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 Turbochargers: Part 4 - Turbo Lag The enemy of every turbocharger. October 31, 2003 - So what do we do about turbo lag? First, the choice of the proper turbo is paramount. A larger turbo will be able to flow more air and thus gain you more horsepower. This power, though, is traded for an increase of the larger turbo in lag time for it to spool up and gain a useable amount of boost. This is especially true in smaller displacement engines (which are seeing most of the turbocharged applications anyways) that already have less exhaust to push the turbo to start with. So what would happen if you stuck a giant turbo onto your Ford Aspire? Provided you can actually get the turbo to spin with this straw-full of exhaust, your potential horsepower gains would be huge--and within the workable range of about 15,000 to 20,000 rpm. No Ford Aspire we know revs this high. The proper sizing of the turbo is important with regards to how the car will be driven. If you're looking to be a street terror (not recommended), faster-spooling, smaller turbos are the answer. For true techies out there, the "speed of spooling" is read out as the A/R on the side of the exhaust housing. If power is more important, such as on the racetrack, the turbos will be somewhat larger to allow for higher boost at rpm that are usually maintained throughout the race (unlike you sitting at the stoplight). As expected, cars that are designed for pure power will usually garner these bigger numbers with larger turbos that flow more air. Ok, so now we've got a turbo that is applicable to the type, as well as the projected use, of the vehicle in question. How do we get this turbo to lag less and be as efficient as it can be? As every fledgling Road Racer knows, exhaust backpressure is the enemy. While this is only partially true with normally aspirated engines - a little backpressure is good for torque (which is more used for day-to-day driving) even though it sacrifices a little horsepower up top - most turbocharged engines want an outlet that is as free-flowing as possible. Exhausts that flow more freely allow the turbo to spool up faster. That's a good thing. Although not much has been said of it, it's probably true on the intake side as well; the less resistance it's pushing against, the faster the turbo will spool. There are inherent devices and modifications to the turbo itself that will allow it to spool faster. Most of them are intuitive. One popular variation that has come on the market of late has been the advent of the ball-bearing turbo. There are three types of bearings that are commonly used in turbochargers - the conventional "floating-type" bearing, the Garrett ball bearing (BB), and the ceramic roller thrust bearing. The Garrett Ball Bearing center section was developed for use in CART and other high-end racing arenas and often finds them mated to other fancy materials. The original concept was to improve durability and also to reduce lag in road racing. They have the potential to be very expensive. These turbos are designed to spool up quickly and allow for quick response to sudden changes in acceleration needs like passing maneuvers. The Turbonetics Ceramic Roller Thrust Bearing (CRB) uses a hybrid type center section that incorporates a ceramic roller bearing on the compressor side and a conventional floating bearing for the turbine section. Although they do reduce friction quite a bit (these are the turbos you can push a little and the blades will keep spinning for a long time, like those 24-inch wheels on your homies' Escalade), the main intent was to create a stronger center section that could handle larger loads for big compressors. So, if you're just looking at center sections, it would seem that a Garrett BB would be more suited for quicker response and spool times while a CRB would be more resilient (as well as spool faster than a conventional). And because most of you don't have umbrella girls following you around, price is also a consideration - A Garrett BB will run you about 250% the cost of a conventional and the CRB about 150% of the same. Sxilvia needs one of these Materials choice is also another way to aid in the creation of better turbos. Some turbos will use blades made from lightweight materials in order to allow the turbo to be moved with less force; making it spool up faster without sacrificing too much in terms of potential. Many options have been explored from ceramic to other more exotic alloys including Inconel, a nickel-chromium alloy that is also used in Formula 1 exhaust systems). All this work just to get rid of turbo lag? Like was said before, it is one of the most bothersome problems with the turbocharger. But, with solutions as well as proper matching of components, the effects of the LAG can be minimized |
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