Having taken a fairly detailed look at the Rotrex traction drive supercharger and how it lured Oscar Jackson out of retirement (the story is available on modified.com and in the May '09 issue), we couldn't resist the lure of testing out this elegant approach to forced induction on our EG Civic race car.
To make this happen, we not only had to order the K-series Race kit from Kraftwerks, we also had to get our hands on a front-mount intercooler and fabricate the custom intercooler tubing and intake. For this we turned to Vibrant Performance, which has an extensive catalog of fabrication parts and supplies, including air-to-air intercoolers in a variety of sizes as well as stainless and aluminum tubing in a full range of diameters and shapes, couplers and clamps of all types - and even a velocity stack for the air intake.
Since the inlet and outlet on the Rotrex C38-61 supercharger we opted for (along with a 100mm pulley) and the Vibrant intercooler have a O.D. of 2.5 inches, SG Motorsport used 2.5-inch diameter stainless tubing for the intercooler chargepipes (which we flared out to 3 inches before the throttle body). But before that we mounted the Rotrex to the block - a cinch thanks to the perfect fit of the Kraftwerks mounting brackets - plus, we installed the Rotrex oil cooler and reservoir, which was very straightforward as well. Where things got a little tricky was figuring out how to route the intercooler tubing while keeping a full-width radiator, but we solved this by notching the front upper engine bay crossmember so we could create just enough clearance to get the chargepipe off the Rotrex to the intercooler.
Results With the front-mount intercooler setup fully fabricated and the Rotrex primed with its special oil, all that was left to do was dump a jug of 110-octane race gas in the tank and strap our trusty old EG to U2Ndyno.com's Dynapack hub dyno so that Sasha could work his magic with the Hondata K-Pro ECU.
According to SG, the fuel and ignition mapping from our normally aspirated tune was surprisingly close to what the Kraftwerks setup needed. Presumably this is because, as Oscar had told me when writing that Rotrex story back in '09, the cool-running Rotrex supercharger builds boost in such a linear fashion that it behaves very much like a normally aspirated engine in terms of the required fuel and ignition timing maps. Obviously, SG had to throw some more fuel into the equation given the higher horsepower and torque output, but changes to the cam timing and ignition timing in the upper rpm range didn't produce any meaningful gains. Instead, SG focused its attention on the area around the VTEC crossover point, where early pulls showed a dip we didn't like. By lowering VTEC engagement a few hundred rpm and adjusting ignition timing in that area, the dip was eliminated and area-under-the-curve in the midrange improved.
With the K-Pro tune safely optimized, we let the engine cool down and then did one last pull for glory. During tuning runs we saw a high of 398 whp, but we wanted to cross the elusive 400-whp barrier. With the engine fully cooled, we blew past that mark to post a very tasty 412 whp and 283 wtq at 7600 rpm and 11 psi of boost from an internally stock K24A2 short-block that previously made 240 whp and 185 wtq with Skunk2 cams and valvetrain upgrades. That's a 72 percent increase in horsepower to go along with a low-heat, low-stress approach to forced induction that should keep our EG running reliably as it blows past unsuspecting Porsches and Corvettes. It's not an easy installation given all the custom fabrication required, but the end result speaks for itself.
'93 Honda Civic CX Hatchback
Engine 2.4-liter Acura TSX K24A2 inline-4
Relevant Mods Skunk2 Stage 3 camshafts & valvetrain, RC Engineering 550cc fuel injectors, Walbro 255-lph fuel pump, Vibrant Performance front-mount intercooler & intake w/ velocity stack, DC Sports K-swap header, Vibrant Performance 3" exhaust, Hondata K-Pro ECU, 110-octane race gas
Key Features Designed to mount to Honda K-series engines where the A/C compressor normally mounts.
Comes with either a Rotrex C30 or C38 supercharger (your choice) and is capable of producing more than 500 hp.
Kit includes a self-contained oiling system for the Rotrex, including a high-quality air-to-air cooler.
Includes high-quality, CNC-machined mounting brackets, AIT sensor bung, Bosch bypass valve, metric fasteners and detailed installation manual.
Requires custom fabrication (eg. front-mount intercooler) and custom engine management/ECU tuning.
For a video recapping the install and dyno test, check out youtube.com/watch?v=XEbKDzdC7GY
Before 239 whp & 164 ft-lbs After 412 whp & 283 ft-lbs