Tell him to get a drop-in filter and make sure yours is new to make it as even as possible.
You could make this test about ten times more informative if you pick up a BT cable and each do some WOT runs and log your ECU data. Will show if the two cars are essentially running in their most healthy conditions, will show you if target ignition timing is being hit, show the A/F ratios and will make this a very well carried out experiment.
If you both do some pulls with the BT cable and find you have your max ignition being met before and after the tune (each tune may be different target but the before-tune runs are the important ones to make sure your cars are operating equally healthy bone stock.
costs a couple hundred bucks but the good thing is its used to read and delete codes on your car and log data for the future, especially if you ever supercharge.