Bravo 3 Propelles RPM Problem ?

E

erick11s

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Feb 25, 2010
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HI,

I put a new engine in my boat cobalt 276 with Mercruiser Bravo March 3 engine GM generation IV 400 HP stock with a holley 4 barrel carburetor, engine specifications say:
Maximo RPO (WOT) 4800-5200 RPM
In my First test with propellers SS pich 26 and the top end only 4400 RPM.
in then second test with propellers SS pich 22 and gave me 4800 RPM but the boat feels very tied into the transmission and the speed is very low about 40 miles expecting a 55 miles.
Question: if I go to a propeller pich 24 the RPM drop further? and need to be close to 5000.

Please I do not what happend ? Please see Boat Picture and mercruiser especifications.

Thanks in advance any comments-

Erick
 

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Bondo

Bondo

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Re: Bravo 3 Propelles RPM Problem ?

erick11s said:
HI,

I put a new engine in my boat cobalt 276 with Mercruiser Bravo March 3 engine GM generation IV 400 HP stock with a holley 4 barrel carburetor, engine specifications say:
Maximo RPO (WOT) 4800-5200 RPM
In my First test with propellers SS pich 26 and the top end only 4400 RPM.
in then second test with propellers SS pich 22 and gave me 4800 RPM but the boat feels very tied into the transmission and the speed is very low about 40 miles expecting a 55 miles.
Question: if I go to a propeller pich 24 the RPM drop further? and need to be close to 5000.

Please I do not what happend ? Please see Boat Picture and mercruiser especifications.

Thanks in advance any comments-

Erick
Click to expand...

Ayuh,... I'd say yer Motor ain't puttin' out, as expected....

Goin' to 24" props, over the 22" props Will lower the rpms...

Btw,... Merc don't use Holley carbs,...
'tween that, 'n God knows what else, is probably some of yer problems...
 
jestor68

jestor68

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Re: Bravo 3 Propelles RPM Problem ?

The MCM 400(Cyclone 400) is a 454CI recreational motor. This is not a "high performance" motor, like those available from Mercury Racing.

Run your numbers through the Mercury selector and you get a 21 pitch, with an expected top speed in the 40's range using a 2.2 gear ratio.


Edited: for clarity.
 
jestor68

jestor68

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Re: Bravo 3 Propelles RPM Problem ?

9.jpg Holley carb for a 1996 Mercury 525 SC. Lots of Mercury engines (including virtually all high performance engines) use Holley Carbs.
 
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Maclin

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Re: Bravo 3 Propelles RPM Problem ?

What was in it before the replacement and what performance numbers did you get then.
 
E

erick11s

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Re: Bravo 3 Propelles RPM Problem ?

jestor68 said:
I believe we are talking about the MCM 400(Cyclone 400) which is a 454CI low compression motor. This is not a "high performance" motor, like those available from Mercury Racing.

Run your numbers through the Mercury selector and you get a 21 pitch, with an expected top speed in the 40's range using a 2.2 gear ratio.
Click to expand...

This Engine is a really Hi performance from Mercruiser, and coming from factory with:
This engine name is Cyclone's was just a series of engines . They were 400,440,and 460 hp. They had 4 bolt main blocks,aluminum high rise intakes,rectangular port heads,forged crank-rods-pistons,and aluminum roller rockers.The 460 hp model was stroked .25" to give it 482 cu. in.'s and 9.2:1 compression. The others had 8.8:1 compression.

and for all of this reasons it is not a low compression and 40 range it is not ok
 
jestor68

jestor68

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Re: Bravo 3 Propelles RPM Problem ?

base.jpg This Mercury Racing's "base" high performance engine; the 525. The MCM line are recreational motors that they put in any boat.

I guess it depends upon one's perception of "high performance". Your MCM 400 isn't going to do much better than mid to high 40's in a 27 ft boat; whether we like it or not. If you seriously want to go fast, you need to talk to the folks at Mercury Racing; the high performance division of Mercury Marine.
 
E

erick11s

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Re: Bravo 3 Propelles RPM Problem ?

Ok, I understand your point, but see this original boat is coming with 7.4 mercruiser 330 hp The same bravo 3, and the top speed it is around 45 miles amd now we have 400 horse power is is much difference , i think we will need 24 pich to take more miles
 
jestor68

jestor68

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Re: Bravo 3 Propelles RPM Problem ?

May I ask what year is the boat? More importantly, what year was the previous motor? The difference in HP rating might be due to the way they rated power in different years, or even by different engine makers.

I might suggest you have a good marine mechanic check the motor's tune because 4800 rpm is at the low end of it's recommended rpm range, which is not bad. Putting more pitch on it will only lower the WOT rpm more. You would need to reduce the pitch to raise the rpm.

If you are turning 4800 rpm with the 22 pitch, you would reduce to a 21 pitch to raise the rpm.

How are you measuring speed?
 
jestor68

jestor68

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Re: Bravo 3 Propelles RPM Problem ?

Are these prop sets; 26, 22 ; the same ones that you used with the previous motor?

If so, what rpm did the previous motor do using the 26 pitch set?
 
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erick11s

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Re: Bravo 3 Propelles RPM Problem ?

The old motor it is a rectangular port 330 HP 7.4----- Five Generation year 1992 rpm range max 440 rpm wot......., The new motor it is a 1985 year four generation call cyclone or Mark 4
 
jestor68

jestor68

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Re: Bravo 3 Propelles RPM Problem ?

It is likely that your "new" 1985 model motor's power(400) is rated at the fly wheel, which would result in about the same power rating as the 1992 motor(330) if rated at the prop.

You were expecting a power increase that is not there.
 
Tail_Gunner

Tail_Gunner

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Re: Bravo 3 Propelles RPM Problem ?

That's a very old engine and used prior to your boat. Id suggest you do a compression test first alleviate yourself some pain. Have your built this motor from previous part"s?

http://forums.iboats.com/mercruiser...iser-id-problem-400hp-578760.html#post3994961

It's a big block Chevy 454. Was called the Cyclone 400 back then. Came out of a 42 ft. boat with twins, so would guess it's not an outdrive, but it's not listed in the manual as an MIE but as a MCM.
 
Don S

Don S

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Re: Bravo 3 Propelles RPM Problem ?

erick11s said:
HI,
I put a new engine in my boat cobalt 276 with Mercruiser Bravo March 3 engine GM generation IV 400 HP stock with a holley 4 barrel carburetor, engine specifications say:

Erick
Click to expand...

You made it sound like you put a NEW motor (or I assumed rebuilt) into the boat. All you did was put a 25+ year old used engine in it.
A compression test is mandatory at this point, and a leakdown test too for that matter.
Those old engines also had a points distributor, is it working as it should? Is the dwell set right? Timing set right? Does the timing advance even work?

And to all that don't remember from one of his previous posts, Merc did use a Holley carb on the Cyclone engines.
 
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erick11s

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Re: Bravo 3 Propelles RPM Problem ?

I did test the compresion and in all cilinders around 150 PSI
 
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