i think both the exhaust and intake ID is already too big (stock). remember, this a de-tuned 500twin. it makes around 100hp/L so no need to go crazy with the ID size. infact i would even argue that larger ID would slow air velocities resulting in poorer performance over all. and even if larger ID is done u probably wont benefit any unless ur screaming past 7,000rpm+ all the time. infact, i welded several washers in my exhaust to reduce ID ( create/increase restriction) which intern increases air velocities. this slightly reduces peak power but it gave me way more Under the curve area. way more usable TQ and tractor factor. ^^ this is probably another reason my bike gets better feul economy when compared to the other crf500L's or the cb500/cbr500s. larger area under the curve = more TQ at any given RPM under 7k= better feul economy= more passing power in low gears.