The money-maker. But the real driving force is torque. Torque is your rhythm section; the drummer and bassist locked in the pocket, or the film director that really navigates the proceedings. Torque is work and, in fact, horsepower is an extrapolation of work (torque) over time.
If we take these platitudes a few steps deeper, the best engine from a drivability viewpoint delivers the greatest total area under a plotted torque curve from idle to redline. And generally speaking, larger displacement engines do the total area thing better. Some trickery can make smaller engines feel big, like supercharging and turbocharging, nitrous oxide and variable valve timing, which should often be termed “variable cam phasing,”
but we’ll grade on the curve here. Yet, all these varied methods are designed to do what small engines can’t on their own unless spun to the stratosphere, which isn’t always achievable in a street car. These methods are designed to process greater volumes of air than the engine can ingest naturally, without an appendage or chemical assistance strapped to its lungs. After all, in overly simplistic terms, an engine is merely an air pump. The more it can process, the more it can deliver.
Take two normally aspirated engines, one a 3.0-liter good for 7,000 max rpm that delivers a peak torque figure of 250 lbs-ft at 5,000 and the bulk of its power and torque beef in the upper range of its power band. The other, a 4.0-liter good for only 5,500 max rpm and 250 lbs-ft at 2,500. Chances are good that the 3.0-liter will feel comparatively sluggish until spun up high and then becomes a more exciting, thrilling engine to use, whereas the 4.0-liter will feel to most drivers as if it digs better and is more powerful. Why?
The bulk of that torque is in a more usable range. What these hypothetical drivers innately know but perhaps don’t think about is that the bigger engine develops a more usable torque curve than the smaller engine, therefore making it a happier partner in driving under most (non-racing) conditions.
Peak power and torque numbers give a false impression of overall power. Peak power is what we all compare, though. It’s the currency of bench racing car geeks. But there’s a better currency. Greater area under the torque curve disbursed over the complete rev range in total units equals better drivability. This is precisely why some manufacturers have, for several years now, been quoting torque figures over an rpm range rather than one point.
For example, Audi states the A4’s base 2.0-liter engine develops 258 lbs.-ft. of torque from 1,500 to 4,300 rpm; quite a spread and a very flexible engine, thanks to minimal turbo lag and sophisticated electronic controls. Hell, Audi is now even quoting horsepower figures in the same manner: 220 hp from 4,450 to 6,000 rpm, putting an even finer point on the broad swath of power delivery.
You’ll likely have noticed engine development within the past two or so years of more and more turbocharged engines serving standard-model duty than ever before. It’s not an accident. Killing two birds with one impeller, a modern turbo engine can be sorted to deliver the seemingly opposed goals of great power and good economy. Fuel economy, with the upcoming hike in federal regulations covering them,
and customer expectations are two of the most powerful forces on engine and car development. The wider performance envelope a turbocharged engine can deliver is simply not ignorable.
In the 1970s, one old turbo saw went something like this: Normally-aspirated engines waste their exhaust gasses to the atmosphere, where turbocharged engines put those exhaust gasses to work for free, netting greater power.
While this made for great sales and marketing copy, it toyed with science and the truth. Without any additional fuel under boost, that turbocharged engine won’t make any more power and will likely die a Chernobyl death due to detonation.
Today, science has progressed to where we have far greater control and flexibility in fuel delivery and mapping, ignition power and timing and more precise machining on a mass scale to alleviate much of the throttle response concern with turbos.
This is why we see almost every major manufacturer using smaller turbocharged petrol engines in lieu of their larger naturally aspirated fathers, to state nothing of diesels. Turbochargers also act as natural mufflers, blanketing off the exhaust path somewhat to the atmosphere.
Porsche just announced the base engine for the 2016 911 will be a 3.0-liter turbocharged flat six making 370 hp, where the prior naturally-aspirated 3.4-liter model generated 350 hp. Even Ferrari, widely known to favor natural aspiration, has also debuted the turbocharged 2016 488GTB with a turbocharged 3.9-liter, 670 hp V8 replacing the prior 458 model which used an aspro,
570-hp, 4.5-liter V8. In both cases, the turbo engines not only develop more peak power and torque, they do so over a far greater rpm range, making them more drivable. Perhaps a trifle quieter, too, but certainly more flexible. (All power figures I cite here are DIN, not U.S.-spec SAE numbers, which will be slightly lower when announced. The difference between the two measurements is another can of worms altogether.)
The unplugged exhausts of non-turbo engines may be on the wane, but greater overall power and area under the curve with improved fuel economy is a decent trade-off for more muted music. And your right foot will certainly be happy.