ford turbo systems
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How Does a Turbo System Work?Note: Listed below is the basic breakdown of the function of a turbocharger system. This breakdown is meant to educate those who have little or no knowledge of how these systems function. For a more detailed/technical description please see the FAQ section of our website. How does a Turbocharger work?A turbocharger allows an engine to produce more power by introducing more air to the engine. This added air, when added with the appropriate amount of fuel will produce more power. So how does a turbo make more air available to the engine? A turbocharger has two "wheels" each of which look very similar to the plastic pinwheels that kids play with. The turbo uses the flow of exhaust gasses to make the turbine wheel of the turbo spin (same principle as a windmill, only on a very small scale). The turbine wheel is mounted to the same shaft as the compressor wheel. When the turbine wheel makes the compressor wheel spin fast enough, the compressor wheel starts to suck in air and spit it out toward the engine faster than the engine would normally suck in air on its own. When this happens, the turbo has "spooled up" and begins to create turbo boost and the engine gets more air than it would normally, so the potential for more power increases along with the boost. The way this system works has a drawback called ‘turbo lag’. A turbocharger doesn't help produce power until it can spin fast enough to create more air flow than the engine would on its own. So, when you step on the gas you have to wait for the engine to create enough exhaust flow to spin the turbine wheel, and the attached compressor wheel, of course. It then creates more air flow than the engine would normally. The time between stepping on the gas and when the wheels start to spin fast enough to work, is the time referred to as ‘turbo lag’. Turbo lag can be reduced by correctly sizing the turbo to the car. A turbo which is too big for the engine won't be able to create usable boost until it's revving very high. This isn't too bad if you're using the car only to race since you can keep the revs up, but on the street, you'll have to constantly downshift even for moderate acceleration. On the other hand, if the turbo is too small, then it will spool up quickly, but it won't be able to keep up with the engine... at high RPM's the engine will be sucking up more air on it's own than the turbo can provide and you car will fall on its face. Turbo lag is often misunderstood. Just because you don’t have boost at the time you floor it doesn’t mean that the turbo is the wrong size. Turbos have a certain operating range of efficiency. If figured correctly, the right turbo head unit will allow a generous amount of power without causing the cylinder pressures to get too high resulting in a blown head gasket. This typically happens when the exhaust housing is too small. You couldn’t put a stock 4 cylinder turbo on a car with 8 cylinders without running a very high risk. So proper turbo sizing per the application is the key factor in an efficient turbo system. The lag of a turbo motor, (if the turbo is the proper size), is an advantage over naturally aspirated and supercharged motors because it gives you more control over traction; off the line or in the lower RPM ranges (typically Idle-2000rpm, any lower and you will run out at the top end or if you modify your motor it will require you to purchase a larger turbo). What does a Blow-Off Valve do?A blow-off valve (BOV), also referred to as a compressor bypass valve, is a valve which opens and closes depending on the status/position of your throttle plate and turbocharger. It is intended to increase turbocharger life by helping to eliminate compressor surge/back spin and increase performance by allowing the turbo to spin freely between shifts. To understand how a BOV works, you have to first understand that a turbocharger's job, described in simple terms, is basically to compress air. It then sends this compressed air to your engine for increased performance. But when you think of what happens during gear changes (when you lift your foot off the gas) and the turbo is spitting out huge amounts of air but your engine is not taking in (hardly) any air the BOV's job becomes apparent. Just like anything that's compressed into a smaller volume than it usually takes up, it wants to expand. So all the air from the turbo keeps pushing toward the (closed) throttle plate and begins to build up pressure there until it finally decompresses and starts to push backwards through your intake tracked back to your turbo where it forces the compressor wheel to come to a very abrupt stop. The turbo experiences what's called compressor surge which, if extreme, can damage your turbo. Enter the BOV. The BOV is bolted or welded or otherwise connected to the intake tube leading from your turbo to the throttle body. Then a vacuum line is connected from a port on the intake manifold to a port on the BOV. When the car is accelerating and the throttle plate is open, the pressure in the intake tube and the intake manifold are relatively the same and the BOV remains shut, allowing all of the compressed air to make its way to the engine. When the throttle plate