I got a custom 4-1 header and i felt a big loss in power especially at 6000rpms+
the custom 4-1 header they made and installed for me was not i had in mind. I told them i wanted 42.6mm primaries into a 2.5" collector(which is similar to jdm4-1 specs) They made me just that but the primary pipes were only at most 20-30 cm long and met into a 2.5" pipe all the way to the cat. Hav u guys experienced in anything like this?? Im trying to either get my money back or tell them to make me new ones ith primaries all the way to the end. Have u guys got specs for the jdm 4-1?