EXCEPT ZR1. Borla Performance Industries Cat-Back system for the celebrated 1986-1991 C4 Corvette equipped with a 5.7L V-8 engine has been engineered to work with either the popular manual transmission or the automatic. The premium, high-quality, T-304 Austenitic stainless steel system is easy to bolt on, is a direct replacement for the much heavier (by some 20lbs.!) stock system. A 3" diameter front pipe is mounted just after the catalytic converter leading to a Y-pipe, which splits into two 2-1/2" pipes exiting on each side of the rear. The muffler and tip assemblies use a 10"x 5" diameter round muffler on each side of the vehicle, with polished T-304 stainless steel rectangular, rolled edge, angle cut tailpipe tip at each split rear exit. Tests have shown an exciting 41% increase in flow for dramatic improvement in power or fuel economy. That now famous, aggressive Borla growl and sexy look proclaim this block may be small, but it means all business ? we guarantee it for a Million-Miles! With race-bred technology that has been transferred from the many successful Borla race programs, it was no accident that this Borla system has won several major Corvette exhaust shootouts. Included in this great and storied past are such famous efforts as the C5-R Race Team that has dominated LeMans along with the Bondurant Corvette program at the Bob Bondurant School of High Performance Driving. Only what you would expect from Borla, the most winning exhaust in racing.