Outboard h.p. ratings

[dshock]

I was wondering if outboard engines have ever been rated by powerhead horsepower instead of propshaft hp. We have a 1981 checkmate that has a 1981 merc 150. While shopping for a 175 (the boat is rated for 180), a couple people said that we would probably get what we needed if we bought a new 150, because of the difference in rating. It kind of seems like a line a salesman bs to me. I thought that all outboards have been rated the same since the 50's or 60's. Can you help me understand this? During the consideration of the repower, we found another checkmate that is in slightly better condition. It is a 1990 with a 1991 blackmax 175. Is this engine significantly better than what we have, or are we going to wind up replacing it because we are unhappy. Both boats are very clean low hour boats. We would be doing a compression test on the 175 before buying. What do you think? We use the boat for cruising and for skiing/barefooting.

Thanks
Dan

[Markus]

Your friends are right. This is the story as I understand it:

When Yamaha entered the U.S outboard market in 1984, they pulled Carl Kiekhafer's old trick of building a X hp engine that was way stronger than the X hp engines of the competitors. They did it by rating the engines at the prop shaft rather than at the crank shaft.

As a result, the other manufacturers followed and a NMMA norm saying that the hp rating of an engine should be prop shaft hp +-10% was introduced.

In addition, there is some effect from whether you follow the SAE or DIN norm for hp that did impact outboards as well that happened at the same time, but I do not quite remember. I think John Tiger wrote an excellent article about it all in B&WB a few years ago.

Anyway, this re-rating did have quite some consequences. For example, the 235 hp OMC cross flow V6 from 1984 became a 175 hp engine after the re-rating.

[dshock]

So the 1991 175 would be significantly stronger (50 hp +) than the 1981 150. They are both black max mercs. Are there any other comments on the ease to modify for either of these engines? Is it agreed that this change was in 1984 for all manufcturers?

Thanks
Dan

[pyro]

The 175 is also a 2.4 L motor, whereas the 150 is a 2.0. The 175 is going to have better torque and power all-around. BIG difference. With some simple mods, you could get over 200 hp from that motor, the 200 is also a 2.4 up to '92.

I think the 150 also came stock with a 2:1 gearcase, and the 175 had a 1.87:1. Someone correct me if I'm wrong :confused:

[dshock]

Great! Any more input??

Dan

[BRENT GILL]

Dan , in the mid 80's when the manufactors went to
rating the horsepower at the prop instead of the
crankshaft it is true that the #'s fell alittle . But to say
the 235 fell to 175 hp. is incorrect.
You can figure it takes away around 5% more
horsepower to drive the lower unit depending on
the horsepower of the motor.

Soon after , the engineers went to work to make up the
diffenence.

Hope this helps
Brent

[dshock]

I thought that there would be significantly more loss in the drive that 5%. With the bevel gear and everything I would have thought it close to 15-20%. Anyway, who else has some input for us?

Anymore comments on 2.0L v. 2.4L????

Thanks
Dan

[Raceman]

I've never heard the Yamaha started the trend and everybody else followed tale before, but wouldn't say for sure that it's incorrect. I'd guess that insurance premiums might have been more of a factor, although I'm sure the companies wised up in a year or so.

I also believe there was more than a 5% difference when the rating axe fell. My memory's kinda foggy on specifics now, but seems like the old 225 Merc was re rated to 200 with no changes at that time. The inline 1400 (late model) was also downrated more than the 9 HP that 5% would amount to. Since horsepower ratings are largely advertising rather than exactly accurate, it's hard to say for sure.

[Raceman]

"Anymore comments on 2.0L v. 2.4L????"

Yep............ I wouldn't give one the knod over the other from a durability standpoint, but there's no substitute for cubic inches when it comes to makin' power.

[dshock]

Great info. Please keep the comments coming.

Dan

[BRENT GILL]

Guy's
5% was a round about #.
Don't tell me you think (20%) your lower unit
is robbing 40 hp off a 200 powerhead.

