To the uninitiated, the Cessna 172 and Cessna 182 are indistinguishable from each other. Both are 4 seat, high wing planes with struts bracing each wing. But for pilots, they are substantially different aircraft.
The major difference between the 172 and 182 are the engines. Both have been produced for over 40 years and during that time have come from the factory with a variety of engines. Since the 172N was introduced in 1977, the factory standard engine has produced 160 hp. Prior to that 172 engines ranged from 145 to 160 hp. Many older aircraft have been upgraded in the after market to more powerful engines, including a popular 180 hp. version. All such changes are accomplished via a STC, or supplemental type certificate issued by the FAA.
Though the 182 has been powered by a several different engines, standard non-turbo models have always weighed in at 230 hp. This difference in horsepower has several implications. One is of course speed. The 182 is 15-20 knots faster than a 172. It can also climb 200 feet per minute faster. Typically aircraft with bigger engines can lift more weight too. A standard late model 172 maximum weight is 2450 lbs, a 182 3100 lbs. Not all of that difference is useful load, an empty 182 is around 300 lbs. heavier than its smaller cousin.
Not all of the differences between the 172 and 182 are as easy to quantify as specifications and performance numbers. Being heavier, the 182 is a more stable aircraft than a 172. It doesn’t bounce around quite so much, and tends to track better in the direction you want it to go. This is a good feature if you intend to do much instrument flying. (Flying in the clouds or without visual reference to the ground.)
With over 200 horsepower and a controllable pitch propeller, the 182 is also considered a high performance airplane. What this means is that additional instruction is needed to be able to fly it, both by regulation and requirements of insurance companies.
As far as price goes, a typical price for a used 1978 172 would be in the low $40,000’s, while a similarly equipped 182 would be at least $20,000 more. A 182 will be more expensive to own too. Insurance, inspections, engine overhauls and operating costs will all be more. For example, a 182 will consume about 3 gallons per hour more fuel.
None of these things makes one plane better than the other. What distinguishes a plane is how you intend to use it. If you want a simple plane that’s relatively cheap to operate, that calls for a 172. If you want to use your plane for transportation and intend to go into weather, a 182 would better suit your purpose.
Finally, as for distinguishing one plane from another, the giveaway is the nose. A 182 has a fuller cowling section to cover the larger engine and a more streamlined windscreen.
How It Flies has technical details and more information on both the Cessna 172 [http://www.howitflies.com/Cessna-172-Skyhawk] and Cessna 182 [http://www.howitflies.com/Cessna-182-Skylane].