merc 800 v 650 what are the differences?

[Yachtzee]

I just picked up an early 70's Merc 800. It is extremely similar to my two merc 650s. It looks like the bore is the same, I am not sure about the stroke.
Does anybody know how they get the extra 15 HP out of the 800 vs the 650? What are the differences between the two?

Also, does anyone know if the lower units are interchangeable? same ratio?

 

[Faztbullet]

Re: merc 800 v 650 what are the differences?

The 65 is a motor all to itself, It uses a short throw crank, smaller rods and bigger pistons(2.938) than the 85 (2.875) and has a smaller footprint. The only parts that will interchange with a 85 is the lower unit and a few electrical parts.

 

[Yachtzee]

Re: merc 800 v 650 what are the differences?

Faztbullet, thanks for responding so quickly.
Just to clarify, this is and 80 hp merc 800 I refer to, not an 85 hp 850

I do not see much reference to the 800 when I search the web.
Is it somewhat uncommon?

 

[Faztbullet]

Re: merc 800 v 650 what are the differences?

The 80 is the same as a 85 except for the following: 85 block has power port 80 does not, the exhaust is "D" shaped on 80 where 85 is square,the 80 usually had the horse shoe trigger and big red coil,carbs are usually wk series