Torque or HP?

[hibbert6]

I was wondering why many boats use a 3.0L GM engine that puts out 135hp, when a typical Japanese engine half the size will match the HP? Same with a 4.3v6 vs. a Japanese 2.5L v6.
The only thing my little mind can come up with is torque, but is that an important factor in a sport boat? (16'-21') It seems the reduced weight of the smaller engine would help offset that...

Dave

 

[Adirondack]

Re: Torque or HP?

I was wondering why many boats use a 3.0L GM engine that puts out 135hp, when a typical Japanese engine half the size will match the HP? Same with a 4.3v6 vs. a Japanese 2.5L v6.
The only thing my little mind can come up with is torque, but is that an important factor in a sport boat? (16'-21') It seems the reduced weight of the smaller engine would help offset that...

Dave

Torque is EVERYTHING in a boat. Horsepower is just a measurement of power that an engine puts out once operating at optimum rpm. If you can't achieve that rpm it's worthless. Your little Japanese car has a four or even five speed transmission for a reason. Try starting out in fourth gear some time. It's not going to work out too well for you. A boat only has one gear. It needs torque to achieve optimum rpm to develope horsepower.

Boats also tend to run at maximum rpm a lot more often than a car ever would. Nothing like big beefy cast iron to keep things straight and ridgid. I know many tout the dependability of say a Honda engine. I doubt it would be all that dependable under constant load at near WOT most of the time. The bottom ends just aren't built that tuff.

Another consideration may be many other small engines tend to have a lot of aluminum components. Heads, or even the complete engine. Not very durable in a raw water cooling system. Particularly in sea water.

 

[Aloysius]

Re: Torque or HP?

horsepower=torqueXrpm/5252

It's all about torque/horsepower at lower engine speeds. The lowly 3.0 may put out only 135 hp, but it does so at a fairly low rpm. Even at 2000 rpms, the 3.0 still produces decent torque, thus the power band is pretty even.

You only get "rated" horsepower at a very narrow rpm band..after that peak, it falls off in both directions.

 

[Brentathon]

Re: Torque or HP?

You'd be surprised at the relatively low horsepower of the engines in big-rig trucks; and you'd be very surprised at their max torque.
Both hp and torque are important in the design, rating, application, and performance of vehicles.