Going to open headers question

Have you made passes with the closed exhaust? run it with open headers, compare the MPH, jet up 2 sizes see if the mph goes up if it does you are in the right direction. Some cars make no difference depending on what the exhaust is? I am running a 3" TTI X pipe deal with hooker Aero chamber muffs and dumps, i doubt i would see much difference other than weight loss, I bet that exhaust system is close to 65-70 lbs