I rode in a friend’s Ferrari (1978 308) recently and while I love how it sounds… I often can not get enough of the turbocharged sound. So if you love the sound of turbochargers doing work here you go:
Link for you RSS peeps.
It may be an older video of ours, but I love it and cannot get enough.
Update: Apparently I decided to post this exactly two years after uploading it to YouTube. Odd.
Since being at home on a short vacation/business trip, I also got to see my garage. Sadly, it is a fine example of what many garages I’ve seen look like, and an even better example of what a garage should not be like. So if your garage looks like this, maybe take some time to get rid of some of the “temporary storage” things that have ended up spending a year or more alone in the garage.
P.S. If you see anything you really want in this picture, we are probably willing to sell it to you, or even give it to you.
Maybe this is a sign I have nothing to contribute today, but I don’t like to look at it that way. I’ll use the excuse that I am at home in Virginia, visiting my friends and family so things will be back to normal come Thursday for me. To the point, I hope to get you excited about what will happen here.
I Expect to see (so that means you should too):
I’m pretty excited about what is to come and I hope you are too. Maybe I’ll even change the graphics of the site, add a Logo and do all sorts of neat things. Thanks for reading, I really do appreciate it.
This is actually a very very complex topic with a lot of things to consider, so I will be splitting it up into several parts. The first one will cover the basics: What a turbocharger does, and how. If you’re already familiar with turbochargers… well, this might be a bit boring for you, but keep an eye out for the later articles where I get into more detail.
To put it very simply, a turbo increases the amount of air flowing into an engine to create more power. If you read the article on temperature and engine power, you’d see that compressing air (by increasing the ‘boost’) increases the density. This means a higher mass in the cylinders, which will be compensated for by more gasoline. The end result of all this is more power.
How does it do that? Well, pretty simply actually. A turbocharger is made up of two centrifugal turbine wheels. One is exposed to the exhaust gas, referred to as the turbine wheel, and the other is exposed to the intake air, and is referred to as the compressor. The two are connected by a shaft, and the whole assembly is free to rotate inside the housing. Typical rotational speeds range from 100,000 rpm to 200,000 rpm at normal boost and airflow rates at full throttle.
What happens is the exhaust gas flows from the turbine housing, into the turbine wheel, and then out the center of the turbine wheel towards the exhaust pipe. The force and velocity of the air from the engine creates enough power to spin the turbine. The compressor wheel works in the opposite fashion. Spinning at high speeds, it sucks in air through the center and expels it out the circumference of the wheel at a high pressure. The pressure of the air is commonly referred to as boost, and is measured in relative terms, meaning 0psig (g for gauge) is actually atmospheric pressure, usually 14.7psia (a for absolute). Then at say, 10psig of boost, the real pressure of the air in the intake stream is 24.7psia, assuming that the car is being driven at sea level. The difference between gauge and absolute pressure is trivial until we start trying to select a turbo for a specific application, so don’t worry about the absolute pressure until then.
For the visual learners among us, like myself, here’s a handy diagram from Garrett that makes the turbochargine process pretty simple:
The following steps are labeled on the diagram:
While turbochargers offer the ability to significantly increase power output with very little weight addition, there are a few downsides.
One often cited one is “turbo-lag”, which can refer to two different things. At lower engine speed, there is not enough airflow through the engine for the turbo to create a significant amount of boost. As a result, turbocharged engines typically do not have very much torque below 2500-3000rpm, unless the turbo is sized very small for the displacement. The other thing is actually lag, when the gas pedal is depressed, it takes some time for the turbine wheel to “spool up”, and spin faster to make more boost to meet the engine demands. Bigger turbochargers typically spool slower and need more engine speed to reach the target boost level, but is less restrictive on the exhaust and can ultimately yield more power in the high end of the rpm band. The opposite is true for smaller turbos.
Another is increased complexity. The ECU has to monitor the pressure going into the engine, and add more fuel, cut back on timing, and restrict the boost level as needed to prevent the engine from detonating or knocking with lots of boost. Left uncontrolled, the turbocharger will create upwards of 30-40psig, which most engines cannot handle.
So why use it? As I said before, it is an excellent way of increasing power output without adding very much weight. For rally racing, this is ideal, since we want to keep the cars as light as possible for good handling. Getting the power that the engines make now without a turbocharger will mean making engines at least 50% bigger, which is a lot more weight.
