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1999 150 EFI lower unit

jessie007

New member
"Hello, I was wondering what y

"Hello, I was wondering what years and hp of different lower units will fit on a 1999 Mercury 150hp EFI saltwater series outboard.

Thanks,
Jessie0007"
 
"The 150's shared a gearca

"The 150's shared a gearcase with the 175's and 200's of similar vintage (1995-on models with the 2.5L powerhead).

BUT, the gears were different on the 150 compared with the 175/200 horse models.

Your model has 2.00:1 gears and the other have 1.87:1 gears.

You can bolt the others right up, make a prop change (to account for the gear difference) and go on your way without issue.

However, personally, I would try and keep the (lower) 2:1 gears since they were installed in that model to improve it's lower end torque and as a by-product, the motor doesn't work as hard, plus it runs cooler than it would with the higher gears.

But depending on how/where your run your boat, that may not be an issue.."
 
"Thanks for all the informatio

"Thanks for all the information. I did have one other question for you. If I got a blown 200hp of the same year, is the parts interchangable between the 150 and the 200? IE: Starter, injectors, computer, ect....?

Thanks again,
Jessie007"
 
"Yes, and No.

I don't w


"Yes, and No.

I don't want to complicate this, but there are two distinctly different 150's out there.

The XR6/XRI model 150's (2.5 liter block) will share about 95% of their parts with the 175/200's - so yes, starters, trim pumps, just about every powerhead component (save the carbs on carb models and a couple other minor things).

The XR2/XR4 (and a few un-named 150 models - 2.0 liter block) share their parts with the 135 horse.

In that case, some, but not all components would be compatable with larger horsepower motors.

As to the engine computer. On fuel injected motors it's often the ECU (computer) that makes the motor a specific horsepower within it's family.

A 150, 175 and 200 usually are "mechanically" identical, the ECU "tells" the motor how many horses to develop.

So yes, an ECU swap can give you more horses (turn a 150 into a 175 or 200), but at least in the US that is very illegal.

Here is an explanation of the EPA regs as they apply to a Merc Outboard -

"EPA regulations prohibit changes to engines that could affect emissions limits. Per the service manual, "The dealer and/or consumer is not to modify the engine in any manner that would alter the horsepower or allow emission levels to exceed their predetermined factory specifications." The only changes permitted are carburetor jet and gearcase/gear ratio changes for high altitude operation as detailed in applicable Mercury Marine Service Manuals."

Basically, if your motor started it's life as a 150 horse, then you can not legally increase the horsepower..."
 
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