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13-02-2011, 10:24 PM
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#1
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Registered User
Join Date: Sep 2009
Posts: 45
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Engine Options
All,
I'm looking at buying a boat which has a 6.2l mpi in it, which on the test run felt too under-powered. So I was wondering your opinions on the best options to squeeze some more beans out of the boat. I was thinking of either a supercharger or to swap it out for a 496 ho. It currently has a bravo 1 leg, would it need an uprated leg for these options? Thoughts gratefully received.
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13-02-2011, 10:28 PM
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#2
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Registered User
Country: Guernsey
Occupation: Engineer
Interests: Restoration
Cruising area: Channel Islands & northern French coast
Join Date: Jan 2009
Posts: 154
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what size boat is it?
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13-02-2011, 10:41 PM
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#3
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Registered User
Join Date: Sep 2009
Posts: 45
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It's 27.5 foot, circa 2 tonnes.
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13-02-2011, 11:15 PM
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#4
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Registered User
Country: uk
Boat make: extreme 24
Engines: 4.7
Cruising area: poole
Join Date: Jun 2010
Posts: 71
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496 ho 425hp you know it makes sence
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13-02-2011, 11:17 PM
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#5
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Registered User
Country: Guernsey
Occupation: Engineer
Interests: Restoration
Cruising area: Channel Islands & northern French coast
Join Date: Jan 2009
Posts: 154
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Did the builder fit larger single engines to the type of boat you're looking at if so I'd go for this
http://www.mercurymarine.com/engines.../mpi8-2lho.php
Or you could PM peterunwin on here re the motors he's gonna be building. They'll produce similar power but will be considerably lighter.
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13-02-2011, 11:30 PM
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#6
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Registered User
Country: uk
Boat make: extreme 24
Engines: 4.7
Cruising area: poole
Join Date: Jun 2010
Posts: 71
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bravo
you will not have two change leg as 496 is ok on bravo 1 leg
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14-02-2011, 08:22 AM
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#7
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Registered User
Country: Job Centre
Location: In a box
Occupation: Chaos's gofer
Interests: Skiving
Boat make: Spectre 30
Engines: 2 x Promax 225
Cruising area: In the bath
Join Date: Mar 2004
Location: In a box
Posts: 5,201
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Quote:
Originally Posted by Coronet Kip
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Look at the RRP for the 8.2, I suspect you wouldn't!
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Chaos for Moderator.
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14-02-2011, 10:57 AM
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#8
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Registered User
Country: Norway
Boat make: Nothing fast...
Join Date: Dec 2007
Posts: 127
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We had a supercharger fitted to this engine and did a complete rebuild as well, and it was done by professionals. All I can say is don't do it. It will end up costing too much and you are left with a boat that has a much lower value. Ours also turned out to be completely useless - it needed 100 octane fuel (only available at selected petrol stations ON LAND!!!) and if I forgot to turn off the silent choice at full whack the engine would blow... Nice. It did 75 knots, mind...
Buy a new engine.
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"If it has tits, tyres or a transom, it will have issues"
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14-02-2011, 12:09 PM
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#9
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Registered User
Country: Guernsey
Occupation: Engineering
Boat make: None, boo!
Engines: Turbines mainly!
Cruising area: The inside of my workshop!
Join Date: Mar 2008
Posts: 2,646
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Bravo leg will be fine for the power you're looking at. If I were you, as suggested, I'd speak to Peter Unwin on here about the ally smallblocks he's looking at. It'd be by far the cheapest and most economical option, whilst having the same or more hp as an 8.2.
Cheers, James
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14-02-2011, 10:16 PM
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#10
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Registered User
Join Date: Sep 2009
Posts: 45
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It looks like a 496 ho it is then. Now all I need to do is find one at a reasonable price! Thanks all.
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15-02-2011, 07:45 AM
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#11
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Registered User
Country: Uk
Location: London
Occupation: Mercury main dealer
Boat make: Baba
Engines: 200xs
Join Date: Feb 2008
Location: London
Posts: 361
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They no longer sell the 496 new it has been replaced by the 8.2 mag. available in 380 hp or 430hp.
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15-02-2011, 08:08 AM
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#12
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Registered User
Country: Job Centre
Location: In a box
Occupation: Chaos's gofer
Interests: Skiving
Boat make: Spectre 30
Engines: 2 x Promax 225
Cruising area: In the bath
Join Date: Mar 2004
Location: In a box
Posts: 5,201
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Quote:
Originally Posted by pro-rig
They no longer sell the 496 new it has been replaced by the 8.2 mag. available in 380 hp or 430hp.
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496HO's, how many would you like? There's still some around, if you know where to look.
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Chaos for Moderator.
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15-02-2011, 08:44 AM
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#13
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Registered User
Country: Uk
Location: London
Occupation: Mercury main dealer
Boat make: Baba
Engines: 200xs
Join Date: Feb 2008
Location: London
Posts: 361
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guess you will be in undated then.
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15-02-2011, 09:15 AM
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#14
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Registered User
Join Date: Sep 2009
Posts: 45
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I'm just after the one. The boat's a 2007 build so I don't mind using a slightly older engine for it (although low hours is a must). I have found one in the states at a reasonable price but if anyone knows of one in the UK please let me know. Do you think it'd fit on the same engine mounts as the 6.2l? I'm hoping yes but perhaps the different block means different mounts.
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15-02-2011, 09:35 AM
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#15
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Registered User
Country: Job Centre
Location: In a box
Occupation: Chaos's gofer
Interests: Skiving
Boat make: Spectre 30
Engines: 2 x Promax 225
Cruising area: In the bath
Join Date: Mar 2004
Location: In a box
Posts: 5,201
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The footprint is the same for both small and big block chevy's. if your currently running transom exhausts, you'll need a bit of nifty pipe work as the risers are slightly wider and higher.
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Chaos for Moderator.
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15-02-2011, 01:30 PM
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#16
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Registered User
Join Date: Sep 2009
Posts: 45
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Looking at the stats on the 496ho it says that it is compatible with bravo 1x leg, I have a bravo 1 leg, which according to mercruiser is suitable up to 400hp only. Do you think not changing the leg will be a problem?
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15-02-2011, 01:44 PM
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#17
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Registered User
Country: Job Centre
Location: In a box
Occupation: Chaos's gofer
Interests: Skiving
Boat make: Spectre 30
Engines: 2 x Promax 225
Cruising area: In the bath
Join Date: Mar 2004
Location: In a box
Posts: 5,201
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A better spec drive is always preferable, but a std Bravo 1 used to be on a 540cu in 500hp Bulldog's. It's normally the nut behind the wheel that breaks the drive.
I raced for 3 years with a std bravo on a 502 mpi, 15 years later the drive is still going strong.
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Chaos for Moderator.
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15-02-2011, 02:01 PM
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#18
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Registered User
Join Date: Sep 2009
Posts: 45
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By nut behind the wheel, I assume mean the person driving the boat rather than a techincal part of the leg? Excuse my ignorance but I'm no mechanic. If I need to change out the leg, it makes the project cost prohibitive.
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15-02-2011, 02:11 PM
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#19
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Registered User
Join Date: Nov 2010
Posts: 176
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Hi General i think wot Tony is saying is take it easy on the pullaways and come off the gas when you are airbourn
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15-02-2011, 02:24 PM
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#20
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Registered User
Country: Job Centre
Location: In a box
Occupation: Chaos's gofer
Interests: Skiving
Boat make: Spectre 30
Engines: 2 x Promax 225
Cruising area: In the bath
Join Date: Mar 2004
Location: In a box
Posts: 5,201
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