It's hard to not to mention the name BMW and not think about
the company's buttery smooth inline-6 engines. With the exception of the
current generation M3, 3-Series models in the U.S. for over a decade have been
powered solely by inline-6 engines. And most recently, BMW has added turbos to
its inline-6 to boost power and efficiency.
BMW is now looking to make another leap in fuel efficiency,
and it means that the company's normally aspirated inline-6 could get the
axe in favor of a new
2.0-liter, turbocharged inline-4 engine. The new engine produces 240hp @ 5,000 rpm and 260 lb-ft of torque at just 1,250 rpm.
For comparison, the 3.0-liter inline-6 produces 230hp at
6,500 rpm and a meager 200 lb-ft of torque at 2,750 rpm when used in the 328i.
The new engine uses the same technology found in the
turbocharged version of the inline-6 (N55) meaning that a twin-scroll
turbocharger, direct injection, and VALVETRONIC intake control are onboard. In
addition, the new turbo four is not only lighter than the naturally aspirated
inline-6, but it is also more compact.
BMW has not released official fuel economy numbers for the
new engine yet, but it will no doubt offer better ratings than the current
naturally aspirated inline-6.
Expect all of BMW's models that use the naturally aspirated
3.0-liter inline-6 (1-Series, 3-Series, X3, X1, Z4, etc.) to switch over to the
quote: undersquare engines are most often tuned to develop peak torque at relatively low speeds.
quote: A larger injector will ALWAYS dump more fuel then a smaller injector at idle.
quote: A piston engine is undersquare or longstroke if its cylinders have a smaller bore (width, diameter) than stroke (length of piston travel).This can be a negative trait, since a longer stroke usually means greater friction, a weaker crankshaft (strengthen with weld, true & balance), and a smaller bore means smaller valves which restricts gaseous exchange; however, with the aid of modern technology, these are not the large problems that they used to be. An undersquare engine usually has a lower redline than an oversquare one, but it may generate more low-end torque. In addition, a longer stroke engine can have a higher compression ratio with the same octane fuel compared to a similar displacement engine with a much shorter stroke ratio. This also equals better fuel economy and somewhat better emissions. An undersquare engine does not overheat as easily as similar oversquare engine. Engines can be modified with a "stroker" crankshaft, which increases an engines stroke from stock, increasing torque. Increased stroke make the piston travel further up and down. Since the amount of time allowed for this movement is not increased, the piston speed increases with a Stroked Crank (piston must move a further distance in the same amount of time). This can sometimes cause pistons to wear more quickly.Undersquare engines produce strong torque at low to mid range rpm's because of the "leverage" advantage of a longer stroke.Large increases in stroke can decrease an engines ability to perform optimally at high rpm.One disadvantage for some applications would be increased piston speed. Excessive piston speed can cause ring seal problems and lubrication problems, which decreases piston life. Piston speed will obviously increase with rpm and it will also increase with an increase in stroke. And then there's the loads on the crankshaft, pistons, the piston pins, connecting rods, and rod bearings that increase dramatically with increases in stroke (or piston speed). In general, a longer stroke leads to higher thermal efficiency through faster burning and lower overall chamber heat loss.A longer stroke will have greater port velocity at a given RPM, more torque due to more leverage on the crank, will achieve it's greatest efficiency at a lower RPM, and have less peak potential than a shorter stroke motor. Smaller combustion chambers are also more efficient, with the flame front having a shorter distance to travel- this leads to being more detonation resistant, and having an advantage for emissions.A longer stroke, however, increases piston speed per engine cycle, which causes greater side-loads on the cylinder walls and decreases maximum rpm's.If you are a torque devotee, increase your stroke. If you are a horsepower (rpm) junkie, increase your bore. If you believe that too much power is just the right amount, you can increase both!The added torque of a stroked engine makes it tons of fun to ride, and if that's what you want, more power to you.Oversquare EnginesAn engine is oversquare or shortstroke if its cylinders have a greater bore (width, diameter) than stroke (length of piston travel).An oversquare engine is generally more reliable, wears less, and can be run at a higher speed. In oversquare engines power does not suffer, but low-speed torque does to some degree, since torque is relative to crank throw (distance from the crank center to the crankpin)—the leverage, essentially. An oversquare engine cannot have as high a compression ratio as a similar engine with a much higher stroke ratio, and using the same octane fuel. This causes the oversquare engine to have poorer fuel economy, and somewhat poorer exhaust emissions. Engines can be modified by being "de-stroked", shortening the stroke to increase maximum rpms and top-end horsepower, at the expense of low-end torque.Breathing is the important thing, then. Over square engines have an advantage here, in theory. In a big bore engine, the edges of the valve are less obstructed by the cylinder wall. This is called "unshrouded" and helps breathing. A big bore can fit larger valves and give them more breathing room, too.Engines used at sustained high rpm usually will be better with less stroke and more bore (oversquare).A short crankshaft stroke reduces parasitic losses. Ring drag is the major source of internal friction. With a shorter stroke, the pistons don't travel as far with every revolution. The crankshaft assembly also rotates in a smaller arc, so the windage is reduced. In a wet-sump engine, a shorter stroke also cuts down on oil-pressure problems caused by windage and oil aeration.Bigger bores with shorter strokes have the potential to turn higher RPM's, and larger/more valves will fit into bigger combustion chambers. Since the HP race involves turning ever higher RPM's to make more power, the oversquare motors have increased in popularity particularly when it comes to motorcycles.
