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.
I spend so much time not talking about sites that I really enjoy and frequent related to the world of Rally. I figured taking one post to go over some sites would be worth it for all of us.
Yep, those are some sites I have found to be really useful/informative. The only site I have an account with is DirtyImpreza because it was worth it as I have an Impreza and I like to play in the loose stuff (I tend to hate registering for things, that is one of the reasons you do not have to register to comment on this site). Either way, check those sites, I do.
Aerodynamics is quite an interesting subject, and also one of the more complex. Seeing as I’m still learning this stuff myself, this series will be an introductory lesson on aerodynamics, I’ll just cover the basic concepts that are a good framework to understanding a lot of other important things.
An important thing to keep in mind is that aerodynamics is more or less the study of how fluids move (aka: fluid mechanics), with the fluid in this case being air, and a car’s body pushing the air out of the way. As long as you think of it as air being pushed around, the rest of the concepts are pretty straight forward.
First up is drag. Drag is a force opposing motion. In the case of aerodynamic drag, it’s the force applied against the car as it moves through the air. There are a few variables that affect the aero drag. The faster you go (velocity, or V), the more drag there will be. Also, more total surface area and frontal area increases drag. The frontal area (Af) can be thought of how much area the car takes up when viewed from the front. Or if the car is moving sideways, the side area would be used, or some combination thereof. There is a coefficient of drag (referred to as Cd) that is a function of the body shape. The final important factor is fluid density. The density of air varies with altitude, temperature and humidity, as I have pointed out in the past.
There is an equation that puts all of these things together to find the aerodynamic drag that will be seen:
Drag = (Density / 2) * Cd * Af * V²
Just make sure the measurement system is the same for all and the answer will be a force. As an example, let’s look at how much drag there is on a VW Golf GTI from the late 80’s going 80mph. I have a book here, Theory of Ground Vehicles by J. Y. Wong that has a list of different cars and their Cd and Af. The GTI has a Cd of 0.35-0.36, and Af of 1.91 m². 80mph is 35.76 m/s. I’ll assume standard temperature and pressure, so the density of air is 1.292 kg/m³.
Drag = (1.292 kg/m³ / 2) * 0.35 * 1.91 m² * (35.76 m/s)² = 552.2 kg-m/s² = 552.2 Newtons
Now for some fun with math to see what this means. Let’s convert the force and speed into power.
552.2 Newtons is the same as 124.1 pounds of force. 80mph is 117.3 ft/s, multiply the two together to get 14,556.9 lb-ft/s. There are 550 lb-ft/s in a horsepower, so this hypothetical GTI needs 26.5 hp to overcome aerodynamic drag at 80 mph. If we increased the speed to 100 mph, that number changes to 51.7 hp! Note that this is power at the wheels, and is neglecting any incline, rolling resistance, drive train resistance, and so forth that increase the power requirements at the crank.
I’m going to cover lift and downforce in a later article, but while it may seem obvious, one major cause of drag is fins and spoilers that create downforce while the car is moving. The extra turbulence and changes in airflow usually turn up as an increase in the Cd. Why is this? Well, the fins are designed to push air up as their way to get downforce. When a car is going down the road pushing lots of air upwards, there will be similar amount of drag. Let’s look at F1 cars, since they make good examples. The car is basically covered in wings that make enough downforce to allow the car to drive upside down at speeds over something like 100mph. They have to make a tradeoff when setting up for every race to balance between downforce and drag, which effectively means they have to choose whether the car can corner faster, or have a higher top speed. Rally faces a similar dilemma, although in rally, there is a lot less space for wings, and there are many slow hairpin turns where wings don’t do a lot, so the emphasis on wing setup is diminished.
So hopefully now it is obvious why when driving down the highway, you hit a speed where the gas mileage suddenly drops off really fast: The power required to overcome aero drag increases with the cube of velocity! Stay tuned for the next part of aerodynamics, and feel free to suggest topics that you would like to hear from me on!
I realize its not Rally, but the Olympics is a huge worldwide competition that I think is extremely impressive. The opening ceremony started tonight in Beijing, China. It was quite a spectacular show.
Check it out on the NBC networks. Sports will be aired daily including things that I used to compete in like Riflery. Gogogo, watch this international sporting event 24/7!!!!
Perhaps Rally Racing should become an Olympic Sport? I know BMX racing just became one. (hah! pipedream)
In keeping up the trend of posting YouTube videos that I find I’ll post a good example of why safety equipment matters:
I usually hate crash compilations (not the reason I watch motorsports) but I think it serves as a great example of what can and will go wrong in a Rally. The video works just as well on mute.
Link for you RSS readers out there.
Perhaps it is curiosity, or more probably writer’s block, but I’d like to know what your dream car is. Everyone usually has a different one so there are some pretty interesting answers out there. So comment below!
