My friends comment was that the two cylinder motors "go better"
Personally, I would not be dead set on a two cylinder engine of the same displacement as it's single cylinder counterpart. Stepping from 6hp to 8hp is obviously going to "go better".
If it were me (
based on your info, I haven't researched current 4 stoke engines)
I would go with a current 4 stroke 6hp at 60lbs of weight.
Twin cylinder engines are better balanced, and thus more refined than single cylinder engines. The internal forces within a twin cylinder engine are better counterbalanced by the movement of the two pistons, and thus they can rev higher while having less vibration. Since there is an extra cylinder on twin cylinder engines, there is naturally an extra piston as well accompanied by all the associated components. With all that extra componentry twin cylinder engines are more complex, and generally more expensive to manufacture.
To displace any given cubic capacity, a single cylinder engine makes use of bigger, heavier components. For the same cubic capacity, a twin cylinder engine will have lighter componentry as the cubic capacity to be displaced is divided in two parts, and a smaller volume needs smaller and lighter components to be displaced. Do note, that while the internal componentry will be lighter, with the need of two separate cylinders and additional parts, the overall weight of the engine will be heavier than a similar capacity single-cylinder engine. The lighter componentry, however, along with a relatively balanced and vibe free nature of twin cylinder engines, makes them more rev happy, so they can reach a higher rpm and produce more power for any given cubic capacity.
On the other hand, while single cylinder engines aren’t the most high-revving, their longer strokes and heavier componentry allows them to create a lot better torque, and that too at the lower end of the rev spectrum, making them very usable and tractable in low to mid revs.
A single cylinder engine creates more torque lower down the rev range, while a twin creates more power higher up the rev range, with somewhat compromises torque delivery at the lower end.
Single cylinder engines - advantages
Better torque and low-end performance
Thanks to their larger bores and strokes, single cylinder engines produce higher torque at lower revs, making them more suitable for load lugging and for applications where high torque is required lower down the rev range.
Fuel-efficiency
While there may be exceptions, where lighter materials and more modern and expensive technology is used, but as a rule, for any given cubic capacity, single cylinder engines are more fuel-efficient as compared to twins.
Lower cost of maintenance
With their simple construction and lesser number of moving parts, single cylinder engines are easy to maintain and repair. The cost of replacement of parts for single cylinder engines is also significantly lower than their twin engine counterparts.
it'll be more comfy that way too
