Prop Shaft HP for Mercruiser 165 inline 6

region4

Cadet
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Aug 12, 2013
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Does anyone know how much shaft output a Mercruiser 165 inline 6 can muster? I see that Merc publishs this data for more modern 5.7 V8s, but can find nothing on the 165. I ask because I am trying to compare apples to apples, with respect to an engine upgrade.
 

180shabah

Rear Admiral
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Mar 26, 2005
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4,995
Re: Prop Shaft HP for Mercruiser 165 inline 6

Crank hp to prop hp difference on a single prop I/O is approximately 30 hp.

So you are starting with 135 at the prop on a NEW 3.7
 

region4

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Aug 12, 2013
Messages
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Re: Prop Shaft HP for Mercruiser 165 inline 6

So, generally speaking a single alpha (or pre-alpha) I/O demands 30hp due to friction, etc. Good to know. Thank you.

A mercruiser 5.7 Vortec 4bbl puts out nearly twice that HP at the prop, which seems like a ton more power, albeit at the expense of 230 pounds of additional engine weight.

My boat goes 49mph (light load at WOT) with a strong Mercruiser 165 inline 6. What can I reasonably expect, in terms of mph, from a solid 5.7 vortec 4bbl?
 

achris

More fish than mountain goat
Joined
May 19, 2004
Messages
27,468
Re: Prop Shaft HP for Mercruiser 165 inline 6

....My boat goes 49mph (light load at WOT) with a strong Mercruiser 165 inline 6. What can I reasonably expect, in terms of mph, from a solid 5.7 vortec 4bbl?

Probably around 60. Power requirements go up in the power of squares. ie, to double the speed requires the power to be squared.

Chris....
R.I.P. DonS
 
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