quote: 4 cylinders is indeed nothing new for BMW and people will not mind a turbo 4. Americans, in general, just want the power and don't care how they get it.
quote: Oh really? Go read a review on the Audi A4 and watch for the part where they wish it were a V6 instead
quote: While the BMW turbo four looks to be a good engine and quite similar to the VW 2.0L TFSI in performance, it is not likely to be well received by luxury car buyers.
quote: I think that a few thousand Audi A4 owners would not agree with that statement. If you'll recall, the A4 is Audi's chief 3-Series fighter.
quote: He is talking about the amount of force required to push the turbo on the exhaust hard enough to compress the intake charge. You really think 17psi comes for free?
quote: What you claim is that all engines use the same amount of gas at idle. Which is not true.
quote: If speed were the only thing that mattered we'd all be riding sport bikes.
quote: agreeing with the idiot who thinks turbo engines get better fuel economy than equally rated NA engines shows that you not only drive a shitty car but will never have anything better.
quote: Borat wanted a car with a pussy magnet, but yours comes with pussy repellent.
quote: P.S. - Yer momma and/or sister don't count.
quote: The explosion inside the combustion chamber is what produces power. That explosion is generated by a mix of air and fuel: you can't make a more powerful explosion, without more air because oxygen is what allows combustion...That is what a turbo is for: allow the same amount of air to be burned than in bigger displacements where air is used at atmospheric pressure, not compressed much beyond that. By boosting the compression ratio you can further enhance power while using less fuel.
quote: So, not necessarily 2 engines with the same power will equate to the same consumption: on bigger NA engines you'll be using about the same amount of oxygen than in a smaller turbo one, but potentially more fuel in the process unless the compression ratio in the NA one is higher enough than on the turboed one.
quote: That holds somewhat true, but you won't see any NA engine, regardless of configuration, giving away much more than 110nm/liter of displacment, while on Turbo engines those figures start at about 130nm/liter in the worst case, with that ration growing steadily as turbo pressure increases.
quote: In turbo engines thanks to the compressed air, you don't need to make the engine bigger to yield better torque: more air pressure will suffice.
quote: What nowadays is being sought for, is to be able to combine good power with low fuel usage, and provided the usage pattern of normal cars is most of the time way below their peak power, downsizing the engine and putting a turbo to get the same power as before is the answer they've found.
quote: Go to a BMW forum and look up turbo lag and HPFP.
quote: There's howls of protest going on right now in bmw forums.
quote: Bavarian Nickel and Dime
quote: Take a look at the dyno posted below and I challenge you to find another stock single turbo motor that has a flatter torque curve.
quote: having torque come on at low rpm is a GOOD thing.
quote: so the Fast&Furious idiots aren't blowing up engines left & right.
quote: I doubt it will have a boost limiter.
quote: My Sonata has over a hundred more horsepower and gets better fuel economy.
quote: Who cares about vacuum readings? All I care about are results.
quote: . Although I have no idea why anyone would keep a car more than 3 years.
quote: but I like nice cars.
quote: Im glad you spend 10 bucks a month on insurance
quote: You have a 1996 something? I bet it smells awesome inside.
quote: go whoop ass on some wanna-bes in their ponycars at the track LOL
quote: Still doesn't help you when you get your ass whooped on the freeway or even from a light by a car that cost $15,000-20,000 less.
quote: Its not all that fuel efficient (20 / 17)
quote: It makes 260ftlbs at 1250 rpms
quote: As you can see, BMW's 4cyl would not have to spin very fast at all.
quote: What you say about the oil is true.