The primary reason for installing an HX-40 is to control soaring EGT's from boosting the fueling. It is able to move considerably more air than either the HX-35 or HY-35 at the same boost levels. On the down side, since the exhaust turbine is larger, it takes more exhaust volume to spool it up and this is manifested as "lag" at low rpm levels. There have been various attempts to reduce this lag by shaving metal off the turbine fins, but a number of these have failed prematurely. KWIKKURT has put together an HX-40 that is suppose to overcome the lag without weakening the integrity of it. It does need a 4" downpipe, but other than that is a bolt-on. Hope this helps.