Upgrading a 1992 Evinrude 9.9hp to a 15hp

[DeanHensler]

I've read a lot about this on Leroy's Ramblings and it appears to me that all I need to do to perform this upgrade on my OMC engine is to put a 15hp carb on. Can someone confirm that? My engine's model number is TE10RELENA

 

[HighTrim]

Seems to be a very debateable subject on here.

Will you get a true 15hp? Nah. But it will definitely up your ponies/acceleration and top end speed some.

They also used spacers under the reed stops to open a bit more, and different exhaust tubes. I think most of the power came from the carb though.

So will just swapping the carb give you 5hp more? I doubt it, it will give you a noticeable difference however.

 

[oldboat1]

Leeroy's Ramblings also gives you a side-by-side look at the throat sizes of the 9.9 and 15. You may already have a 15 carb body. The carbs are jetted differently -- .034 for the 9.9 and .054 for the 15. Whether going to a 15 carb will get you across the lake faster is debatable, but if you believe it does....

Think I would want to get the 9.9 in top running shape first and see what it will do, if you haven't done that. I have the '91 version, and it seems pretty quick on a light boat. It's all fun.

 

[DeanHensler]

I believe on the 1992 the reed stops and exhaust tubes are the same on the 9.9 as the 15hp. Meaning the ONLY Difference is the carb.

 

[Silvertip]

It doesn't matter if you actually get 15 HP from the 9.9. Unless RPM goes up you will go no faster. It is propeller rpm and pitch of that prop that determines boat speed. The extra ponies may get you on plane quicker and possibly a little faster because the existing prop may be at the top of the performance curve for the 9.9. The 15 may allow spinning it faster but at the risk of overreving. The fix for that is to increase prop pitch. That then would bring the speed up. It's all a crap shoot however unless you have a tachometer and get some sort of a baseline with the 9.9 as it is, before launching into the conversion.

 

[flyingscott]

Right around 1988 OMC gave all the 15 hp goodies to the 9.9 hp except for the carb. So to answer your question Yes you will get 15 hp out of the motor. The 10" pitch prop was the common prop for both motors. Check the prop pitch you have will probably be ok. The operating range for the 15 hp is between 6000 and 7000 rpm BUT they make their power closer to 6000. The 9.9 makes it's power closer to 5500.

 

[boobie]

For the 5 HP gain all the work and money wouldn't be worth it to me. JMO.

 

[scout-j-m]

What hull and load do you plan to use the motor on?

I have a 16' Alumacraft flatbottom that is typically loaded with me at 170 lb, bow mount trolling motor, group 29 battery, 3 gal fuel, 60 lb flooring, fishing gear, plus a little bit of other random stuff....with my 1982 9.9 hp Evinrude it will do about 17 mph on glass water at 5400 rpms with an OEM 10" prop, which results in about 20% prop slip. Same load and prop but with my 1992 9.9 hp Johnson with a 15hp carb and it will do about 21 mph at 6500 rpms which is closer to 17% prop slip.

Top speed there isn't a big difference but the holeshot is much more noticeable. It is also helpful to have that extra 5 hp or so for going with multiple people. My boat will hold 3 people comfortably for crappie or catfishing and for 3 people having 15hp paired with an 8" prop is super nice.

 

[jimmbo]

. In theory, a bigger carb should produce a soggier/weaker hole shot, and more power at the top as it is getting more air and fuel. Since both the 9.9 and 15 of any given year have the same gear ratio, the higher HP engine will be able to turn the same prop at a higher rpm. Whether or not it can turn the same prop up to the 15 hp rpm range is something to find out. But... was the same prop letting the engine turn in the 9.9s rpm range when it was still running the original carb?

 

[scout-j-m]

. In theory, a bigger carb should produce a soggier/weaker hole shot, and more power at the top as it is getting more air and fuel. Since both the 9.9 and 15 of any given year have the same gear ratio, the higher HP engine will be able to turn the same prop at a higher rpm. Whether or not it can turn the same prop up to the 15 hp rpm range is something to find out. But... was the same prop letting the engine turn in the 9.9s rpm range when it was still running the original carb?

I can't answer that as that motor came with 15hp carb when I bought it. That was the reason it was such a good deal for me as those 15hp carbs pull a premium on Ebay and other places due to demand.

But I get what you are saying...the difference in my 1982 9.9hp and 1992 9.9hp is more than the carb as the 1992 model has the reed shims and tuned exhaust while the 1982 doesn't. Who knows how much those two help without the larger carb throat. So it is in fact not an actual apples to apples comparison despite having the same displacement.

 

[tomhath]

It doesn't matter if you actually get 15 HP from the 9.9. Unless RPM goes up you will go no faster. It is propeller rpm and pitch of that prop that determines boat speed.

Think about how a carburetor works. At anything less that wide open, the throttle plate restricts flow through the throat. So until the 15 hp carb is being run wide open you won't see any difference - 9.9 small throat vs 15 with restricted throat. The bigger carb should give you more RPMs at the top end, but it can't give you anything at less than WOT

 

[ondarvr]

A larger carb can frequently result in less power at lower RPMs due to it being less efficient.

 

[jimmbo]

The bigger carb should give you more RPMs at the top end, but it can't give you anything at less than WOT.

What can happen at lower rpms is, the carb being bigger allows air thru at a lower speed/pressure drop at the Venturi, This lower differential results in the main fuel circuit being delayed till a higher rpm and can make for a soft hole shot until the main circuit is flowing