n2582d wrote:Personally I doubt it's worth the effort to switch from the doghouse plenum style baffling. That being said, if one were looking for "acceptable data" for a field approval to use the existing cowl together with the '53 and later style baffling, the L-19 might be an example to show that this combination has been used by Cessna.
Before you randomly change the airbox plenum for a pressure cowl, consider the airbox contains all of the ram air pressure from the cowl intakes and none of the cowling is carrying the internal pressure from the airbox. Changing to a presure cowl transfers all of the ram air pressure to the cowling itself. Even the relatively low psi pressure of the ram air over the entire area of the upper cowl inside the baffles will add a large stress to the cowling which was not designed for it. There will probably be unintended consequences such as increased latch failure or cowling wear.
On the other hand, a pressure cowl mod might reduce or eliminate the “cowl sag” mentioned above on the airbox style plenum by “inflating” the cowl and making it more rigid. Who wants to give it a try? Not me.