ForesterES said:
First off...My plan is to do intake and exhaust, and eventually a header, but not much more than that.
My question, though, is...What is the inside diameter of the stock 2.0L exhaust pipe, and is the stock pipe mandrel bent?
I'm asking because I'm trying to decide if a full cat-back exhaust is worth the money over an axle-back. I've seen some under-car pics of the stock cat pipe mating with an aftermarket cat-back and they look almost the same size. If the stock pipe is 60mm and mandrel bent, then there's really no point in a cat-back for my planned mods is there?
Thanks!!
Your plans sound similar to what I've done. In order of completion, I did the AEM SRI, Magnaflow cat-back, and OBX header. Unfortunately, I wasn't able to dyno after each step, so everything has been based off of the extremely accurate 'butt-dyno' system. (thumb)
The intake alone was on my car nearly 2 years before I added the exhaust. I don't know if I noticed any improvement, but at least it gives you the illusion (however brief) of having a turbo. (first) If you don't know what I'm talking about, when you shut off the engine, you can hear the air leaving the intake in a nice 'whooooosh' sound. (hah) Yeah, I know, but beggers can't be choosers.
After adding the magnaflow nearly a year ago (chosen because of the nice deep tone), I did notice a bit of gain on acceleration, most notably around 3k and up, but it wasn't excessive. The diameter of the magnaflow is 2.25", and is mandrel bent IIRC.
However, after adding the OBX header in August, I definitely noticed an improvement, and not just above 3k. From the normally sluggish 2200-3k rpm, I could tell that there was a definite gain, and above 3500 rpm, it pulls very nicely.
If you do the combo of the three, I think you will be happy. I can't give feedback on whether the same gain would be noticed with the intake, header and stock exhaust, but I don't think it would be as noticeable as with an aftermarket one. btw, I have kept the second cat as well as the resonator. Unless you want your car to sound like a sewing machine on wheels, don't take out these two items; I've heard a P5 with the same setup as mine without the 2nd cat and resonator, and it sounds horrid, IMHO.
I believe the inside diameter of the stock exhaust is 2", but I don't know if the piping is mandrel bent. Perhaps someone else could chime in on this.
Hope this helps!
