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TOPIC: Increase HP and keeping economy on a '79/85hp ER

Increase HP and keeping economy on a '79/85hp ER 1 year 10 months ago #121848

  • g3bill
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Increasing HP and keeping economy close to original on a '79/85hp Rude, Is there a place to look for small DIY modifications that wont cost tons? Maybe opening the carb a bit and different reeds or whatever. prop, mine is stock alum 3 blade? Just thinking to increase speed from 30 to about 35. Bill

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3 cd g3's
1 seafair sedan

Re:Increase HP and keeping economy on a '79/85hp ER 1 year 10 months ago #121881

All power increases use more fuel -- there is little that can be done for efficiency. Bigger carbs/jets and lighter reeds will add power, but will eat more fuel for sure.

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Re: Increase HP and keeping economy on a '79/85hp ER 1 year 10 months ago #121882

  • ed-mc
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Bill, a stainless prop might give a bit better performance. If I recall, the OMC stainless props have thinner blades which slice thru the water with greater ease.

You might also take a look at the transom height of your motor; you may be able to raise it up a bit for less drag. I'm assuming it's on the Seafair Sedan and that's not exactly a hi-perf boat, but most rigs do respond to raising the engine a bit from std height.

The biggest concern in doing so would be ventilation during cornering and when the engine is trimmed out. A 4-bladed prop would help with that, although 4 blades ain't necessarily gonna be faster than 3 blades!

Pretty much any older, crank-rated 2-stroke is gonna suck down fuel at a rate per hour of its HP rating divided by 10, at full thottle. I.e., your 85hp will use approx 8.5 GPH at full throttle.

It's a little trickier when trying to figure out a newer motor that is prop-rated, they're gonna burn more at WOT than that formula would indicate, since the formula only works with crank-rated HP values.

If you were to repower with an E-TEC that'd probably be the most fuel-efficient (albeit very expensive) way to go. A 4-stroke is efficient as well, but the weight penalty offsets a lot of that.

Check out this 90hp E-TEC HO, Sweet!



That's a "90" 4-cyl that puts out almost 100HP at the prop!

Even the 3-cyl 90hp would most likely move your boat faster and more efficiently than the old 85hp Beast:


Lighter than its 4-cyl mate, as well.


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