When did OMC and Merc rate HP at prop?

[The twoms]

I am fixing up a 1993 fish and ski combo and plan on being ready to purchase a motor for it in a few months. The max HP rating is 120. My boys still like to ski and both are pretty good size. Therefore, I would like to get as much HP as possible. I here different things such as a 1992 Evinrude 90 has as much HP as a 1981 115 because of how they were rated (powerhead vs. prop). When buying a motor, I would like to be able to compare apples to apples. When did OMC and Mercury change rating from powerhead to prop and what is the effect?

 

[phatmanmike]

Re: When did OMC and Merc rate HP at prop?

1986 was the OFFICIAL start of prop rated hp

 

[Dhadley]

Re: When did OMC and Merc rate HP at prop?

The OMC crossflow V4s were "re-rated" in 1985.

 

[The twoms]

Re: When did OMC and Merc rate HP at prop?

So how would a 1984 115 HP moter compare to a 1987 115HP motor? I have heard that you lose about 20% when comparing the powerhead to the prop. Is that true?

 

[Dhadley]

Re: When did OMC and Merc rate HP at prop?

Well, there wasnt a 115 in 87 but lets look at it like this -- in 1984 the "bubble back" V4 was a 140. In 1985 the same motor was a 115. At one time a 112. And a 110. Now, the 84 115 was basically the same motor with a flat exhaust plate. Real close to the same port timing. Same bore, stroke and gear ratio. <br /><br />You really have to spin one up to take advantage of the "tuned" exhaust. Many times in the past we've sold a crossflow 140 to someone who had a 115 and unless the boat was a pad bottom design the performance was almost, if not exactly, identical.<br /><br />However, dont try to compare a 1984 140 crossflow to a 1985 140 looper. The looper makes a ton of torque and will blow away a crossflow.<br /><br />Basically if youre looking for pure pulling power, look for a 120 - 140 looper. Even the newer 60 degree 90 and 115 looper will out perform a crossflow. By a lot. Not that you cant ski with a crossflow because you can and it'll do well. Dont worry about the horsepower so much as the torque.

 

[The twoms]

Re: When did OMC and Merc rate HP at prop?

Are all OMC motors after 1985 "looper" motors? One moter I looked at that I thought was a good price was a 1996 Evinrude 90. Is it a Looper? And if so how do you think it would compare to a 1981 Johnson 140 for pulling power?

 

[Dhadley]

Re: When did OMC and Merc rate HP at prop?

There is a 90 crossflow and a 90 looper in 1996. Does the powerhead look very similar to your 1981? Or totally different?<br /><br />Crossflow V4's were made thru 1998.

 

[The twoms]

Re: When did OMC and Merc rate HP at prop?

I will have to go back and look at it. I'm not sure. But, if it is a looper motor how would it compare to my old 1981 Johnson 140 and if it is not how would it compare? I know it is hard to compare and there are a lot of other factors, but I am just trying to get a general idea.

 

[Dhadley]

Re: When did OMC and Merc rate HP at prop?

Like I said, there's no way a crossflow will make the torque a looper does. If you looked at it once and didnt see any differences then it too is probably a crossflow. If your 81 and the 96 (crossflow) are both running correctly, I doubt youll see a difference worth much $. <br /><br />The wiring changed in 1996 so you will have to get the adaptors or a new boat harness. No big deal, just worth noting.

 

[The twoms]

Re: When did OMC and Merc rate HP at prop?

Sorry, I don't think I asked my question clearly. OUr old boat was a 1981 Glasstron 17'6" V-hull (max rating 140HP) with a 1981 Johnson 140. A few months ago I bought a 1993 Starcraft 17'3" V-hull without a motor (max rating 120HP). I am now in the market for a new motor for the Starcraft. Our old boat with the 140 Johnson seemed to barely have enough power to pull our sons on deep water starts in skiing. Our frinds boats with less motor was not enough. I just wan't to get a motor that is comperable. Ideas? Suggestions. I thought about takeing the 140 and put it on the newer boat, but several people on this forum suggeted that I not over power the boat. (140 on a 120 max boat.)

