Questions on the Merc GEN+ Crate Engine, HP rating and stuff...

[NorthwestChap]

I am replacing a 1997 Mercruiser 5.7 LX with a 4 Brl Weber driving a Bravo 3 with this:

http://www.mercurymarine.com/media/mercury/pdfs/repower/350_Gen_Crate_Engine_Information.pdf

It's a Mercruiser 5.7 GEN+ Crate engine with 325 HP at the crank (Bravo version). It has the Vortec heads and intake.

My original engine had 250 HP at the prop shaft. My question is... what is the HP difference? I've found varying numbers for the HP loss from crank to shaft, but nothing conclusive. I can't find any HP numbers for the original engine at the crank.

Also, It was my understaning that Mercruiser started using a block that required a plastic timing chain cover around 1997 (my original engine had the plastic cover). The crate engine has the old style steel timing chain cover. Any clues to why?

Thanks

 

[NorthwestChap]

Re: Questions on the Merc GEN+ Crate Engine, HP rating and stuff...

Anyone?

 

[Bondo]

Re: Questions on the Merc GEN+ Crate Engine, HP rating and stuff...

I am replacing a 1997 Mercruiser 5.7 LX with a 4 Brl Weber driving a Bravo 3 with this:

http://www.mercurymarine.com/media/mercury/pdfs/repower/350_Gen_Crate_Engine_Information.pdf

It's a Mercruiser 5.7 GEN+ Crate engine with 325 HP at the crank (Bravo version). It has the Vortec heads and intake.

My original engine had 250 HP at the prop shaft. My question is... what is the HP difference? I've found varying numbers for the HP loss from crank to shaft, but nothing conclusive. I can't find any HP numbers for the original engine at the crank.

Also, It was my understaning that Mercruiser started using a block that required a plastic timing chain cover around 1997 (my original engine had the plastic cover). The crate engine has the old style steel timing chain cover. Any clues to why?

Thanks

Ayuh,.... Most of the horsepower numbers are dictated by the induction systems,...

Donno where they're gettin' the blocks, as not only are metal timin' covers a thing of the past, the mechanical fuel pump ain't been used in Along time,..

I'm guessin' yer old 250 hp motor is a 2 bbl. carbed motor, probably 'bout 230 hp at the crank,....

The Bigger carb, 'n the Vortec heads account for most of the difference,...

 

[NorthwestChap]

Re: Questions on the Merc GEN+ Crate Engine, HP rating and stuff...

Ayuh,.... Most of the horsepower numbers are dictated by the induction systems,...

Donno where they're gettin' the blocks, as not only are metal timin' covers a thing of the past, the mechanical fuel pump ain't been used in Along time,..

Yeah, that's why I'm puzzled. Old block, new heads and internals. Maybe a way to use up some old stock that was sitting around.

Ayuh,.... Most of the horsepower numbers are dictated by the induction systems,...

I'm guessin' yer old 250 hp motor is a 2 bbl. carbed motor, probably 'bout 230 hp at the crank,....

The Bigger carb, 'n the Vortec heads account for most of the difference,...

Agreed about the induction system and the heads making the difference in HP.

You missed the point that my old engine is a 250 HP 4 BBL. The 250 HP is at the prop shaft. I'm looking for a bigger number for the HP at the crank. Basically subtracting the HP loss from the outdrive and accessories to get a HP value at the crank.

 

[alldodge]

Re: Questions on the Merc GEN+ Crate Engine, HP rating and stuff...

Even though the document is currently on the Merc website it is dated 2011. As Bondo mentioned there are many items which can change HP output. The 275hp unit is probably the same engine you have, after subtracting the drive your probably back around 250 at the prop (Guessing Merc rounds numbers). If you get the Bravo model it probably wouldn't work do to timing curve issues. No expert here between Alpha and Bravo design of the 350. Seeing the mechanical fuel pump just makes it more versatile for other and older applications. If one doesn't need it, just remove and install the block off plate.

I would go to the horses mouth and call Merrc customer service and they should be able to tell you.

 

[NorthwestChap]

Re: Questions on the Merc GEN+ Crate Engine, HP rating and stuff...

AllDodge, I can attest to the accuracy of the document (at least for my situation), as I currently have the engine sitting in my garage. It is a 2012 manufacture.

I think you may be partially right. There is a different ICM (ignition control module) for the two versions. As far as I can tell, that is really the only difference between the two. The Alpha is probably de-rated a bit. Looks like the same cam and other internals on the parts lists.

My question isn't about the differences between the engines on the document though. I want to know how much power this new engine has vs. my old 1997 NON-Vortec head engine.

250 HP at the propshaft (Bravo 3) vs. 325 HP at the crank.

You are probably right about contacting customer service, maybe I can get a hold of someone that has the info, but I thought I might try here first.

 

[Fun Times]

Re: Questions on the Merc GEN+ Crate Engine, HP rating and stuff...

From my understanding, The average horsepower difference between crank and prop shaft horsepower is said to be between 25-35 HP depending on internal setup of the drive.

3.3.1 and 3.3.2 will give you an idea of why the ratings are different between the two from a manufacturing selling perspective.

3.3.1--Power shall be declared as Propeller Shaft Power at the propeller shaft of engines sold with complete propulsion units, and at the couple to the propeller shaft of engines sold with reduction or reversing gears.

3.3.2--Power shall be declared as Crankshaft Power at the engine output shaft of engines sold without reduction or reversing gears, stern drive or sail drive units. In such cases, the power declaration shall be accompanied by a statement that usable power will be reduced by gear losses.

More information can be found in link below if interested,
Classic Whaler: Boston Whaler: Reference: ICOMIA Engine Horsepower Standards

 

[NorthwestChap]

Re: Questions on the Merc GEN+ Crate Engine, HP rating and stuff...

From my understanding, The average horsepower difference between crank and prop shaft horsepower is said to be between 25-35 HP depending on internal setup of the drive.

That's similar to info that I was able to find for HP loss due to the drive. Nothing concrete for the Bravo 3 though.

 

[Bondo]

Re: Questions on the Merc GEN+ Crate Engine, HP rating and stuff...

That's similar to info that I was able to find for HP loss due to the drive. Nothing concrete for the Bravo 3 though.

Ayuh,.... 'bout the only way yer gonna get Concrete numbers is with real Dyno runs,...

A Bravo I would be rather easy,... Donno if there's B-III adapters or not,...

 

[NorthwestChap]

Re: Questions on the Merc GEN+ Crate Engine, HP rating and stuff...

Good point Bondo. Not gonna happen. I think I'll go with 10% loss and round down to 290 HP. That gives a net increase of 40 HP at the prop shaft. I'll have to see what the RPMs look like with it in the boat. Might need to re-prop.