Factory tune here with Stillen CBE, Gen 3's and Berk HFC.. 299hp 233tq on a mustang dyno. My AFR levels were safe, infact id need to lean it some to get some gains. Uprev/COBB tune should net me a few HP and TQ.

Wait till you have your other parts then look into tuning. Dyno to check AFR is upto you..

Once you already have exhaust and HFC the gains by adding the Gen3's are minimal and no where near 20hp. Yes, on a stock car they can be 15+ but on a car that already has bolt on's they are only good for another 5-6hp.