350 Mag broke a rod.

[wca_tim]

I'm seeing mid 70's depending on prop and loading, etc...

 

[ezstriper]

1st 4500 is far from high reving, and the point being missed here is that longer stroke is going to do for you is more torque and thats what moves a boat....sheer h/p means little other than bragging rights...

 

[winter]

1st 4500 is far from high reving, and the point being missed here is that longer stroke is going to do for you is more torque and thats what moves a boat....sheer h/p means little other than bragging rights...

Pretty true words. We seem to always use HP for our numbers. Always wondered why outboards used HP for marketing . The simplest way to define hp vs. torque is this....

Torque is how much work an engine can do.
HP is how fast it gets it done.

Driving any diesel powered truck will emphasize that.

 

[wca_tim]

Pretty true words. We seem to always use HP for our numbers. Always wondered why outboards used HP for marketing . The simplest way to define hp vs. torque is this....

Torque is how much work an engine can do.
HP is how fast it gets it done.

Driving any diesel powered truck will emphasize that.

so then why is a boat fastest when propped so that wot is at max horsepower? and not maximum torque?



Not trying to start anything, and am actually smiling and just trying to add a little..

horsepower = torque x rpms.

horsepower is the rate at which you can do work (ie how fast the boat can be pushed through the water) and is a more useful number when considering how fast you're going to be able to go at wot. Peak horsepower determines max speed (all other things being the same)

Torque that's available at a given rpm minus the torque it takes to maintain that rpm is what determines how quickly you can accelerate to a higher rpm (and rate of doing work / horsepower). Torque is a more useful number to determine bottom end and mid range seat of the pants performance, ability to get on plane, pull skiers, accelerate, etc...

Also, don't forget that torque changes as a function of gear ratio - if you run more gear reduction you get more torque at the prop, but the same amount of horsepower.

Just something to think about...

 

[ezstriper]

who said that they are ???? they just give you the specs where the rpm should be at WOT, but anyway the torque is what pulls you up to the top rpm/speed in normal type boats...all out race stuff different, also all newer spec of H/P are taken at the prop, so that confuses things also. all these marine engines are trying to get as much H/P and torque at the lowest rpm they can....drives don't like high rpm for very long...

 

[wca_tim]

who said that they are ???? they just give you the specs where the rpm should be at WOT, but anyway the torque is what pulls you up to the top rpm/speed in normal type boats...all out race stuff different, also all newer spec of H/P are taken at the prop, so that confuses things also. all these marine engines are trying to get as much H/P and torque at the lowest rpm they can....drives don't like high rpm for very long...

if you look at the torque / horsepower curves for a marine engine, the boat will run the fastest on top end if propped so max rpm at wot is right at peak horsepower output...

for example max torque in a mercruiser 350 mag is somewhere around 3500 rpms, max horsepower is somewhere around 4800 rpms...

and yes, torque is what accellerates the boat... and is inherent in horsepower... rpm's multiplied by torque equals horsepower...

the main reason you can't turn a marine engine up a lot higher rpm to get more horsepower out of it is because that engine wouldn't have any torque at the bottom end of the rpm range and would suck out of the hole. and yea, I'm sure if you spin a stock outdrive up for long, withj an engine that makes more horsepower than it's rated for, it might just come apart....

anyway, fun stuff to think about...

OH, and by the way ezstriper.. your boat is awesome!