Always use a dynojet, so you can compare with other cars.
Dynojet can't be fooled or tricked like other dynometers.
I've tuned maybe 20 or 30 of these, they always do like this:
make sure its below 11.8 and above 10.8 a/f ratio,
You really need some aftermarket low lift cams, like poncam 256, to take advantage of the sr20 head and keep boost low enough to be practical. always match sr cam to sr spring, i.e. tomei cam + tomei recommended spring.
Stock exhaust is fine up to 320rwhp in my experience, no issues using internal gate. You just need a quality boost controller like the profec B spec-II.
You can use the stock exhaust to 350 or 380rwhp if you know what you are doing, it requires an external gate and knowledge of exhaust gas pressure vs valve diameter