TL/DR The other day I started mocking up all my turbo components for the FR-S. (Spare motors are awesome BTW)
There has always been a debate when it comes to the FR-S/BRZ twins over power. On one hand, it’s the hardtop Miata enthusiasts have been dreaming of for years, and on the other, it’s pretty damn slow for being the only real sports car in either Subaru or Toyota’s lineup (no, the WRX doesn’t count). It has become clear at this point, that any factory “hot” versions will leave the drivetrain largely alone, which leaves the aftermarket for anyone wanting a little more kick out of the platform. I’ve always loved the way the car handles but wished it had just a little more pull out of corners, I’m not looking to run 10s or spin the tires through 5th gear, just a bit more pickup. Now, the smart option (I’ve been told, ad nauseum) would be to go out and buy a WRX/Mustang/Camaro/whatever, but none of those really check all my boxes. As such I’ve decided to take matters into my own hands.
Now, the first question for people who want more power from the platform is whether to turbocharge or supercharge. With probably a dozen or more of each type kit available there certainly are quite a few options. I’ve driven a number of supercharged FA20s and none of them really “felt” all that special to me. The roots/twinscrew blowers had a good kick down low, but many ran out of steam up top. The centrifugal blowers make good peak numbers but just don’t feel that fast with such a linear torque gain.
This leaves turbocharging, which, properly done, should give the low down torque of a roots blower and the top end of a centrifugal. The problem with turbochargers is that they make a LOT of heat, go look around the engine bay of a factory turbo car and see just what kinds of lengths OEMs go to for heat management. One way around this is to mount the turbo down by the transmission, away from any heat sensitive components in the engine bay. Unfortunately this places the turbo really far away from the exhaust ports so spool happens later. Also due to the placement, charge piping needs to be significantly longer which leads to more lag.
The other option is to place the turbo right in front of the engine, as close to the exhaust ports as possible. This gives the best possible response, but also injects a ton of heat right into the engine bay.
I chose the latter option, which brings up the question “how do I manage all that heat?” First off, I’m preemptively installing some heat shielding to block the engine from radiant heat
Secondly, I’ll be putting some heat extracting vents into the low pressure zone on the front of the hood.
And finally I’m currently having all the hot parts in the bay ceramic coated in hopes that it will keep as much heat in as possible. If I need to, the next step is to upgrade radiator fans and play with the calibration to turn them on earlier.
Overall goal for the project is to get 300 or so HP with room to upgrade and more importantly reliability on track. That last point is the hard part, not a lot of people have successfully been able to make turbos work on track, but I don’t think I’ve seen anyone with as much preemptive heat management planning yet. We’ll see, I’ll update once things start getting bolted on in earnest.