now i dont have a vortec supercharger, but i do have a 6-71 blower on my engine, I havent dyno'd it yet we think im doing around 600hp with a 383 sbc. From what i have always heard that with a 6% under drive ( which is common for a 6-71 street blower setup ) that it will add around 100-150 hp. I couldnt imagine that vortec adding 350hp without running major boost, which I doubt you could run on pump gas. Also you think your 2bolt main will hold up to 900hp? I am a engine noob so we will see what others have to say.