A higher capacity fuel pump, 550 cc/min injectors, a retune, and intercooling upgrades are the bare minimum requirements for running stacked pulleys and 21 psi.

I would highly recommend a wideband O2 sensor to monitor the air/fuel ratio.

Insufficient fuel delivery under load can catastrophically damage an engine, so I went further than the above mods and also installed a tank to rail to tank return-style fuel system including a new filter, check valve, 8 AN supply line, modified fuel rail, adjustable regulator and 6 AN return lines.

I run 65 psi fixed fuel pressure, which @ 21 psi of intake manifold pressure is the same pressure differential across the injectors as stock.