People basically have two views on turbo lag, one is when the engine is below the boost threshold and the other is when the engine is in the threshold. The video on the OP shows the engine below the boost threshold which inturn produces less acceleration which is interperated as turbo lag by some. Prime example on Top gear (google it if you have not seen it) they did what they called a turbo lag test with a EVO, notice it was started at 30 mph, high gear and low revs well below the boost threshold of the EVO this will off course hinder the accelaration of the EVO as its well below the Threshold, a common miss interperation of turbo lag. That test was to show that the car is not that good for day to day running as the turbo is so large. Turbo lag: A measure of the delay between when a turbocharged engine’s throttle is opened, and a “significant portion” of the maximum boost pressure is available. Basically its measured when you hit full throttle when then engine is at the right revs for the turbo to work. Boost threshold: Turbo lag should not be confused with boost threshold, which for simplicity’s sake we’ll say is the engine RPM above which the turbo is capable of producing a “significant portion” of its maximum boost pressure. For example, stamping the throttle open at 1500RPM and having to wait until 3000RPM for boost is not so much lag as it is a function of the engine and turbo system’s boost threshold. Once the engine is operating above the boost threshold however, then the delay when the throttle is opened can be assumed to be turbo lag. Again basically to measure turbo lag the engine needs to be above the boost threashold, when the engine is in the threshold apply full throttle and if it does not respond straight away that is lag. There will always be a delay in acceleration when the accelerator is applied in cars with large turbos ( newer cars not so much now) when you are below the the threshold as they are not made to be driven around at low revs they are made to be driven in threshold, EVO's are a great example you have to keep them revs high or you will not get full use out of the car. I've not tested lag in GT5 so I couldnt tell you if there is or there isnt but the way to test it is to apply full throttle when the engine revs are after the boost threshold and see if there is a delay.