Garrett Turbo

James Flammang asked:

making their redesigned debut for 2007, the current-generation coupes were “redesignated” for 2009, topped by the new 335i xDrive coupe with all-wheel drive and a 300-horsepower, twin-turbocharged 3.0-liter six-cylinder engine. This is BMW’s first twin-turbo inline six. In fact, turbocharging has not been used on BMWs since the 1980s, when it appeared on a handful of models.

Engineers decided to revive turbocharging, because of recent technical developments. Relatively small turbochargers minimize the dreaded “turbo lag,” since they build up pressure much faster than does a single, larger unit. BMW also offers a 328i coupe with a 230-hp, naturally aspirated 3.0-liter six-cylinder that uses magnesium-aluminum construction. Transmission choices for both include a standard six-speed manual gearbox, or an available six-speed Steptronic automatic.

Each model is offered with xDrive, which is BMW’s version of all-wheel drive. On smooth, dry roads, xDrive delivers what BMW calls a “sporty, rear-wheel-drive feel,” which is precisely what most shoppers are seeking. Along wet or snow-packed roads, on the other hand, xDrive “automatically sends more torque to the axle with more traction,” promising helpful front/rear weight balance. Making iDrive an option lets those who favor high-tech control select that unit, but allows those who prefer a simpler, traditional configuration to omit the love-it/hate-it system.

Headlight design, taillamp detailing, outside mirrors and interior appearance were created specifically for coupes. Two-doors feature a long wheelbase, short overhangs, a setback passenger compartment, and a low, sleek roofline. The long hood reflects BMW’s tradition of inline six-cylinder engines. Corona light rings that serve as BMW-distinctive daytime running lights accent the standard xenon adaptive headlights.

Rear occupants in the four-passenger coupes have a center console between individual seats with separate storage boxes, additional air outlet vents, and footwell lights. Standard leatherette upholstery comes in Black or Cream Beige, with leather optional. BMW’s iDrive controller is an option, too. One helpful feature is the seatbelt feeder arm, which automatically moves forward, presenting the seatbelt to the driver and front passenger when doors are closed and the key inserted. Access to rear seats has been made easier, according to BMW, but it’s still a chore for the less agile.

There’s nothing the least bit gaudy or garish about a 3 Series coupe, which relies strictly upon clean lines and smooth curves to establish its presence. Performance is precisely as energetic as expected from BMW. The twin-turbo engine has all the go-power anyone will need, available in an instant. In typical BMW form, the manual gearbox shifts with ease and finesse, requiring a mere flick of the wrist. Adeptly matched to the gearbox, BMW’s clutch engages with smooth confidence.

Engineers have given the 335i a surprisingly comfortable ride, considering the coupe’s impressive level of road-hugging expertise. Rear-drive 3 Series coupes are well known for their sure-footed behavior, but xDrive adds an extra helping of assurance. Ordinarily, there’s no evidence of its existence apart from a badge on the fender. When the pavement turns wet or slick, however, it’s ready to take action as needed.

Only a light rumble can be heard from the twin exhaust pipes. Otherwise, the 335i is fairly quiet. Steering feel and response don’t get much better, or more satisfying. Particularly comfortable front seats provide sufficient space all around, though the front compartment is a bit on the snug side.

Prices start at $38,125 (including destination charge) for a 328i coupe with rear-wheel drive. For a 335xi coupe with the twin-turbo engine and all-wheel drive, the outlay escalates to $44,625. An automatic transmission adds $1,325. Additional options include Active Cruise Control, rear Park Distance Control, a navigation system, heated front seats, an iPod/USB adapter, and a Premium or Sport Package (including upgraded tires).

Mason

Marc Formeister asked:


Few would debate that the Ford Taurus of past generations was about as unexciting and commonplace as a loaf of bread. But the new Taurus SHO (Super High Output) is attempting to shatter that dull image with the vibrancy of a very potent 365 horsepower engine. But this Ford offers more than just power. One of its main selling points is that this new Taurus has the power of a V8 and the fuel efficiency of a V6, in this case a 3.5 liter “ecoboost” V6. How did Ford manage to strike such an ideal compromise between horsepower and efficiency, and between excitement and utility? It certainly wasn’t due to new, innovative engineering, nor cutting-edge technology. They simply did what most car companies (including themselves!) did back in the late 1970s and early 1980s in response to the energy crisis: they added a turbocharger (two in the case of the new SHO) to an existing engine in their lineup.

