Horsepower vs. Torque

[Frank Acampora]

Re: Horsepower vs. Torque



TOM--- Repeat: Practically speaking the torque curve on your 150 HP engine does not matter. As long as you are not in a huge, heavy boat the engine will have all the power and acceleration you need. Repeat: Use two different pitched props--One low pitched prop for skiing and a higher pitched prop for general use and tubing. Numbers? Not possible to tell you what diameter and pitch without knowing the hull, size, average load, and current maximum RPM at wide open throttle.

Now, as an example only: I have a 21 foot cuddy cabin powered by a 140. I do not know the maximum torque generated or torque curve for this engine and I do not care. I use a 13 X 19 for general use and a 13 X 17 for heavy loads (more than 4 people) and water skiing. Tubing does not need the lower pitched prop as acceleation on a tube is not critical. I do use stainless props to maximise the engine's potential. In this application they are about 2-3 MPH faster than equivalent aluminum. Oh, S*** I just started another discussion about stainless vs. aluminum. Oh, well. How about throwing in oil brands or ethanol?

While technical discussions of this nature are interesting and fun, for most people they will have no relevance to having fun on the water with their boat. Practically, we simply change props for best performance.

 

[tomstehr]

Re: Horsepower vs. Torque

Thank you Frank! I keep seeing al these numbers and comparisons and getting sucked into the debate versus what actually matters! Sorry. And by the way where in SE PA are ya from and what is the red coneon your prop?

 

[Frank Acampora]

Re: Horsepower vs. Torque



I am about 30 miles west of Philadelphia, in West Chester.

Late Chrysler and early Force engines (white ones) had an extended prop shaft to take the streamlined tailcone. around '78-'79 Chrysler redesigned the lower unit to a more streamlined shape which did indeed give about 3 MPH more top speed. However, the midleg was one inch shorter and the engines ventilated a lot. So, Chrysler designed the "flare" or "Anticavitation" washer. The attached photos show the difference.

Since I don't like the black plastic, I paint them to match the engine accent color.

 

[tomstehr]

Re: Horsepower vs. Torque

Sweet! I grew up in PA around Elizabethtown. Spent a lot of time on the Susquahana either boating or jet ski-ing! And thanks for the lesson on engine design history!

 

[Rancherlee]

Re: Horsepower vs. Torque

Only time torque would really mater is if the boat was under powered/heavy load and was on the verge of getting up on step. A weaker motor might not have the TORQUE to TWIST the prop hard enough to get the boat up, where as strong motor could TWIST the prop hard enough to get up on step and go. This can be counter acted by a lower pitch prop BUT then the lower torque motor wouldn't run as fast because it would be hitting the rev limiter where as the stronger engine still has the steeper pitched prop. Rare, but it happens. I had a fishing boat where I switched from a 50hp twin to a 50hp triple and both ran the same top end speed but the triple pulled tubes ALOT better and could get up on step alot easier with a heavier load thanks to mid range torque.

 

[QC]

Re: Horsepower vs. Torque

I agree. Rare with runabouts, but not uncommon with heavy planing cruisers.

 

[tomstehr]

Re: Horsepower vs. Torque

I see.. so i just need to add another engine or two! Just kidding.. or am I....

 

[seahorse5]

Re: Horsepower vs. Torque

 

[seahorse5]

Re: Horsepower vs. Torque

 

[QC]

Re: Horsepower vs. Torque

Good find seahorse, but . . . these charts beg the question: what are you going to do with this information? I submit the only thing is buy the Evinrude vs. the Yammie if hole shot is what you are after. But once you owned the 'rude, seriously, what would you do with this information? This does not prove what RPM has the best fuel economy. And it does not suggest an alternative way to select props. What would you do with it?

 

[seahorse5]

Re: Horsepower vs. Torque

Good find seahorse, but . . . these charts beg the question: what are you going to do with this information? I submit the only thing is buy the Evinrude vs. the Yammie if hole shot is what you are after.

The charts help the OP who said he could not find torque charts, so I posted 2 that I had.

Secondly, to bolster the torque vs. hp posts, one can see the differences in engine design and how the outboards would perform, especially on a heavily loaded boat.

Thirdly, for those who viewed the Evinrude vs. Yamaha video with one of each outboard on the stern of a 33' center console, by viewing the 225 torque chart it is easy to see how the Evinrude can plane a large boat on one engine and the Yamaha 225 could not.

The 150 torque chart illustrates how the large difference in midrange torque enabled the 150 Evinrude E-TEC to pull a F150 Yamaha backwards and swamp it in the widely viewed "tug of war" video.

