9.9 power increase

[Dave1999]

Hello<br /><br />I have a 1976 Evinrude model #10624 9.9 two stroke. <br />The motor is in very good condition and runs strong. I have it on my inflatable boat and would like a bit more power. <br />Is the 9.9hp the same motor as the 15hp,just tuned down a bit?<br />What would be needed to increase the HP (carb jets, reeds, exhaust port work?)<br />I would rather put a few bucks into my 9.9 to increase the power over buying a new 15hp. Mainly for the reason I know my 9.9 has been very reliable, not to mention the cost of a new 15hp.<br /><br />If anyone has had experience with this sort of tuning your input would be great.<br /><br />Thanks

 

[DHPMARINE]

Re: 9.9 power increase

My guess is you'll need at least a new carb (bigger venturi),and a new exhaust adapter. this will cost big bucks. <br /><br />I also wonder about adding more HPto a motor this old.<br /><br />Good Luck !<br /><br />DHP

 

[OBJ]

Re: 9.9 power increase

Hey Dave. The carb for your motor (15hp carb) is not longer available unless you pick it up on ebay or the like. And I really don't think you would see that much increase in power once "all is said and done". I would suggest that you change the set up of the engine on the transom....like raise it up a bit and maybe get a smaller pitch prob....like an 8* pitch. This would do a lot for your performance and would also save some $'s. Changing your engine over to a 15 would mean a different carb....one with a larger throat and larger high speed jet. Really not worth the money you'd put into it even though the rig is good. Try getting more of the lower unit outta' the water but not so much as it will not pick up water. You can do this with a block of wood under the transom bracket. Give it a go and see what ya' think.

 

[BoatBuoy]

Re: 9.9 power increase

Also see this thread<br /> 9.9 Thread

 

[Solittle]

Re: 9.9 power increase

This is one of the few engines that you can easily tweak a bit. I think the only difference between the 9.9 and the 15 is the carb and that is a direct swap.

 

[OBJ]

Re: 9.9 power increase

Yep...what SoLittle said. But really, I just havn't seen the power difference on the ones I've done.....might be there on the "hp meter"....but havn't really seen it on the water. I'm still convinced that you can get more outta' a 9.9 performance wise with just some basic changes in the way the engine is set up on the transom and a prop change. Lotta' guys will lug there 9.9's and complain that the other guy passes him up with the same rig.....well...close to the same rig. I tell them, Get the engine up a little and get the rpm up. Big difference. It works.

 

[Snowdrggn]

Re: 9.9 power increase

I have done several 9.9 to 15hp conversions for use on light weight inflatables. The only way to do them is to swap ALL the parts required, as there was some variance throughout the years as to what the differences actually were. The ones that made the most noticable differences were the ones where the exhaust tubes were different. The increase came at the top end where the exhaust tube helped it breathe. From idle to 5500 rpm the difference was pretty much undectable, it was only the increased rpm of the 15hp were it showed strongly. It should be mentioned that some of the dead slow, troll all day idle of the 9.9 is sacrificed when you switch them over. Following the conversion careful setup and then correct prop selection is critical to getting the most benefit. If you are concerned with abslolute maximum speed, then do it, otherwise it is not worth the effort for what you gain. Once you do the the conversion, and maximize your setup, try to prop the motor to run in the 6750-6950 rpm range at WOT. If you have to pay new prices for the parts, it would be more cost effective to just hunt down a good used 15hp (and put a 9.9 cowl on it, if that is your goal)<br /><br />Cheers,<br /> Snow.<br /><br />Here is a link to a previous duscussion on the topic which I think seems to cover most of the basic issues: http://www.iboats.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=28;t=026842#000002

 

[umblecumbuz]

Re: 9.9 power increase

As Snow said:The increase came at the top end where the exhaust tube helped it breathe.

That's the rub. You will need to change a lot of things - the exact changes depend on where the motor was made - and ALL the increased power comes from increased revs. What you're doing, in fact, by changing the carburetor and exhaust tube (and also possibly the reed setup - some had stops and shims, some didn't) is giving the engine more breathing ability, and that results in more revs.<br /><br />Bulletproof little motor.

 

[wayne h]

Re: 9.9 power increase

1976 ? what is your compression readings on this motor it might just be getting tired and need a rebuild.

 

[herters]

Re: 9.9 power increase

The larger throat 15 hp carb will give you a little more power (top end) but it will use more gas. Because of the age of these motors (74-76) most of them will benefit from a good tune up,link-n-syn and a new full sized prop.