closes, the BOV experiences pressurized air where it connects to the intake tube, but vacuum (because the throttle plate is shut) from the intake manifold. This difference in pressure opens the BOV and allows the compressed air to exit from the intake tube via the BOV. Since none of the air reaches back to the turbo two benefits are realized by keeping the turbo spinning: 1) compressor surge does not occur, increasing the longevity of the turbo, and 2) since the turbo never stops, you spend less time getting it up to speed again when you reach your next gear and begin accelerating again. A little confused? Then, here's another (less detailed) attempt to explain it. Imagine the air which has been compressed by the turbo rushing toward the intake manifold. Then, it's time to shift gears, the gas pedal is lifted which closes the intake manifold from accepting anymore air, and all of the compressed air has no place to go. But, the turbo is still spinning and pushing more air down the tube. Ultimately, this air will want to spring back to its uncompressed self and start to push back into the turbo. The BOV gives the air a way to exit from the intake tract by routing this air into the engine compartment instead of backwards through the turbo. Note: there's a sound that the compressor surge makes. It sounds like a mechanical fluttering. If you here this, then something is wrong. With the right sized BOV you will hear that classic turbo hiss which means all is well, throttle away. What is an Intercooler?An intercooler works on the same principle as the engine's cooling system's radiator (they even look very similar in design); all it does is exchange heat from what's in it to the air rushing by around it. The difference is most intercoolers only have air in them... the compressed air from the turbo. A byproduct of compressing air to create boost is heat... in fact, anything that gets compressed gets hotter. The heat created in the air that the turbo compresses is not desired and in extreme cases can be dangerous to your engine. To address this, many turbocharged cars have an intercooler. The compressed air leaves the turbo but before making its way into your engine, it flows through the intercooler. The air transfers its heat to the intercooler's fins where it is dissipated into the surrounding air rushing by. What does a Wastegate do?If you don't know how a turbocharger works, first read How does a Turbocharger work at the beginning of this section. It'll explain some ideas referred to here. As you know, when enough exhaust gas flows past the turbine wheel of the turbocharger, boost is created. The faster it spins, the more boost you get... the more boost you get the more air the engine consumes... and the more air it consumes, the more exhaust gasses flow... and the more exhaust gasses flow, the faster the turbine wheel spins... and the faster the turbine wheel spins, the more boost you get... the more boost you get... well, you get the picture. Potentially, the engine will just put itself into an unending loop of increased power. But at some point, the turbocharger or motor will eventually blow up (unlimited power just by having a turbocharger is just too good to be true!). This is why the wastegate is essential in any turbocharged engine. How it works is with a vacuum line that connects from the compressor outlet to the wastegate actuator. The vacuum line provides the wastegate with a constant input of what level of boost the turbo is making. When a predefined boost level is reached, the wastegate opens and redirects some of the exhaust gasses to exit the engine through it instead of through the turbine wheel. When exhaust is vented through the wastegate, not all of the exhaust can make the turbine wheel spin as it goes directly out of the wastegate to the exhaust. This bypassing of exhaust keeps the boost under control and keeps the turbocharger from damaging the engine or itself. Boost Creep ExplainedRemember that the more boost introduced to the engine, the more power the engine makes; the more power it makes, the more exhaust gases it will make; and the more exhaust gases, the faster the turbine wheel spins; and the faster the turbine wheel spins, the more boost. Well, the wastegate is supposed to stop this infinite circle, but on some cars, when enough modifications are made, the wastegate is just too small to bypass enough exhaust from the turbine wheel to keep the boost at the desired level. The end result is a boost level which is higher than you anticipated... the boost "creeps" up to higher boost levels. This is an all to common problem with V8 turbo systems.
A NOTE FROM VTS We, at Velocity Turbo Systems, firmly believe in educating the customer to the fullest extent of our knowledge of turbo systems and its components. We really hope that the information provided in the “How Does a Turbo System Work?” and separate FAQ section helps you make an informed decision when purchasing a turbo system, whether it is one of ours or not. We are a family owned and operated company that will go to the greatest of lengths to both help the potential customers make an informed decision and maintain our reputation of having one of the best systems available. –VTS Staff |
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