Turbo lag is affected by a number of different factors, including turbo size relative to engine size, the state of tuning of the engine, the inertia of the turbo's rotating group, turbine efficiency, intake plumbing losses, and exhaust backpressure.
In short, turbo lag is the delay between pressing the accelerator and feeling the turbo kick in. This usually takes about 1 second in newer cars.
Now we know how it works and the advantages, let's look at some disadvantages. Anti lag is actually quite brutal. All of that backfiring can cause extra wear and damage to the rally car engine and turbo. Turbochargers are manufactured to extremely fine tolerances and not designed for explosive pressure waves.
In practice, keeping the RPMs up is the simplest way to avoid or minimize turbo lag, at least well past boost threshold. But with modern cars, turbo lag is by far less of a thing than it was even just 15 years ago.
Some engines have nearly zero turbo lag, some have a ton. But there isn't an engine out there that can deliver an immediate hit of boost below its boost threshold RPM. It's simply not possible.
A smaller sized turbocharged diesel engine delivers power equivalent to larger sized engine; Turbo Lag is the time required to change power output in response to throttle inputs. Turbo lag results in slow increase of speed when we press the accelerator pedal.
Let the car idle for 30 (minimum) - 60 (maximum) seconds before you drive off. Use this handful of seconds to set the right playlist, climate control, mirrors and seat position. Be gentle to your car when she's cold. Maintain a low rpm level (below 2,000) until the engine has reached operating temperature.
A turbo is driven by the heat and gas expansion in the exhaust not the velocity of the exhaust. Turbo's have been effectively used in diesel engines for decades. Since load/heat is so important that turbo's, if correctly sized for the application can kick in at 1,000 RPM consistently.
Twin-scroll turbos
A twin-scroll turbo effectively brings together twin-turbocharging into one neat package. Using two inlets for the exhaust gases instead of the conventional single inlet, this form of turbo is designed to operate at small and high exhaust gas flow rates, reducing the effects of turbo lag.
Less than 1% of turbos fail because of manufacturing defects. Most failures are caused by the three 'turbo killers' of oil starvation, oil contamination and foreign object damage.
2. Turbo Flutter is Harmless. That fluttering noise that some turbocharged cars make when the throttle is suddenly closed, such as during gear changes, results from a compressor surge. It's a reasonably complex phenomenon which we explain in far more detail here.
High amounts of carbon build-up within the VNT mechanism and lever arms indicate a blocked DPF, and the driver may experience turbo lag or over boost of the turbo.
What anti lag does is basically raise the exhaust energy (temperature and volume) when the engine is unloaded. Rally style anti lag can surely be had on a diesel by injecting fuel into the exhaust manifold (and some modern diesels do exactly that to get some heat into the diesel particle filter).
Both systems have their merits, but the benefit of a twin-turbo is that it has the potential for reductions in turbo lag compared to one single turbocharger doing all the work. The twin-turbo delivers lower boost pressures to reduce turbo lag, but the combination of the two turbines creates plenty of power.
In today's engines, the turbos are often water cooled, meaning they are kept at a temperature that's safe for the turbo to operate long term. This design should make the turbos more reliable, and it means you don't need to “idle down” a turbo engine. It's already constantly being cooled.
Now I understand that it can destroy your valves, exhaust and turbo as well as making braking a little bit iffy but is it legal ? Could I be pulled by plod if they hear it and see it ? No. It's not legal.
Anytime a turbocharger ingests something — be it dirt, dust, a shop rag or a bolt left in the intake — it can spell disaster. Unfortunately, outside debris making its way across the blades of a compressor wheel (the intake side) accounts for 80 percent of all turbo failures.