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.
Don’t Drive Like a Douche…until the corners.
What I mean by driving like a Douche is tailgating, accelerating like a bat out of hell stoplight to stoplight (red light racers) and lots of pedal work on the road. So don’t do that. Accelerating like crazy (braking and gas) wastes energy needlessly, so if you really care about your MPG calm down with your pedals. That also means don’t do any of the neat stuff we’ve been telling you how to do like J-turns.
When you will want to drive like a douche is the corners, if you can safely not slow down for a corner then don’t. Driving for lower gas consumption is like winning a race in a low power car, it is all about preserving momentum. That doesn’t mean keep your foot planted on the accelerator through the corner!
So be nice to those pedals and dont mash them, drive around the speed limit (wind resistance increases with velocity duhhh), if you can, keep your speed up going into the corners and last of all calm down. Hopefully you can adjust the nut behind the wheel this summer and save a few bucks.
I have been asked how will gas prices change rally cars. My answer is that they wont…much. Gas is such a small cost compared to registering for a race, buying tires, prepping the car and buying parts to replace broken ones.
Lets Do Some Math
Assume that a rally car rolls for about 300 miles a rally, including transits. Assume the race team pays $6/gallon for 100 octane gas. Their race car, throughout the whole weekend, averages 13 miles per gallon. They’re going to have to buy at least 23 gallons of gas for $138.
Lets Compare
Races often require $500+ registration fees to cover event insurance, marshal’s pay, and tons of other stuff (most staff are volunteers). I can find cheap rally tires at $150 a pop, so that’s $600 a set. Teams usually have a few different types of tires that they can use over a couple rallies. Assume a tarmac, gravel and snow set so that is $1800 in tires per few events. Hotels cost about $60-100 a night for 2 people so a team of 4 (small team!) that stays near the rally for 2 or 3 nights will run anywhere from $240-$600 an event. Feeding your crew costs too (food price is positively correlated with gas price). Not to mention the amount of things that can break on a rally car, and do break! You have to be carrying spares for almost everything, which increases the upfront and between race costs.
Hopefully you’re starting to understand that gas prices aren’t a big deal to most racers. Sure gas prices make it that much more expensive to compete, but the increase in cost is small compared to all the other costs associated with racing. The interesting thing is that the more gas prices increase, the fewer competitors the SCCA is seeing. I guess most racers really are racing on the margins.
If you’re a racer I would to hear what you think about increasing gas prices, comment below.
The FIA cleared up rule changes for the 2010 World Rally Championship. They decided that the WRC will adopt rules similar to Super2000 (aka S2000) in an attempt to make the WRC cheaper and easier to enter.
One of the new rules is that they will impose a price limit on the car. However I think big teams will still be able to get around this. The Subaru World Rally Team (SWRT), for example, is handled by Prodrive and they could absorb much of the design cost of the car and not “charge” as much as they should for parts. Even so, I think the lower priced cars will draw more manufacturers and competitors alike, so that is a good thing.
Hopefully, they do not ban forced induction, ie turbochargers, as that is one of the rules in S2000. I am fond of turbochargers, but I do understand that adding a turbocharger and making a reliable setup can be expensive, but I just love them too much. I seem like a giddy schoolgirl around turbochargers and will giggle uncontrollably when hearing them spool. However this rule may make sense if the FIA also introduces a lower power limit (280HP for S2000 vs 300HP for WRC).
One rule that is present in S2000 and not the WRC is the transmission requirements. In S2000 you must buy an official gearbox (sequential duhhh) while in the WRC the top teams make their own. It will be interesting to see if and how this rule is implemented. I doubt that it will make entering the WRC any cheaper and could pose a problem if teams are not allowed to redesign a mediocre sequential gearbox that they must buy.
Im glad that the rule changes are going to be less drastic than people thought at first (Front-Wheel Drive Only, 1600cc limit, etc…). It is bringing the WRC back to the “Real Cars, Real Roads, Real Fast” that rally is so often described as.
With people so concerned over the price of gasoline I will post gas saving tips, no matter how strange and minute they may be. Today’s gas saving tip is Fill Up When It Is Colder.
