whats actual HP?

[ronward]

Just sitting here with a cold one, taking a break from getting boat ready for tomorrow. I got to thinkin (usually not a good thing) that older motors are HP rated at the crank, then what HP am I actually getting out of a 1973 85 horse Johnson at the prop? I dont really care because it pushes my boat great. But, like I said, I got to thinkin.

 

[BonairII]

I'm guessing about 15% through parasitic loss....so it probably puts out what a newer(post 1985?) 70hp does.

 

[F_R]

I'm no engineer, but in my opinion there isn't enough loss to notice. But I suppose there is an engineer out there somewhere. Hhm.m.m., wonder why cars are rated at the engine instead of at the tires? Somebody picking on us boaters?

 

[ronward]

The one's picking on us are probably the one's fishing from the dock while we launch our boats. Oh well, time for another cold one...or six

 

[emdsapmgr]

In the mid 80's OMC re-rated their 200 hp V6 crossflow. In 1983 it was crank rated at 200. In 1984 it was rated at 185 hp-probably due a change to prop rating.

 

[ronward]

As I said, I don't really care that much. I was just wondering. My wife says it's plenty fast enough and that's evident by the white knuckles on the hell handle. So apparently it's fast enough...lol. Thanks for the replies

 

[F_R]

I really don't know, but I'll bet there were more differences between the1983-1984 200/185 motors than rating method. A real quick glance shows right away that they had a number of different cylinder heads and head gaskets. With that, I quit looking.

 

[Faztbullet]

Several years ago a salesman came by selling the Dyno-mite hp dyno at one of my dealers . We played with it and ran a 78-79 115hp and at 5700 rpm it only made 88 hp at prop.

 

[emdsapmgr]

My point is that the difference between the 83 and 84 powerhead ratings is 9%. Could be even less when design changes are taken into account as FR indicates. The NMMA permits powerhead ratings to vary within 10% of the decal on the side of the cowling-so what's the real hp difference? Hard to tell.