View Full Version : Can I change Mercury Optimax 75 HP 3 cyl to 115 HP 3 cyl

07-31-2009, 08:59 AM
Some people say that is possible. My Mercury Optimax 75 hp year is nov/2008 with 40 hours of use. Is it only reprograming the PCM? I whould like to know more details about this.

I am from Brazil and here we don't more information about this.

Thank you!

08-03-2009, 06:27 PM
"Hi Bruno,

That is indeed a very good question. I have a 2005 Mercury Optimax 115 hp and I have seen that there is a new 125 hp engine out, and I logged on to ask if anyone knows if it is possible to reprogram my 115 hp to 125 hp. Does anyone know anything about this?


08-07-2009, 10:06 AM
"115hp out of a 3 cyl? mmmmmm, doubt it. 75 is about the upper design limit of a 3 pot motor.

I might be wrong, but have yet to see motors over that hp with 3 cyl. Most have 4 cyl when going higher than 80 hp.

Some motors can be re-mapped for more hp, but need some extra hardware to breathe easier. There are exhaust restrictors [Johnson / Evinrude] on certain motors, others need bigger carbs [non EFI] and so on.

Before looking for more horses, make sure that tub is rated for the power and rather look into a bigger displacement motor than try tweak an outboard. The boat motors are not as easy to mod like a car's. Reliability can cause issues too.

Also, going from 75 to 115 will not really improve top-end speed so significantly as opposed to the fuel consumed. Unless of course, you ski and tube to need the extra grunt out of the hole.

So, in short, re-power the boat as per manufacturer's spec's and enjoy it as such."

08-07-2009, 12:15 PM
"In the US where the Opti's are made it is very ILLEGAL to change the horsepower of an outboard to something greater than what is on the emissions sticker.

So it is well possible that a 75 Opti can (maybe) be reflashed to a 90, or a 115 to a 125 etc, you are most likely not going to find any open source literature on it.

Additionally, any reputable Merc tech that may know how to do it is certainly not going to risk breaking the law so that you can minimally increase the horsepower on your motor.

Rule of thumb - for every 50% increase in horsepower you see a 15% increase in "on boat performance".

That means that there is virtually nothing you can do to any "production" motor that will make a noticable performance difference (75 horse to 90 is just on a 20% horse increase or about a 6% performance increase).

So if your 75 is say getting you 35 mph going to a 90 would increase that to 37 mph at wide open and cause you to burn more gas.

There is however the "mental" upgrade - you "think" that the 90 is so much more powerful and maybe you feel good - even if actual performance numbers do not support that.

Guys, don't mess with you motors and possibly screw something up. Unless you can DOUBLE the horsepower, which means hangin' a second motor beside your present one, be happy with how it's running now..."