by Evan Griffey
Source: MSN Autos Editorial
December 12, 2008

Revving a lumpy-cammed V8 muscle car at a stoplight on Main Street USA has long been an American rite of passage. The 1973 film American Graffiti continues to define this ritual for many hot-rod traditionalists. However, the rules of the game have changed in the 21st century. Graffiti has been replaced by The Fast and the Furious. Big displacement, multicarb V8s with flames shooting out their open headers have been substituted with relatively minute, fuel-injected four cylinders with turbo boost shooting through their veins. These smaller engines offer all of the advantages of their larger predecessors (lots of power) without the pitfalls (inefficiency and dreadful fuel economy).

Compare Evo MR , 911 Turbo and Cobalt SS

The Basics
A basic explanation of how the internal combustion engine works is necessary to understand many of the concepts discussed here. If you put a tiny amount of high-energy fuel (such as gasoline) mixed with air in a small, enclosed space (a cylinder) and ignite the concoction, an incredible amount of energy is released in the form of expanding gas (the combustion event). If you create a cycle that sets off explosions like this hundreds of times per minute and harness the resulting energy, you have an automobile engine.

You see, horsepower is basically a chemical reaction. The act of burning fuel makes power, and the more fuel an engine burns — at the appropriate ratio of fuel and air — the more power said engine will make. So in theory, engines with more volume/size or displacement naturally have the capacity to make more power than smaller engines, right? Not so fast.

New Muscle Cars

The Improvements
While the laws of physics cannot be totally broken, modern automotive technology has managed to bend them a bit, allowing smaller engines to act like bigger ones.

Turbochargers
Simply flooding an engine with more fuel is only half the power equation. You have to maintain a proper fuel/air ratio for the combustion event to be effective. So if you want to inject more fuel into the equation, you also have to add more air. An engine’s ability to ingest air, however, is limited by its physical size, or displacement. Or is it?

Enter turbochargers, or turbine-driven forced induction compressors. They are the ultimate equalizers because they inject air (aka boost) at higher pressure and greater volume into an engine’s intake system. Force-feeding air into the combustion chamber leads to a more intense explosion, or combustion event, when the mixture is ignited. On the performance side, a turbo can significantly increase an engine's horsepower output (up to 50 percent) without significantly increasing its weight. Adding a turbocharger itself does not save fuel, but it will allow a vehicle to use a smaller engine to achieve the same power out as a bigger one when needed, then go back to acting like a smaller one (read: more fuel-efficient engine) when it doesn’t.

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Variable Valve Timing
This technology emerged in the early ‘90s as automotive engine computers, or electronic control units (ECUs), became more powerful and precise. Variable valve timing (VVT) systems change the valve train events inside the engine on the fly.

Valves control the flow of air and fuel into an engine’s cylinders and the exhaust from them. The camshaft uses lobes (called cams) that push against the valves to open them as it rotates. At different engine speeds (rpm ranges), the vehicle’s ECU activates alternate lobes in a way that allows it to change when and how long the valves open (timing) and how much the valves move (lift).

So what's your favorite kind of muscle: big and bulky or lean and mean?

There are two benefits to this system. First, VVT allows for the intake valve to stay open longer so the cylinder can breathe more of the fuel/air mixture, leading to a more powerful combustion event. Thus, the vehicle develops more power and torque. Second, it uses internal exhaust gas recirculation. A little bit of exhaust gas is left in the combustion chamber as the fresh fuel/air mixture is sucked in, causing a more complete combustion, which cuts down on emissions.

Direct Injection
Direct injection (DI) is a new, leading-edge technology that does what it says: Fuel is squirted directly into the combustion chamber so that the timing and even the shape of the fuel mist can be more precisely controlled so that it more thoroughly mixes with air in the cylinder. Traditionally, fuel is injected into a port or pre-chamber and allowed to mix with air before entering the cylinders. Delivering fuel directly into the combustion chamber from an injector positioned in the cylinder produces a more precise fuel/air mixture, or fuel atomization. The result is a more complete combustion, maximizing power and minimizing emissions.