 

[ddaigle]

Re: When did OMC and Merc rate HP at prop?

An old 81 140hp is not overpowering a 93 120 hp rated boat. Actual prop hp is probably 110. Something you might try is a lower pitched prop. You can get a stump puller prop and still run 30 plus mph. plenty fast for skiing. I ski with a 1971 60 horse and six people in the boat with a 15 pitch prop and still run about 34 mph.

 

[Dhadley]

Re: When did OMC and Merc rate HP at prop?

I would agree. Youre not overpowering the boat. Go back to the torque deal. A 120 looper is going to put more stress on the boat than the 140 crossflow simply because of torque. <br /><br />ddaigle is also right about the set up. A ski set up is way different than a non-ski set up. You may end up with a ski prop and a cruise prop. Its a matter of using the right set up to put the least strain on the motor for the load.

 

[The twoms]

Re: When did OMC and Merc rate HP at prop?

I didn't believe that a 1981 Johnson motor with a 140 decal on it would be too much power, but some people on this forum a couple of months ago said I should not put it on a boat thats rated for a max of 120. There reasoning was mainly due to liability. Also, that here in Oklahoma lake Patrols are starting to check for over powered (above max rating) and not letting them on the lakes. THOUGHTS?

 

[Dhadley]

Re: When did OMC and Merc rate HP at prop?

That would be a good reason not to. The cops cant be concerned about torque and such. They check for advertised ratings and do their job accordingly. Same for lawyers and insurance folks. <br /><br />If there was an accident, heaven forbid, and someone discovered that, you could be in a world of trouble.

 

[BillP]

Re: When did OMC and Merc rate HP at prop?

Here's where you will see a major difference in the crank vs prop ratings...I replaced a perfect but old 1965 Johnson 75hp with a new 1991 Johnson 70hp. MAJOR performance difference in all respects...not even close. The old 75 seemed to run closer to a modern 50-60hp.

 

[The twoms]

Re: When did OMC and Merc rate HP at prop?

Thanks BillP, thats really what my question is. If an older 75 runs like a modern 50-60 then what would an older 140 run like in a modern moter, and what would be classified as a moder motor?

 

[Boilermaker]

Re: When did OMC and Merc rate HP at prop?

I don't mean to steal this thread, but could you explain to us the differance in appearance between the looper & the X-flow???<br />Is the looper the 60deg.engines & x-flow the 90deg. vees???<br />Also, what would my 1978 115Hp Johnny be rated at today??? A carbed 99cu.in. x-flow of similar design in the more modern HP ratings??? (why don't I EVER see HP/TORQUE cuvrves on these engines???<br />Thanks

 

[Dhadley]

Re: When did OMC and Merc rate HP at prop?

V4 and V6 OMC crossflows use a 90 degree block design. There are 90 and 60 degree OMC V4 and V6 looper designs. The easiest way to tell a looper from a crossflow from the outside (V4 and V6) is the the crossflows have bolt on by-pass covers, bolt on exhaust covers and bolt on water jacket covers on the heads. <br /><br />A 1978 115 is about the same as a newer (1985 & up) 90 hp crossflow. But again, it will never make the torque of a 90 hp looper.<br /><br />Torque curves are something the factorys have never published.

 

[Boilermaker]

Re: When did OMC and Merc rate HP at prop?

Thanks Dhadley!!! You always seem to have the answer to what I ask!!! (Not that others DON't have the answer )<br /><br />WOW - Over 20 % loss in the HP figures from Crank to Propshaft!!! <br />Is that the actual losses of the 90 deg. direction change gear-set??? OR is there something I'm missing here?

 

[Dhadley]

Re: When did OMC and Merc rate HP at prop?

We generally see about a 10-12% loss thru the outboard lower unit. Keep in mind the NMMA allows a certian variance between actual and advertised horsepower. <br /><br />And if youve ever run a horsepower read-out dyno you know that horsepower is calculated with a correction factor. That factor can vary - a lot!