That means, since it is summer now, fill up late at night or on cooler days. Why? Because a gallon of gasoline is a volume not a mass. Higher temperatures of gasoline means less mass per dollar when compared to the same price at a lower temperature. While the effect of this is small, it could make a difference in the long term.
The effect of temperature is not minute enough to scrape by the law books. Most states (probably all) have laws related to the sale of bulk volumes of liquid, especially gasoline. They have to be sold as the volume they would fill at a defined temperature. For example, in Arizona all bulk sales have to be sold as the volume they would be at 60ºF. So, during the summer, a gasoline truck actually carries less gasoline than it does during the winter even though they are carrying the same volume. By the way, Arizona is WAYYYYYYYYYYY hotter than 60ºF during the summer, so people at the pump are losing a good amount of mass per gallon.
Also, when it is hot out, gasoline likes to evaporate faster. So you could be losing some mass to evaporation before it even gets into your gas tank.
Recap: Fill up when it is coldest (at night).
I’m going to take a brief break from the turbocharger! series to make a little segue into what I hope to by my next topic that I will take a close technical look at: Aerodynamics.
Really, we only care about two things here:
Hopefully I’ll explain how these two things come about in a pretty simple fashion that explains it a little bit better than “Oh, the body pushes air out of the way.” However, before that, I have noticed some very disturbing trends among the modding community.
The most incomprehensible to me is the addition of only a rear wing to a front wheel drive car. This is really a double negative. The wing creates downforce in the rear of the car, behind the rear wheels. The wheels act as a fulcrum, and this downforce that is generated in the rear actually lifts the front of the car up at speed. Totally counter-productive, since it will decrease traction on the drive wheels, and increase the amount of understeer. Keep in mind that front wheel drive cars already tend to understeer a lot, a wing in the back will just make it worse.
The other negative of the rear wing is one you will have to deal with almost every time you try to generate downforce by pushing air up: Lots of drag. The engine has to put out a bit more power to overcome the extra drag, which increases with the square of velocity. So now we have a situation where when the wing is putting down the most downforce is when the front tires are applying the most force to the ground to propel the car forward through the air. If this downforce was applied up front, or if it was a rear wheel drive car, this would be a great thing. Since it’s not, the drag slows the car down, and increases understeer through turns even more!
The other are body kits that add ‘features’ to the body that don’t actually do anything. Some things are useful, like a front bumper that allows less air under the body of the car should reduce drag, however, many are just as counter-productive as a rear wing on a FWD car. A classic example is the intake vent on the hood and before the rear wheels on the some of the more recent generations of Mustangs. The protrusions do exactly that, protrude into the air stream. This adds extra turbulence to the airflow over the body, which is almost always a bad thing since turbulence usually increases the amount of drag on the car. It’s possible to use turbulence to your advantage, but that’s a complex topic to cover, and requires some pretty precise placement of fins to make the air go where you want it to, think F1 for an example here.
One thing that Charles said to me while we were discussing this article is that we have a pretty utilitarian view on what looks good on a car. If it improves performance somehow, we’re almost always for it. If it does nothing, is counter-productive, or just adds weight, we typically hate it and immediately reject the idea. The things that make the car ‘go fast’ also look/sound good to most people, since we associate that with performance race cars. Maybe what we should do when we get our car to modify into a rally car is mask the things that make it look fast. Sleeper race cars, ready GO!
If you did not know already I play Richard Burn’s Rally competively against whomever over at the Rally Sim Driver’s League.
Anyhoo, after my poor performance in the ‘oh so scary’ Rally France I was ready to do well in Finland. With good reason too, VMethos and I are in a tight race for 3rd place in the championship. He squeaked by me in France and gained 2 points overall on me.
Today was race day for me (you have about two weeks time to do your race in one 90 minute session) and I had a hard time getting into the rhythm of the race. I felt out of control and sloppy…that is until I noticed my times for the day. I set 5 Personal Best times out of the 6 competition stages, and on the stage I did not set a personal best I had a non-race ending Roll that lost me 5 or 6 seconds (ONLY!!!).
