to the rest of my mods. There are plenty of good chips available for either 740s or 615s, so either would idle fine and manage fuel delivery appropriately. Since my turbos are rated for 530 hp and I don't want to do anything beyond bolt-ons, I figured the 615s would be sufficient -- and might actually make my engine idle a little smoother, save a little fuel, etc., because they're better matched to the fuel flow needs of an engine generating the power mine does.