99GT: mufflers or cat-back?
 

My brother just pulled up in a 99GT auto w/ the anniversary package. Its is an sweet car and it only has 900 miles on it (damn I am jelous).
Anyway, I removed the air silencer for him and sent him over to the speed shop to grab a K&N, but I have a question about the exhaust.
He wants to have the rumble that my Stang had (2 chamber Flows and O/R X-pipe), so his first step is the catback. The factory catback seems pretty decent, so should we just weld in a set of new mufflers or is it wise to go w/ a new catback. I can't see that there is more then a couple HP in a mandral bent catback, so i think the money that would be spent on that could go to the H-pipe instead. What have you guys/girls done?
Ohh yeah, if he wants an H-pipe we are going to go w/ 2chamber Flows, but if he decides on a X-pipe, we were thinking of Dynomax Ultra flow SS welded. Does anyone have these and how do they sound? Thanks.

the factory h-pipe is 2 1/4" while a bbk or etc. is 2 1/2". bigger = better flow. You can weld in a set of flowmasters but then if you go with an h or x pipe the system will go from 2 1/2" back to 2 1/4" which can be a little restrictive. Best is to change tail pipes and all. I have the bassanni x with cats and 2 1/2" flowmasters(2 chamber) and 2 1/2" tailpipes. The car thunders threw the gears. plus it has a nice rumble at idle. My neighbor has a 00 gt with stock exhaust and there is a big big difference in the sound. He is going with the same setup next month. I dont recommend getting headers since they only net 2-5 hp plus they are a PAIN IN THE A$$ to install. the factory ones are aok! IMHO. If you have the cash, go with the steeda pullies and timing adjuster too!!!!!!!!!!!!!!!!!!Awsome power adder!

Joe

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01' Black GT
2 chamber Flows Mach 460, Leather 17"thrust wheels, bassanni x-pipe with cats, BBK Cold Air, Steeda pullies and timing adjuster @ 13*, Steeda Satin Shift Knob
Tri-ax shifter A pillar Double gauge pod, Auto meter White Phantom Gauges Fuel Pressure and Vac, Richmond 3:73's
Steeda Subframe Connectors.Strut Tower Brace
13.41 @ 102.1mph

Do not waste your money on a catback system unless you want a different exhaust sound. Gains will be minimal. Go for the x- or h-pipe with or without cats for performance. Otherwise, just weld in new mufflers. Also, you mentioned that you removed the air silencer or boot. I've read that this actually caused a loss or 1-2 hp in the 99' & up stangs. The 99-01s breathe pretty well except for cats so I would go with the x- or h-pipe.

Offroad H with flowmasters welded in sounds just like the old 5.0's. The gains from changing the whole cat back would be practically non existant. Maybe 1 HP, not a good buy in my book.

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00 GT, MAC Offroad H, Steeda Pulleys & Timing Adjuster, 4.10’s, Flows w/turndowns, UPR shifter, UPR Pro Series LCA’s, Lakewood 70/30’s & 50/50’s, 253.8 RWHP/292.8RWTQ
12.91@101.93 (1.74 60ft)
M/M 100, 7085
2001 Mod Motor Shootout 2V NA Champion
Recent Pic from Moroso