Asked by Sep 17, 2008 at 11:24 AM

Question type: Car Customization

what is the anti-lag ?

7 Answers


A lag is sometimes felt by the driver of a turbocharged vehicle as a delay between pushing on the accelerator pedal and feeling the turbo kick-in. This is symptomatic of the time taken for the exhaust system driving the turbine to come to high pressure and for the turbine rotor to overcome its rotational inertia and reach the speed necessary to supply boost pressure. There are different methods to eliminate turbo lag. One of them is retarding the ignition, another one uses a bypass to pour more air in the exhaust.

Thank you very much, it was of great help!


A by pass pouring more air in the exhaust How the hell do you do that????? Turbo chargers are driven by HEAT. To reduce lag one can look at a number of options and pouring air isn't one ofthem. You can either use a hybrid turbo with a smaller exhaust housing. You can also get a set of headers with smaller radius made and ceramic coated. You can get an exhaust housing cover ...there are many ways. Please can you explain this air pouring in the exhaust concept. maybe I can use it on my race car. I have a 6cyl BMW multivavle motor with a T66 charger.


It's useful in down shifts coming out of turns. Instead of venting into the intake or to atmosphere, the excess gas is vented into the exhaust manifold and keeps pressure across the impeller higher. Tuning is done the same as if you vent to open atmosphere or low side intake. Just keeps the turbo spooled higher while throttling out.


So what you are saying is that you reroute the dump valve to the exhaust ??? How would that do anything for lag ??? Also what happens in the case where Exhaust pressure is higher than intake such as low boost applications???? Also what dump valve would you use that would handle the kind of heat ??? I've been in the turbocharging business for about 5 years but have never seen thing done.

Anti-lag systems work in two methods: Retarded Timing - When the anti-lag is activated, and you are off-throttle, the computer retards the ignition timing. This means that when the exhaust valve opens, the air-fuel mixture is still under extreme pressure and temperature. The rapid expansion of these still burning gases causes the turbo to spool (or remain spooled), resulting in negligible power losses during shifts/launches. Air Injection - When the AntiLag is activated, air is directly injected into each of the exhaust runners. This introduction of oxygen into a very hot fuel-rich environment causes the rapid ignition and expansion of any remaining fuel. This, in turn, forces the turbo to spool (or remain spooled), which again results in a negligible power loss. Of these two methods, air injection is the one employed most often. While both forms of Anti Lag are extremely detrimental to the longevity of the turbocharger, the air-injection method is less so.


there is also a new turbo out now that uses a mini electic motor to keep pressure high even before exaust speeds rise

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