7 This log-style integral intake manifold is a big reason for six-cylinder fuel distribution problems that cause rough idle and an overall lack of performance. These manifolds can be honed and ported to improve performance. Manifold end plugs can be removed for this purpose. Be assured, honing and porting does not come cheap, but it can make a difference in performance. A carburetor spacer will help torque, but watch out for hood clearance.