The 15 Most Power-Dense Naturally Aspirated Cars of 2015

Specific output, power density, or, in its simplest representation, horsepower produced per liter of displacement, is a largely trivial metric by its lonesome. Unless you're in charge of a racing team faced with engine-size restrictions, and then hp/liter would be pretty important.

You could get a better picture of an engine's overall efficiency and cost if specific output were tag-teamed with other yardsticks such as brake-specific fuel consumption, brake mean effective pressure, recorded cylinder pressure, and volumetric efficiency across the powerband. But ranking cars not destined to spend their lives on racetracks by hp/liter is meaningless. So why do it at all? Because numerical order has its appeal, too.

The qualifications list is short. The cars must have a naturally aspirated engine and be federalized for sale in the U.S. within the 2015 model year. We also have to know the stock horsepower and liter ratings, and, most critically, we must be able to divide.

Porsche 911

Specific output:102.9 hp/liter

Engine:3.4L/350-hp/287-lb-ft DOHC 24-valve flat-six

Peak power engine speed:7,400 rpm

Being able to spin the hell out of the crankshaft without fear of anything tearing asunder is a guaranteed way to earn a spot here. With 350 hp available at a singing 7,400 rpm, the 911 Carrera and its associated variants (Targa, Cabriolet, etc.) ties for the lowest peak power engine speed of the list.

Specific output:103.5 hp/liter

Engine:6.3L/652-hp/504-lb-ft DOHC 48-valve V-12

Peak power engine speed:8,000 rpm

The family Ferrari has room for more than your typical Ferrari: spouse, two kids, luggage, backseat entertainment system for said kids, and all-wheel drive (first through fourth gears only). There's also a quite large V-12 underneath the hood.

Porsche

Specific output:105.3 hp/liter

Engine:3.8L/400-hp/325-lb-ft DOHC 24-valve flat-six

Peak power engine speed:7,400 rpm

Didn't we just see a 911? The "S" trailing "Carrera" adds a 5mm bigger bore to each cylinder over the base 3.4-liter flat-six for a total 0.4-liter displacement boost. More importantly, there are 50 additional ponies to play with.

Audi R8

Specific output:105.8 hp/liter

Engine:5.2L/550-hp/398-lb-ft DOHC 40-valve V-10

Peak power engine speed:8,000 rpm

V-10s have helped create some of the more iconic exhaust noises in history despite their relative rarity. Merely four cars of the 2015 vintage pack V-10s -- technically, one is the convertible version of another -- and two are on this list.

Specific output:106.3 hp/liter

Engine:6.5L/691-hp/509-lb-ft DOHC 48-valve V-12

Peak power engine speed:8,250 rpm

The angry-sounding 6.5-liter V-12 mounted in the middle of the Aventador is worlds different from the V-12s motivating the Rolls-Royce Wraith and Mercedes-Benz S65 AMG. The Lambo outwardly looks much angrier than those two grand tourers, as well.

Specific output:107.1 hp/liter

Engine:4.2L/450-hp/316-lb-ft DOHC 32-valve V-8

Peak power engine speed:8,250 rpm

Audi protects the RS 5 from the standard R8 by way of 20 more horsepower. The net result is the RS 5 coupe and cabriolet make the list's cut, whereas the V-8-powered R8 at 102.4 hp/liter misses it.

Specific output:113.2 hp/liter

Engine:3.8L/430-hp/325-lb-ft DOHC 24-valve flat-six

Peak power engine speed:7,500 rpm

The 911 Carrera S tricks its way onto the list again thanks to the $17,800 Powerkit. For the cost of a fully loaded Mitsubishi Mirage ES, Porsche will tweak the 3.8-liter engine's intake camshafts and cylinder heads, fit a new intake manifold, and shift the power peak 100 rpm higher.

Specific output:113.2 hp/liter

Engine:3.8L/430-hp/325-lb-ft DOHC 24-valve flat-six

Peak power engine speed:7,500 rpm

GTS equals Carrera S with the Powerkit and a specific blend of mechanical, exterior, and interior equipment. The key differentiator is black contrast design elements. Oh, and they start about $16,300 more than their Carrera S counterparts, but have more standard stuff.

Lamborghini

Specific output:113.8 hp/liter

Engine:6.5L/740-hp/509-lb-ft DOHC 48-valve V-12

Peak power engine speed:8,400 rpm

The super-exclusive Veneno is certified for sale in 2015, even though all nine examples were assembled by 2014. It lands in seventh place on this list with the most powerful engine of the lot. A 740-hp Italian V-12 rotating at 8,400 rpm: Where do we sign up?

Specific output:115.8 hp/liter

Engine:5.2L/602-hp/413-lb-ft DOHC 40-valve V-10

Peak power engine speed:8,250 rpm

At 8,250 rpm, the Huracan's V-10 endures a peak piston speed of 114.2 mph. In contrast, the Veneno sees "only" 95.7 mph at its 8,400-rpm power peak. Suffice to say, both engines would look frantic were they cut open while running.

Specific output:116.0 hp/liter

Engine:6.3L/731-hp/508-lb-ft DOHC 48-valve V-12

Peak power engine speed:8,250 rpm

The powerful front-engine F12 mows down the 0-60-mph run in 3.6 seconds, which, amazingly, doesn't sound all that quick nowadays, although its classic Ferrari long hood should be more than enough enticement to take it out for a spin.

Specific output:124.9 hp/liter

Engine:4.5L/562-hp/398-lb-ft DOHC 32-valve V-8

Peak power engine speed:9,000 rpm

The power-density leap from the F12 to the 458 Italia/Spider is big, with a difference of 8.9 hp/liter. The scintillating 9,000-rpm peak power speed helps get more performance out of each of the V-8's cylinders, the tradeoff being the need for a robust (read: expensive) reciprocating assembly.

Specific output:125.0 hp/liter

Engine:3.8L/475-hp/324-lb-ft DOHC 24-valve flat-6

Peak power engine speed:8,250 rpm

We were smitten with the 996 GT3 when it had a then-drool-worthy 381 hp. The latest iteration induces a similar reaction. Although all naturally aspirated 911s make you feel like you're at Le Mans when they're operated in anger, there's something about the GT3 that just feels so right.

Porsche 918

Specific output:132.2 hp/liter

Engine:4.6L/608-hp/398-lb-ft DOHC 32-valve V-8

Peak power engine speed:8,700 rpm

Of the three hybrid hypercars we've driven (918 Spyder, Ferrari LaFerrari, McLaren P1), we have the most hands-on experience with the Porsche. And it's been amazing each time. Part of our amazement stems from the flat-plane V-8 that howls into the air directly above the car (not behind it).

Specific output:132.7 hp/liter

Engine:4.5L/597-hp/398-lb-ft DOHC 32-valve V-8

Peak power engine speed:9,000 rpm

Ferrari is so proud of its hot-blooded 458 Speciale that it plugs its 132.7 hp/liter specific output as the "world record for a road-going naturally aspirated engine" on its website. As it should be. Tuning and extracting maximum power from a naturally aspirated engine will likely soon be a lost art.