Ok I did a search and did not find quite what I needed to know.

I recently ditched the 2.8 that my 87 daily driver came with and went with a 3.4L. I only did a simple block swap. The car still has the 2.8 top end and accessories. Trying to keep it simple since its my only running car!

My muffler shop is telling me the dinky 2 1/4 exhaust with its horrible non mandrel bends & flowmaster is plenty. Well, proved them wrong: I had them install a 2.5 in. cut out before my cat. With the cut out open I gained 8.2hp and 4.3 torque on the dyno.
This proved to me the exhaust is way inadequate.

Mods to engine:
Engine swap: 1995 Camaro 3.4L V-6
SunCoast Ram Air Box
K & N Air Filter
MAF sensor screen removed
Throttle Body coolant bypass
EGR System eliminated
19lb Ford fuel injectors
Holley Adjustable Fuel Pressure Regulator
MSD Dual Connector Coil
Performance distributor cap and rotor button red with brass contacts
Distributor blueprinted
Taylor Spiro Pro 8mm Wires
AC DELCO Rapid-fire plugs
Reed Cam: TM276/282H12A2 (223/228 w/ 471/480 lift on 112 int C/L is 108)
Comp Cams timing chain set, lifters, & springs
ASP Underdrive crank pulley
Sneaky Pete NOS system
Gasket match ported & polished: Plenum, Runners, Lower intake, & heads.
PF&E 304 stainless headers & y-pipe
Car Sound 2.5 in. high capacity catalytic converter
Flowtech 2.5 in. cutout
2 ¼ in. pipe from the cat back
Flowmaster Muffler w/ dual 2 ¼ in. outlet pipes
160 degree thermostat w/ Hypertech fan switch
TransGo shift kit
Neil Racing 2800 stall converter
3.73 disc brake rear

*Planning to open up the airflow with a bigger TB, porting the heads more, and possibly extrude-honing the plenum and runners. Custom chip for tuning!

************
On to my question. Here are my possible options based on what I have learned:

The 3.4 cars came with what size exhaust from the factory 2.25, right?

I have seen people say adding a ws6 or ss take off exhaust works well. From what I have read this will give me a 2.75 exhaust. Now would that be mandrel bends? And I know it will not be a direct bolt up since I have a 3rd gen.

My other idea would be to stick with flowmaster, I know it gives a good sound for this car. Now the big question is what size pipe for this car? Do I just go with a 3in flowmaster catback for a v8 3rd gen. Or is this too big of pipe for the car with its mods?

Then the next question, what to do with the piping directly after the headers come together and b/w that and the cat? Weld in a 3in. pipe? Also what size cat... I have been told to go with a reg cat, but step it up a 1/4 in diameter in and out.

Thanks!

 

no 2.25 is not big enough IMO , a 2.75 " catback should be plenty , however that is a pretty healthy cam.. so a 3" catback might be necessary, how much power was that making with the cam and such?

 

Not near enough...I think the lack of air flow along with the exhaust restriction is a problem, along with a lack of tuning...

Dyno:
Max Horse Power = 134.1 @ rear wheels
Max Torque = 207.4 @ rear wheels

1/4 mile:
R/T: .532
60’: 2.363
330: 6.894
1/8: 10.681
MPH: 64.92
1000: 13.976
¼: 16.812
MPH: 78.46

**had nasty traction issues and the car is way heavy
***this with the tranny not shifting into its top gear @ full throttle

Shifts fine now though!