These diffusors were designed by JKF Aero right before he was hired by an F1 team. These were developed to work with flat floor cars as well as dirty floor cars. They are "modular" in that each section is its own tunnel. So you can opt to not have the outer most tunnels if there are any major space constraints. In the future we will be coming out with thinner outer sections to fit cars with less room between the rear tires. You could also opt to slightly notch the diffusor for tire clearance. At the moment we have the diffusor as pictured which is 51" at the front and flares out to about 62" at the rear (not to include canards) and is 44" long. The depth of the center tunnel is 8.5" at the rear, mid tunnels are 7", and the outer tunnels are 5.5". The kit contains all 5 diffusor sections and rear canards. Mounting is up to the installer.
CFD Data on an S550 Mustang without a flat floor. Flat floor numbers are about double the dirty floor numbers.