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  1. #1
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    1980 140 hp. L6 crank,rod,piston-assy drop into 1978 150 hp. L6? yes-no?

    would a 1980 140hp. L6 crank-rod-piston assy. drop into a 1978 L6 150hp.? thanks
    smako78

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    Drop in,yes...correct,no.The Pistons in the 140 don't have boost ports,the 150 does...So,it will fit but performance will suffer,Chris

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    Is compression and port height the same other the the boost ports, can you port the 140 pistons to match?

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    Not sure when the high dome piston was superceded by the low dome,mid 70's I'm guessing.The Pistons without the boost ports may have the reinforcement ring around the boost port area,if yes then you could port your Pistons and all should be good.If no reinforcement I don't know how they'll hold up.

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    thanks for your reply

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    my 78 150hp. s.n. is 475- with 622-# old style rod this 140hp has power ports on the starboard side with 624# new style rods. there both low dome! What's different the port Size? or where the port is drilled?

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    So if displacement bore stroke is the same. How is it a 150hp. in1978 and 140hp. in 1980-81?

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    Marketing to fit the 140 segment and then say that Merc has the best.

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  11. #9
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    Ok,sorry,my mistake regarding the 140.Yours(1980) is the same as the 150...I was thinking of the first 140 Merc sold in 1972 that had no boost ports.Your 1980 140 is really a re-decaled 150...since Merc offered a detuned v6 175 as a 150 at that time they decided to call the inline a 140...later it even dropped to 115 at the prop,it is considerably less powerful than the v6....sorry to mislead,Chris

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    Even 115 at prop was a understatement for market share.

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    So I just bought a 1980-81? 140hp. crank,rod and piston assy. it was listed 1982 140hp. for parts. I'm going to use the 3 best piston in the 1978 150hp. because I haven't used her in 20 years ( very low hours ) I don't think Merc. made a 1982 140hp.?
    Hopefully in a couple a weeks I'll be fishing Lake Superior Lake Trout out of Big bay Mich. P.S. to everyone I rebuilt this 26 years ago so Change your impeller pump every 4 YEARS Steve.

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    I think last year. Lakers , can't be too deep yet, riggers or divers . No kicker , troll the L6 or big jigs with white grub ?

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  18. #13
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    I have to drag a bucket or drift sock behind to get 1.6-2m.p.h. for south shore trout! Would you power port all 6 pistons? Does it help fuel economy ? Stay low dome stock and use 91 octane? With 87 octane I'd burn 3 to 3.5 gals. per hour at 28 knots. Calm to 3 foot choppy water. So again power port? yes/no

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    I can't imagine using the L6 for trolling , build her like the boost port 150 and she would used a bit more fuel I suspect . 3.5 / hr is good at cruise .At one time guys were machining the block and milling the case so the crank center line would be closer to the deck giving more compression .That would give a bit more power without the extra fuel but you would need to find the hands on knowlegde for the amount and what to do with the ports. Find a 4 stoke 9.9 and hang that on the side , troll the whole day for $5. Now that I think about it , us said big water, might want a bit more than a 9.9 just to fight the wind.
    Last edited by FMP; 05-02-2016 at 08:13 PM.

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    I guess I'll end this post. I'm staying with a all stock ''78'' 150 hp. If any one wants to mod. your old Merc. type Harry r. Brinkman pdf. There's 88 pages of GOOD STUFF
    Remember !!! a bad day of Fishin is better than a good day at Work!!!

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