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GRiP_GAME | Posted: Jul 20 2008, 02:50 AM |
IDW Senior Member Group: Members Posts: 78 Member No.: 29,846 Joined: Jun 19th 2008 Location: Update Profile | I'm sure you've all heard the term Anti-Lag, but do you know how it really works? In layman's terms: First, you have to understand how a turbocharger works. Exhaust gases from the engine push against a turbine wheel in a turbine housing that spins the turbine wheel at very high speeds. This side of the turbo, or the 'hot side'/'turbine section', is connected to the 'cold side'/'compressor section'. This allows the compressor wheel to suck in ambient air, compress it, and fling it into the cylinders (aka 'forced induction'). When you shift a force induced vehicle, your foot is pulled off the gas pedal, and the throttle body is left slightly open (as if the vehicle were at idle). Once this happens, the turbine blades will slow down because exhaust gas velocity has dropped. Intake boost pressures drop as well (due to a By-Pass Valve or BOV). For the next gear, the turbine wheel has to spin to fill the volume of space in the intercooler piping (this is what is called 'turbo lag'). This is different from boost threshold. Most Anti-Lag systems work when you pull your foot off of the gas pedal. When this happens, unburnt fuel is sprayed into the exhaust manifold. The heat from the exhaust manifold causes the unburnt fuel to combust. As this happens, exhaust gases produced by this allow the turbine blades to continue spinning in the middle of a shift - almost (if not) completely eliminating turbo lag. There are two different ways in achieving this. One way is through an aftermarket Anti-Lag system that comes with an aftermarket ECU which will adjust (retard) ignition timing during closed throttle to where the exhaust gases become extremely rich with unburnt fuel. Most of these programs will retard the timing 20-40 degrees after TDC (Top Dead Center). The other, which is often used in rally/road racing, is placing separate fuel injectors on top of the exhaust manifold. These fuel injectors directly inject fuel into the exhaust manifold during closed throttle situations. Not all of the mixture will combust completely in the exhaust manifold, causing the fuel to run down the exhaust system. This is why the vehicle will spit flames rapidly. Anti-Lag systems are a great way to eliminate turbo lag, however there are some drawbacks. The lifespan of a turbocharger will decrease dramatically due to the constant combustion and heat coming from the exhaust manifold. It explains why most of these systems are used in rally/road races only because it would not be practical enough for street use, setting aside the fact that your vehicle wouldn't pass emissions with it. So there's an idea of how Anti-Lag works! Hope everyone learned something. ================================================== Next: Turbocharging 101, twin vs. single turbochargers, turbocharger efficiency based on engine configuration, and whatever else I think of at the time. This post has been edited by GRiP_GAME on Jul 20 2008, 03:18 AM |
Jardim | Posted: Jul 20 2008, 07:22 PM |
Willing to throw 5's on the blunt your smoking. Group: Advanced Members Posts: 2,659 Member No.: 15,519 Joined: Jan 21st 2006 Location: Hudson, MA | Nice, now that other thread about ALS and how cool it actually is can now be declared useless. I like this one better thanks, i'm looking foward to the next segment. This post has been edited by murphanation on Jul 20 2008, 07:23 PM |
GRiP_GAME | Posted: Jul 20 2008, 08:27 PM |
IDW Senior Member Group: Members Posts: 78 Member No.: 29,846 Joined: Jun 19th 2008 Location: Update Profile | Thanks man! Trying to make this place better. I'm sure many people here have "heard" of many-a-things but aren't exactly sure how they work. |
backalleyracer | Posted: Jul 20 2008, 10:12 PM |
IDW Goldmember Group: Advanced Members Posts: 1,770 Member No.: 7,122 Joined: May 1st 2005 Location: Las Vegas | pretty cool info, btw, show us some pics of the car that is presented in your sig !!! |
GRiP_GAME | Posted: Jul 20 2008, 11:27 PM |
IDW Senior Member Group: Members Posts: 78 Member No.: 29,846 Joined: Jun 19th 2008 Location: Update Profile | I have an introduction thread in the Welcoming forums. Thanks btw. |
Riker | Posted: Jul 21 2008, 12:54 AM |
IDW Expert Member Group: Members Posts: 136 Member No.: 30,000 Joined: Jul 5th 2008 Location: HR | Anti lag was at it's prime during the B group era, those cars didn't nothing but burn tyres and spit flames... |
kos | Posted: Jul 22 2008, 09:47 AM |
IDW Member Group: Members Posts: 22 Member No.: 30,144 Joined: Jul 21st 2008 Location: 480:Arizona | any information on the long term effects of ALS? |
Fused | Posted: Jul 22 2008, 01:57 PM |
/IDW/ Spartan Driver Group: Members Posts: 332 Member No.: 22,506 Joined: Dec 21st 2006 Location: Auckland, New Zealand | Couple of corrections: The heat of the exhaust is not responsible for the ignition of the fuel during off-throttle, what you have described is injector-overrun, used to cool the pistons, which is what you see V8 Supercars doing, ignition timing is not retarded past 20*ATDC With ALS there is fuel injected more than necessary (overrun) but ALSO, as you said, the ignition timing is shifted to well ATDC, resulting in the plug firing about 90* BBDC usually, which results in half the burn being conducted with the exhaust valve open. Just posted to avoid confusion, with ALS the exhaust heat is NOT responsible for the ignition. Long term effects: -burned/crisped exhaust valves from conducting a burn with the valves open -cracked exhaust manifolds due to extreme heat -ovalised turbo housings due to heat+stresses, resulting in decreased efficiency and jammed turbos -corroded exhaust system from the burning fuel. This post has been edited by Fused on Jul 22 2008, 01:58 PM |