383 stroker

[alldodge]

Ok. 20” on a bravo 3 twin prop then ? Strange pitch maybe ?
so it’s not a 383 stroker. It’s the new merc built engine ?

B3 props are even numbers normally, you can find odd with XR style
It is a 383 stroker
It is a bored block (used) but everything else used on the motor should be new

 

[QBhoy]

B3 props are even numbers normally, you can find odd with XR style
It is a 383 stroker
It is a bored block (used) but everything else used on the motor should be new

I thought he said it was one of the new merc made in house engines ? Would that not make it different from the 383 ? Sure they are slightly less than 380ci ?
yeah. About the prop. Just that I know similar sized boats with a 350 mpi and B3’s. But they are running 24” and the other 26”
the latter is a 50mph boat.

 

[Rick Stephens]

I thought he said it was one of the new merc made in house engines ? Would that not make it different from the 383 ? Sure they are slightly less than 380ci ?
yeah. About the prop. Just that I know similar sized boats with a 350 mpi and B3’s. But they are running 24” and the other 26”
the latter is a 50mph boat.

If you follow the serial number it comes up as a 383 MPI, which is the SBC stroker.

 

[alldodge]

I thought he said it was one of the new merc made in house engines ?

Dealer lead OP to believe it was a brand new (100%) motor. Doing research, its a 90% (lets say) brand new motor, the block was bored. The good thing, is with boring there is more displacement, and we all know there is no replacement for displacement

Would that not make it different from the 383 ? Sure they are slightly less than 380ci ?

This is nits, 377 or 383 is just 6 cubic inches, so they both can be called 383, but one one actually is.
This is why when Merc first started making the Scorpion they called it a 377

Is all in mathematics

Radius squared x Pi x stroke x 8 cylinders

 

[hnt]

Prop shaft HP vs Crankshaft HP may have something to do with it...

Just for comparison purposes, I have a Pursuit 2460 Denali. A bit lighter than your boat with less dead rise but maybe not that far off.

This year I upgraded my 5.7LXEFI Bravo III (250 HP at the shaft) to Vortec heads which made it into a 5.7LXEFI Gen+ (280 HP at the shaft) ie 30HP increase Both configurations call for WOT range of 4,400-4,800

before the upgrade 22P, WOT at 4,650 rpm 38 mph, 24 gph
after the upgrade 24P, WOT at 4,650 rpm, 41 mph, 25.46 gph

The motor before the upgrade with 24P only turned turned 4,200

This may not translate to your situation but I thought you might find it useful as a reference point.

Good luck!!!

 

[QBhoy]

Ok. So we are back to 320hp as I first thought ?
haha.

 

[alldodge]

Nope, mixing things up
All boat motors, inboard, sterndrive, outboard started indicating hp rating at the prop in the 80's

A 350hp 377 or 350hp 383 is 350hp at the prop.

One caveat, I'm not so sure the 377 and 383 hp ratings would be the same. One has more displacement, yet Merc list both bore and stroke to be the same. Someone does to much cut n paste

 

[QBhoy]

Nope, mixing things up
All boat motors, inboard, sterndrive, outboard started indicating hp rating at the prop in the 80's

A 350hp 377 or 350hp 383 is 350hp at the prop.

One caveat, I'm not so sure the 377 and 383 hp ratings would be the same. One has more displacement, yet Merc list both bore and stroke to be the same. Someone does to much cut n paste

AD. I’d rarely doubt you...but I’m almost certain this particular GM 383 (6.2 mpi) is 320hp at the prop ? Is it not ? Same era as the all but most recent mpi in house motors. It’s not the old school one.

 

[alldodge]

All I can say, is it was mandated by the Fed that all hp ratings will be done at the prop and not at the crankshaft. Same goes for car/truck and its at the wheels

 

[QBhoy]

I may be wrong, but I thought merc mpi motors and their modern quoted figures were measured at the prop.
to explain my thinking...
merc 5.0 mpi 260hp
VP 5.0 GXi same engine 270hp (presuming flywheel)

Merc 350 mpi 300hp
VP 5.7 GXi same engine 320hp (presuming flywheel)

you get my reasoning maybe ? To presume the GM 6.2 mpi and it’s quoted 320hp....would surely be a prop power rating ? Otherwise VP have magically found more power out the same engines with the 4.3, 5.0 and 5.7 versions ??

 

[QBhoy]

All I can say, is it was mandated by the Fed that all hp ratings will be done at the prop and not at the crankshaft. Same goes for car/truck and its at the wheels

How do VP get their higher figures ?

 

[Rick Stephens]

How do VP get their higher figures ?

Paint them silver and put a magnum sticker on them? (That's what Stihl does with chainsaws )

 

[Scott06]

I have no way to confirm this but there was some discussion on here or one of the other boating sites that VP uses a different cam and possibly different upper rpm limit.

 

[QBhoy]

Paint them silver and put a magnum sticker on them? (That's what Stihl does with chainsaws )

Haha. Had an out loud laugh at that !!

 

[Scott Danforth]

All I can say, is it was mandated by the Fed that all hp ratings will be done at the prop and not at the crankshaft. Same goes for car/truck and its at the wheels

when sold as a package. the same motor as just a bob-tail is rated at 350hp crank.

just like the 225hp mercruiser replacement V6's which are the 205hp when packaged with a drive.

 

[Scott Danforth]

How do VP get their higher figures ?

VP has a different mix of parts. different cams, different valve springs, different induction.

the newer VP's are GM build LT engines where Mercs old stuff was in-house assembled SBCs from GMPP and now the in-house built motors

 

[alldodge]

when sold as a package. the same motor as just a bob-tail is rated at 350hp crank.

just like the 225hp mercruiser replacement V6's which are the 205hp when packaged with a drive.

Do you know where this is documented?

 

[QBhoy]

VP has a different mix of parts. different cams, different valve springs, different induction.

the newer VP's are GM build LT engines where Mercs old stuff was in-house assembled SBCs from GMPP and now the in-house built motors

Are sure Scott ? I think the 5.0 and 5.7 mpi is the absolute identical, in every way engines to the 5.0 and 5.7 gxi. Could be wrong though. I haven’t ever noticed a difference in them. Referring to the GM engine ofcourse. A typical example year of which would be 2003-2006 for a certain period of time at least (and a bit beyond)
rpm ranges are identical. Ecu are too, I’m sure.

 

[Scott Danforth]

Do you know where this is documented?

AD, its on the Mercruiser reman'd engine site. they list 350 Crankshaft HP for the 383 (second link below) included both links to show that even the 4.3 is listed at 225 crankshaft hp.

https://www.mercurymarine.com/en/us...emanufacturing/plus-series-alpha-sterndrives/

https://www.mercurymarine.com/en/us...emanufacturing/plus-series-bravo-sterndrives/

 

[Scott Danforth]

Are sure Scott ? I think the 5.0 and 5.7 mpi is the absolute identical, in every way engines to the 5.0 and 5.7 gxi. Could be wrong though. I haven’t ever noticed a difference in them. Referring to the GM engine ofcourse. A typical example year of which would be 2003-2006 for a certain period of time at least (and a bit beyond)
rpm ranges are identical. Ecu are too, I’m sure.

based on a conversation with the VP chief engineer back in 2008-2009 time frame, yes. they specified a different cam profile than the standard GM offering. what they are doing after 2012, I do not know. the ECU hardware for a few years is the same, however the fuel mapping, etc. is completely different. that is also why VP used GM IAC's and Mercruiser ran out of pins and used the Ford IAC (2 wire vs 4 wire)