The Dyno

Test 1: Tomei Poncam Type-R Camshafts

The conclusion of the last Test & Tune put us at 268.9 horsepower and 261.5 lb-ft torque. As we begin this test and tune session, we start with new camshafts from Tomei Power. Even when we did a side-by-side comparison between the factory cams and the Poncams, the differences were quite visible. Once the cams were installed, we headed back to Garden Grove, California. With the S15 strapped down to XS Engineering’s DTS Dynamometer, resident tuner Koji Arai began tuning the PowerFC to optimize the contributions of the Tomei Poncams. The result was an increase of 4.9 peak horsepower, and 10.0 lb-ft of peak torque. While this may not seem that impressive, the Poncams truly to 40 lb-ft of additional torque in the low to mid RPM range, these bumpsticks excel as street camshafts. The potential power gains at higher engine speeds are not yet evident due to the flow limitations of the factory turbocharger. Our stock turbo is maxed out of airflow at this power level.

273.8 WHP
261.5 LB-FT TQ

The Tomei Poncam Type-R camshafts yielded an increase of 4.9 peak horsepower and 10.0 lb-ft of peak torque at 1.2kg/cm2 of boost pressure. Power was gained throughout the entire RPM range, with up to 20 additional horsepower and up to 40.0 lb-ft of additional torque in the low-to-mid RPM range.

Test 2: Peak Performance Exhaust Manifold

Equal-length tubular manifolds are the performance alternative to the cast “log- type” manifolds typically found in factory turbocharged vehicles. Equal length piping channels the exhaust pulse more efficiently into the turbine housing to equalize power production across each cylinder. Fitment was spot on, as we encountered no problems lining up the studs. Back on the dyno, the manifold helped to generate an additional two-to-five horsepower between 4,000 and 5,000 RPM and five-to-seven horsepower between 6,500 and 7,000 RPM.

275.7 WHP
276.1 LB-FT TQ

Peak Performance’s stainless-steel exhaust manifold generated an additional two-to-five horsepower between 4,000 and 5,000 RPM and five-to-seven horsepower between 6,500 and 7,000 RPM. Torque increased by 5-10 lb-ft between 4,000-5,000 RPM and up to 7 lb-ft between 6,000-7,000 RPM. Boost was maintained at 1.2kg/cm2.

Test 3: Rockett Brand Race Fuel 100-Octane

Rockett Brand Racing Fuel 100-octane unleaded race fuel was mixed in equal parts with 91-octane pump gas before the SR20 was fired up again. With some ignition advance and fuel tuning, the 95.5-octane solution yielded 9.2 peak horsepower with gains of 5-15 horsepower between 5,000 and 6,800 RPM. When burning higher octane fuel, the risk of detonation is reduced, allowing leaner air/fuel ratios and more advanced ignition timing. These conditions yield more power, but should only be done if the fuel octane has been raised. This brings our grand total to 284.9 peak horsepower and 268.9 lb-ft of torque for this round of tuning.

284.9 WHP
276.6 LB-FT TQ

Rockett Brand 100-octane street-legal unleaded mixed with equal parts 91-octane pump gas was optimized by the fuel and ignition tuning. After Koji leaned the fuel tune and advanced the ignition timing, the Silvia gained 9.2 peak horsepower with improvements of 5-15 horsepower between 5,000 and 6,800 RPM. This brings our grand total to 284.9 peak horsepower and 268.9 lb-ft of peak torque. The power curve is also smoother with the higher octane fuel mixed in. Boost remained at 1.2kg/cm2.

The Bottom Line

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Parts List

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Coming Attractions

These three rounds of upgrades have helped our S15 to nearly reach the pinnacle of the stock GT28R turbocharger’s performance. For our next round, we plan to improve the ignition system with an HKS Twin Power DLI II ignition amplifier. We will also evaluate a Tomei oxygen-sensor housing upgrade to demonstrate the amount of restriction caused by the unit. Finally, we will test a Tomei ARMS B8446 sport turbocharger upgrade that will take maximum advantage of all the components tested to this point. Stay tuned.