Short Runner Valve. The 6.4 intake has a short runner mode and a long runner mode and the module that flips it is on the back of the intake and crashes with the firewall if the motor is in the stock location. Holley mounts move the motor forward 1.75" to avoid that issue along with a couple of others, but the TTI and Shumacher mounts require you to either run a different intake, cut your firewall or lock the 6.4 into one mode, which I think is the long runner mode.