Difference between '81 & '86 Merc I6 115 powerhead?

[gregpro50]

I had the powerhead go bad in my '86 115 so I switched to a good '81 115 powerhead. It runs great but doesnt have the power of the old powerhead. I was told that sometime after about '82 the motors were rated at the prop instead of the crank. Is there an actual difference between these two powerheads? Also, if I wanted to have the power of the old powerhead does that mean I would have to find one newer than '82? Are all the '82 and newer powerheads the same?

Thanks guys!!

 

[Droll]

Re: Difference between '81 & '86 Merc I6 115 powerhead?

Your 81 115hp power head became a 90 hp whey they started rating them at the prop.

If you want more power, you will have to replace it with:
1983 > 1988 115 hp, prop rated ( ADI ignition ).
1972 140 hp crank rated ( Thunderbolt ignition )
1973 > 1977 150 hp, crank rated ( Thunderbolt igntion
1978 > 1982 140 hp, crank rated ( Thunderbolt ignition until mid79 > ADI ignition from mid 79 )

Short story...the 150 hp became 140 hp ( new decals only ), the 140 became 115 in 1983 ( got a different reed setup + slightly lower exhaust porting, some early 115 might have used 140 blocks ).

Your "90" hp could be modified up to 140 spec ( 1972 140 hp ), but it will require total a disassemble + some heavy port work ++ , I have done it but........


Arne Kjetil

 

[gregpro50]

Re: Difference between '81 & '86 Merc I6 115 powerhead?

Thanks Arne that answers my question. I do have a '87 Mariner 115 powerhead that I think I will put on there since I now know that is rated the same as the '86 powerhead that went bad. I have a couple '81 powerheads that I have collected thinking they were the same but now I think I will sell them.