Testing Facility: Raceline Development USA
Honda’s dominance in the subcompact market has been accredited to the simple ideology that an economical vehicle doesn’t have to be just another boring commuter car. The fifth-generation Civic’s lightweight, nimble, and affordable platform has been considered for many years the ultimate blank canvas for enthusiasts in building a competitive vehicle.
Unfortunately, all ’92-95 Si and EX models possess an inherit weakness under the hood, namely their 1.6L VTEC engine (D16Z6 engine code), pushing a meager 125 hp.
Prior to testing this month, we should note that our 1.6L engine was equipped with a DC Sports 4-2-1 header, RSR cat-back exhaust, Random Technology high-flow cat, K&N short-ram intake, and Hondata S300 ECU. With those modifications, the D16Z6 engine netted baseline power figures of 121.1 hp and 99.3 lb-ft of torque.
Blox Racing 66mm Billet Throttle Body (tuned)
Blox throttle body, gasket, TPS sensor, installation hardware, stickers
10 and 12mm sockets, ratchet, extension, screwdriver, 8, 10, and 12mm Allen wrenches, pliers, Teflon tape, vacuum cap
Blox Racing billet throttle bodies are available in sizes ranging from 66mm to 76mm for the Honda and Acura D-, B-, and H-series engines. The billet throttle bodies feature brass throttle plates, stiffer throttle springs, and a pulley designed with sealed bearings that allows for smooth pedal modulation.
With the OEM throttle body measuring 55mm in diameter, using the Blox 66mm throttle body requires port matching of the OEM intake manifold for best results. Installing the Blox throttle body requires repositioning the factory throttle cable bracket closer to the throttle body in order to reduce cable tension and high-rpm idle, along with sourcing a rubber cap to seal off a vacuum port on the manifold.
The Blox Racing throttle body was tuned with our Hondata S300, delivering an increase in horsepower and torque across the board, with a gain of 3 hp and 3 lb-ft of torque through the low to mid range and at 6,500 rpm. Many consider the throttle body excessive in size, but more extensive engine work, such as larger cams and higher-compression pistons, demand increases in airflow, thus justifying a larger throttle body.
Honda OEM D16Y8 Intake Manifold (Untuned)
Intake manifold, fuel rail, throttle-body gasket (dealership part), silicone
10, 12, and 14mm sockets, 10, 12, and 14mm open-end wrenches, ratchet, extension, crescent wrench, plyers
It was clear that Honda engineers intended the D16Z6 engine to be an economical powerplant—not a fire-breathing monster. Why come to that conclusion? A good reason is found when looking at the intake manifold, and then comparing it to the D16Y8 manifold found on all ’96-00 Civic Si and EX models. When comparing both units side by side, the D16Z6’s smaller intake runners and more compact intake plenum were designed for better low-end acceleration. The D16Y8 manifold we sourced from local junkyard features shorter, fatter runners with less curvature, along with a larger plenum, which—in theory—should be more efficient at producing high-rpm horsepower.
Installing the manifold requires transferring a number of parts, including the fuel injectors, EGR control solenoid valve, PCV valve, as well as purchasing a new throttle-body gasket and intake manifold gasket. We discourage anyone from reusing gaskets, to ensure a leak-free seal.
We began phase three of testing upon installing our new intake manifold this time without altering our previous Hondata map, to better expose the importance of tuning. The Civic idled rough, struggled on the dyno, and surprisingly made only 121.5 hp and 102.2 lb-ft of torque—a loss of 2.2 hp and 0.1 lb-ft of torque over our previous run. A quick analysis showed changes to our previous air/fuel ratio, as the engine was running rich (12.8:1 A/F ratio) from idle to 5,000 rpm, and lean from 5,100 rpm to redline in VTEC. Although we suffered significant horsepower and torque losses throughout the powerband, we were confident that with proper tuning of our Hondata S300, we could recoup the power losses during our final stages of tuning.