I got 2001 Impreza wrx with forged engine, LINK ECU, 750CC INJECTORS etc currently running 300 bhp. I want to push it to 450/500bhp. I was told a md321 or GT3076 OR DOES ANYONE HAVE ANY OTHER RECOMMENDATIONS

 

You will need a gearbox capable of the power so plus another 2k ish

Either that or stick an old vf35 or a billet 18g

Stock box will be getting pushed above 350ish

 

if your forged engine doesn't have a closed deck conversion then that WRX block is going to transform itself into a meccano set at that power. Six speed conversion, decent breather setup and something like a SC46/SC52/MDX555-450/MDX555-500/RCMPT07.

450 will be easier to achieve than 500 it's a big price jump to take everything up and if your still on standard WRX heads you'll probably have to get some work done there as well or you'll have a very narrow power band as the engine struggles to breath.

 

currently running 300bhp on 750cc injectors??

If you want a detailed answer you may want to give proper details on your engine spec, modifications etc. Some people class a forged build as a set of pistons in an open deck block with wrx rods.

As stated above, your venture into 500bhp could be a few K, or 10+ depending on what you already have.