Whats the difference between a 75 and 90 Merc 4 Stroke?

[DVHammer]

Want to run something by the experts.....

I have a friend who bought a boat at a local boat show a few years back that had a 60 on it. GREAT Price but it was WAAAY underpowered. He complained to the dealer and they swapped out the 60 for a 75 at no cost. Guessing they put a cheap package together to entice a buyer. He has been running it but still complaining that it is under powered.

I remember when I was a kid that my dads 15hp Johnson tiller was the same as other similar sized motors with the exception of the carb allowing the manufacturer to make a few motor sizes that had the same castings and only have to produce different carbs (as I was led to believe and not sure if it is true or not) with that in mind my buddy claims that everything is the same on the 75 as the 90 (bore and stroke) is this claim also true??

My Duramax has a programmer that allows me to turn up the power when needed. Does an outboard have the same capabilities??? Maybe a chip or a new computer? Might be a way of him getting more power without buying another motor.

Thoughts??....

[Transom]

The latest versions of the 75-90-115 are very similar and can be flashed up. If i remember correctly it takes an ecu flash and the removal of a restrictor in the intake. The gearing is different in the series too if I remember correctly. That could make propping some boats problematic. Fwiw I would never do it to an engine in warranty but if mercury is no longer standing by it the risk of excess wear may be worth the reward.

[DVHammer]

Sounds like it may be an option.

I sent him a text asking for his model and serial numbers and will post it when he gets back to me.

[jethro1]

Reminds me of the saying "the bitterness from the lack of HP remains long after the sweetness of the low price is long forgotten".

I can't recall anyone ever saying they were sorry because they spent too much and bought a motor with too much HP.

I suspect that it might be difficult to find someone that can reprogram the ECU. Simply insufficient demand I would think. What might be possible is to install a 90 HP ECU in the 75 HP model, if that is one of the differences between the HP ratings. In conjunction with other configuration changes (air intake restrictor plate for example) if there are other differences between the two similar HP models.

It takes a bit of time but once the two models are known, the Mercury parts catalogs for each can be inspected so as to determine the precise differences between the two models. Then, if feasible, install the 90 HP peculiar parts on the 75 HP motor so as to turn it into a 90 HP model.

[Lowerider58]

Contact Simon Motorsports and talk to them. They con do the reprogramming of your ECU and bring your 75hp up into the 115hp range. There are several people on the tin boat forum that have had it done on their Mercury motors.
http://www.simonmotorsports.com/

[DVHammer]

Contact Simon Motorsports and talk to them. They con do the reprogramming of your ECU and bring your 75hp up into the 115hp range. There are several people on the tin boat forum that have had it done on their Mercury motors.
http://www.simonmotorsports.com/

Great lead Thank You!

He replied with his motor info:
Model: 1F754131D
Serial: 2B225882

Next problem is his warranty is not up until 2021. Assuming playing around with computer will void any and all warranties. Sounds like he has a decision to make if so.

[jethro1]

However a 75 HP motor gets converted to a 90 HP equivalent model the warranty is going to be affected.

Verbiage in the owner's manual clearly states that warranty coverage may be denied for an unapproved modification.

Decision may have to be made, is the warranty more important or is the additional HP more important. I suspect that Mercury would be more likely to deny warranty coverage due to the use of a non-Mercury part (ECU flashed by Simon) than they would if the motor were to be modified using Mercury parts.

Mercury Customer Support is but a phone call away. See what they have to say.

[DVHammer]

Agreed.
Most likely void the warranty even if using OEM parts and installed by a merc dealer but that is going to have to be his decision.

Will definitely advise him to call Customer Support regardless.

[Lowerider58]

Great lead Thank You!

He replied with his motor info:
Model: 1F754131D
Serial: 2B225882

Next problem is his warranty is not up until 2021. Assuming playing around with computer will void any and all warranties. Sounds like he has a decision to make if so.

When you said it was bought a few years back I assumed it was out of warranty. Assume gets me in trouble sometimes.

[DVHammer]

LOL, "ASSUMING" gets us ALL in trouble!

This whole 60 hp ordeal started in May of 2014. Complained enough that in the fall of that year they agreed to swap motors over the winter and store his boat as well so he took them up on the offer.

Somehow the paperwork shows 2016(?? not sure how or why) He then bought an extended warranty that must be a 5 year plan to expire in 2021..

Sent him all the info but not heard back from him yet. I know if it was me and I put out hard earned money for an extended warranty I would certainly wait but cannot speak for him.

Will keep you posted.....

[DVHammer]

What is the standard warranty that comes with his motor?

He cannot find anywhere that the extended warranty is on his 75 hp. He "ASSUMED" (here we go again....LOL) that the extended warranty that he bought with the 60 was rolled over to his 75 since they never offered an extended warranty on the new one or gave him a refund for the unused portion of the 60 hp extended warranty.

If I am reading this correct it appears to be a 3 yr.
https://mercurymarine-gsdesign1.netd...7_warrchts.pdf

[jethro1]

Yes, standard warranty is for three years, assuming no commercial use. If commercial use is involved it decreases to one year.

An extended service contract, purchased by the owner or obtained via a Mercury Promotional event, does not transfer from one motor to another.

If your friend got a new 75 HP at no further cost in exchange for a used 60 HP motor that was a very good deal. To also be expecting a service contract for the new motor to be provided to him at no additional cost would be a great "stretch".

[DVHammer]

Agreed.
He isn't really too upset with the extended warranty being gone, chalks it up to it being part of the deal to get a bigger motor.

He is more concerned with how soon he can get his ECU flashed because he doesn't want to throw away the entire warranty but is okay with cutting it a little short as long as he can get most of it out.

His 75 was installed in May 2016 so after this boating season he will have 2 years of his warranty used up. After talking it over with him it sounds like he is going to get the upgrade the winter of 2017-2018 while the boat is in storage and only give up 1 year of warranty.

Have to be honest and come clean.... I am REALLY anxious to see what flashing his ECU will do and how it changes his boat so I am probably pushing him a little harder than I should to do it before his warranty is up. He does of course still have the last word but a little nudging never hurts right? And if he is willing to give up his last year of warranty why not do it at the end of this season??

[EuropeanAM]

Technically illegal to modify the HP or Emissions footprint of an EPA Rated engine (which these are).

You cannot just "flash" a lower HP engine into a 115. If you're being told that, the "teller" needs to lookup the cylinder head and camshaft for the different models.

[Senkosiggy]

Technically illegal to modify the HP or Emissions footprint of an EPA Rated engine (which these are).

You cannot just "flash" a lower HP engine into a 115. If you're being told that, the "teller" needs to lookup the cylinder head and camshaft for the different models.

What about going from 75hp to 90 hp. I can't seem to find any difference besides the ecu and restrictor. I still have 2 years on my warranty but may think about doing this at that time. I saw a 90hp used ecu on eBay a while back for <300 really thought about it but just got the boat this year.

[DVHammer]

Technically illegal to modify the HP or Emissions footprint of an EPA Rated engine (which these are).

You cannot just "flash" a lower HP engine into a 115. If you're being told that, the "teller" needs to lookup the cylinder head and camshaft for the different models.

I trust that there are differences going from 75 to 90 to 115 but the ultimate goal is simply to get a little giddyup to get out of the hole and on plane. Are you saying that throwing a new program will not gain HP? The coast guard has deemed his hull worthy of a 90 so I would think that he is safe and 'legal' up to that point.