Turbos

Turbocharger lag is, for practical purposes, the time it takes the Turbocharger to spin up and make usable boost pressure after you plant your right foot. The turbocharger is driven by hot exhaust gases passing through the turbine side of the turbocharger assembly. Before the turbo can make positive boost pressure, that is pressure above atmospheric pressure, there must be enough exhaust energy to spin the turbine. The only way there can be a substantial amount of hot, high velocity exhaust gases passing through the turbine, is if the engine is under a significant load. Once that occurs boost pressure is created, more fuel can be injected, and hence more hot exhaust gases produced to spin the turbo even faster. What a wonderful cycle!

So why am I saying that this nonsense about turbocharger lag is unfounded? Well, in the old days of turbochargers, such as some of the first Porsche 911 turbos, large turbochargers (by today's standards) were used. These turbos contained heavier metals and hence took more energy to spin up. So, when test drivers got on the gas there was a significant delay before (BAM!) loads of power was produced. This was deemed undesirable and given the name turbo lag. These engines also had poor low end torque, because the turbo would not spool up to create usable boost until higher RPMs were reached. When magazine articles were written about cars using turbochargers, lag was 'driven home' to the engine designers as a very bad thing. So, back to the drawing board they went, and they came up with the idea of using much smaller turbochargers and eventually using much lighter materials to help eliminate lag. In my opinion they succeeded greatly. For whatever reason magazine editors, when they see that an engine is turbocharged, have to bring up lag as a negative issue, even if, in reality, it isn't at all.

A Turbocharger is often considered more efficient than a supercharger because they are using the "wasted" energy of the exhaust gases in the exhaust stream as their power source. On the other hand the fact that a turbocharger causes an increase of back pressure in the exhaust system, which steals power. Also a turbocharger gives less boost until the engine is running at higher RPM.

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