Turbochargers allowed car companies to use eco-friendly, efficient, and small four-cylinder engines without completely sacrificing power. But as the energy crisis and obsession with efficiency and gas mileage waned in the early 1990s, naturally aspirated V6s and V8s (without turbos) made their triumphant return. Only a few manufacturers, such as Audi/VW, Volvo, and perhaps most ubiquitously, Saab, continued employing the proven formula of small turbocharged engines. And anyone familiar with Saabs knows of their legendary fuel efficiency—and it’s no coincidence that their cars used small turbocharged inline-fours almost exclusively.

Without a doubt, today the turbocharger has whooshed its way back into engine bays, and this time it seems that it will be here to stay. These new turbo engines are much more performance-oriented than their predecessors, and have found their way into sporty cars instead of pedestrian ones. Budget imports like Subaru’s WRX and Mitsubishi’s Lancer Evo, and domestics like the Dodge Neon SRT-4, all use turbos. The immense popularity and affordability of these cars, their reputation for thrilling performance, and movies like The Fast and the Furious, which abounds with turbocharged cars chirping their blow-off valves, have created a generation of car tuners lusting for that oversized snail lurking beneath the hood.

Above all, turbocharging in its various guises has become such a popular modification because it is by far the best bang-for-your-buck, assuming you know what you’re doing, of course. A large intercooler conspicuously showcased behind the front bumper, the “pshh” sound of a blow off valve between gear shifts, and the intoxicating, jet-like sound of a spooling turbo are all bonuses that tastefully alert any tuner to the fact that your car is packing a lot more than your average import.

Obviously, a turbo kit is a desirable upgrade for anyone looking to substantially augment their car’s power. But what exactly is a turbocharger, and what’s so special about it? At its most basic level, a turbocharger is simply an air pump/compressor driven by hot exhaust gases. On non-turbocharged engines, the exhaust gases from the engine run uninterrupted through an exhaust manifold(s) and through the rest of the exhaust system and out the tail pipe.

A turbocharged engine is a bit more complicated. On such an engine, instead of flowing straight through to the muffler, exhaust gases first travel through an exhaust manifold (turbo manifold), which collects and directs all of the exhaust gas into a large opening of the turbo that leads to the exhaust turbine (see picture below). From here, some of the gases flow out of the back side of the turbo, through a down pipe, and out the muffler like in a naturally aspirated engine. But the majority of the hot gases flow into the exhaust turbine, and in doing so the moving air spins the exhaust wheel (a small metal fan with many blades) inside of the exhaust turbine. This moving air causes the wheel to rotate very quickly—sometimes as high as 120,000 RPMs. The exhaust wheel sits on a shaft that rotates with it; on the other end of the shaft there is another wheel, known as the compressor wheel. This wheel spins at exactly the same rate as the one in the exhaust turbine, but it does nothing with the exhaust gases. Instead, ambient air is drawn through the turbocharger’s inlet pipe, where the rapidly moving compressor wheel literally compresses the air above atmospheric pressure, and then sends it out of the compressor’s outlet, where it then flows to the inlet of an intercooler en route to the engine’s throttle body and intake manifold.





The amount that this air is compressed varies widely depending on things like the stoutness of the engine’s internal parts and the fuel and engine management systems. This amount is measured in pounds per square inches, and is commonly known as “boost.” So low boost is around 5-10 psi (above atmospheric pressure), medium boost is around 10-15 psi, and high boost is 15-20+ psi. While this is a huge over-simplification, the more boost a certain engine produces, the more power is generated. In general, an increase of about 10 horsepower accompanies every 1 psi increase in boost. Right off the bat, it’s obvious that a lot of power can be made from boost—at only 5 psi the engine would still be producing roughly 50 more horsepower than if it did not have a turbocharger. Compare this power increase with what could be had by a set of expensive, difficult-to-install camshafts on a non-turbo engine, which might afford the engine 10-15 horsepower more, and it is obvious that turbocharging is the way to go for serious power increases.

Be sure to come back soon to the Raleigh Tuner Car page for the step-by-step process of turbocharging the engine of a Nissan 240sx, and in doing so increasing power from 155 to 400+!

Questions? mformeister@cox.net



Emil