The theory here is that the increased intake volume will increase the time it takes to fill the pipe at the higher pressure. The larger the pipework the greater the volume. Initial testing showed that the 2.5″ pipework was ideal for the air required to meet the fuel delivery capabilities for the engines covered. 2″ pipes are easier to route in tight engine bays, but will choke the potential.
On a Landcruiser 1HDFTE with around 160rwkw, a check was done with no intercooler and then after the Performance Diesel Intercoolers Front mount kit was installed. The results showed the boost built slightly quicker with no intercooler, but almost immediately the intercooled setup built torque faster and was much stronger throughout the rest of the power range. There was a 50rpm range where no intercooler was better.
The test clearly showed that lag should not be something to be concerned about when considering a PDI front mount intercooler kit.