IN THE ONGOING SAGA OF KA VERSUS SR, there has been both progress and setbacks as Jeren and Richard continue their builds. Here is the latest news from both camps as they move closer to the final competition.
PROJECT SR UPDATE
In the last visit with the SR, the increased displacement, cylinder head work and camshafts put more power under the curve and earlier in the RPM range. However, peak power was limited, as the upper limits of the TOMEI POWERED 8446 turbocharger had been reached. To attain greater peak power levels, a larger turbocharger was in order.
Garrett’s latest performance turbocharger series, the GTX, features a lightweight aluminum compressor wheel CNC milled from a forged billet of aluminum. Garrett states that this design delivers a 10-percent gain in flow and pressure ratio compared to its GT-series equivalent. Garrett’s GTX3076R turbocharger was selected as the spec turbo for the KA vs. SR competition. The billet compressor wheel features a 76.6mm major diameter and 58mm inducer. The compressor housing relies upon a ported shroud for surge resistance. The 60mm turbine wheel is enclosed by a 0.82 A/R turbine housing featuring a V-band outlet.
Making the Connection
Garrett engineers recommend a -4AN oil feed line with a 0.035-inch restrictor for their ball-bearing center cartridge. Ball-bearing turbochargers do not require as much oil to be delivered and would suffer premature failure and oil leakage if too much oil is delivered. A -10AN oil drain line and -6AN water feed lines complete the turbocharger’s cooling and lubrication system.
The exhaust manifold and turbine housing were sent to Swain Tech Coatings to receive its White Lightning ceramic Thermal Barrier Coating. Swain Tech states that its White Lightning coating reduces radiant heat by anywhere from 35-to-55 percent. This reduction in irradiated heat maintains exhaust gas velocity in the pipes and improves scavenging. To further contain the underhood temperatures, Design Engineering Inc.’s Titanium exhaust wrap covers each exhaust runner, the downpipe and dump tube. A Titanium Turbo Shield covers the turbine housing, leaving no exhaust component without insulation.
Fabrication by Design
A top-mount exhaust manifold was sourced to properly fit the larger GTX3076R turbocharger. This particular stainless-steel manifold, manufactured by a company that is no longer in business, features a lasercut flange and equal-length tubular runners. The top-mount location required a new downpipe and new intercooler piping. Vibrant Performance provided V-band clamps with flanges, 3-inch stainless-steel, mandrel-bent U-bends and 2-inch stainless-steel U-bends for the new downpipe. In addition, 3-inch aluminum U-bends and Vibrant’s VanJen clamps were provided for the new intercooler plumbing. The Silvia was brought to Design Craft Fabrication where fabricators Gary Castillo, Len Higa and Ben Schwartz fashioned the downpipe to fit within the confines of the engine bay. A Turbosmart Hyper-Gate45 external wastegate plumbed back into the exhaust regulates boost pressure. Plumbing the wastegate dump tube back into the exhaust ensures accurate tuning at the dyno, especially when the tuner needs to be able to listen for knocking. Vibrant’s VanJen Clamping System features O-ring seals and the flexibility to deflect up to 12-degrees to accommodate misalignment, vibration and engine movement in the new intercooler piping. Capable of holding up to 110 psi, these aluminum clamps eliminate the worry of hose couplers coming undone. Bungs for the intake air temperature sensor and the water/methanol injection nozzle were welded in, along with a tube for the idle air control module.
Boost N' Blow(off)
The spec manifold relies on an external wastegate so we chose Turbosmart’s Hyper-Gate45 as the spec wastegate for the competition. In addition, a Turbosmart Race Port serves as the spec blow-off valve. Both the Hyper-Gate45 and Race Port feature V-band clamp connections, compact chassis designs and end-user serviceability.
Raising the Bar
After fabrication, the Silvia was dropped off at Drift Speed to be tuned by Koji Arai. Initially, the new turbocharger yielded 413 horsepower at 1.0 Bar (14.55 psi), similar to the previous setup at 1.3 Bar (18.9 psi). Next, the water/methanol injection system was activated starting at 1.0 Bar and peak power numbers were targeted. With boost increased to 1.6 Bar (23.3 psi), the new turbo system output 528.1 horsepower at 7,000 RPM while torque jumped from 360.2 lb-ft to 466.2 lb-ft at 5,200 RPM. Koji noted that the 1,200 cc/min RC Engineering injectors reached a 90-percent duty cycle during tuning and the fuel pressure would begin to fluctuate. Koji comments, “In our experience, the S15 fuel supply lines leaving the tank are smaller than those found on the S14. Fortunately, the S14 supply lines can be installed on the S15 fuel tank to remedy the situation. However, since some of the lines are difficult to reach, the fuel tank and rear sub frame must be dropped in order to make the conversion.” Since 1,200 cc/min injectors can usually support horsepower levels in excess of 700, it is likely that the supply issue is the reason for the injectors nearing their maximum capability prematurely.