Torque of Mercruiser 4.3 MPI

Discussion in 'Propulsion' started by Willallison, Dec 8, 2011.

  1. Willallison
    Joined: Oct 2001
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    Willallison Senior Member

    Can anyone tell me the max torque of a Mercruiser 220 Hp MPI?
    Even better would be a torque curve, but the numbers would be a good start...
     
  2. CDK
    Joined: Aug 2007
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    CDK retired engineer

    No, nobody can tell you that. The figure is so disappointing that Mercruiser guards it as a secret. Look at the GM Vortec site for reliable information about these engines.

    Other people may chime in and say that the Merc has different cams, injection settings etc. but I have sincere doubts.
     
  3. powerabout
    Joined: Nov 2007
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    powerabout Senior Member

    yes 220 ftlbs?
    I was party to some dyno work on several Mercruiser v8's 20 years ago and they all made in torque what the label said in horsepower, the 220MPI does refer to Horsepower does it??
    Stock Merc would be the same ( if its the same version block as they have been different in the past) as the GM marine range.
    The only problem is you have no idea what exhaust system that GM use to get their numbers and or in some cases induction.
    http://gmpowertrain.com/MarineEnginesControllers/ProductPortfolio.aspx

    Outboards pretty much make in torque the horsepower number.
     
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  4. DCockey
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    DCockey Senior Member

  5. PAR
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    PAR Yacht Designer/Builder

    268 is about right, though it's pretty easy to get more, even a lot more if you want it. This generation of Vortex has the parts to develop a good bit of power and is, considering what they are. To get what they're claiming, they've used roller valve train, higher compression, more duration and overlap and several other "hot rod" tricks. These make the engine tweak out a bit more then you'd think at first glance. The torque curve is pretty typical for a marine engine and basically flat across the range. At 220/268 the 4.3 Vortex is getting into the maxed out range for a reliable marine engine, unless you're driving a fairly light boat. As I mentioned you can get much more from it, but engine life/durability will decrease sharply, unless the reciprocating assembly gets some improvement (aftermarket parts).
     
  6. Willallison
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    Willallison Senior Member

    Near enough... thanks gents:)
     

  7. Yellowjacket
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    Yellowjacket Senior Member

    A good rule of thumb for most OHV normally aspirated engines for years has been about 1 ft pound of torque per cubic inch of displacement. This is at the torque peak. Where the torque peak occurs and how much power the engine makes is more dependent on how fast you twist it (the old HP = torque x rpm/5252) and what kind of manifolding (headers and intake) are used.

    This rule obviously works well for the Vortec (262 cubic inches, and 268 ft pounds of torque), and it worked well for the small block LT Chevy's for years in the Corvette, but gets less accurate if you start using really good exhaust systems an running at high rpm and are getting significant cylinder charging effects from an advanced intakes and more aggressive camshafts (the LS engines are doing better at 1.1 ft lbs/cubic inch) so you have to know what the installation looks like. But for a pedestrain engine like a marine motor the 1 foot pound per cubic inch is still a pretty much a good ballpark number.
     
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