The Cars
We have charted a cross section of cars that employ — to varying degrees — the aforementioned technologies to generate eye-popping power from small 4- and 6-cylinder engines. We also tossed in a few high-tech V8s and a low-tech V8 pickup truck for good measure.

The volumetric efficiency advantage of the turbocharged platforms is plain to see, as they are able to make awe-inspiring power in relation to the size or displacement of the engine (hp/liter). We also included power-to-weight ratio, measured in pounds (vehicle curb weight) per horsepower, as an indicator of the car’s performance potential, fewer pounds per pony being better. This is only an indicator, as aspects such as engine redline, gearing and other parameters are not considered here. Fuel efficiency of each model can be compared, but any conclusions should be weighed against the technology checklist chart.

New Muscle Cars

Power Versus Displacement Versus Mpg
[Ranked by power-to-displacement ratio (hp/liter)]

Car Engine Hp Hp/liter Mpg Lbs Lb/hp
Mitsubishi Evo X T2.0-L4 291 145.5 17/22 3517 12.08
Porsche 911 Turbo T 3.6-L6 480 133.3 16/23 3660 7.62
Chevy Cobalt SS T 2.0-L4 260 130 22/30 2975 11.44
Subaru WRX STI T 2.5-L4 305 122 17/23 3395 11.13
Mazdaspeed3 T 2.3-L4 263 114.3 18/25 3153 11.98
Honda S2000 2.2-L4 237 107.7 18/25 2864 12.08
MINI Cooper S T 1.6-L4 172 107.5 26/34 2634 15.31
Subaru WRX T 2.5-L4 265 106 18/25 3174 11.97
BMW 335i T 3.0-L4 300 100 17/26 3571 11.90
Honda Civic Si 2.0-L4 197 98.5 21/29 2899 14.71
Infiniti G37 Coupe 3.7-L6 330 89.1 18/26 3633 11.00

T=turbocharged

V8s Engine Hp Hp/liter Mpg Lbs Lb/hp
Audi R8 4.2-L 420 100 12/19 3605 8.58
Chevy Corvette 6.2-L 430 69.3 16/26 3217 7.48
Chevy Silverado 5.3-L 315 59.4 14/20 4798 15.23

 

Technological Checklist

Car Variable Valve Turbo Direct Injection $
Mitsubishi Evo X X X n/a 32,990
Porsche 911 Turbo X X n/a 26,200
Chevy Cobalt SS X X X 24,095
Subaru WRX STI X X n/a 34,995
Mazdaspeed3 X X X 23,410
Honda S2000 X n/a n/a 34,795
Mini Cooper S X X n/a 22,600
Subaru WRX X X n/a 24,995
BMW 335i X X n/a 39,300
Honda Civic Si X n/a n/a 21,850
Infiniti G37 X n/a n/a 34,900
Chevy Corvette X n/a n/a 49,415
Audi R8 X n/a X 114,000
Chevy Silverado V8 n/a n/a n/a 20,895

 

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Putting it All in Perspective
The top of the power chart vividly illustrates the potency of turbocharging. A traditional mind-set would indicate a 430 horsepower ‘Vette is a powerhouse. But evaluate it by referencing displacement, and the Corvette develops only 69.3 horsepower per liter, less than half of the much smaller Mitsubishi Evo. The standout here is the Cobalt SS, which uses all three technologies to pump out 130 horsepower per liter yet return 22-city and 30-highway mileage. Talk about having your cake and eating it, too.

So what's your favorite kind of muscle: big and bulky or lean and mean?

Dropping the hammer as that Main Street light flashes green doesn’t have to mean the gas gauge will fall more quickly than the tach rises. Today’s small-displacement performance engines rely on high-tech superpowers that provide mind-boggling horsepower but get commuter-esque fuel mileage, all while burning cleaner than ever. These cars are a win-win for anyone who wants an engaging, euphoric driving experience and a sign of things to come for all types and classes of motor vehicles.

Evan Griffey served as an editor of Turbo & High Tech Performance, a pioneering publication about sport-compact tuning. Today Griffey freelances for Import Tuner, Sport Compact Car, Car Audio and Siphon.

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