Sometimes rally racing is too expensive for the real world, so a cheap solution is video games. This time I’m competing with Richard Burns Rally against a few of the guys from DirtyImpreza.com. I just completed my USA Rally with a painfully slow time of 24:16:82. Although to be fair, I was just trying to complete the rally without DNFing, and I came mighty close.
In the 2nd stage I crashed into a tree and lost gear controls, so I was stuck in 2nd for the last few corners of the stage. In the 3rd stage I ran into a camera man and rolled the car. In the 4th stage I took a turn too fast over a crest and rolled at least four times. Luckily the rally prepared Toyota Corolla I was driving managed to keep on going. Making it to the end of 6 special stages was, eventually, taken slow. Why not all out? Because the season is about gaining points, and as many as possible.
Here are my stage times for fun:
Prospect Ridge I - 4:40:27
Prospect Ridge II - 4:52:42
Diamond Creek I - 4:07:55
Diamond Creek II - 3:52:64
Hulapai Nation - 4:24:36
Frazier Wells - 2:19:58
Maybe I’ll see you out there on the intertubes.
I’m sure that everyone has heard or experienced first hand how cars have more power when it is colder outside. This may strike some of you as being counter-intuitive, but from a technical standpoint, it makes a lot of sense. Let’s break it down to see what is happening when it gets cold out.
The engines in cars burn gasoline (or diesel) and oxygen to create energy. The heat created by this explosion causes the air inside the cylinder to expand, pressing down on the piston, which creates a torque in the crankshaft. There is a very specific ratio between the amount of gasoline and air that provides peak power. This ratio is called the Air/Fuel Ratio or AFR, for obvious reasons. Get too far away from this ratio, and the gasoline won’t even ignite! As a general rule of thumb, engines run with around 12 to 16 pounds of air per pound of gasoline. Below 14.7:1 is called “rich”, while above that is “lean”, while 14.7:1 is “stoichiometric” for normal gasoline. Typically cars run lean for better economy when subjected to low load conditions, and rich when the pedal is to the floor, to help prevent overheating of the engine. Getting into optimal AFRs will be an article for another day though.
Why does all that matter? Well, notice that it is pounds of air and fuel. Engines have a constant volumetric displacement, but it’s possible to vary the mass of air flowing into the engine by changing the density of the air flowing into the engine. In fact, this is exactly how a throttle valve works. When the throttle is partially open, the air flow is restricted such that the density of air in the cylinders is very low, so there is very little mass. The ECU is aware of how much air is in there and injects an amount of fuel to match to get close to the AFR that it wants. A turbocharger or supercharger takes this in the opposite direction and increases the density of air by compressing it.
All of this has a point, don’t worry! Many of you have surely taken some sort of chemistry class, either in high school or college. To make things simple, air can be modeled as an “ideal gas”, which means we can easily say how four very important things relate as you change one of them: Density, Volume, Temperature and Pressure. The density and temperature terms are the critical ones for explaining why engines have more power when it is cold out. As temperature decreases, the density increases. That means when it is cold out, the engine will be able to contain a higher mass of air than at a higher ambient temperature, assuming the same throttle position and engine speed. When there is more air, there is more force from it’s expansion when the gasoline burns, which translates to more torque and power.
We can take this a bit further though. Notice the pressure term. At sea level, the air pressure is much higher than it will be somewhere like Independence Pass, Colorado, at 12,095ft. At this point, the pressure is down to about 60% of the pressure at sea level. Pressure and density have a direct relationship, so at 60% of sea level pressure, the engine is flowing 40% less mass, which will then correspond to a loss of about 40% of the engine’s power that it had at sea level (This is a rough approximation and it will be more or less depending on load and engine design. Having a turbocharger is a good way to get around this loss in pressure, but a significant power reduction will still be there). Pretty substantial, isn’t it? Now you know why the WRC racers were complaining about how slow the cars felt in Mexico, as they were racing at around 6,000ft for much of the course.
Another thing to note: With lower air temperatures, while the engine power increases due to the increased density, the drag from air resistance increases as well. The body of the car has to push more dense air out of the way as it is moving forward. This will negate a lot of the benefits of the extra power at higher speeds, but drag is a very minor part of the forces a car must overcome when accelerating at low speed. A similar effect is going on at high altitudes.
Hey, so Mark and I have been looking for cars we can afford (<$1000) to turn into a rally car. We need your suggestions but there are some rules:
Also we would like any suggestions as to the type of car you suggest we rally, even dream rally cars.
