i am building a stealth stock street race car. i am going to use nitrous but i want to keep my stock heads and intake manifold. how much power will i pick up by porting the heads and intake ??
depends on who does them...seriously can't answer that question without flow numbers provided by a shop with a reputation for 'porting' intakes and heads...guys like thumper on this site will be able to give you VERY close to correct numbers after the work is done. Don't expect the same results from just anyone, all 'port' jobs are NOT equal.
For what it's worth, my buddy did a gasket match job and really lightly cleaned up the exhaust ports on a set of E7s (i wouldn't even call it a port job, more like just gasket matching to Felpro 1250s) and he picked up 11hp at the wheels, shown by back to back dyno tests. He was also running an E303 cam and Edelbrock intake before and after the head work.