I currently have a 305 in my Bird. But I was thinking of swaping it for a 350. I have already put headers on my 305, which was probly a big misteak since I want to do this now, but would the headers for the 305 and the custom Y-Pipe I had made work on the 350? I'm guessing the headers could possibly work, but I don't know about the Y-Pipe.
Thanks for any info you can give me on this. Sorry, I'm sure this has been asked before though.

 

They'll work fine any they have to be better than stock manifolds anyway so don't worry about it

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-Tas
'89 Formula WS-6 made in Van Nuys, CA, U.S.A.

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

 

I was thinking more in terms of size though, such as bolt patterns, and the size of the block fitting between the headers and Y-Pipe. But, thanks for your info. I'm sure they are very close.

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1988 Firebird TBI 305 (Beast hahah, right)http://www.geocities.com/tzfbird/tzfbird.html

Mods:
Dynomax headers, Custom Y-Pipe, 13X2.5 Open Element, Sanding/Painting Wheels

 

Bolt patterns are identical. Unless you are getting some sort of maxed-out aftermarket heads, the size won't be an issue. If you have a 2-1/4" minimum downpipe on each side going to a 3" pipe to a 3" cat, you should be fine.

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82 Berlinetta, orig V-6 car, now w/86 LG4/TH700R4, 2300 stall TC. Ported World 305 heads, Crane PowerMax 2050 cam. ZZ3/4 intake, oil pump, pan & baffle. Accel HEI SuperCoil & module. Hooker 2055 headers, 3" Catco cat & 3" catback w/dual-opposite Flowmaster 80. 2.93 limited slip. Spohn SFCs waiting to be installed. 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).

 

I'm not sure what size the custom Y-Pipe is, but it is pretty damn small. I think I messed up when I went in to have it made. I failed to specify a size, so I pretty much killed myself there. Anyway, it's probably a 2-1/4. But, it comes right out of the headers, turns, and the two sides hookup, then enter the cat. It's got a lot better flow than the stock pipe I'm sure. It's 2-1/4 all the way back. Will a 350 work with that, or am I going to have to get all that redone? I will most likely be getting a cat-back sometime in the future. But I don't know about the cat. Is that going to need a change as well?

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1988 Firebird TBI 305 (Beast hahah, right)http://www.geocities.com/tzfbird/tzfbird.html

Mods:
Dynomax headers, Custom Y-Pipe, 13X2.5 Open Element, Sanding/Painting Wheels

 

2-1/4" all the way back is about one side's worth for a 350.

You'd be better off getting a minimum of 3" when both sides come together and not going any smaller until it splits again.

 

So, basicly what you are saying is that I can leave the Y-Pipe, but just put on a 3" cat and cat-back? From the point where the two sides come together and the cat, there is maybe 6 inches of 2-1/4, then it goes into the cat.

 

2-1/4" is only good for one side. After the two are joined, you want a minimum of 3". So, have the y-pipe modified so it does not have any 2-1/4" after the two sides are joined.