I just got a flowmaster 3 inch cat back as well as a twin cat Y pipe, and the exhaust manifolds from a 1989 350 TPI motor. I am wondering: 1) how much better is this Y pipe than the stock LG4 one? and 2)Do these manifolds flow any more than the LG4 manifolds? Thanks in advance.

 

Okay you may not want to hear this, but removing your manifolds is half the work of putting headers on, so why not?

I believe the dual cat setup was worth about 10 horsepower on an L98, I would be surprised if you saw that much of a gain if your LG4 is stock(or is it a 383 now?). If the manifolds are different, Im sure they will flow better since they were put on a larger motor. Im not sure if they are different, though. Congrats on the exhaust, Im sure you will enjoy it.

 

I'd go with headers too, but if you've never done get some help. As for the y-pipe, I just had one made at a local muffler shop. Do you have a pic or part number for the flowmaster y-pipe? I would like to see it. I didn't know anyone made them for duel cat systems. My car has two cats and it flys. There is no way I would ever go with one cat.

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91 Z28 1LE 5.7 automatic
SLP headers, random technology cats, borla muffler, Accel 8.8 wires, Hotchkis STB

boycott Sam Pierce Chevrolet

 

The outlets on the 350 exhaust manifolds are slightly bigger, but they are still restrictive enough that its not worth swapping, unless you are in some racing or showcar category that requires stock manifolds.

The dual cat y-pipe is definitely better, as the junction is more parallel after the cats, rather than almost a right angle before the cat. Also, 4 cylinders flowing thru 2 pipes is better than 8 cylinders thru one pipe.



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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=-

 

Will L98 manifolds work on that LG4? What about the A/C bracket location, Alternator, or belt setup? Will either of those screw up the manifolds fit?

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Hugger Orange '91 L98 Z