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New Merc 4.5L V6 sterndrive

Yup. The Mercury Marine dog-and-pony show came to the marina with a Bayliner 195 BR rigged with the new 4.5/alpha this fall, very impressive. Not only is it pretty, but the extra 30-40 hp over the 4.3 added some much needed zip to the hull. Also, probably about 20% quieter than the 4.3. Oh, and the fuel consumption was astounding- just over 7 gph at 3500 rpm on the smartcraft. I'm thinking it's time to repower the deck boat, but I think I'll wait a year for Mercury to iron out any wrinkles (new stuff always has wrinkles. :eek:
 
Just one observation.... It's torgue that turns the prop and moves the boat, and its CID displacement that makes torque. HP = torque x RPMs, so for a given HP, lower torque requires higher RPMs... or to put it another way, at any given RPMs, less torque from a smaller CID engine. If you are considering putting a V6 in a smallish low to mid deadrise hull it will work out. In my case, I have a 5.7L carbed 260HP on a high deadrise 23ft hull. At cruise ( 2600...about 22-24 MPH) I also burn 7 GPH. The actual "cruise RPMs" for this engine is just over 3000 RPM, but that pushes the boat too fast in Barnegat Bay's short steep chop for the "Admiral's sensibilities" :)
 
bilge rat jim said:
Yup. The Mercury Marine dog-and-pony show came to the marina with a Bayliner 195 BR rigged with the new 4.5/alpha this fall, very impressive. Not only is it pretty, but the extra 30-40 hp over the 4.3 added some much needed zip to the hull. Also, probably about 20% quieter than the 4.3. Oh, and the fuel consumption was astounding- just over 7 gph at 3500 rpm on the smartcraft. I'm thinking it's time to repower the deck boat, but I think I'll wait a year for Mercury to iron out any wrinkles (new stuff always has wrinkles. :eek:
Click to expand...


OK, have heard similar praise from others. I understand it's an iron block with aluminum heads and intake. Did the one you saw have closed cooling?
 
Ayuh,.... On the bright side, it appears, after readin' the links posted, they stroked the 4.3l to get the 4.5l,.....

Longer stroke, Better torque,.....

'course, they gotta spin it to 5200 rpms to make the 250 hp,....

Don't care for the catconverters either,...
 
bondo said:
Ayuh,.... On the bright side, it appears, after readin' the links posted, they stroked the 4.3l to get the 4.5l,.....

Longer stroke, Better torque,.....

'course, they gotta spin it to 5200 rpms to make the 250 hp,....

Don't care for the catconverters either,...
Click to expand...

The new 4.5 250 is not a stroked GM 4.3, it's a completely new, Mercury Marine in-house design, right from the structural oil pan up. This is an industry first, a complete engine designed strictly for marine use, rather than an adapted automotive engine.
 
bilge rat jim said:
The new 4.5 250 is not a stroked GM 4.3, it's a completely new, Mercury Marine in-house design, right from the structural oil pan up. This is an industry first, a complete engine designed strictly for marine use, rather than an adapted automotive engine.
Click to expand...

Ayuh,.... I understand that,.... The 4.3l basic formula is stroked out to the 4.5l,....

The 4.3l is a 4" bore, 'n a 3.48" stroke,....

The new 4.5l is a 4" bore, 'n a 3.60" stroke,....
'bout 1/2 of the stroke increase We use on the SBC Strokers,...
 
bondo said:
Ayuh,.... I understand that,.... The 4.3l basic formula is stroked out to the 4.5l,....

The 4.3l is a 4" bore, 'n a 3.48" stroke,....

The new 4.5l is a 4" bore, 'n a 3.60" stroke,....
'bout 1/2 of the stroke increase We use on the SBC Strokers,...
Click to expand...

Exhaust manifolds are unusual too - appears to be a tube shaped portion on the top and what looks like it might be a threaded plug insert.
Only 4.5 ion block I could find after a search is a Navistar diesel- could be?
 
mongo said:
Exhaust manifolds are unusual too - appears to be a tube shaped portion on the top and what looks like it might be a threaded plug insert.
Only 4.5 ion block I could find after a search is a Navistar diesel- could be?
Click to expand...

Ayuh,.... The big hicky on the manifolds is the cat. converter,...

No,.... It Ain't a Navistar diesel,...
 
mongo said:
Exhaust manifolds are unusual too - appears to be a tube shaped portion on the top and what looks like it might be a threaded plug insert.
Only 4.5 ion block I could find after a search is a Navistar diesel- could be?
Click to expand...

The block and heads are cast by a third party to mercruisers' specs and design. All machining and assembly is done in-house at Fond du Lac. There are no parts on this engine that are used on any automotive engine.
 
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