For me there are so many choices, but this obsession with rally narrows it down a little. Rally Prepped cars are so different to drive than your standard car, but I really do dream about driving them. I would have to say my dream car is a WRC Citroen Xsara. It just seems like such a fun car to drive, check it:
A link to the video for your RSS junkies.
So what is your dream car? An M3? Subaru WRC Car? McLaren F1? Go crazy.
Without an anti-roll bar, when a car turns left the inertia of the car would cause the right side suspension to compress and the left side suspension to extend. This is primarily due to the center of gravity (CG) being above the axis about which the suspension rotates. A higher CG means a larger tendency to roll, as many of you have probably experienced with driving different sized cars. A roll bar keeps the suspensions at similar compressions/extensions and that makes the car body roll less in corners. It is a pretty simple concept.
However with any simple concept there are many implementations of it in the real world. Sway bars, another name for the anti-roll bar, connect the left wheel to the right wheel (front with front and rear with rear). Most of them tend to be torsional springs (springs that are designed to resist twisting rather than compression) but there is at least one electronic method.
The trick to the adjusting the bar is to allow for the “correct” amount of roll to keep the tires on ground. If you go too stiff and corner real hard, you will end up lifting a wheel off of the ground (inside front or rear, depending on if you’re accelerating or braking). If you go too soft (ie none) the car will have grip, but the car’s response will feel sluggish. In Rally it comes down to a combination of overall suspension stiffness, driver preference and style with a mixture of stage terrain requirements. While there is some science behind suspensions, a lot of it is just finding a setup that inspires confidence in it’s handling.
A final note: I have noticed many individuals refer to a strut tower brace as a sway bar. That is just plain wrong, hopefully this video can show you how a strut tower brace would not be a sway bar.
The X-Games this year was AMAZING. This is the third year where Rally Racing was present as an event in the X-Games. In pure X-Games fashion the crossover jump was the biggest it has ever been. It was pretty spectacular to watch. Lots of drama and lots of up and comers including a father son team that did better than expected.
Unfortunately the only non-Subaru (Mitsubishi) racing DNFd over the jump. It was driven by Andrew Comrie-Picard, who is trailing Travis Pastrana by 1 point in the Rally America series. ACP ended up coming short on the jump (just a few mph) and the impact on the rear wheels caused him to flip end over end. What makes this more heartbreaking is it was his first race (semi-finals) of the week and he had it won if he made the jump. Why would he have it won? Dave Mirra hit the wall pretty hard and knocked his steering out of alignment right before that (and he thought he DNFd). Luckily for Dave, he was able to finish albeit painfully slow involving many excursions into reverse. There are videos of it popping up all over YouTube: here and here for example. Better luck next year ACP!
It all ended with a battle between last year’s gold medalist and the original X-Games gold medalist: Tanner Foust and Travis Pastrana. Travis was racing with a new co-driver (not too big of a deal on a Super Special) as his current co-driver fractured a vertebrae in the Freestyle Motocross the previous night. These guys are super competitive in everything they do. Anyway, Travis was able to steal the gold from Tanner in their heads up. What an exciting X-Games.
The podium was filled with 4 drivers. Travis Pastrana, Tanner Foust and a tie for bronze between Dave Mirra and Ken Block. I sure hope you caught it on ABC.
Last time I posted about my S70’s engine, I had just replaced some vacuum lines. Although it helped, there’s still something strange going on. I had ordered a new Compressor Bypass Valve (CBV) diaphragm to replace the worn out one that is allowing air to escape from the compressor outlet back to the inlet. Unfortunately it was out of stock everywhere I looked, so I had placed an order and waited for the part to arrive.
Now, a few weeks later, I get home from work to find a small package at the door. “What could it be!?”, I wonder. Opening up the bag reveals the impossibly rare diaphragm:
(Click for larger view)
What this diaphragm does is open and close to allow air out of the compressor outlet back into the inlet to prevent compressor surge when there is a sudden decrease in airflow through the engine at higher loads. The actuation method is pretty simple. There is a spring that pushes the valve assembly closed under most conditions. The pressure from the compressor pushes against this spring. There is a air hose that runs to the intake manifold that allows for a change in pressure behind the diaphragm. When near or at WOT, the pressure in the intake manifold is close to that of the compressor outlet, meaning the spring holds the valve shut. When the throttle is suddenly closed so that there is a lot more pressure in the compressor outlet than in the intake manifold, the spring can no longer hold the seal closed, allowing air to flow past it.
Over time, the heat, oil, cyclic action, vibration, dirt, etc., break down the diaphragm, it stiffens up, develops holes and tears, which generally decreases its performance. When there are holes in it, air can always escape through the CBV, significantly decreasing turbo performance and efficiency.
So I plan to change the diaphragm in my car soon. It isn’t a terribly complex job, there is just very little room to work, as it is wedged between the turbo housing and engine block, with a bunch of stuff in the way from both the top and bottom.
It’ll be a fun project to work on, and I’ll be sure to make a post when the old one gets replaced!
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