In '12, we embarked on a wild adventure with our '13 Scion FR-S, also known as "Ratchet Bunny." At the time, our car was sort of a big deal—one of the first Rocket Bunny kits to hit the States, BBS Motorsport wheels, AP Racing brakes, and a rare green color from Aston Martin. If we don't mind saying, it was quite a sexy beast! But under the hood is where the love-hate relationship starts...
In the rush to get to market, HKS used our FR-S to help develop its U.S.-spec GT Supercharger System for the 2.0L 4U-GSE. We can all agree, the FR-S begs for forced induction, but factors like its mill's high-pressure direct injection fueling and American octane standards commanded more time and attention from engineers to get the boost formula just right.
The Guinea Pig
When this odyssey began, HKS sent us its kit presumably ready to rock. It included a centrifugal blower, intercooler, charge plumbing, F-CON iS piggyback fuel and ignition timing controller, a plethora of hardware and silicone couplers, a couple of pulleys, a replacement accessory belt (which drives the supercharger), and an air filter. A traction fluid supercharger oiling sub-system is also a part of the setup (with tank, filter, cooler, hoses, and proprietary fluid).
We plugged in everything and then took our Ratchet Bunny to renowned tuner shop Evasive Motorsports in Santa Fe Springs, California. Since this was the first HKS kit installed on a U.S.-spec FR-S in California with crappy 91-octane fuel, Keisuke Morita from HKS came out from Japan to tweak the F-CON iS, seeking out the best parameters in hopes of milking the most power while keeping it daily driveable.
After a couple hours, Morita-san made adequate gains throughout the rev range. The biggest jump in horsepower happened between 5,400-6,250 rpm, where it peaked at 201 whp, an increase of about 50 ponies over stock. The largest peak gain was at 5,940 rpm, where the FR-S picked up some 55 horses. Torque showed similar improvements between 5,100 and 6,360 rpm, maxing out with 176 lb-ft, a bump of roughly 50 lb-ft. Overall, the kit made in the ballpark of 28 percent more power. The blower was irrefutably making the FR-S more potent and therefore improving its critical power-to-weight ratio. Our six-speed Scion weighs roughly 2,758 pounds, making its stock power-to-weight ratio around 17.7 pounds per horsepower (lb-hp). The power made by the supercharger lowered that figure to 13.7 lb-hp, but at the end of the day, the sad truth was that most people weren't all that impressed with the modest improvement in power.
Version 2 and 3
HKS heard FR-S and BRZ owners loud and clear and always knew more development was in the pipeline for its kit. Part of the solution involved developing its Flash Editor, an ECU upgrade flash tool similar to the Accessport sold by Cobb Tuning. With a better game plan, HKS loaded up its Flash Editor with maps both for supercharged and naturally aspirated 4U-GSE/FA20 and again traveled back to California to use our FR-S and work out the bugs for Version 2 of its U.S.-spec supercharger kit.
Testing started on Christmas '13, and although crappy fuel and our FR-S's stock exhaust manifold continued to give their engineers headaches, HKS was still able to pull another 20 whp out of the car.
Fast-forward to the summer of '15, and HKS returned with Version 3. But this time, instead of only adjusting the programming, engineers also came armed with a bevy of upgraded hardware. It included a different bracket for the supercharger, new plumbing, and a couple different pulleys.
In order to slow the compressor and limit its workload, developers came up with an intake pipe that featured less restriction via wider opening at the compressor end. HKS also includes a bigger diameter 110mm pulley for 91- and 93-octane applications that allows 9.5 psi of boost pressure. And a flat, machined pump bracket replaces the cast one from Version 1 of the kit so that all the new and old pieces gel together.
Somewhat unexpectedly, HKS also has provisions for running E85 fuel with the system, which are basically just a 100mm, 11.5-psi pulley and correspondent belt. If you're going to run E85, however, you'll also need a higher capacity fuel pump and 700cc injectors, and we hear you'll likely have to swap out all the fuel lines, too—none of which is included in the kit; but we decided to see how Ratchet Bunny would react anyways!
We're pleased to report this story has a happy ending... Running an ethanol fuel blend coursing through its veins, our Ratchet Bunny made an impressive 324 whp with no alterations to the bottom end. Pretty frickin' rad! When we took out the E85 components and tried our luck with 91 octane, we made a respectable 255 whp—not bad considering we're still using the stock injectors and fuel pump (HKS has tested it in-house to 269 whp on 93-octane).
HKS tells us it can beat competitor pricing, offering the complete kit with Flash Editor for $4,100 suggested retail ($3,800 MSRP without Flash Editor). For just the pulley upgrade alone, you're looking at $360. If you're like us and prefer to rock JDM parts under the hood, you now have no excuse not to supercharge your FR-S or BRZ!