The Y-pipe IS NOT 2.5" It is only 2.5" where it mates up to the intermediate pipe, but the individual branches are a smaller diameter and will fit up inside a GT H-pipe (which IS 2.5".)
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2005 Windveil Blue V-6, Manual Trans, GT Dual exhaust and mufflers, FRPP X-pipe, JBA shorty headers, CA Spec X-Charger 3.0 pulley, XXtuning tune, throttle body coolant bypass, 180 F thermostat, Moss Mustang Oil Cooler, GT 18" Fanblades, SSI Ducktail Spoiler, CDC chin spoiler, FRPP strut tower brace, FRPP lowering springs, FRPP struts and shocks, GT front and rear sway bars, Stewart Warner boost gauge in Roush vent pod. 275 rwhp, 294 rwtq.
Was thinking of getting my Exhaust custom so was just wondering what the size was.
For starting mods Stars.Fade get a C&L CAI and DiabloSport Predator Tuner, you won't be disappointed. C&L is basically top of the line CAI for 2005+ mustangs and Diablo is a really good company with awesome tunes that are easy to install IMO.
All the piping under my car is 2.5" and its stock so I dont know what to tell you.
If you look at your Y-pipe you will see that where they joined the two branches together to the exit the piping is smaller than the exit itself. The GT H-pipe is the same size throughout.
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2005 Windveil Blue V-6, Manual Trans, GT Dual exhaust and mufflers, FRPP X-pipe, JBA shorty headers, CA Spec X-Charger 3.0 pulley, XXtuning tune, throttle body coolant bypass, 180 F thermostat, Moss Mustang Oil Cooler, GT 18" Fanblades, SSI Ducktail Spoiler, CDC chin spoiler, FRPP strut tower brace, FRPP lowering springs, FRPP struts and shocks, GT front and rear sway bars, Stewart Warner boost gauge in Roush vent pod. 275 rwhp, 294 rwtq.
Piping Question 
Why?
