i want to bang my head ye sb na kro tou kya kroooooo, hps engine power reduce krta hai,,, eps is gud cz its electrical no alternations in engine bay and can be installed easily, yes tyres are bigger ,aur bro cut out valve is now kind of old but most people in pakistan dont know of this ,wt u do in straight piping and performance mufflers is like u made the easy way out for smoke without any resistance from engine to mufflur end , on the other hand cut out valve is much simpler , u can install it from where the piping starts underneath of ur car, it has 2 ( Y type valve ) and is remotly or switch controlled , once ur switch is off ur car sounds like stock car and uses the slience piping for smoking out ,, but once the switch is on the valve is open and insted of using pipe for smoking out it uses the other valve which was closed earlier ,,so the smoke directly goes out from there without having much resistance and will thus result in more power and accelerration ,according to my knowledge its only aval in karachi,but you can check it out from youtube as well,,,,,