hi bro,
i could frankly tell you that the fuel saving thingy is just a bull shit.. just another product ppl who just want ot make money out to...
no hard feeling.. i try oredi...
last time you just change the blowoff only izzit? well i guess that wont do any harm to your car de... well, i must admit a lot drivers including me like the sound of it.. hehe...
but if you change 4-2-1, well, that need to retune the whole system again le.. weli.. thats wat my foreman tell me la.... hehe...
beside that, did you check your air filter ?