Why do many cruiser motorcycles have huge displacement (1200cc+) engines but make so little power?

First learn how to read a dyno chart and know that torque is measured by lb-ft (or N·m).

http://www.ducati.com/bikes/multistrada/1200/2015/...

You will see the torque rises steadily from idle to 7250 and drops off as steadily from 7600, the HP goes up to 140 fairly rapidly and then slowly creeps up to 160 (look at the steepness of the data curve).

Compared to the donor bike the Testaretta engine is strangled and shackled to a heavier bike.

H-D actually claim 97 lb-ft

But you cannot rely on either sets of figures, the manufacturer's claims are often wildly optimistic and are calculated from computer predictions, rather than run on a dyno. In the real world they never quite match up.

As for the reason the HP does not match the expected from the amount of torque the answer is simple – revolutions per minute – that is what dictates horsepower. And air-cooled engines cannot turn as fast as liquid-cooled, friction and heat see to that.

Power Cruiser Motorcycles

Cruisers work differently from sport bikes. They're made bigger not for more power but for more smoothness on the highway, more comfort, etc. 75 hp is enough to cruise all day at 85, so why would you need more?

There's something now called a 'power cruiser' that's faster. Like a Roadstar Warrior or a V-Max.

It's partly the design of the engine, especially when you are looking at the Harley twin. They keep the design because of tradition. They sell the design on the feel, the sound and the nostalgia. The engine has a lot of torque and a cruiser has a long slung out design that doesn't lend itself well to high speed, so most people just enjoy the stoplight to stoplight performance which these bikes do well on.

My VStrom 650 twin puts out about 65HP. The Harley 96inch(1584cc) engine puts out about 66hp in stock form. I can buy two or three VStroms to one Harley. The VStrom weighs less than half of a bagger. No, it's not as 'cool' as a Harley, but it gets me down the road and has never let me down.

The information you've provided doesn't tell the whole story. It's not all about peak power you know?

The extra torque and spread of power that the Harley has would make it far better at smooth riding and cruising on the motorway.

Typically, the extra power generated by higher powered bikes comes much higher in the rev range. Harleys only usually rev to around 5/6000rpm - hence they don't make a high peak power. However, because of that nature, close to peak torque and power will be made through almost all of the rev range that it does have.

--Mikey B--

Ultimately, you're comparing apples and oranges. Harley's are tuned for a broad power band and loads of torque, which makes inner city and highway riding enjoyable. Typically, if an engine produces more torque than power, it's going to be easier to drive They're also air-cooled engines. Air isn't nearly as effective as liquid cooling, but far more reliable and no maintenance; that isn't to say liquid cooling is unreliable, but it has points of failure, where air-cooled systems do not. Now, with that said, the more power you create, the more heat you're going to have dissipate, and liquid cooled engines can dissipate far more heat, much quicker, with much less space but then you have a massive unsightly radiator taking away from the massive centerpiece. Air cooled engines can cool effectively, but they need more surface area, meaning more cooling fins on cylinder heads, thus a larger engine with less power.

Cruisers are as much about style as they are about ease of riding, so massive air-cooled engines with lots of torque and broad powerbands are highly desirable for that very reason; they're stylish and make torque very early in rev range where most people spend most of their time driving/riding on the day to day basis. With that point, while the Ducati may make more peak horsepower/torque, the Harley engine may make more torque at the lower end revs; The Harley Fat Bob makes it's peak 99ft-lbs of Torque at 3000RPM (according to Harley Davidson's site for their latest model Fat Bob), where you might cruise on the highway or in the city, where the Ducati makes it's peak 100.3ft-lbs of Torque at 7500RPM, so at cruising RPM of say 3000 RPM, the Harley engine is making way more torque.

Pistons have to move on an incredible speed and only the smaller and lighter pistons make modern power engines that we did not have in the days. Chain driven bikes have further advantage. Liquid cooling, hydraulic valve lifter systems and heavy counterweights on the crankshaft make up for more difference. I have a twin spark, for reliability, with revving bikes extra room on the header is sooner used to accommodate extra intake or exhaust channels.

you forgot to put in that a cruiser has about 850pounds to move and a Ducati has to move only400pounds

but to answer your question Because Cruising is a slow thing like riding down main street during bike week

it is all about showing off your new paint or chrome 30inch front wheels ....Cruisers are just for show not for riding every day..

depends on what motor though. S&S makes a 145 HP V twin now. Based on HD motor but heavily upgraded. But yea stock from the factory those big Vee twins arent impressive until you ride one. Its not about all out speed. After all the speed limits are not over 80 MPH so how fast do you really need to go?

Fast don't last.