Rear diffusers do two things: they help accelerate the air under the car to generate underbody downforce; and they help drive a wing to be more efficient. Because the surface area under the car is so large, even small pressure changes can have a big effect. A diffuser is an important part of this. Check out the dark blue area under the diffuser in the CFD rendering, that's low pressure that's forcing the rear of the car into the ground. You can also see how the low pressure extends further under the car when combined with the splitter and side skirts. FS Performance Engineering and RGR Engineering collaborated on the design. It's CFD designed with real-world confirmation, and includes nice touches like end plates that separate the chaotic air coming off the rear tires from the working part of the diffuser. The biggest problem with diffusers is that they're usually fairly difficult to install. That's solved that with a clever design that can be installed quickly with no modifications to the rest of the car. Compatible with most dual exhaust designs. Be aware that while it does not decrease overall ground clearance, your departure angle is affected so there is a greater chance of dragging the diffuser in general, especially when leaving a ramp or coming off a trailer. There are 7 bolts involved in removing/installing the diffuser once the bracket is in place, so you could remove it for daily use if necessary. Note that if you have swapped in an NB subframe, the diffuser will not bolt up. You would be better off with an NB diffuser and some modification to the bracket that attaches to the rear of the car. Also, the diffuser attaches to the same mounting points as the rear subframe braces and they are not present on 1990-91 subframes. You will need to weld some tabs on to the subframe or change to a newer subframe to mount the diffuser. Made of aluminum to a very high standard and powder coated black. If we have stock, we are able to ship immediately with no waiting for production. Shipping in the US is included.
