APS

Now I know a lot about cars BUT, can someone please explain rotary engines, like in the RX-7. I really havent had any experience or exsposure to them? How are they different? And what makes them so great? Thanks.

TwilightX

iTrader: (1)

From how stuff works:

Rotary Engines Explained

Key Differences
There are several defining characteristics that differentiate a rotary engine from a typical piston engine.

Fewer Moving Parts
The rotary engine has far fewer moving parts than a comparable four-stroke piston engine. A two-rotor rotary engine has three main moving parts: the two rotors and the output shaft. Even the simplest four-cylinder piston engine has at least 40 moving parts, including pistons, connecting rods, camshaft, valves, valve springs, rockers, timing belt, timing gears and crankshaft.

This minimization of moving parts can translate into better reliability from a rotary engine. This is why some aircraft manufacturers (including the maker of Skycar) prefer rotary engines to piston engines.

Smoother
All the parts in a rotary engine spin continuously in one direction, rather than violently changing directions like the pistons in a conventional engine do. Rotary engines are internally balanced with spinning counterweights that are phased to cancel out any vibrations.

The power delivery in a rotary engine is also smoother. Because each combustion event lasts through 90-degrees of the rotor's rotation, and the output shaft spins three revolutions for each revolution of the rotor, each combustion event lasts through 270-degrees of the output shaft's rotation. This means that a single-rotor engine delivers power for three-quarters of each revolution of the output shaft. Compare this to a single-cylinder piston engine, in which combustion occurs during 180 degrees out of every two revolutions, or only a quarter of each revolution of the crankshaft (the output shaft of a piston engine).

Slower
Since the rotors spin at one-third the speed of the output shaft, the main moving parts of the engine move slower than the parts in a piston engine. This also helps with reliability.

Challenges
There are some challenges in designing a rotary engine:

Typically, it is more difficult (but not impossible) to make a rotary engine meet U.S. emissions regulations.

The manufacturing costs can be higher, mostly because the number of these engines produced is not as high as the number of piston engines.

They typically consume more fuel than a piston engine because the thermodynamic efficiency of the engine is reduced by the long combustion-chamber shape and low compression ratio.

frekyjason2002

i want to know too, people talk about that engine as if it were from a ferrari.

silverdevil

iTrader: (5)

Another good thing about the rotary engine is the amount of power that can be extracted from such a small engine. Most of Mazdas Wankels are 1.3 litre (13B) but the first gen carried the 1.2 litre (12A) unless you bought the GSL-SE which had the first version of the 13B but only put out 125 BHP as compared to 146 and 160 for the 86-88 and 89-91 respectively.

Most people don't know that there were no RX-7s produced in 1992. Yet you see many people advertise that they have a 92. They sold left over 91s because of the changeover to the 3rd gen (FD) body style.

The new rotary, a remodeled 13B called the Renesis, creates 250 BHP from a naturally aspired engine. Let me repeat this, 250 BHP from a naturally aspired 1.3 litre engine. I dare anyone to extract that from a piston engine of the same displacement.

Now for the bad part of the rotary engines: They burn "Dirty" air. Your emissions suck because rotaries inject oil into the compression chamber to lubricate the Apex seals on the rotors. This creates a dirtier air as compared to just burning gasoline. To add to the problem there are two combustion phases and one exhaust. The two combustion phases try to burn as much fuel/oil mixture as possible and the exhaust and intake phase takes place in the same "stroke" if you will allowing exhaust air to mix with the clean intake air making a "dirty" air mixture.

I'm not aware of exactly how, but the renesis engine is said to perform better on the intake/exhaust "stroke" eliminating more of the exhaust gases before the intake is allowed to pass into the chamber. It is timed better, I believe. That is how they are able to produce so much more HP with a naturally aspired engine. Increased Exhaust pipe size and eliminating the three factory cats and installing a high flow cat or straight pipe helps dramaticly with power production, even more so on the turbo models. But, it does kill torque a bit below the 3000 RPM mark. Well worth it in racing situations since you are rarely under the 5 grand mark. This is also why the fuel efficiency sux on the rotary too. I got an average of 22 MPG in my 88 FC and that was good. Most of my friends got around 19-20 for their N/A engines while the turbo gets between 16-17.

LITTLE KNOW FACT: If anyone knows about Corvettes then you know that there was not an 83 model. This is because they had a four rotor wankle engine they were planning to put in the Corvette, eliminating the piston engine in them. This engine was a monster, but it also sucked fuel like crazy. With the energy crisis just over and the prices of gas at the time, the GM brass decided to cut the plans, skip a year and redesign the car. Hence the new, redesigned 1984 Corvette. I wish they had put that engine into the market, it would've blown the doors off of anything else out there.