4 banger vs twins

[renault_megane_dci]

In my opinion it is all down to what the manufacturer meant for the bike.
Very high HP per liter engines usually waste fuel.
Recipe is simple : long duration camshaft with a lot of overlap, very short stroke for a lot of RPM, short inlet track for high RPM max power.

But the recipe for high FE is pretty much the other way around ...
Except for the general freer breathing

Then it's a matter of vehicle efficiency :
sports bike offer longer gearbox ratios and refined aero, top notch accoustic tuning of exhausts and inlets, state of the art injection and other fancy equipements.

My conclusion is, for a given capacity, less cylinders is usually better if you want to stick to sensible speeds.

[Hersbird]

I vote single cylinder "thumper". I wanted a Royal Enfield but there were none in my area and even going a day's drive only had $4000 examples. So my $800 CB550 Four ended up being a bargain. Put another $700 in it and could probably get over $3k for it now. If I were going to buy a new bike I would look closely at the Suzuki TU250x or the Cleveland Cycle works Misfit.

[cRiPpLe_rOoStEr]

I'm also favorable to single-cylinder engines.

[renault_megane_dci]

Long stroke engines of reasonable capacity are the best candidates but there are only a few :
Kawasaki W650,
Royal Enfield Bullet 500
Buell Blast
Older beemers like a R60 ...

[gil]

Someone in here was riding a BMW 650cc bike named Teresa, he was getting impressive numbers. As far as I understand a single big cylinder is the most efficient. A automotive article from Car & Driver emphasized that 500cc cylinders, with long stroke, where becoming standard size for engines of the big car manufacturers. Weather it be a 4 cylinder or eight, 500cc per cylinder was determined to be the most efficient.

Why 0.5-Liter Cylinders Will Soon Dominate Automotive-Engine Design

gil

[cRiPpLe_rOoStEr]

Another good one is the Yamaha XT 660. IIRC its engine is also used in one of the MT-series road motorcycles.

[Hersbird]

There is a real clean 82 Honda 450 twin on Craig's list here for $1400 asking. Windscreen and small saddle bags as well. That would be good.
82 Honda CM450E, great bike

[renault_megane_dci]

I like singles best but the issue is they usually come in trail-riding trim wich is not really aero friendly and that thumpers don't like too much being over-geared a lot.

But there we can see that sports oriented bikes with high hp per liter engines don't do too good, irrespective of the number of cylinders.

[sendler]

The more pistons, the more surface area in the combustion chamber for any given displacement, the more wasted heat. The longer the stroke/ bore ratio, the more leverage and the less wasted heat. A fuel injected single is the most efficient.

[RedDevil]

I had a Suzuki XF 650 Freewind single and loved it.
Best tanks on that were around 65 mpg - not hypermiling at the time, just steady pace cruising through Spain on a camping trip.

Having said that, FE was bad at highway speed (because of the short gearing) and city (because it was a bucking mule below 3000 RPM, so you always had to shift down even if you did not need the power).

Twins will allow a better ride at lower RPM (than singles) and may be more economical because of it.