Young Version — August 1999

With the same tuning setup, the S15 Silvia is definitely faster than the S14. As the adjacent article about Yasio Factory’s project car shows, simply raising the boost pushed it past 340 [PS]. Yet the engine is still the same SR20DET as in the S14, apparently with the N-side variable valve timing. So why is it quicker? Nissan’s new-model technical guide does not explain it. There is a rumor that the camshaft profile changed (and that the cams differ between early and late PS13 and S14 models, too). But the most likely explanation is the turbo specification. Nissan’s launch materials only say that the S15 adopted a high-efficiency turbo. The S13’s S14 turbo is a popular swap, but if the stock S15 turbo performs better, it ought to work in an S14 as well!

The housing shape has changed. But from the outside, the only visible difference from the S14 stock turbo is a divider-like piece near the actuator swing valve. The housing itself appears unchanged in size, and the blade count and angles also seem unchanged (only the blade material changed to Inconel). You’d normally think that alone couldn’t make a difference in power. However, YV’s own investigation uncovered new information from an industry source: compared with the S14 turbo, the S15 turbo’s actuator bypass passage is machined 1.6 mm wider in diameter. We also heard that otherwise they are virtually identical. But can that really change both power and feel? We’ll have to fit stock S15 turbos to S13 and S14 cars and find out.

In the May issue, the car produced 341.0 PS and 46.7 kg·m at 1.3 kg/cm² boost after replacing the intake and exhaust components plus the ECU. For context, only the intercooler and airflow meter (a stock Z32 unit) had been changed; the injectors and fuel pump were still stock. It now has a bolt-on GT2540, but next issue it’s set to evolve into a surprising, original secret setup!