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BMW 540i Modifications
About 20 years ago I was very active in a motorcycle club in New York. One of our active members had an observation after giving up after trying every tweak he could to his new bike. "I've tried everything on my new bike, and you know, it's never run as well as when I first got it."
Why is that?
Every vehicle manufacturer has huge engineering staffs at their disposal. Compared to you and I or aftermarket tuners, these real engineers:
1.) Have complete access to every piece of secret insider data about what's going on inside the vehicle. They have supercomputer plots of airflow. They know about the micro differential temperature variations across the hood. They know what's going on inside a combustion chamber simulated out to the individual molecular level. When they do a simulation they have all the CAD data for accuracy. We don't.
2.) They are real engineers with degrees with the deep technical backgrounds required to understand what's really going on, as opposed to hobbyists and tuners who work by fuzzy feelings. It's tough to explain if you're not a degreed engineer. I do have an engineering degree, and all that calculus really lets you get inside what's going on.
3.)They get paid to work all day and night. That's all they do.
4.) They have huge budgets for research, since what they do is spread out among the many thousands of production vehicles for even the most exclusive model.
5.) In addition to the ubiquitous dynamometers, they also have wind tunnels and flow and combustion analyzers to know what happened and why.
Any tuner can improve on one or two aspects of anything. Most tuners have dynos, some might have wind tunnels. None of them have all the data BMW has, or it's research budget. The whole point of a BMW is to do everything well over all conditions. That's why it makes no sense to waste time trying to outsmart BMWs engineers at their own game. Even if you had a supercomputer, wind tunnel and research engines loaded with probes you still don't have the base data from which to start calculating.
Back in the 1950s cars were so primitive and under stressed that it was easy and safe to hotrod them.
In the 2000s every car is running as well as it can. It already has every reasonable tweak incorporated as part of its very soul. Unless you're doing a ground-up complete rebuild, there is nothing you can bolt on to make an overall better car. You may be able to trade off one aspect for another with something serious like adding a blower, but BMW knows better than anyone how to make their cars as good at as many things as possible all at the same time. Add a blower and you'll probably pop your U-joints a lot faster than stock, for instance.
Tweaks are for people who enjoy tweaking for its own sake. I don't bother with them.
Most or all BMW enthusiasts are middle aged men. These guys love to play with things. We take great pleasure in fixing and improving things. I personally would rather drive than tweak.
It's easy to improve things by tweaking. My subtle point is that if you tweak something well enough to improve one thing, like adding stiffer springs, something else suffers, like ride comfort. I'm odd for a BMW enthusiast: prefer to keep my hands off and enjoy the perfect balance my Bavarian brothers designed into my car. I really am 1/4 Bavarian.
I realize this will probably get me a lot of hate mail because guys who love to screw with their cars don't want to hear this. Personally I take great pleasure in being the only guy with a car exactly as it left Bavaria. This becomes more fun as a car hits 10 or 20 years old, when few BMWs are left as they were intended. Sure you can add a blower and dust me, but then I'll still have more cruising range leading to better speed made good over long journeys, etc. It's all a trade off and I prefer the balance struck by BMWs real engineers.
Cold Air Intakes and Induction Systems
Cold air has more mass than warm air. Using colder air allows the engine to make more power, since you have more air mass per unit volume. More air means you can burn more fuel and make more power.
The factory system pulls cold air in from under the front fender. This is good. There is a filter box inside the hood between the engine and the fender.
For some reason all the aftermarket cold air induction systems I've seen use a filter dangling at the end of the engine's air intake where the standard air filter used to be. These aftermarket systems pull in warm air from under the hood, making them less effective than the standard system!
I don't get these tweaker guys. Does anyone really think BMW would save $5 and use too small an air filter and loose horsepower, which is a major competitive number? Have a look at the 540's filter element. It's huge, and it sucks air directly from the cool outside air, not the hot air under the hood.
People do this to look cool. Supposedly it helps the brakes stay cool, too. There are at least two problems if you get carried away here:
1.) Drilled holes reduce the brakes' swept area, making them less effective.
2.) The loss of rotor mass means that the rotors have to get hotter to absorb the same amount of heat from any particular stop, compared to an undrilled rotor.
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