusional!

 

[Bondo]

Anyone know of how to get a hold of those graphs?

Ayuh,.... To the best of my knowledge, that don't exist,.....

For what you were lookin' for, a 383 Stroker motor woulda been My choice,....
Lotsa low end grunt,...

 

[Orbitter]

Yea, that was under consideration and in the end may be what we have to get as the 357 just ain't cutting it for low end torque. Unless we down prop I suppose to get get into the powerband while trying to plane.

 

[HT32BSX115]

Yea, that was under consideration and in the end may be what we have to get as the 357 just ain't cutting it for low end torque. Unless we down prop I suppose to get get into the powerband while trying to plane.

Was this engine a "built" engine by some machine shop, or "Marine" engine rebuilder or is it a Mercury REMAN engine?

A Mercury reman engine would be pretty much what they say it is. An engine built by a machine shop where they "claim" HP or torque might not make the claimed performance especially if they used a NON-marine/RV/truck type camshaft.

Ok.....Just went back and re-read your first post. If it is in fact a MERCURY REMAN engine, It should at least perform as good as the previous engine performed. It shouldn't run worse than the original 260..............If it doesn't, there's something "wrong" with it, your induction and/or fuel system........

Even if you have a 2.20:1 drive, I think it unlikely a 350 cu-in engine would turn 26p props very well........





Looked back through all the posts..........What exactly is your DRIVE RATIO?

 

[NHGuy]

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?

 

[HT32BSX115]

Well I always thought the 350 efi motors were rated 300 crank horse power. So if the 357 is 325 horse that makes a little more sense.

All the newer engines are rated at Propshaft HP. My 1997 454+ Bravo is rated 300 PropHP. I don't know what year they made the switch (from crank-HP) but I am pretty sure it was in either the late 80's or early 90's.

If his original engine is a 1999 (or equiv) That 260 HP number was PROP HP, making the engine probably around 285-300 (crankshaft)HP.

The newer 383's are also rated at 300 propshaft HP I believe. Mercury sold them as "replacements" for the 454 being and claimed the "same" HP at the prop for a considerable weight savings and cost of operation.

 

[Tail_Gunner]

KEY NOTES:
This is a 99 Chaparral Sig 240, Bravo 3 Drive, 26" pitch props, Bone Dry with just myself & 1/2 tank of fuel on board.
Stock engine 350 EFI (Not the MAG MPI Engine) @ 260HP would push right up on plane NO PROBLEM and quickly.
New engine is 357 Mag Bravo 4V @ 325HP and gets up but SLOWLY, and with 3 adults and 5 kids about 10 yrs old would BARELY GET UP!
Took about 100 yards to get up on plane. With just myself it will get up but is most certainly SLOWER then before with the old engine.


26p... 2.20...12% slip =48mph

24p....2.20....12% slip=45mph

22p....2.20.....12% slip =40mph..............................:drum:


24' boat 325hp 5300lbs dry...40 to maybe 45 mph

 

[Bondo]

However, that doesn't really explain the lack of power as you go from 3/4 throttle to full throttle while trying to plane and the RPM's decrease by 200-300.
It has more torque at 3/4 throttle while trying to plane then if at full throttle while trying to get up...

Ayuh,.... The fuel system is a common thing 'tween the motors,.....

If it ain't gettin' the fuel it needs, it'll loose power, as I'm guessin' it's got the T-Bolt V ignition, which has a spark knock sensor, 'n cuts the timin',...

Check the Contents of the fuel filter, throw on a new one, 'n run it on a remote tank with fresh clean gas in it,....

 

[NHGuy]

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...emanufacturing/plus-series-alpha-sterndrives/
You were sold a smaller output engine unless there's something we don't know about it.
Scream bloody murder.