Car Motors vs Boat Motors?

[hostage]

I have been looking at boats with a 4.3L V6 (175hp) engine and I noticed that the HP ratings on all the Mercs are far less than my 3.5L V6 (265hp) in my MDX. I know that the cooling systems differ in the boats. (have yet to see a boat with a radiator)

I a mechanic by any means, but I am wondering why so little HP for Displacement?

Thanks,

Hostage

 

[cr2k]

Re: Car Motors vs Boat Motors?

The 175 HP is has a 2bbl carb. I am guessing your MDX has FI and runs at a lot higher RPMs.

Although marine engines are rated by HP it is torque that really does the work.

 

[CharlieB]

Re: Car Motors vs Boat Motors?

Automotive engines are rated at PEAK HP.

If my selective memory is functioning today,

Marine engines HP rating is taken as an average between PEAK TORQUE and 5250 RPM.

Hence, marine engines are generally specified WOT RPM 4800 to 5200 RPM.

 

[Howard Sterndrive]

Re: Car Motors vs Boat Motors?

I have been looking at boats with a 4.3L V6 (175hp) engine

then you're looking at boats a lot older than your MDX (whatever that is) I suspect the 1989 version of your MDX didn't have 265HP.

The new 4.3's make 220HP at the prop, about 250HP at the crank, with MPI injection and at a much lower RPM than the rev's your car's engine turns at its 265 rated HP
If you revved the 4.3 to the same rpm's your MDX engine is spinning at rated power, it would make much more power than the 3.5 car engine.

But a boat's outdrive cannot deal with those rpm's

 

[Simoniz]

Re: Car Motors vs Boat Motors?

Boat engines are not as highly tuned as car engines, to make them more reliable, a bit like aircraft piston engines - a 160hp Lycoming as fitted to a Cessna 172 has a capacity of 320 cubic inches or 5,25 litres. Also its redline speed will be 3000 rpm, less again than the boat engine.