Saturday, January 26, 2008

Blow Off Valve - HKS Super Sequential

Ever wonder why rally cars make that sound you hear when you open a bottle of pop? Well, maybe not exactly like that but more or less similar to the sound of air being released (air, not gas!). You usually hear this when you let off the throttle, sorta sounds like a woosh!. In effect, what you are hearing is the sound of built up boost pressure being released from the intake system. The reason for this is that the turbocharger will keep spinning even after you let off the gas. So as you close the throttle plate, allot of pressure builds up in the intake system. This becomes problematic in that this excess pressure can cause the turbines to seize. Ultimately, this would destroy the turbo unit. For this reason, we incorporate BOV's, bypass or diverter valves. These mechanism work because on the other side of the throttle plate, vacuum gets built up in the intake manifold. Blow off valves, diverter and bypass valves all work by detecting this vacuum. Having done so, they use this vacuum to mechanically open a valve in order to relieve unnecessary boost from the other side of the throttle plate.

Forge Diverter/Dump Valve

Now let us differentiate BOV's, diverter and bypass valves. First, a blow off valve (seen top ) is common to high performance applications in that it provides the least bit of compromise. A BOV essentially releases this pressure straight out into the atmosphere. Quite often you will find that these units take on particular shapes, making them resemble musical instruments. I guess some people out there really like to flaunt their gadgets. Just wait ti'll you see how much they impress the ol' 5-0. Aside from this legal dilemma, the second problem you encounter with BOV's is that the mass air flow sensor will cause the engine management system to "think" that the air will go into the engine and in turn will release an appropriate amount of fuel for it. However, a BOV system will vent this air out before it gets to the injectors causing your mixture to run lean. In turn, this will result in unburned fuel to escape into the exhaust system. This is why you often see flames and hear those "pop's" in rally cars. It is unburned fuel exploding in the exhaust system. Doesn't take a genius to figure out that this is not the smartest application for the day to day car. For this reason, reasonable tuners will usually employ a bypass or a diverter valve (see left). These units essentially redirect this pressure back behind the compressor causing the net flow of air to remain constant. This in turn slows the turbine down gradually and allows the air flow sensor to work appropriately.

Saturday, January 12, 2008


Working principle

A turbocharger consists of a turbine and a compressor linked by a shared axle. The turbine inlet receives exhaust gases from the engine exhaust manifold causing the turbine wheel to rotate. This rotation drives the compressor, compressing ambient air and delivering it to the air intake of the engine, resulting in a greater amount of the air/fuel mixture to enter into the cylinder. The objective of a turbocharger is the same as a normal supercharger; to improve upon the size-to-output efficiency of an engine by solving one of its cardinal limitations. A naturally aspirated automobile engine uses only the downward stroke of a piston to create an area of low pressure in order to draw air into the cylinder. Because the number of air and fuel molecules determine the potential energy available to force the piston down on the combustion stroke, and because of the relatively constant pressure of the atmosphere, there ultimately will be a limit to the amount of air and consequently fuel filling the combustion chamber. This ability to fill the cylinder with air is its volumetric efficiency. Because the turbocharger increases the pressure at the point where air is entering the cylinder, and the amount of air brought into the cylinder is largely a function of time and pressure, more air will be drawn in as the pressure increases. The additional air makes it possible to add more fuel, increasing the output of the engine. Also, the intake pressure can be controlled by a wastegate, which controls boost by routing some of the exhaust flow away from the exhaust side turbine. This controls shaft speed and regulates boost pressure in the inlet tract.

The application of a compressor to increase pressure at the point of cylinder air intake is often referred to as forced induction. Centrifugal superchargers operate in the same fashion as a turbo; however, the energy to spin the compressor is taken from the rotating output energy of the engine's crankshaft as opposed to exhaust gas. For this reason turbochargers are ideally more efficient, since their turbines are actually heat engines, converting some of the thermal energy from the exhaust gas that would otherwise be wasted, into useful work. Contrary to popular belief, this is not totally "free energy," as it always creates some amount of exhaust backpressure which the engine must overcome. Superchargers use output energy from an engine to achieve a net gain, which must be provided from some of the engine's total output; either directly or from a separate smaller engine, perhaps electrically driven from the main engine's generator.

Enter the dragon


Now we're torn. Yesterday we saw the Aston DBR9 Le Mans racer in Gulf livery and were certain we'd found the coolest racing car of the year.

But now Nissan has gone and taken the wraps off the awesome GT500 GT-R, in Tokyo, and we're all torn.

Because, well, just look at it. The GT500 is, as you might have guessed, a racing version of the GT-R (Top Gear's Supercar of the Year, no less), set to compete in Japan's Super GT Championship.

It'll race in the top category, the GT500 - quite possibly the fastest GT series in the world thanks to a list of regulations that reads something like: 'Do more or less whatever you want, so long as you keep under 500bhp.'

As the road-going GT-R puts out some 480bhp, that means it won't be much more powerful on paper. But, as a quick look at (and, more important, a quick listen to) this video of the car in testing reveals, there has been some pretty serious work put into the GT-R's 3.8-litre twin-turbo V6. What a noise.

