1979 175. Can it be detuned to a 150?

[Thompy_04]

Just found out I broke a ring of my '79 150 but have available the same year 175 for a powerhead replacement. Can this 175 be detuned to run as a 150? I was hoping they used the same long block and simple carb swap helps me out. Coast Guard says its a no-no to run over 150hp on my boat.
Model #'s
150 - 150TL79C
175 - 175TL79R

 

[emdsapmgr]

Re: 1979 175. Can it be detuned to a 150?

The crankcase assemblies are the same part number and the rotating assemblies are the same. Only difference is the size of the carbs. You can use your 150 carbs and it'll make 150 hp. Only problem will be when someone checks the engine I.D. which is stamped on the casting plug on the top of the new block. It will say 175 and you'll have an issue trying to explain the carb/block swap. See attached pic for a typical casting plug.

 

[Joe Reeves]

Re: 1979 175. Can it be detuned to a 150?

The crankcase assemblies are the same part number and the rotating assemblies are the same. Only difference is the size of the carbs. You can use your 150 carbs and it'll make 150 hp. Only problem will be when someone checks the engine I.D. which is stamped on the casting plug on the top of the new block. It will say 175 and you'll have an issue trying to explain the carb/block swap. See attached pic for a typical casting plug.

Solution.... Carefully change the core plug. This is what I've always done when installing replacement powerheads in order to have the ID of the powerhead match the ID plate located elsewhere on the engine assembly.