We need someone with a land and sea dyno
to step in here.

Your hp rating is done at 5000rpm's or so
and once the gears are spinning , well Its kind of
like your water pump.
Its hard to get going but after its spinning
it takes nothing to keep it going.

2 cents

[chris_lacey]

I tend to side with Brent on this. A complete automotive power train doesn't use up 20%. I'm thinking 5-10% max for a gear case.
If I remember correctly, the old 225 mercs had 7 petal fronts and all the old 200's had 5 petal fronts. When they made 225 the 200 had vertical reeds and after 82 they had horizontal reeds.
As far as the 235's we'd better ask racer, Bill Gohr or the like. They would know for sure.

[dshock]

I am no expert on outboard engines, but I can speak to a few of your comments. The whole idea behind hp is the ability to accelerate somthing. Your comment that like a water pump, it takes a lot to get it going, not keep it going, is the esscence of hp robbing. Secondly, many automoblie drivetrains rob 25% +. Granted, automatics are the real power hogs and manual vehicles fall closer to the 15% range.

I don't think these arguments are particularly relavant to the discussion. I am sure someone has done the dyno runs and can tell us for sure. I am also sure that this figure varies a great deal between, manufacturers, models and even size classes.

Anyway, great stuff, keep it coming,
Dan

[Markus]

It seems like the OMC 235 example caused some confusion. That specific example was not just due to power losses in the lower unit. I guess other factors were coming into play, e.g. whether you want to be on the top or the bottom of the slack allowed by the rating, at what conditions (temperature, humidity) hp is measured, etc. I think it is true, but I am of course not quite sure. Maybe one of the OMC gurus could enlighten us.

5-10% hp loss in the lower unit is what most people use for reference, by the way.

Further comments:

A new Mercury 150 will be based on the 2.5 liter powerhead and will be fed behind the liner. Assuming that Merc. is close to the 10% limit on this one, the XR-6 engines supposedly are, it will output close to 165 hp on the prop shaft. It will be noticably more powerful than your old 150. However, a new 175 will of course be even more powerful.

[Sorry Dog]

I don't have any data to back it up but out of the people I have talked to I seem to think the Zooks were prop rated early on. The inline140/115 didn't change until later on.

My wild guess would be that Merc or OMC didn't give too much of a **** how zuki or yammy rated them but thought it was a good idea and tried to one up each other.

[wrechin2]

I hope you can see it! If you can't the horepower is about 20-25 hp higher on most than it is rated except for the merc 225 is is rated at the same horsepower. This was a article in a land-and-sea catalog.

[wrechin2]

Goto this link aand you will see the chart on page 2.


http://forums.screamandfly.com/forums/showthread.php?s=&threadid=39707&perpage=15&highlight=bridgeport&pagenumber=2

[Markus]

If you suddenly face a competitor whose engines are not only cheaper and of superior quality, but also stronger for the same hp rating wouldn't you worry?

Closing the hp rating gap was the easy part. It has taken 20 years to work on cost and quality. Mercury has done a decent job, but we all know the fate of OMC.

[wrechin2]

around 85 and newer it is rated at the prop. 84 and older is rated at the crank. So some are at the crank and some are at the prop.

[AlaskaStreamin]

As far as dyno readings go,... The 300 promax puts out 285 hp at the prop and the 300x is 328hp. I'm sure no two motors will be exactly the same. The promax's reportedly get their 300ish hp at 4800-5000 rpm's and hold it to redline. The torque starts dropping off over 5000 rpm's.

[wrechin2]

+/- 10 percent variance or something like that isn't it? So on a 200hp engine it can be a 180hp or a 220 hp engine. So much for being close huh.:rolleyes:

[Jeff_G]

Back in the early days of the Merc vs OMC wars Mercury deliberately understated the HP of their motors. For example they maight have a motor badged at 25 hp but actually put out 40. In this way they had a better, stronger, faster than the competition. This continued through the 60's and 70's.