Watch the GT500 on YouTube

Nissan hasn't released any technical details on the GT500 yet, but we do know that it won't be allowed traction control, ABS or stability control. Whoever takes control of that thing needs cojones of carbon fibre.

The organisers of the Super GT confidently assert that over the past few years, they've introduced more stringent regulations regarding aerodynamics, aiming to bring GT500 cars in line with GT1 cars. By the looks of the rear end of the GT500, those regulations aren't too strict yet: look at the size of that rear wing and diffuser.

The GT500 also shows off Nissan's new works livery, which owes much to the paintjob on the current Fairlady Z race car. According to the Nissan spiel, 'the red symbolises the passion for racing, while the black signifies the high performance of the new GT-R'.

Even if you painted the GT500 pink and plastered it in fluffy bunny decals, it'd still look scary enough to make Ross Kemp weep. We'll find out more about the GT500 GT-R at the end of this month.

Thursday, January 3, 2008

How to Save Money on Fuel




Step
  1. Don't drive. Don't drive a car when you don't have to. Ridesearch or Carpool, walk, take the bike, or take a bus. These will not only save gas, but also will help save our environment and may be better for your health. Do you really need to drive to the store that is only a couple of blocks down the street?
  2. Get a credit card. Some right credit cards offer gas savings when you use the card for purchases. This works in much the same way that some credit card companies allow you to earn frequent flyer miles when you use their card for purchases. But watch for interest rate charges. However, some stations still charge a higher rate for using a credit card.
  3. Get a better air filter. More efficient brands of air filters cost a little more but will pay for themselves in most vehicles in fuel savings.
  4. Get Low Resistance Tires. Some tires, such as Michelin Energy MX 4 Plus are supposed to increase gas mileage.
  5. Give your car a tune up. While properly maintaining your car won't actually save you money at the pump, it will save you gas. Using less gas saves you money. Have the oil changed, and have a certified mechanic give your engine a look over.
  6. Buy a hybrid car. Not only do hybrid cars give you immediate savings at the pump, the U.S. government and your local state offer tax breaks for people who use gas-saving cars. Federal deductions for using gas-saving cars can be as high as $2,000.00, but check before buying to see if they're still in effect. If you can't afford the growing number of hybrid cars out there, consider getting a regular car with good MPG (miles per gallon). In general, the smaller the car, the better the mileage.
  7. Reduce your commute. Move closer to work, work closer to home, or take public transportation to your job. While you're considering spending all that money on a new hybrid or diesel vehicle to 'save money', you could move closer to your job, or get a job closer to your home. Then you will be able to walk or ride a bike on nice days, and spend a lot less time in the car when the weather isn't so nice. You may even be able to get rid of one family car. If you walk or ride almost all the time, it doesn't matter what sort of mileage your current car gets while it collects dust in the driveway.
  8. Avoid idling. While idling, your car gets exactly 0 miles per gallon. Although starting the car used to use a lot of gas, it's now the same as idling for about 30 seconds. Idling to warm up is particularly bad, as the engine needs extra fuel to warm up. After start up, allow your car to idle 15-30 seconds, then drive conservatively until it reaches normal operating temperature. Park your car and go into the restaurant rather than idling in the drive-through. Idling with the air conditioning on also uses extra fuel.
    • Stopping and starting the engine frequently will cause extra wear. Don't stop the engine if you are going to idle for less than a minute.
    • In very cold environments, it is recommended to allow the vehicle to idle and warm up, rather than just start it and take off. You might save gas, but your engine oil won't do its job until it's fully liquid, so you'll spend more money on overhauls.
  9. Plan your trips in advance. This can prevent wasting fuel and wasting time. Plan to use alternative routes. Often back roads can prevent you from stopping at traffic lights and more importantly sitting in traffic jams.
  10. Check the tire air pressures weekly. Buy an inexpensive air pump and an accurate tire gauge (not a pencil gauge as they are not accurate). Keep all tires inflated to the pressure as recommended for your car. Go by the tire wall; the sticker on the door frame, fuel filler flap, or manual is for comfort, not fuel efficiency. Generally speaking, a slightly higher pressure will improve fuel mileage and handling, but too high will degrade traction and wear the tires rapidly.
  11. Drive at a consistent speed. Avoid high acceleration and hard braking. Use cruise control when you can.
  12. Clean out any unnecessary items in your car. If you have heavy objects in your car that you don't need, remove them. If your car is lighter, it will use less fuel to get where you're going.
  13. Slow down. Air resistance goes up as the square of velocity. The power consumed to overcome that air resistance goes up as the cube of the velocity. Rolling resistance is the dominant force below about 40 mph. Above that, every mph costs you mileage. Go as slow as traffic and your schedule will allow. Drive under 60-65 since air grows exponentially denser, in the aerodynamic sense, the faster we drive. To be precise, the most efficient speed is your car's minimum speed in it's highest gear, since this provides the best "speed per RPM" ratio.