While the upper portion of the car was kept stock with a factory wing, I’ve always been a fan of large diffusers with big fins, like those found on the Ferrari 599 GTO or new Viper GTS. And the one that closest resembled this for the Supra—that I could find at least—was designed by Shine Auto Projects.
The Shine Auto Projects PRO diffuser is a 3-piece unit, beginning with the main tray, the optional center air-diverting tunnel, and optional little vortex generators on the side. It's all overlaid with carbon fiber as well.
In case you're wondering about the exhaust, that's just a straight through 3.5-in system fabricated by Modified by KC using a Magnaflow muffler and 5-in tip.
Once MKC secured the rear diffuser with extra reinforcements, I was able to test it at speeds up to 170 MPH with no problem. In fact, one of the cool things about it is I don’t get all of the dust and discoloration on top of the bumper that I used to, since the air now just shoots quickly out the back.
Here’s another look at the aggressive Shine diffuser with the car on Modifed by KC’s dyno. Hey that’s right, let’s get some dyno pulls going!
The red line represents the previous setup this car boosted with, before the engine mishap featured in Part 1, with 93 octane and methanol injection at 25 PSI, versus the current setup on the 17 PSI wastegate spring (blue line). We'll talk a lot more on the next page regarding the two setups, but for right now pay attention to the spool-up difference, which is a whopping 600 RPM improved. Sure, it's easy to say it's all because of the Precision 6766 CEA (Competition Engineering Aerodynamics) ball-bearing turbo, but when you take into account how much larger several of the new components are, you'd think this new setup should be much laggier. Well, it's not.
The red line represented where I'd left off with the previous Precision 71-GTS (.81 open AR) turbo setup, and at the boost level (25 PSI) I mostly used on 93 octane and methanol. The car did have a previous best dyno pull of 764 WHP at 29 PSI, which we showed in Part 9, but we decided not to use it here for comparison because it was a run using a different sized tire, which greatly changed the spool-vs-RPM/MPH due to the different gearing. It also wasn’t the boost pressure this car really operated with—we just ripped it once like that on the dyno with the old setup.
On the next pages we'll analyze more runs to see the true difference in both spool-up and power!