Turbo lag in a turbocharged engine is the time it takes for the driver to feel the push of the car, due to torque, from the minute he puts the throttle down. This is caused due to the delay in the engine block to produce sufficient exhaust pressure in order to spin the turbocharger and force compressed intake air into the engine. Turbo lag is usually more perceivable during low rpm since exhaust gases and, consequently, air compression is at its lowest.
Nominally, there are two adverse scenarios for turbocharged engines which can lead to an inefficient or underperforming car or even catastrophic failure of the turbocharger. The first scenario is when the turbocharger is too big for the engine, meaning that the engine will need to surpass a specific rpm number in order for the turbo to start spinning and produce power. The second in turbocharger failure. Of course the most prudent scenario is to achieve a compromisation between the two, which will ensure optimum efficiency and safety.
In general, there isn't a unique solution to eliminate turbo lag, but there a quiet a few methods that can help to reduce it. Below we present five ways:
1: Add Nitrous Oxide
If you’re looking for a way to reduce turbo lag that’s akin to magic, look no further than nitrous oxide. Since a shot of nitrous makes cylinder pressures go crazy, that same energy then gets directed out of the exhaust, spooling a turbo in almost no time. We’ve seen correctly used nitrous systems cut spooling times by a factor of four, but be warned, if your air/fuel ratio isn’t corrected for the extra oxygen during spooling, a pretty big backfire and engine damage can occur.
2: Increase your Engine's Compression Ratio
In the 1980s, it was common to see turbocharged engines using compression ratios in the 8:1 range to compensate for the heat and pressure as boost came up. But until the boost hit, you were basically driving an over-cammed, low-compression engine that made no power. As fuel and intercooling improved, it’s now common to see turbo engines in the 9:1 to 10:1 compression range, and those extra points of compression really do wonders for spooling turbos.
3: Add A Wastegate to your Turbocharger
A turbo can be tuned with a smaller exhaust housing that will spool the turbo quicker, and an exhaust wastegate can then be added to bleed off excess exhaust pressure at high engine rpm. In most cases, at least three or four different exhaust housings are available for a single turbo frame, so this type of change is relatively easy to make.
4: Narrowing the Power range of your Engine
Turbochargers are best at supplementing an engine that’s at a constant airflow state, so having a narrow powerband is useful in reducing turbo lag. Larger-displacement engines (for a given power level) and multi-speed transmissions both keep turbo lag to a minimum, because the turbocharger will already be operating close to its peak power-producing range.
5: Sequential Turbocharging
Sequential turbocharging works by pairing a small turbo making power from, say, 2,000 to 4,000 rpm, and a second turbo that takes over from 4,000 to 6,000 rpm, effectively making for an engine with a huge operating powerband. Unfortunately, these systems are complicated and expensive, and are rarely used in the gasoline world—although they have been common in diesel performance for more than 40 years.