I was sitting here the other day wondering ...

Do I really need to spend the money for headers, or would a 3 inch Y-pipe from the headers to the cat do the same effect?

I plan on getting that plus High-flow 3in IN/OUT Cat, 3 inch intermediate pipe, and some type of dynomax, borla or flowmaster muffler. Do I really need to spend the 300+ for headers??? Will they make that much of a difference?

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1988 Firebird Formula 305 TBI, T-Tops, RED.
Of course ... 5-Speed

 

You can improve the overall flow by opening up the stock manifolds and doing the piping behind like you suggest. But, you'll still fall short of what the exhaust can do for performance with headers.

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R4, 2200 stall TC. Ported World 305 heads, Crane PowerMax cam. ZZ4 intake, oil pump, pan & baffle. Accel HEI SuperCoil & module. Hooker 2055 headers, 3" Catco cat & 3" catback w/dual-opposite Flowmaster. 2.93 limited slip, Spohn SFCs. AMSOIL syn lubes bumper-to-bumper. Daily year-round driver. Best ET, speed TBD...
57 Bel Air, my 1st car. '66 396, 9.7:1 forged TRWs, Weiand Action+, Holley 750VS w/4150 conversion, GK 270 cam, Magnum rockers, Jacobs Omnipack, 1-3/4" Hedders & 3" Warlocks, TH400 w/TCI Sat Night Special conv & Trans-Scat shift kit, MegaShifter, 3.08 8.2" 10-bolt w/Powertrax, AMSOIL syn lubes bumper-to-bumper. Idles smooth @ 700 RPM in D. Best 15.02/95.06 @ 5800' Bandimere (corrected 13.93/102.4 @ sea level).

 

will a muffler make a difference?

you seem to think so, so does everyone else, yes headers will make a difference; if you can't afford it, then save up.

 

headers make the most differance in the exaust system

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-Tas
'89 Formula WS-6

305, TBI, 700R4, P.A.W. 14x3 open element with K&N, Milodon 160* thermo, functional Formula hood, cross-flow Flowmaster, '99z28 rear pipes and tips, Hooker 1-5/8" 50 state legal headers, Dynomax 3" I pipe (PN 44063 and 43248)
Super GRK_Taz World
F-Body Dual Exaust
EFI & Intake Options