xx07ghost

okay guys new here and am looking every where for help... i have a 07 mustang gt that i just put in a brenspeed 326 long block in and a hellion 76mm turbo it starts and runs i took it to a tuner but it only made 286 rwhp on 8 lbs!!! should be around 500-600 in that range they say its mechanical i think it might be there tuning...car starts and idles runs fine i drove it 400 miles to Denver and back but when you hit the gas it starts going but the more you push on the gas no response its like once you hit 20% gas it stays at 20% gas no matter how much more throttle you give....any ideas?