Mid 80's Evinrude 15 7000 RPM outboard

[thatone123]

Anyone out there know why the mid 80's Evinrude 15 went all the way to 7000 RPM. Never have heard a satisfactory answer to this question. Some plates on motor say that they produce 15 hp at 6250 and Operating range is 5000 to 7000 RPM. Most of the plates say only that max operation is at 6250 for 15 hp. So why do some of these outboards have 750 additional RPM available. A real stumper as none of the experts seem to know? I know a number of these are used by limited class hydroplane racing in the upper Mid-west. Did OMC make some of these motors since back then the factory was in the area - for that limited clientele or what. Inquiring minds want to know. Most knowledgeable OMC folks I have talked to have not even heard of this mystery?

 

[Scott Danforth]

could be the RPM band was wide so that when OMC dropped the motor on an OMC built boat that the prop selection was right to get the WOT into the 5000-7000 RPM range

the mid 80's is when OMC owned many boat lines.

 

[flyingscott]

It was a marketing thing. The 15 evinrude was not competitive in the 80s anymore. The Yamaha,suzuki and even Mercury were making stronger 15 hp motors. There are 3 different exhaust tuners for those motors each one has a different RPM Range. They kept redisigning the tuners to keep it competitive it worked somewhat. The racing motor was a stock powerhead with a racing lower unit.

 

[jimmbo]

In 1986 the WOT range was 5500 - 7000. That was when OMC was switching to prop rating the engines, so to keep the 15hp rating they had to spin the engine a little faster.

 

[thatone123]

THANKS....all good answers and logical.

 

[thatone123]

P.S. Would this 7000 RPM have any advantages for me. I operate on twisty sloughs mostly with the longest strightaway a half mile long so hardly never get over 1/2 to 3/4 throttle. I sometimes carry heavy loads and need a lot of power then. In shallow water I need to get on plane right away to clear the mud and weeds, but then throttle back right away. It seems to me one of these 7000 RPM outboards really go when opened up, but maybe that is my imagination. I use a 12 ft. Jon boat..

 

[flyingscott]

Here is the thing any of the 15s after 1984 is capable of running to 7000 rpm. There is no difference in the prop,lower unit or powerhead on any of those motors. Put a tach on yours and see if it is even reaching 6000 rpm.

 

[Chinewalker]

The racing motors, often referred to as the 15A, are still in use in APBA's smaller outboard classes. My 9-year old will actually be running one this fall in a boat I need to have delivered soon. He'll be running the J-class, which is the Junior racing division. They run the 15A with a restrictor plate - still does over 40mph!

 

[thatone123]

That sounds like a lot of fun for him to race a boat like that! So...I get it, these are capable of 7000 RPM "if" they are souped up! Maybe I'll try a jury rigged 20 hp carb...Just kidding!

 

[flyingscott]

This is straight from the owners manual of my 1985 15 hp Evinrude. This is just a plain shortshaft motor.
BIA HP 15 AT 6250
POWER AT PROPELLERSHAFT ACCORDING TO ICOMIA 28-83 IS 15 HP AT 6250 RPM.
FULL THROTTLE RPM RANGE IS 5500-7000 rpm.
So nothing special about the 7000 rpm range

 

[Chinewalker]

No souping up required. Propping it for your hull and load is what's needed.