Patrick,

I have a similar looking system on my 360, first flown in 92, 1700+ hrs,
no cracks.

The ends are held together with a stainless steel hose clamp, the screw is
safety wired. The theory is that the two parts help damp vibration in each
other. The clamp was applied before final torquing of the nuts to minimize
preload stress. The ends are trimmed parallel to the slipstream where they
leave the cowl to minimize drag and shield the belly from sound waves
emanating from the pipes. The ends are unsupported.

If it did crack, my plan was to add two rigid tubular struts from bolts on
the engine sump forming a triangular support to stiffen the system.

I?m not keen on firewall supports except for systems with a flexible joint
upstream of the hanger. When a cylinder is misfiring the engine can move
around a lot. If the firewall support is stiff it adds stress to the
pipes, if it is flexible it adds dead weight which lowers the resonant
frequency. The range of flexing required to fatigue this large bore tubing
is small compared to the distance the pipes move with respect to the
firewall in the course of normal operation.

Have you had the prop dynamically balanced? That may lower vibration
levels.


=====
BILL HANNAHAN
WFHANNAHAN@YAHOO.COM






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