For 300 whp, you'll need bigger than the t28 which comes off of the GTi-R motors. A t28 will get you upper 200's, but I don't think anyone has done 300 yet with a t28 (though it might happen soon with a new intake manifold). There is a company,
www.o2induction.com which makes an intake manifold for the SR which has dyno'd at around 50+ whp over the stock intake manifold on a big turbo car. The GT2835? turbo will get you to 300 I think. Pretty sure it's a dual ball bearing turbo which spools instantly, but it cust mucho money. There's also the GT 3037 which is even bigger and probably costs more but I think it supports over 400. The most t3/t4 hybirds are very popular and will get you there no sweat. That's what most of the se-r guys are using right now. I'd say the GT turbos are better as they are a new design and have the ball bearings, etc. but they also cost a ton more. With the t3/t4, by choosing the appropriate trim and A/R housing size, you can get the characteristics you want as far as power and spool up are concerned. Anywayz, there's a ton of info on se-r.net (in the archives), sr20deforum.com and probably in this forum too somewhere (just joined). As far as fuel and managment, I think 50lb injectors, Cobra Maf, and JWT ecu will do just fine. Oh yeah, a bigger fuel pump such as the Walbro 255lh or a 300zx TT pump will be necessary too.
Khiem