Most outboards of that era were rated at the crankshaft. Some of the same games were going on in the late 70's as well. When Merc came out with the 150 V-6 motor Merc rerated their 150 inline to 140 so they would not have 2 motors of the same hp. When merc came out with the 150XS they rated it at 155 hp. The only change was the jets, and slightly higher port timing. I have measured one at 165hp a few years ago, although it did have a few slight mods.

The 70hp OMC is a good example of an underrated motor. In the SST60 form it gives out about 90 to 95 hp and the stock 70 isn't that far behind it.

In the mid 80's in response to the NMMA, National Marine Manufacturers Association, the motor manufacturers begain to rate the motors at the prop shaft instead of the crankshaft. Previous to this they were rated at both areas.

The measurement of the day was +- 10%. Some of the foreign motors were again deliberately underrated. For example a 90 hp motor could actually put out 81 to 99 hp and be rated a 90!

Some manufacturers also restricted some motors slightly to produce a smaller hp motor. For instance some 15hp motors had a different carb set up so the 9.9 version didn't open the throttle plate as much as the 15. Change a $5 part and your 9.9 becomes a 15! There was a lot of "cheating" going on.

With the EPA mandates of the late 90's all motors must state the true propshaft hp and the requirements are very stringent. So no more fooling around with the hp figures as it also effects the EPA pollution figures.

But in reality hp is only a very general guide as to the performance of the motor. It is just a very simplistic way to distinguish motors to the general public. It really has very little bearing on the performance of an individual boat.

But if you put the hp figures of the past together with the hp ratings of a particular boat then things really get interesting!

[Toffen]

Hi!

Just a little comment from Norway. Merc 500EFI inboard pulls 500 hp on drive train and 470 HP on the prop. It is commonly referred to in most powerboat magazines such as HotBoat, Powerboat, etc.

Powerboat Mag did an article on Promax 300X. The engine they did a story on pulled 329 hp on the powerhead (dyno test). The old Promax 300 is told to pull 300 hp on the powerhead. This give approx. 285 hp on the prop for the old one and approx. 315 hp on the new version.

Cheeers, Toffen G

[wrechin2]

Only part of the it. Torque plays a very large part on performance. You can have two identical engines but have one with more torque and it will be stronger. Has anyone ever seen a spec sheet on a 2 stroke with torque numbers?

[Mark75H]

yes

[wrechin2]

was it on?

[1BadAction]

Originally posted by wrechin2
Only part of the it. Torque plays a very large part on performance. You can have two identical engines but have one with more torque and it will be stronger. Has anyone ever seen a spec sheet on a 2 stroke with torque numbers?

that is the reason why a 2.5L 150 pulls harder than a 2.0L 150, and why a 3.0L 200 pulls harder than a 2.5L 200.

if you go by this HP=Torque/5252xRPM or Torque=HPx5252/RPM. if a 2.5 makes the power @ 5500 and the 2.0 makes it @ 6000

a 150 2.5 makes 143 ft/lbs
and a 150 2.0 makes 131.3 ft/lbs

i'll have to check where they make the power at to get more accurate.

jim

[Techno]

The other item with the torque thingy is how high the engine can spin. Isn't that the advantage of the hipo 2.5s compared to the newer optimaxies?
Like a 260 Vs a 280?
So if your looking at engine replacement get the most powerful you can, this way you won't be asking how to squeeze more power out of too soon.
I'm thinking that all 2.5s wiegh the same. There is the question of economy and lower end porting stuff though.

[Mark75H]

Here ya go, James.......ask and ye shall recieve:

[Mark75H]

edited to make Merc look good:p

[Mark75H]

another

[Mark75H]

just enough to tease you ... the less you know the better we look, ignorance is bliss as they say:D

[BarryStrawn]

Too bad Merc can't find a dyno that will record data more frequently than every 1000 rpm. I like how someone extended the data to zero. Makes me confident the rest is gospel.