Sure I’m a bit late telling you to buy these things, but they’re for a good cause. Check out ColinMcrae.com for the details of where the proceeds go.
These neat stickers can be bought at the NASIOC Store. They’re $10 a pair and they look pretty decent.
The driver is the most important part when it comes to the performance of a vehicle. An out of shape, untuned driver will make even the fastest car go slow and while driving is the best way to figure out how to go fast, physical fitness keeps the ability to go fast through out a day.
But Charles, driving a car isn’t that physically demanding. Good point, but working your body to its limits does not only help your body, but also your mind. Racing might not be hugely physically demanding, but it is extremely mentally demanding. Travis Pastrana mentioned in his biographical documentary “199 Lives” that after a motocross race his body would be exhausted but his mind was energized, yet after a rally race his body would be ready to run a 5k yet he couldn’t think straight. Exercise improves your ability to concentrate for longer periods of time and that is the key benefit we get from exercise in a motorsports setting.
Also, why bother saving 5 pounds on a part in the car when you could, perhaps, more easily and cheaply save 5 pounds on the driver (and co-driver). Weight savings coupled with a driver who can concentrate for longer periods of time will speed up a race team. Don’t just take my word for it though, look at all the top race teams in the world. WRC, F1 and even NASCAR all stress the importance of physical fitness. The top drivers are in very good physical shape and could beat you and me in a foot race, let alone a car race. Don’t even take their word for it: go try it. Do something fun outside (sunlight is good for you too) with a friend and make it a habit. Your lap and stage times will decrease, you’ll feel better after a day of racing, you’ll be more confident and you’ll even look better. Go play!
Being inspired by my own writing, or perhaps it is a need to not be hypocritical, I have started cycling again. The hardest part about exercising again is the first two weeks, and I keep telling myself I have to clear those two weeks and I’ll be golden. I figure I have plenty of pounds I could shed for some weight savings, and I might as well do that before I have a rally car. Plus looking good for some cameras is not a bad thing when it comes to scoring some sponsors. A warning: As with any new physical activity or return from an extended break, don’t rush in right away because you will just hurt yourself or become unmotivated.
Unlike most motorsports, in Rally Racing you have two people in the car. That second person in the car is called the Co-Driver, or sometimes the Navigator. They are not dead weight either, they serve an extremely important purpose: to tell the driver what is ahead. They will remind the driver of how fast to take the next corner and what the corner after that is, in order to setup for corners.
While a closed circuit where drivers drive countless laps of the same eleven corners may be memorizable, in Rally the cars might see the same corners twice (depending on how many times a stage is run). A single Rally stage could have a hundred corners, so memorizing them is out of the question. The Co-Driver will read notes to the driver, describing the corners and what to expect (Jumps, bumps, trees on the inside of the corner). In some rallies the notes are provided, in others the drivers and co-drivers will have a Recce, where they drive the stages at slow speeds and write down every bump, jump, corner and danger. The accuracy of the notes by the best co-drivers is so good that a good driver can drive solely off of the notes.
Of course, since reading notes and keeping your place in them is not hard enough already, the Co-Driver gets stuck with other tasks too. Some of these tasks include, pulling on levers as you enter a water crossing (Subarus on the SWRT), watching so many gauges an airline pilot wouldn’t know what to do, activate the wiper blades, be blamed if anything goes wrong, push the car out of anywhere it is stuck and of course dealing with the rally officials.
With all the stress a Co-Driver takes, they have to be a pretty relaxed person. They also have to be extremely organized with everything related to the car, because they tend to be the ones dealing with people not on the rally team. So next time you see a Co-Driver, thank them for everything they do (even if they’re not doing it for you).
The point of this is simple: look where you want to go.
While this all may sound simple, it has really helped me. Not looking at things I don’t want to hit doesn’t help alone, looking at the places you want your car to be does. Your brain likes to follow your eyes (we are very visual animals), and because of how automated our brains have made driving, our cars also follow our eyes. Ever catch yourself looking off to the side in your car, and your car starts drifting over in that direction even if you’re trying to keep it from doing that?
Looking far ahead also helps our brains out by making everything seem like it has slowed down. This keeps us nice and calm. Our mind being kept at ease keeps us from thinking about how we are going to hit that tree just to our left and lets us focus on driving. This even works in racing video games, so go try it there if you’re skeptical. I first put it to use in Toca Race Driver 2.
Remember, look far ahead! It takes some getting used to but I guarantee it will make you faster on a race course.
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