How can I increase HP on 1996 125 Merc 4 cyl.?

[barefooter13]

My 1996 SeaRay 175 bowrider has a maximum OB motor size of 125 HP which is why I rigged it with the 125 Merc. It is adequate for most everything. I don't necessarily want to go faster just want to get to top end faster. I have a four bladed aluminum prop which helps a lot. I seem to remember reading the specs for the 125, 135, and 150 which were all similar. Are these basically the same motors with different carbs or something else to get the higher HP? Is it feasible to purchase or rebuild the carbs to achieve higher output? Is it a cost effective thought?

 

[Spidybot]

Re: How can I increase HP on 1996 125 Merc 4 cyl.?

This question comes up every now and then. Many get the idea that there may sit some unused hp in the engine and that those can be released by simple means.<br /><br />The common answer is, that it's not a matter of re-jetting carbs, turning a screw or replacing a few items. It involves (much) more, isn't that easy to accomplish and costs more than expected.<br /><br />Conclusion most often is: If you want more power, buy a bigger motor.<br /><br />This said it should be noticed, that some have lost power reclaimed by tune-up and prop tweaking.<br /><br />Judged by your description it sounds as if you're already pretty close to best performance with the gear you have. What rpm do you get at wot? A more sophisticared prop design or a tad down in pitch will get you up there in shorter time if your current pitch is a little high.

 

[phatmanmike]

Re: How can I increase HP on 1996 125 Merc 4 cyl.?

how bout ventialting yur prop .... i did it and now i have a hole shot that literally throws you from the seat

 

[quantumleap]

Re: How can I increase HP on 1996 125 Merc 4 cyl.?

Your 125 is a inline 4 cyl. that runs on the 2+2 design. The 135 and 150's are v-6's. Totally different engine. Your motor is the highest HP of the midsizes of that design. Maximize your engine's power by using the lowest pitch prop that won't put you over 5250 rpm's at WOT, or use a ventilated prop to spin up the rpm's quicker as your motor runs on only 2 cyl's below 1800 rpm. Also the carb sync. must be set correctly to get maximum efficiency out of that motor. [edit] I see PMM already suggested the ventilated prop as I was posting.

 

[emckelvy]

Re: How can I increase HP on 1996 125 Merc 4 cyl.?

A stainless prop will give you better hole shot also, without a loss in top end, if pitched correctly.

 

[phatmanmike]

Re: How can I increase HP on 1996 125 Merc 4 cyl.?

to get more hp, take that motor off, replace it with a bigger motor, and get some new stickers that read "125hp, really"

 

[Clams Canino]

Re: How can I increase HP on 1996 125 Merc 4 cyl.?

Or replace it with a 1968 or '69 125 Merc. <br /><br />-W<br /><br /><br />

Originally posted by phatmanmike:<br /> to get more hp, take that motor off, replace it with a bigger motor, and get some new stickers that read "125hp, really"

 

[quantumleap]

Re: How can I increase HP on 1996 125 Merc 4 cyl.?

Originally posted by phatmanmike:<br /> to get more hp, take that motor off, replace it with a bigger motor, and get some new stickers that read "125hp, really"

I've got that same motor on my 19ft fish and ski loaded down with gear, batteries, and fuel and it will get 47 or 48 mph top end. not bad for a 125, really.

 

[FlyBoyMark]

Re: How can I increase HP on 1996 125 Merc 4 cyl.?

One of the best things you can do is install Boysen Reeds. They'll give ya about 100-200 rpm increase VERY smooth idle and MUCH better accelleration and hole shots. and only cost 100-200 bucks at the most and will not harm the engine in any way...

 

[barefooter13]

Re: How can I increase HP on 1996 125 Merc 4 cyl.?

thanks for all the input. I get about 48 MPH with the 4 blade, and I am very happy with the performance overall. I was just looking for a tweak. I think I will investigate the Boysen reed valve change as suggested by FlyBoyMark. I guess the real problem is with SeaRay specifying a max of 125 HP. If it weren't for the high cost of replacing the motor with a 150 or so, the 125 stickers also sounds like a great idea from Quantumleap. Thanks for all the comments. Let's close this one out. Thanks again everyone.

 

[phatmanmike]

Re: How can I increase HP on 1996 125 Merc 4 cyl.?

just a note: manufactures HP ratings and the atctualy COAST GUARD HP ratings are usually 2 diffrent things<br /><br />to figure out the CG ratings:<br />Length of boat X 2 X width of boat at transom -90<br />example:<br />17' center console with 6 foot transom<br />17 X 2 = 34 X 6 = 204 - 90 =114hp<br /><br />most new 17'CC come factory with 1 75hp or a 90hp, but to get a 115hp you usually have to go up to a 18 or 19, stock