Total Racing Products Speed Density Kit – R35 GTRTuning your R35 GTR using Speed Density allows your vehicle to have a much more accurate tuning solution based on MAP data instead of MAF data. Aside from the accuracy and reliability of tuning on Speed Density, you can also add vent to atmosphere (VTA) blow off valves without causing a fuel mixture issue. Lastly, a Speed Density based tune is better mannered for the street and removes the obstacle of dealing with maxing out the stock MAF sensors.