As for the times that I set (barring any penalties):
SS1 - Sikakama - 5:52:18 (PB)
SS2 - Kaihuavaara - 4:06:05 (PB)
SS3 - Kaihuavaara II - 4:14:44
SS4 - Mustaselk - 5:21:08 (PB)
SS5 - Mustaselk II - 5:24:92 (PB)
SS6 - Autiovaara - 3:41:93 (PB)
Total - 28:40:60
Special Stage 3 is the stage I rolled on, yet miraculously landed on my wheels and was able to get right back onto the stage. However I did have a very close call with damage on Special Stage 4. I got extremely lucky that I did not end my race by running into a log on the side of the road. It punctured the radiator and ripped the front fender off.
Let’s hope I can fend off VMethos and gain some points as we go into Rally Japan, the final rally of the season.
Update: I placed 3rd overall in this event behind Wild Swede and turbo. This has brought me within 1 point of 3rd place overall. In order to guarantee I get 3rd overall, in Japan I must place 1st…or 2nd with VMethos behind me.
Welcome back to the Turbochargers! series, where I get to have fun rambling on about one of the most effective ways to create a lot more power from an internal combustion engine. If you haven’t done so already, I recommend reading part one and part two and grabbing a snack before continuing on with this one.
There are several things I left open ended in part two that I would like to cover this time around. First is compressor efficiency, and other things, like how having a turbocharger affects the engine itself, will follow.
Simply put, the efficiency of a turbocharger is how much work is put into compressing the air compared to how much work would have been done in an ideal world. What is different about the ideal world? Well, things like turbulence, heat transfer between the blades and the air, the effects of sound, air’s high and low pressure points within the compressor wheel, and so forth. Nothing can ever be 100% efficient, so we just try to get as close as possible. Newer turbos are generally more efficient than older ones, thanks to improvements in modeling technology, more experience in design, improved bearing tech, and stronger materials to name a few.
The efficiency of the turbo really affects two things:
Both of these are very important things to keep as low as possible. I’ll touch on exhaust pressure (commonly referred to as back pressure) more later, since it ties in with a few other important things regarding turbo selection and engine design. The intake air temperature is pretty obvious, the lower the temperature at a given pressure, the more dense the air is, which means more air can get into the cylinders per stroke, mass-wise. This ultimately means more power, if it is not immediately obvious why, I have gone over the effects of temperature on engine performance in more detail before.
I won’t get into detail on the theory behind the calculations involved with efficiency and intake air temperature, but if you really need to know this stuff for some bizarre reason, go do some research on adiabatic compression. For the calculation, you need to know 4 different things to find the compressor outlet temperature, which I will designate as To for temperature outlet:
This may seem a little messy, but it is straightforward. Plug the values into the upcoming equation and you have the outlet temperature.
We can find the pressure ratio to help us simplify the final equation, and help us relate to the compressor maps, since they are given in terms of airflow and pressure ratio between the inlet and outlet pressures:
Pressure ratio (Pr) = (Po + Pi) / Pi
The equation used for finding the compressor outlet temperature:
To = ((Ti*Pr)^0.283)-Ti)/n+Ti
So if we have a car that is running with an 80ºF inlet temperature, 14.2 psia inlet pressure, 10.0 psig outlet pressure and 70% efficiency…
Pr = (10 + 14.2) / 14.2 = 1.704
To = (((80ºF + 459.67) * 1.704^0.283) - (80ºF + 459.67)) / 0.7 + (80ºF + 459.67)
Do the math and you get To to be 665.2ºR. The units are significant here, since we did all the temperatures in absolute value due to the ratios involved, the result is an absolute value. To convert, just simply subtract the number needed to convert it back to relative, 459.67 for imperial units (Fahrenheit and Rankine) and 273.15 for metric (Celsius and Kelvin)
So the outlet temperature is 206ºF, I usually round to the nearest integer, since these calculations are hardly accurate due to the complexities involved. Either way, that is pretty warm, eh? It gets much hotter with more boost and less efficient compressors. This is what we use intercoolers for.
