I have a 2004 Chevy impala 3.4L. I am looking to buy a flowmaster 40series muffler. From my understanding, I need the offset/ center muffler and the 2.25 size. Would that muffler fit my car without any major modifications? I can weld and I can purchase clamps if needed. Willing to also use 40 series delta flow.
Per Flowmaster’s own fitment checker (on the link you provided) it doesn’t list your car... so, no it doesn’t fit.
If the question is “can I make it fit?” Then yes - of course you can! BUT if you fit a muffler that isn’t designed for your vehicle, you could adversely affect the performance of the motor, so I don’t recommend that. Unless you understand all the data related to mufflers and how they impact motor performance that is. If you understand this well, then you’ll be able to tell if the muffler will work or not.
The easiest solution is to find a muffler that is spec’d to fit your vehicle. Per Flowmaster, they don’t make one. The don’t even have kits for the 2004 Impala at all.