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TOPIC: can we get 250hp from a 200hp Mercruiser 4.5L?

can we get 250hp from a 200hp Mercruiser 4.5L? 22 Apr 2017 20:54 #1

  • dicko
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just left the boatshow with some strange information. I told the Bayliner salesman I wouldn't mind the 250hp 4.5L and he said there is no difference between the 200hp and 250hp. The 200hp's computer module will push the engine to 250hp to get the boat on plane then settle back to 200hp. I never heard such a thing before on any engine, but since he may end up being my dealer for a new VR5 would like some more info on the 'new' Merc 4.5L, anyone else know how the computers work on these engines?

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attempting to purchase a 2017 VR5

can we get 250hp from a 200hp Mercruiser 4.5L? 23 Apr 2017 02:39 #2

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I've sure like to be able to verify if that is true. I've been wondering/asking if there is a conversion available to take the 200 to 250.

Certainly wouldn't hurt my feelings to give it a quicker hole shot.

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can we get 250hp from a 200hp Mercruiser 4.5L? 23 Apr 2017 18:46 #3

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The guy's been smoking tough,
the biggest BS I've heard this year...

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can we get 250hp from a 200hp Mercruiser 4.5L? 23 Apr 2017 21:18 #4

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Getting up on plane is as much about thrust / toque as it is HP. That is why a 4 blade prop will give you a better hole shot, more thrust.

Variable HP. OK, how does the boat know you are trying to get up on step and therefore increase the HP?

Here is the deal, Mercury has been very, very tight lipped about the 4.5 so there are so many "theories" as to the engine. Some claim it is just a 4.3 stroked. Some claim it is a 6.0 with 2 cylinder's chopped off. Who knows for sure about the block. Some things are for certain, the intake and fuel delivery systems are not off the shelf. They have been purposely designed along with service points that make sense for a marine engine.

When it comes to engines you never hear someone saying they wish they had gone with a smaller engine package for their boat. Could there be a chip out there someday for the 4.5 200HP to increase HP and torque, perhaps. Small market may drive the cost so high that it may not be worth making.

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can we get 250hp from a 200hp Mercruiser 4.5L? 23 Apr 2017 21:44 #5

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There is an after market fuel remapping chip for both 200 / 250 already...

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can we get 250hp from a 200hp Mercruiser 4.5L? 23 Apr 2017 23:58 #6

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Your gonna get close with a 4.3L hp wise, way less expensive for parts, they have made the 4.3 l engine for a very, very, long time.

Do a comparison for say a mani or any other part.

Oh by the way who knows how to work on a 4.5l ?

4.3 is a snap in my opinion the best 6 cylinder ever designed.

You want to boat and enjoy yourself or have your boat in the shop all the time.

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can we get 250hp from a 200hp Mercruiser 4.5L? 24 Apr 2017 13:09 #7

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"just left the boatshow with some strange information. I told the Bayliner salesman I wouldn't mind the 250hp 4.5L and he said there is no difference between the 200hp and 250hp. The 200hp's computer module will push the engine to 250hp to get the boat on plane then settle back to 200hp"

I have heard all kinds of things at boat shows over the years...
One method we adopted to clear up some of these is to simple ask the salesman/dealer to just put it on the quote.
Yes - just put down in writing exactly what is said above guaranteeing that the boat will be delivered as promised and as described.

I predict there will be a brief pause - then a very in unique/creative and unusual reason why they cannot memorialize their claims in writing.
Then we end up pondering this , if they distorted one item about the boat/deal how many other items are also distorted?

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Northport NY

can we get 250hp from a 200hp Mercruiser 4.5L? 24 Apr 2017 14:50 #8

  • Norton Rider
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dicko wrote: just left the boatshow with some strange information. I told the Bayliner salesman I wouldn't mind the 250hp 4.5L and he said there is no difference between the 200hp and 250hp. The 200hp's computer module will push the engine to 250hp to get the boat on plane then settle back to 200hp. I never heard such a thing before on any engine, but since he may end up being my dealer for a new VR5 would like some more info on the 'new' Merc 4.5L, anyone else know how the computers work on these engines?


Maybe, maybe not.... As Chief Allen stated, a way to find out would be to check for part number differences on key components: ECU, Intake manifold, camshaft, pistons, heads, etc. Even if the only difference is the ECU, would Mercury sell a 250 ECU not tagged for a particular engine s/n? For example, I have a Suzuki 20hp EFI outboard. Out of curiosity, I did a part number comparison with the 15hp outboard and found that the ECU was in fact the only different key component.

As other mentioned, there are some aftermarket fuel curve re-mappers available already. These devices basically trick the ECU into changing the air/fuel ratio and/or ignition timing at various points. I am very familiar with doing this on motorcycles and it takes some dyno time to get it right. Have these aftermarket outfits put the engines on a dyno and optimized the fuel/air and ignition timing or are they doing it by seat of the pants?

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can we get 250hp from a 200hp Mercruiser 4.5L? 24 Apr 2017 16:46 #9

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Mercruiser is known to do this to their engines, all pretty much the same engine...
Mercury 4 stroke EFI 75, 90, 115 HP
Mercruiser 357 A4V 285HP, 357 B4V 320HP
Mercruiser 4.5 200HP, 4.5 250HP

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can we get 250hp from a 200hp Mercruiser 4.5L? 24 Apr 2017 16:54 #10

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Ruffryder wrote: Mercruiser is known to do this to their engines, all pretty much the same engine...
Mercury 4 stroke EFI 75, 90, 115 HP
Mercruiser 357 A4V 285HP, 357 B4V 320HP
Mercruiser 4.5 200HP, 4.5 250HP


Do you know if the differences are ECU programming alone, or if other internal components are changed?