Notice that other companies have not published torque charts as asked by the OP at the start of this thread.

 

[aerobat]

Re: Horsepower vs. Torque

being myself an owner of a direct injecter rude V6 i also saw this torque curves and must say it seems to be a marketing fairy tale. lets look for a second on the 225 hp table and remember the formula for calculating power . powe = torque x rpm / 5252 .

since the rude due to this picture produces over the entire rpm range significant more torque than the yamaha it does not mean anything less that the rude has more power output than the yamaha - at any given rpm !

when we look closer we see the rude peaks at 270 lb/ft at 4700 rpm... 270 x 4700 / 5252 . so the 225 hp rude pushes at just 4700 rpm impressive 241,6 hp !

max power occours at about 5500rpm where it still pushes 240 lb/ft . so 240x5500/5252 = 251,3 hp !!! ???

the yamaha peaks at weak 215lb/ft at 4700 rpm pushing here 192,4 horses. max power occours at 6000rpm where it develops 195lb/ft torque what results in 219,3 hp peak power.

so what ? the 225hp yamaha is in real a 219 hp and the 225hp rude is in real a 250 hp? i also saw the video where the same rated rude destroys a yamaha and i see two conclusions :

1 ) the video is as well the torque curve a marketing fake

2) the torque curves as well the video are real but that means nothing other that a 225 evinrude in real develops 250hp and is strong as hell in midrange ( 247hp at peak tq!) where the yamaha does not reach its rated power and weakens over the entire rpm range.

in this case it would be no surprize that a 225 etec destroys a 225 yamaha .

and we always come back to the conclusion that finally the power output of the rude destroys the yammi , not the torque value as a number.

 

[QC]

Re: Horsepower vs. Torque

Yes ^^^^^ and the 2 stroke should be stronger in the midrange anyway.

My point was that once you owned either, the torque output would not change how you approached choosing a propeller or even operating them. Yes, the higher peak torque unit (more horsepower at any RPM) would have better hole shot or help with a heavier boat that struggles to get on plane.

sea horse,

The OP already has his engine, so if he had the torque info I am not sure what he would do with it That has been my point from the beginning.

 

[tomstehr]

Re: Horsepower vs. Torque

Yes ^^^^^ and the 2 stroke should be stronger in the midrange anyway.

My point was that once you owned either, the torque output would not change how you approached choosing a propeller or even operating them. Yes, the higher peak torque unit (more horsepower at any RPM) would have better hole shot or help with a heavier boat that struggles to get on plane.

sea horse,

The OP already has his engine, so if he had the torque info I am not sure what he would do with it That has been my point from the beginning.

..... I would buy a new cam to give it a better curve so i could out run the rude's on the lake?? I don't really know what I would do with it, I was just curious.. There are a lot of spare minutes to fill. I am sitting at my computer here in Kuwait wishing I was home in Texas, or more so, on my favorite lake in Oklahoma.. and I was wondering about it, and thought this was the best place to ask!

 

[QC]

Re: Horsepower vs. Torque

And to further that . . . Yes, I'd want to know too, but the question was why isn't it published. That's why I keep asking what would you do with it. Funny you mention cam, as that is the number one thing guys with street performance experience try with I/Os, and there is a unique issue with marine as they will suck water back in through the exhaust valves if the cam is too radical. One of the reasons this conversation comes up often. All good, dude.

 

[CaptainKickback]

Re: Horsepower vs. Torque

..... I would buy a new cam to give it a better curve so i could out run the rude's on the lake?? I don't really know what I would do with it, I was just curious.. There are a lot of spare minutes to fill. I am sitting at my computer here in Kuwait wishing I was home in Texas, or more so, on my favorite lake in Oklahoma.. and I was wondering about it, and thought this was the best place to ask!

I assume from your profile you are stationed there in the military. I know you'd rather be back here, but thank you for your service to our country.But just think how much iboats will have you knowing about boats by the time you get back here.

 

[randy2112]

Re: Horsepower vs. Torque

Hi, Torque can be informative in choosing a engine for marine use. two boats rated for 175hp will not perform the same with the same engine if one is bigger and/or heavier than the other. Lets go with a pair 175hp. engines... In a light boat you can run a small displacement engine that produces less torque and be fine. Put that same engine in a heavy boat and it wont get on plane very fast if at all.... Now get a large displacement engine that produces the same 175hp but more torque at a lower rpm and it will get on plane faster... What peple seem to be missing is that the small engine that is producing 175hp is doing it at a much higher rpm and has to get past the first 3 to 4 thousand rpm to produce the same power that the large displacement engine can at 2 thousand rpm. Neither torque nor horsepower are informative by themselves...