Many intercoolers are rated up to a certain horsepower, but I find this a rather silly notion. The calculations involved with the temperature drop across the intercooler are quite complex due to the nature of the geometry of the intercooler, and I will omit them simply because we usually don’t know things like the fin height, depth, thermal resistance between the plate and fin, and so forth. It is possible to calculate the outlet temperature based on an airflow speed through the intercooler, speed of the intercooler through the air, and a lot of geometry, but it’s still an estimation at best.
So when picking an intercooler, my advice is to use as big of an intercooler as will fit in the area you’re working with, since bigger intercoolers can remove more heat and usually have a smaller pressure drop across them, which means your turbo can do less work to get the same pressure at the intake manifold. Just remember that the more volume it has, the more air must be put into it when the boost pressure increases (read: throttle response time increases)
In a similar vein, be careful of how much tubing is used to install the intercooler. The bigger the diameter, the less restriction, which is always good, but there is more volume. To avoid excess restriction, try to use as few bends in the intake path as possible, and when you need them, use a bend with as large of a radius as will fit, since that will give the least restriction to the airflow. The whole idea with the intake is to allow it to flow as freely as possible without increasing the volume, thus lag, too much. This is something that you will have to figure out on your own, or talk to other people who have done similar modifications on the same car as yours to find their opinion on how to set things up.
The same thing applies to the exhaust side of the engine too. There are two evils with exhaust restrictions, reduced power and increased exhaust gas temperatures.
I see people say things like “This engine needs a little bit of back pressure to perform properly”, and then I end up laughing a lot. The camshaft profile was designed to create optimal torque with some specified amount of back pressure. Reducing the pressure may reduce torque, but only because that is how the cam profile is set up. Change the profile some and you will end up with more power with less pressure. I’m not going to get into cam profiles yet, since it is an area that is beyond my understanding for now. With turbocharged engines, this is not a concern at all, since the turbine creates an enormous amount of back pressure.
This pressure is created by the work needed to spin the compressor wheel, and the geometry of the turbine wheel and housing. The smaller the overall turbine assembly is, the more pressure it generates at a given airflow. This is why larger turbos tend to generate more power at the same boost level as a smaller turbo. However, as we went over in part two, a larger turbo almost always spools later in the RPM band. This means that while the peak power will be higher, the total amount of energy the engine is capable of putting down to the road is lower.
Getting back to what I was talking about before with back pressure, with a turbocharged car, it is best to keep the back pressure as low as possible, since the turbine generates a substantial amount of pressure for the engine to deal with. This pressure is not constant either. Increasing the boost increases the back pressure even more, since neither the turbine wheel or the compressor wheel are 100% efficient.
In addition to this, the turbine creates energy through the difference in pressure between the inlet and outlet of the turbine wheel. Once again, due to the nature and inefficiencies of the turbine, every small increase in pressure after the turbine wheel creates a larger increase in pressure before the turbine wheel.
Why is this so bad? Well, as I pointed out before, you can make more power with less backpressure. You may have to modify the cam profile to make full use of it, but the net result is more power, which is our goal. The other is equally important. Higher exhaust pressures increase the exhaust gas temperature (EGT) with everything else being held constant. When pushing an engine close to it’s limit, a close eye needs to be kepts on the EGTs to make sure that ridiculous things like melting a piston or warping the manifold don’t happen. Plus, lower EGT’s typically mean a longer engine lifespan, since there is less thermal stress on the parts.
So how to reduce exhaust pressure? Quite simple really, use the biggest diameter exhaust pipe you can fit into the car, straight-through mufflers are a huge plus, use as few bends as possible, and possibly most importantly, the part known as the downpipe must be capable of supporting the airflow.
The downpipe is often the most restrictive part in the exhaust after the turbo (known as the turbo-back, all the parts after the turbine housing) aside from the mufflers, because the exhaust is the hottest in that part. Hot air means low density, which means a high volume for the same mass. This low density creates a high airflow velocity, and drag increases exponentially with velocity. Just like the rest of the air stream, try to ensure that the downpipe has a large diameter, smooth bends, a smooth interior surface (roughness causes more turbulence, which almost always increases the resistance to flow), and the turbo will thank you.