Real dyno charts on outboards have always seemed to be deep dark secrets. Way back in the early 80's I was discussing a powerhead with Second Effort. They said they would dyno test my powerhead when they finished the mods but they would not send me the data. Goofy.

[Jay R.]

here's they way i heard it at OMC school.
.the change to prop shaft rating was to make a more consistant rating among differnet brands. and i was told roughly 10%.
the other thing I've noticed. and it's been mentioned is Rpm's at HP rating. i can't think of an example right now excpt my truck. its rated at 230 at 4200 rpms i think (been a while) but its rpm range is 5000 to 5500. they did that so there bigger V-8 could keep its rating above my engine.

[BarryStrawn]

Sam - Got your PM. I didn't intend to be negative about Mercury, just commenting about the entire lack of useful information from everyone. My sarcasm was misplaced. Since Mercury obviously has the information and allocates space in the race catalog, I don't understand why there isn't more detail. But at least they publish something. Second Effort (OMC) wouldn't even give me a chart if I paid for the test on my powerhead.

[Mark75H]

Yep, I agree with you, more detail would be more interesting, these graph's are set up/edited as a propagandist would.

I wondered for years about outboard torque/hp dyno charts and these skimpy things are the only ones I've ever seen


PS: thanks for your reply here in the thread, it brings balance and shows your true clear-headedness

[Markus]

I have a link on my links page to a place called boatsetup.com that used to have dyno curves with torque and power for Mercury's 3 liter 225 and Yamaha's 3.1 liter 225, but that site does not seem to work very well anymore.

[wrechin2]

Sam,
Thanks for the information. They are kinda skimpy.:rolleyes: But at least they are there something to go by.:)

[Sorry Dog]

If you suddenly face a competitor whose engines are not only cheaper and of superior quality, but also stronger for the same hp rating wouldn't you worry?


Me personally? Yes.


But I was more or less trying to see through the eyes of the 800 pound beaucratic corporate gorilla. GM and Ford only respond to sales numbers Their response was the Cavalier/Cimmeron. I don't know much about Brunswick but similar behavior back then wouldn't surprise me. Again - I dunno, but I don't think Zuki ever sold that many here and they probably didn't start to worry until more Yammys started showing up.

[Markus]

(Bringing up this old thread again)

Sorry Dog, my understanding is that Brunswick was quite aware of the threat posed by Yamaha, probably due to their business dealings with Yamaha Motor in the Sanshin JV. I remember reading in some business literature many years ago how they responded to the end of Sanshin by improving their production set-up (before, they used to make all 50 hp engines for the entire season, after they switched to making 75 hp engines for the entire season, etc.) and improving quality.

OMC, I believe, reacted more like GM or Ford in your example, but they did change to propshaft hp ratings to "make a more consistant rating among differnet brands", as Jay R. pointed out.

[QUICKSILVER]

I'm not sure why it came about, but I do know that the 1982, 200 Merc had 7 petal horizontal reeds just like the 1981, 225 had. The only difference between these two years was the decals. Both engines made the same horse power. In 1983 the 200 had 5 petal horizontal reeds. The 1981, 200 had 5 petal vertical reeds. I thought the propshaft rating came about in 1982 when the 225 disappeared.

[transomstand]

I always thought the explosion of the bass fishing market had a lot to do with it. Seemed like all those guys started popping up with their own TV shows in those days. As I recall, bass competition was limited to 150 HP, good motivation to reduce your published horsepower figures, and keep your factory sponsored Roland Martin (?) out front. I seem to recall he was a world champion and his show was basically a Merc commercial.


Disclaimer: The details of this post are from my limited memory, please forgive any innacuracies about bass fishing ( I have personally never caught one) I hope Roland Martin was not an OMC guy.

Pete

[Mark75H]

related thread (http://forums.screamandfly.com/forums/showthread.php?s=&threadid=45063&highlight=xr2)