Ok. I have the L03 engine, stock, to give you a starting point. I know what you are all going to say. Why don't you just get headers? My answer to that is that i want my engine to look like a stock motor. But I still need to free up my exauset some. I was curious about putting on some 5.0 or 5.7(even better?) TPI manifolds with the Y pipe. I'm going to get a new cat soon, so i will do it all at the same time. Will used ones be ok, or are new ones cheap? How bad will the installation be? Will they bolt right up and look like the ones on there now? Any insight or info anyone can give me on this will be great.

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1989 Firebird Formula L03
Stock except for K&N, Flowmaster, Centerforce Clutch, MSD 8.5, and Accel Cap and Rotor.
87k on the clock and running smooth.

 

BTTT

 

Look through the archives on this....it was discussed awhile back that the TPI manifolds had a different casting number than the TBI ones. Not sure if there was much/if any performance increase. And unless you are on a tight budget it may not be worth the time/money necessary for the swap.

If you are bent on keeping a "stock" look, more power to ya. But in my opinion, outside of rebuilding the engine itself, headers are one of the best improvents you can make.

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92 Camaro RS, LO3, 5-spd, T-tops

Performance:
K&N Open Air Filter, Edelbrock performer TBI intake, Fastchip Prom, Timing +4 degrees, Centerforce clutch, Xact 8mm wires, SLP 1 3/4" Headers (coated), Flowmaster Catback Exhaust, Z28 Grille w/aftmkt fog lamps, MacEwen white-face guages
Electronics:
Alpine 8030 Alarm System, Valentine One Radar Detector (How did I ever drive without one?), Pioneer DEH 7450 Head Unit w/6-pack CD changer, Pioneer DEQ 7600 Sound Processor, 2 Kenwood KAC-846 Amps powering 2 12" Pro Red subs, 2 Pioneer 6x9 and 2 MTX 4x6 speakers.
NEXT UP: TBI mods, 3.42 gears w/Torsen posi

 

The dual cat 305 TPI and 350 TPI exhaust manifolds are the best, but that is subjective. I really doubt you would gain much from them. The big gains is in the y-pipe and exhaust itself. The stock y-pipe joins together at almost a 90º angle, killing power as air doesnt flow very well that way. No those exhaust manifolds will not bolt up to your stock y-pipe. Nothing will. If you're going to do this swap, get a better y-pipe to go with it, one that have both pipes joining together parallel to each other. For that you'll need it custom built.

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1991 Camaro Z28
5.7L 5-Speed (originally 305)
13.23 @ 107.62 MPH
Southern California
Member: SoCal 3rd Gen F-Bodies
Webmaster: SoCal F-Bodies
-=ICON Motorsports=-

 

I have a set of 350 TPI exhaust manifolds for sale if you want them for your "stock" looking motor. They are from my '89 L98 IROC. I threw the stock y-pipe away! It was the ugliest piece of exhaust piping I'd ever seen.........if I were GM I'd be embarrased for having put that on a 'performance' car!

Just email me if interested......

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Phil87IROC
Blue '87 IROC, 383 Crate Motor, KB pistons, AFR 190 heads, ZZ-9 cam, Edelbrock RPM intake, Hooker SC/LT headers, Edelbrock 750 cfm Carb (#1411), stock T-5, GM 3.42 rear w/Auburn posi.
Ohio Valley Dragstrip Trophy Bracket WINNER - 8.39 ET on a 1.82 sec. - 60'. Best MPH = 84.44. Still Tuning Carb!
Red '89 IROC L98, TES, 700R4, T-Tops, K&Ns w/open air boxes, 160 T-stat, Hyper Chip, gutted MAF & CAT, Jacobs Ign., 53kv coil, MSD wires.