Horsepower Ratings

[garnett33]

Can someone tell me how HP Ratings work. I'm looking into going up in HP on my 16 ft Bass boat. After looking at the new E-Tec 40, 50 and 60 I noticed that all weigh the same, have the same bore and stroke and displacement.
The only changes in the specs are the H/P, RPMs and WOT range.
So can I get some input on how they achieve the different H/P on what appears to be the same powerhead and guts?

 

[JB]

Re: Horsepower Ratings

On 2 stroke blocks with the same displacement different peak HP ratings are achieved with changes in port timing (similar to cam timing in a 4 stroke) compression ratios, ignition advance curves, exhaust geometry and, in DFI engines, software differences in the 'puter. In carbed engines they often have different size carb venturis.

It is important to understand that a higher peak HP in a given block doesn't mean higher HP at all rpm. Often the higher peak HP rated engine delivers less HP at lower rpm or even at cruise rpm.

Horsepower ratings are a marketing (and pricing) tool that shouldn't mean a lot to a savvy boaters, but makers seldom, if ever, publish the whole story of engine output at all used rpm levels. The only factor I named above that affects engine output at all rpm is compression ratio and sometimes the ignition advance curve. They can only go so far with either of those without risking a blown engine.

In real world usage about the only real difference you would see with one block rated at three different HP levels is top speed, and you would probably have to read that on the speedometer (or GPS).

 

[steelespike]

Re: Horsepower Ratings

I can't speak specifically to the etec but speaking generically porting timing and size, intake design , ignition timing,possibly compression,exhaust manifolding.etc etc.It does appear that the 60 has slightly more efficient GPH (gallons per hour)per horsepower figures than the 50 or 40.If I could afford it
I would get the 60.You get the extra 20 hp in the same package and when driven within the 40s speeds the motor is loafing and gets close to the same gph.as the 40.

 

[CATransplant]

Re: Horsepower Ratings

It's really convenient for the manufacturers to use one platform to deliver different horsepower ratings. Detuning a 60hp outboard to knock it down to 50 or 40 hp is pretty easy, so you have three outboards coming off the same assembly line, using the same castings, etc.

In reality, they all cost about the same to build, although you'll pay more for the more powerful one.

Even on the small end, like my 6hp Johnson, it has an 8 hp big brother. I don't know what the exact differences are, but the 8 hp delivers the 8 at a higher RPM, so it's probably a breathing thing, given the 2-stroke design. I don't really care, because the 6 performs just fine for me.

 

[marquette]

Re: Horsepower Ratings

question for JB
if i understood what you are saying is that 2 or 3 outboards built on the same block will preform pretty much the same from low to midrange but the top end will be where the difference is felt. i have a 14 1/2 ft tuffy trihull i am looking for a motor for. so i have been looking for a 25 or 30 hp.(and i am not brand shoping) but the 20hp built on the same powerheads are significantly less expensive. so would a 20hp put the boat up on plane as fast as a 25hp but just have a lower top end speed? the boat weighs 350lbs and put a couple of people and gear in it i assume it will be about 1000lbs in the water. or are you saying that with each 5hp increase there is a proportionate increase in torque and torque is what planes the boat?

 

[wbeaton]

Re: Horsepower Ratings

There is a difference in torque, but it may not be noticeable on some set-ups. If the 20 hp doesn't struggle to put you on plane then the main difference will be top speed.

 

[steelespike]

Re: Horsepower Ratings

I think your getting a little too involved in the torque question.
I think we can assume a torque increase with hp increase.It is also
generally agreed that more cubes produce more torque.More cubes also produce more weight. 77 up 25/28 hp E/J motors are 31 cubes pre 77 25 hp are 22 cubes. in some cases about 20 lbs difference.If I was you with the weight your pushing the bigger the better.

 

[Silvertip]

Re: Horsepower Ratings

Torque generally follows displacement. On higher HP engines with the same block, torque generally moves up the rpm curve with HP increases but the amount of torque doesn't change to a significant degree but depending on the combination can be fairly significant. Think about the small block Chevy V8. That engine has had probably 50 or more HP ratings over the years. Same displacement, just cam, compression, timing, exhaust, and carburetion changes. While I haven't done a significant study, the only difference that stands out between a 40 and 50 HP Suzy 4-stroke is the intake cam profile. Very likely the ECM has different programming to provide different injector profile.

 

[seahorse5]

Re: Horsepower Ratings

The 60hp is a bit different than the other models. It has a higher rpm redline and in the mid-section there is a water valve that cools and tunes the exhaust on acceleration.