Just really curious….I have a 135 Opti and was looking at the 150`s and 175 Opti`s. The bore and stroke are the same but the lower units are geared alittle different. So what makes the power different? Could it be just a different ECM? If that were true I could change my 135 to 150 just by changing out the ECM. It would change my hole shot, the lower unit is 2 to 1 on my 135 and 1.83 to 1 on the 150. Just curous about this. Any one have any ideas? 
Tom I know the 135 Opti actually outputs close to 150 (147) hp. Not sure the difference besides gearing. Jon Jordan probably has this answer. 
I talked to a Merc Mechanic about the same thing…Going from my 90 Opti to a 115 by changing the ECM…the Mercury card that you talk about(if were talking about the same thing here) would cost you more then trading in your Opti for a larger HSP one…they did that on purpose.
That and some exhust port modifications that no dealer will touch. It’s illegal for dealer to modify motors (Both car and boat motors) that alter the emissions. And, if you did the mods yourself, it would be uninsurable and illegal to sell the motor as a 135 or 150.
Edit.
As a side note, most people just slap on a bigger prop on the 135’s. You can get away with it on the lower gear ratio. For instance, the biggest prop I can turn on my 150 opti is a 21 pitch. Your 135 can turn a 23 pitch with everything else equal. In other words, you could turn a 23p prop on my boat with a 135. I can’t with a 150.
-J.
I have a 135 opti tiller on a 2090 warrior with a 19 pitch prop what is the benefit with a 21 pitch prop?
Could be wrong here, but I believe it would be slower hole shot, but higher top end speed.
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It’s illegal for dealer to modify motors
I knew there was something else I was going to add 
I am not sure about this statement.
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It’s illegal for dealer to modify motors
A dealer can chip a motor, may void any warranty but it is not illegal. A dealer can add headers. manifolds, cams. bigger injecters, etc.
And why would it not be insurable my boats rated for a 175. They insure my freinds tunnel hull with reworked 250 Mercs now pushing 450 HP each. Top end 127 GPS.
And why would it be illegal to sell it?????? How many hopped up cars and boats are out there for sale.
It`s really a mute point I was just curious the differnces between engines. If it was just the ECM that is just a plug an play type deal.
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I have a 135 opti tiller on a 2090 warrior with a 19 pitch prop what is the benefit with a 21 pitch prop?
With a 19″ prop, you’ll have better hole shot. Better for getting up on plane faster.
with a 21″, you’ll still have decent hole shot, but the top speed is better.
‘Pitch’ means for every revolution the prop turns, it pushes the boat forward either 19 or 21″.
This topic is written about frequently in Bass & Walleye Boat magazine. I should clarify that any mods to the exhaust/emissions is illegal. Many mods to increase HP include changing the exhaust. But, speeding is illegal and people still do it.
As far as insurance goes, you will want to make darn sure you are covered in the event of a claim. Getting insurance is one thing, getting paid on a claim is another.
Generally, going to a prop with more pitch will increase speed and drop RPM’s. If you are in the upper end of your RPM range as I would expect with the 135, going to a 21 or even a 23 pitch would be worth a try if you are looking to strictly gain top end. You will give up other qualities the 19 p has such as hole shot, bow lift, staying hooked up in turns, ect.
-J.
Did a little more digging and asking questions about the difference between the Opti`s 135, 150, 175. Local certified Mercury engine rebuilder told me change injectors and ECM is all one would need to do to up horse power. His words were find a 150 or 175 that was blown up pull injectors and ECM plug and play. The only glich in the deal would be if they had to hook up there computer to do updates to the software. Mercury would frown on that. They want us to buy a new motor if we want more HP.
Just FYI
Hi Tom, i would like to the same to my 135 optimax and can’t find the convincing info to go ahead and do it. Please contact me if possible thanks Ed
Hi Tom, i would like to the same to my 135 optimax and can’t find the convincing info to go ahead and do it. Please contact me if possible thanks Ed
Welcome to In-Depth.
This thread is 10 years old so the info contained in it maybe outdated.
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