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1999 3788, Cummins 270 "Freedom"
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can we get 250hp from a 200hp Mercruiser 4.5L? 24 Apr 2017 17:35 #11

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Same bore & stroke, same tuned scroll intake, same digital inductive ignition,
So the differences are ECM programming alone, but that is strictly just my opinion since I haven't tear down these 2 motors side by side yet :)

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can we get 250hp from a 200hp Mercruiser 4.5L? 24 Apr 2017 19:33 #12

  • Norton Rider
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You probably don't need a teardown. Some time with the parts manuals will reveal the answer. As a matter of fact, if Mercury already has long or short block P/Ns that's all that is needed for the comparison.

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can we get 250hp from a 200hp Mercruiser 4.5L? 24 Apr 2017 20:05 #13

  • cfoss1
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The ECM is very likely not the difference.

There are three options I can think of. Of those, only one makes sense:

1) Detuned timing (reduced advance)
2) Lower compression
3) Different intake

#3, the different intake, is the normal route that manufacturers use to detune performance.

#1 is the only one you could change on the fly, but really it would just be creating a less efficient engine...unlikely that they would do this.

With a gasoline engine, you need to match the mass of the air with the correct amount of fuel (Within an air fuel ratio band, but pretty tightly controlled). Because of this, the typical way to detune an engine is to reduce the airflow, not ecm programming.


Chay

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can we get 250hp from a 200hp Mercruiser 4.5L? 24 Apr 2017 20:09 #14

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Wait, I have to contradict myself.

If the engine has variable valve timing/lift the ECM could control airflow and therefore hp.

It probably does, being a new engine, perhaps that's how it's done.

Chay

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can we get 250hp from a 200hp Mercruiser 4.5L? 24 Apr 2017 20:32 #15

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Nope no variable valve timing.
& Intake is exactly the same between these 2 engines.

www.perfprotech.com/mercury-marine-parts...591/100?umodel=20119
"On new generation fuel injected engines you are not able to adjust the Air to Fuel Ratio in order to add more power output with re-jetting, like on carbureted models.
Typical performance tuner device wires inline with the signal wire of Intake Air Temperature (IAT) sensor
This fuel injection remap is designed to fool the ECU thinking the intake air much more cooler, then the Electronic Engine Management will send more fuel for a richer mix, "
Not by reducing or adding airflow...
On a Porsche 580 HP engine, HP difference fluctuation can be up to 80 horses hot day driving VS cool night.

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Last Edit: by Ruffryder.

can we get 250hp from a 200hp Mercruiser 4.5L? 25 Apr 2017 02:48 #16

  • scout265
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Just an FYI the Mercruiser owners manual that came with my 4.5L 200 has a pic of the 250 on the cover and I was told by the dealer the manuals for the two are one and the same. Been running it about 18 months now with zero issues.

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can we get 250hp from a 200hp Mercruiser 4.5L? 25 Apr 2017 02:58 #17

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Because they're the same pretty much,
You sure you don't have one of those adaptive variable HP engine? :whistle:

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can we get 250hp from a 200hp Mercruiser 4.5L? 25 Apr 2017 03:33 #18

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Ruffryder wrote: Because they're the same pretty much,
You sure you don't have one of those adaptive variable HP engine? :whistle:

Well if I do or not, or could upgrade with a chip or not, its only a matter of curiosity to me as I've been very happy with the motor and am content to leave it as is. Wish the rest of the boat was as trouble free as the motor has been. Gauge issues, trim falling off, transducer remounts, and more. But I zeroed in on this boat more for this motor than anything else and it hasn't disappointed.

Cheers

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can we get 250hp from a 200hp Mercruiser 4.5L? 25 Apr 2017 04:01 #19

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cfoss1 wrote: The ECM is very likely not the difference.

There are three options I can think of. Of those, only one makes sense:

1) Detuned timing (reduced advance)
2) Lower compression
3) Different intake

#3, the different intake, is the normal route that manufacturers use to detune performance.

#1 is the only one you could change on the fly, but really it would just be creating a less efficient engine...unlikely that they would do this.

With a gasoline engine, you need to match the mass of the air with the correct amount of fuel (Within an air fuel ratio band, but pretty tightly controlled). Because of this, the typical way to detune an engine is to reduce the airflow, not ecm programming.


Chay


It could very well be the ECU. On these engines they control the timing.

As I mentioned before, the only difference between my 20 Hp outboard and the 15 hp outboard is the part number of the ECU. I personally checked the parts list for all the other parts that could contribute to power changes. So that's a 33% power increase with only an ECU change.

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can we get 250hp from a 200hp Mercruiser 4.5L? 25 Apr 2017 12:24 #20

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alot of people know how to work on them. the motor is based on the 150 outboard. shares lots of the same parts.

Chief Alen wrote: Your gonna get close with a 4.3L hp wise, way less expensive for parts, they have made the 4.3 l engine for a very, very, long time.

Do a comparison for say a mani or any other part.

Oh by the way who knows how to work on a 4.5l ?

4.3 is a snap in my opinion the best 6 cylinder ever designed.

You want to boat and enjoy yourself or have your boat in the shop all the time.

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