dohboydds

Hey Guys:

I'm not an expert at this at all so I'm asking for some explanations.
The BMWUSA website has the gas mileage of the 535 at just 1mpg worse than the 528.
That's 1mpg less for 70 more horsepower! I never realize turbos are so efficient at producing hps without increasing gas use. (More I think about it more I should have dished out a little more $ for the 535) I don't suppose a quad turbo can make 370hp for a less mile than the 535? Is twin turbo the most efficient system there is in terms of turbos achieving an ideal compression for the most efficient combustion?

Also, what would be the gas mileage of a naturally aspirated engine that produces 300 be versus the turbo of the 535?
Also, I noticed that gas mileage dropps quite a bit from the 535 to the 550, why does this extra 60hp cost so much more than the +70 gain going from 528 to 535?
Finally, if turbos increase power so efficiently, as it appears to be doing for our 5 series, why isin't it used more universally if for nothing but for improving gas mileage over naturally aspirated engines producing similar power? Cost? turbo lag?

eddy

Well, as being a driver of turbo cars (tuned and non tuned) and normally aspirated engines it's as follow:
a V8 like an 550i needs the cil. always filled with air and gasoline. A smaller turbo engine has a smaller capacity, thus needs with lower rpm less fuel.
However when stretched out, the turbo comes in play while it is driven by the exhaust gasses, and produces pressurized air. To combust these large amount of air you need a lot more fuel to have a combustible mixture.

On the test cyclus 50-70 mph, a turbo engine works at an rpm range of about 2500. (the bigger the engine, the slower). At that rpm the turbo produces few extra air, so no fuel is needed. Stepping on the gas will produce a healty thirst. On a chiptuned car, this effect is even stronger. BTW my last car was a VW Passat 1.8 turbo with 150hp 210 nm. After tuning it had 204hp/260nm. Fuel usage was with easy driving 48 mpg, with sporty driving 40 mpg, wiith a really heavy right foot 25 mpg. Which is fairly equal to a V8.
If you dont push the car, it will use less fuel compared to an V8, if you step it and use the power, there won't be as much difference.

Turbo cars a a lot more expensive than a normal engine (turbo, intercooler, extra hoses/pipes, electronics etc. ).
The new CO2 discussions in Europe and US (Al Gore btw) force the car manufacturers to develop cars with smaller engines but equal performance (downsizing), For example VW has an engine 1.4 ltr with direct injection, a turbo AND supercharger and produces 170 hp. Compare that to the above mentioned 1.8 turbo with 150hp.


Eddy.

sleepyca31

I am guessing the engine also has the variable valvetronic crap as well-and any listed gas mileage is if you are driving granny style around town or normal freeway driving (not 100mph plus). The minute you push the engine around town or have fun the mileage plummits and the more power, turbo or not-the more gas it will suck. Go race around in a 528 and race in a 535-the mileage will suck either way. Drive slow and normal it will be the same pretty much. The variable valve crap bimmer uses and lots of other cars means when you dont need it-and are up to speed or driving slow-and no acceleration is really needed, the car barely uses any valves so its like driving a 4 banger in a sense that when it doesnt need the engine power-it uses only a small piece of the engine. This is an analogy obviously and not "technical" but thats my understanding.

When I drive the crap out of my 530-pretty much same as a 528-I get 15mph and that is flooring it at every change. Still not bad when you think of it. Even driving pretty racey for tank but not full out-I can get 19-20 and that is still driving like crap. These machines and engines are pretty damn fuel efficientl

Now once you go V8 or higher mileage just tends to suck as you climb over 350 horses

pennetta

A good example is comparing the 530i and 535i with the old 545i:
Both the 535 and 545 cars have similar acceleration numbers.
Both the 530 and 535 cars have 3.0 liter engine displacement. The 545 has a 4.4 liter engine displacement or a 50% increase over the 530/535 engine.
The turbo is a "demand type" boosting system that can make the engine act like anything between 3.0-4.4 liters, and as it acts like the bigger motor its fuel consumption will act like it as well.
The extremes are driving on a highway at a steady speed (no boost and great gas mileage) and driving like the cars on the TV show "COPS" where you drive it like you stole it (full boost and bad gas mileage).