powerhead swap.. 150 gt to 200..

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railrdin

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Sep 18, 2011
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i left the boat ramp in a lil jackpot yesterday morn & about a mile out my engine broke a rod... its a 1990 johnson 150 gt.... i found a late 80's-90 model 200 hp evinrude w/ a good price & i was wondering if a powerhead swap would b possible if years & numbers match up or should i scrap that idea from the git go?? i will b able to get some more detailed info with numbers & what nnot in the next few days... any info would be greatly appreiciated... thanks..
 
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Dhadley

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Re: powerhead swap.. 150 gt to 200..

If the 200 is a crossflow it'll swap out easily. Some - note, some - of the 150 XP/GTs did use a 200 block. My gut feeling / guess is that the "late 80's-90" 200 is a looper. If so, the 200 looper will have way more power than you'll ever see from any crossflow but the powerheads will not interchange.
 
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railrdin

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Re: powerhead swap.. 150 gt to 200..

How can I identify if the 200 hp is a cross flow or a looper??
 
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guitman32

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Re: powerhead swap.. 150 gt to 200..

Is the exhaust manifold flat or curvy (the xflows have a "bubbleback" curvy exhaust cover)?

If you have the engine's serial number you can go to Shop Evinrude . com and cross reference parts...
 
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emdsapmgr

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Re: powerhead swap.. 150 gt to 200..

Why not just replace the crossflow with the looper? The controls are the same up throug 1995.
 
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Dhadley

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Re: powerhead swap.. 150 gt to 200..

Actually the crossflow powerhead that will interchange with your 150 will have a flat exhaust plate even if it is a 200. The crossflow with the bubble exhaust will not interchange. A crossflow will have exhaust plates, cover plates on the heads and by-pass covers on the sides of the block that bolt on. The looper does not have these covers and plates.

The model number, rather than the serial number, will tell us exactly what the 200 is.
 
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railrdin

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Re: powerhead swap.. 150 gt to 200..

ok fellows... i didnt get the #s but my cuz was mistakened.. the 200 hp is a 1978 model that has been rebuilt... it has been sittin for quite sometime (covered up for 6+ yrs) but the motor felt very smooth when turning it by hand, the plugs still looked goodbut mainly the compression was 60psi on all 6 cylinders. also the exsaust manifolds look to be exactly the same on both engines.. its the flat manifold.. i guess the differences were the electronic ign. & i noticed the starter solenoid were in diff. locations... ill swap the whole engines if need be or should i just run away from this..
 
BonairII

BonairII

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Re: powerhead swap.. 150 gt to 200..

If your compression numbers are correct(which I doubt)...run away from this motor. If the motor was rebuilt then why was it sitting for so long? Probably not a good rebuild.

Get another compression gauge and verify the compression.
 
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emdsapmgr

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11,551
Re: powerhead swap.. 150 gt to 200..

The 78 200 will bolt right on. The problem will be the difference in the shift linkages. The older engine uses the bellcrank system to shift and I believe the gearcases on those engines shift backward (from the later models) due to the linkage differences. That presents a significant problem.
 
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Dhadley

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16,978
Re: powerhead swap.. 150 gt to 200..

If you use the intake manifold from the 1990 150 you can use all the correct linkage for the 1990 lower unit. There will be some slight differences in ignition and accessory mounting bosses between the 2 years but nothing you can't overcome.
 
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