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Exhaust Systems
For some unknown or uncertain reasons, Chrysler made some pretty restrictive exhaust systems in their FWD models. The Dynasty isn't an exception.
Fair sized gains can be obtained by using larger diameter pipes- within reason, higher flow mufflers, and highflow cats. Its also been found that getting rid of that resonator in the middle of the system in place of a consistant shaped one is also worth trying for minor gains.
As a very important side note: The 02 sensors in these cars went before the cat and if the flow is too good, then the 02 will read more air in the exhaust gases, and thus your computer will not use the correct amount of fuel (as the 02 is used to tune the engine!). I do not know if aftermarket 02 sensors are a fix for this or not. So before you go greater then 3", and/or lose the muffler & cat, consider this. One idea may be to get an A/F gauge and basically get used to seeing what the 02 reads with a stock exhaust. If the o2 reads the same with the new exhaust, then your fine.
2.5 or 3" is a good diameter size for these engines, and as far as exhaust systems go, just about anything would be better then the stock ones. All in all, gutting the cat and runing a pipe through it generally helps as well (but is illegal). Exhaust cut outs are also helpful, but can be illegal depending on where they are placed and where you live. And GUTTING the cat is illegal if you plan on using your car on the road. If you stay off road with your car, you should be fine with that aspect of the emission law. Some insist that cats can not hurt performance. I've seen it go both ways.
Mufflers are always a topic for argument. I personally like a muffler which gives the car a good sound. Fart pipes on ricers just don't sound right to me, nor does the sound of the car with an open exhaust with no pipes, cat, or muffler, as that can sound pretty bad on some cars.
In terms of pipe material, stainless is good in staying rust free, as does some of the more expensive chrome pipes. But if you figure you'll be replacing pipes every so often anyways, then its really up to what you want (or don't want) to pay.
Also, if you really wanted a project, you could install a cutout which opens up the exhaust system a ton for WOT. As WOT is when the PCM ignores the O2 sensor, and thus you don't need to worry about the backpressure making the O2 values incorrect/off.
If you will be using your 3.3 or 3.0 Dynasty for a boost application, we know that from harv's supercharged lebaron- the OEM and sometimes even the 2.5" pipes will literally get blown apart from a boosted 3.x. You really want to be at 3" for boost applications, or a true dual 2.5"
My exhaust system is all 3", highflow 3" cat, followed by a 55" long 3" diameter glasspack muffler welded to the cat, from there I have a pipe mendral bent to take the exhaust outlet to right before the rear driver's tire. It sounds at idle like THIS.
An other thing to bare in mind with FWD Mopars is that if you open the exhaust up too much, you will actually find a decrease in performance *unless* you also upgrade the intake system (and I do NOT mean merely throwing a cone airfilter on the engine).
I.e. if you plan on doing a 3" exhaust on a 3.3 I would also suggest the 58mm throttle body, a cold air intake (using a cone airfilter) and a ported TB neck on your manifold.