Turbo lag definition

[marctwo]

OK, I'll admit that I was a little confused as to the exact definition of lag. If I floor it in 5th at 1500rpm nothing really happens until 2500 when it starts to boost and then at 3000 it really kicks in. Is this lag? I believe I am not the only one who was confused about this so I decided to look it up in Wikipedia:

<font color="green"> Lag is not to be confused with the boost threshold, however many publications still make this basic mistake. The boost threshold of a turbo system describes the minimum turbo rpm at which the turbo is physically able to supply the requested boost level. Newer turbocharger and engine developments have caused boost thresholds to steadily decline to where day-to-day use feels perfectly natural. Putting your foot down at 1200 engine rpm and having no boost until 2000 engine rpm is an example of boost threshold and not lag. </font>

The full article is here: http://en.wikipedia.org/wiki/Turbo_lag#Lag

However, this raises another question. Say I drive along in 2nd at 4000rpm. Then I floor it. It seems to react pretty much immediately so does this mean it has very little lag? Does driving on constant throttle at this rpm mean the engine is 'on boost' or will it only boost when accelerating?

 

[RichA3Turbo]

If driving at 4000RPM, and you floor it, even then there will be a brief period between you hitting it, and the turbo spinning up to speed....This is lag.... When you change gear and the turbo takes a second to get back on boost, this is lag... Thats why rally cars for example, have anti-lag...Keeps the turbo spinning duing changes by dumping neat fuel into the exhaust upstream of the turbo... Explodes and keeps it spinning.

Rich

 

[marctwo]

Thanks Rich. I can safely conclude that my S3 has very little lag then /ubbthreads/images/graemlins/smile.gif