Well, I think that’s enough for this time around. I didn’t cover quite as much as I wanted, but the topics I did cover were gone into a lot of detail, which is good. On the plus side, I already have a few ideas for part four. I always welcome comments, questions or suggestions, so feel free to ask and I’ll do my best to help you out.
So what is everyone’s personal motto for the next month? Less restriction is better!
I am always learning about WordPress in an attempt to make this site better. So I just added Random Post/Page functionality thanks to the oh so famous Matt.
http://twoguysrally.com/?random should take you to a random post or page and might make it easier to get to some new stuff you haven’t read.
Hopefully I’ll have the new theme for the site up and running soon! Enjoy the new feature.
The standard transmission, a.k.a. manual, is found in most cars with an H-Pattern mechanical gear selector. But there are faster and easier ways to select gears. What I would like to focus on in this post is the Electromotive Sequential Transmissions.
Sequential Transmissions
First I need to explain what the difference between a standard transmission and a sequential transmission is. In the standard transmission it is possible to select any gear at any time (given enough force). However in a sequential transmission you must either select the next or previous gear from the one the transmission is using. For example, if I were in 3rd gear I could either choose 2nd or 4th. It would be impossible to skip to 5th or 1st without going through the next in the sequence, hence their name ’sequential’. I am told that this can make the mechanical workings of the transmission simpler (see motorcycle transmissions) but I wont even attempt to explain it (ask Mark).
Motorcycles are the vehicle most commonly associated with sequential transmissions. Their gear selector has 3 positions: Up Shift, Down Shift and No Change. the ‘No Change’ position is the default position. If we transition the sequential transmission into a Car nothing changes. There will be 3 positions for the gear selector, but we may make the transmission a little more complex in order to reduce weight.
Electronic Gear Selectors
Mechanical gear selectors are heavy, and depending on how they are constructed may make it harder to select gears, so we can make the gear selector electronic. That will save on weight (what is used to shift is a few thin copper wires) and allow us to place the selector anywhere in the cockpit. It also has the added benefit of reducing driver fatigue as it will be physically easier to select gears. It is not just as simple as saying “Let’s make it electronic” and then we’re done: we have to get the force to select a gear from somewhere. That somewhere can be a few places. We can use compressed air to operate a pneumatic arm that controls a short mechanical linkage on the transmission. Perhaps, if we have enough electrical current coming from the alternator we can use that to power a solenoid to operate a short mechanical shifter (on the transmission).
Both Electro-Pneumatic (Electro because the gear selector is electronic) and Electro-Mechanical Sequential Transmissions have their downsides. The Pneumatic variety require compressed air to be stored in the car, but this could be lighter than the alternate Electronic Solenoid approach. However refilling or punctures could make a less competitive race car or even end a race day. While the Electro-Mechanical types have much more weight associated with the system and are slower to respond (shift time matters!!!).
WRC vs Rally-America
Electro-whathaveyou Sequential Transmissions are a common sight in the WRC, but the H pattern is the only transmission allowed in the rules of Rally America. And that brings me to this: Why does Rally-America disallow Electromotive Sequential Transmissions? Is it a strategy to make Rally Racing cheaper and more accesible? Is it to keep the cars closer to stock so fans can say: I DRIVE THAT! ? I’d like to hear your opinions on this and I would like to go into further detail about Electro-Pneumatic Transmissions in the future.
Dan Summers wrote the Layman’s Guide To Rally Racing, and in it he stated that in order to seem like you are knowledgeable about Rally Racing just mention Colin McRae. The funny thing is, a short entry about Colin McRae Stickers resulted in the largest amount of search engine traffic to the site. I cannot imagine how many people are searching for Colin McRae if enough of them are going to the second page of Google results to get here.
He didn’t claim that it would increase traffic to this website, but I’m sure he knew it would. Perhaps that is the future of any website: Colin McRae. Regardless, you should read what Dan Summers writes, and hopefully he will write something again for this website.
Powered by WordPress | Blue Weed by Blog Oh! Blog | Entries (RSS) and Comments (RSS). | 