comparing HP on boats

KD4UPL

Senior Chief Petty Officer
Joined
Feb 13, 2010
Messages
653
My current 20.5' boat has a 210 HP 5.7L with a 2 barrel carb. I want to upgrade to around a 24' boat. I see a lot of them with only a 5.0L engine. It doesn't seem like I want a 4' longer boat with a smaller displacement engine.
From a HP standpoint a lot of the MPI 5.0L engines are making 240 up to I think around 270 HP. This would seem like a good upgrade from my 210 HP but with a bigger boat that must be heavier seems like I'd be breaking about even.
I've always wondered why no one ever lists the torque rating of a boat engine. Is it that irrelevant. As I understand it HP, torque, and RPM are related. I know these new 5.0L engines aren't turning that many more RPMs then mine so that would mean they have to be making more torque, right?
I know ultimately I'll need to test drive a potential purchase but I'm afraid that won't tell me much. I typically boat with 6 to 11 people in the boat. I'm pretty sure getting a group like that for a test drive is going to be difficult.
 

mr 88

Commander
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Nov 3, 2010
Messages
2,115
You typicaly boat with 6-11 people on a 20.5 boat,must be a lot of kids. A 24' boat with that load, your running twins if you want to get out of your own way.
 

KD4UPL

Senior Chief Petty Officer
Joined
Feb 13, 2010
Messages
653
Thanks for the link. I don't know at what RPM my boat engine makes it's rated HP but I would assume around WOT of about 4,500. Using the formula of HP=T x RPM / 5252 I must be making about 245 lb/ft of torque. One of these new 5.0 engines making 270 HP at the same RPM would be making about 315 lb/ft. That's a significant increase.
Mr. 88, It's usually my family of 4 with another family of around 4 that we invite along so it ends up being about 4 adults and 4 kids. If it's me and my brother's families and my parents come along then we're at 4 kids and 6 adults.
I've been thinking I'd really like a big block. I haven't seen many 24' bowriders or deckboats with twins.
HP wise it seems like the new 5.0 engines are almost the equal of a 15 year old big block. I know there has to be more to it than that.
 

Bondo

Moderator
Staff member
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Apr 17, 2002
Messages
70,468
Ayuh,...... I wouldn't buy a 24'er without at least a 5.7l, or bigger,.... regardless what induction system is used,....
 

thumpar

Admiral
Joined
Jun 21, 2007
Messages
6,138
A duoprop or bravo 3 with the twin prop would help get it out of the hole. A 7.4l or bigger would be my first choice but a 5.7l mag would work.
 

tpenfield

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Staff member
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Jul 18, 2011
Messages
17,621
When I had a 24 foot boat, it had a 7.4L . . . 5.0 would be a trolling motor.
 
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