I recently blocked off the EGR intake on my V6 diesel Vectra,but this brought up an 'insufficient EGR flow' spanner light.But with a little experimentation I have now had no problems for months by reducing the intake hole size to about the size of a five pence piece where before it was larger than a fifty pence piece! There are others that have done this mod and so far have reported no ill effects.
The benefits are better pick up (mixture is not contaminated by exhaust gases when you initially floor it),better warm up (higher combustion temps),better mpg (slightly),less soot (higher combustion temps = less soot particles),and less contaminants (soot particles) finding their way into the oil and therefore prolonging oil/engine life.
The only downside is a slight increase in NOx which isn't tested for at an MOT anyway,whereas soot is.
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