FYI Titanium is not recomended for DP applications with sustained temps over 1600 high pressure.
(taken from Burns Stainess)

Based on its price and availability, it is hard to believe that titanium is the ninth most abundant element in the earth's crust and comprises 0.5% of the earth's crust.* In fact, titanium is more plentiful than copper, zinc or lead. Though the supply of raw ore is nearly limitless, it is extremely difficult and expensive to produce.* Titanium is a unique high-strength alloy that has excellent corrosion resistance, is extremely lightweight and has excellent high-temperature properties.
Titanium has been of strategic importance in the aerospace industry having been used in aircraft engines, airframes, missiles and spacecraft.* It has also been used extensively in industrial applications where strength and corrosion resistance is of utmost importance including petrochemical refining, nuclear waste storage, power generation and pollution control

Since becoming commercially available in the 1950's, worldwide production of this exotic, "space age" metal has grown to over 50 million pounds annually, and is available for many consumer products including bicycles, computer cases and motorcycle exhausts.* It is expected that as processing technologies evolve and as production capacity expands, titanium will become more economical to use.

In addition to commercially pure (CP) titanium, there exist numerous titanium alloys that are available to industry.* Titanium alloys are generally categorized as alpha, alpha-beta and beta alloys. The alpha alloys exhibit good weldability and have excellent strength characteristics and corrosion resistance due to presence of aluminum. 3Al-2.5V is an alpha-type titanium alloy used for consumer products, sports equipment and aircraft ducting.* Alpha-beta alloys contain beta-stabilizing alloying elements that result in heat treatable alloys, significantly increasing their strength. 6Al-4V is an alpha-beta alloy that has become the "workhorse" alloy in aerospace applications. This alloy offers high-strength, good weldability and fabricability. It is used for airframe components, ballistic armor, sports equipment and space vehicles.* Beta alloys can be heat-treated to very high strength levels due to the high percentage of beta-stabilizing alloying elements. These alloys are used for components such as aircraft landing gear and petrochemical production components.

Burns Stainless uses Commercially Pure, Grade-2 (CP-2) titanium for tubing bends. With a room temperature elongation of 20% at room temperature, CP-2 tubing can be bent on a mandrel bender.* CP-2 also exhibits excellent weldability and can be used for fabrication of exhaust headers in limited applications. Burns Stainless recommends CP-2 titanium for exhaust headers in applications where weight is a primary concern and where significant air-cooling is available such as for motorcycle headers.* It is also excellent for under-car exhausts.* Burns Stainless does not recommend using CP-2 titanium for turbocharger headers or where high exhaust temperatures are present.* 321 stainless steel and Inconel are better choices for these applications. The tubing specification is ASTM B338-99 - Standard Specification for Seamless and Welded Titanium and Titanium Alloy Tubes, for Condensers and Heat Exchangers.

CP and most titanium alloys can be welded using a variety of welding processes.* Burns Stainless recommends that titanium be welded using gas tungsten-arc (GTAW), also known as TIG welding. Although still prevalent today, it is not necessary to use an inert chamber or glove box when welding titanium. By following the welding procedures outlined in the header construction tips article, successful welds with titanium are possible.* As previously mentioned, proper gas shielding is essential for welding titanium.* It is important that the inert shielding atmosphere is maintained until the metal temperature cools below 800F this can be accomplished with a good post-purge.* An argon back-purge is also essential to ensure a proper weld with titanium.* Solar Flux is not recommended for welding titanium.

Weld color can be a good indication of weld quality. Proper gas shielding is evidenced by bright silver welds. Dark blue or white powdery oxide on the weld is an indication of an improper gas purge and a poor weld. The importance of surface cleanliness and the correct use of shielding gas (argon is recommended) cannot be overstated. Since molten titanium reacts readily with oxygen, nitrogen and hydrogen, exposure to these compounds during welding can adversely affect weld properties and must be minimized. Titanium cannot be welded to most other metals due to the formation of embrittling compounds that can lead to cracking.

it might be best to use a SS DP then a Ti catback IMHO