Exhaust tubing diameters - 3.0i vs 4.4i vs 4.6is vs 4.8is
 

So I have a 4.6is and I put an x-pipe on today. Sounds great but I want just a little more rumble. I'm thinking about putting on a pair 4.8is mufflers. It's a different part number with different looking cans. Does anyone know if this is a direct swap (bolt on with same hangers)?

I have read about it being 63mm tubing on the 4.8is. Not sure about the 4.6is. The 2.25 inch magnaflow fit baggy around the stock pipes on my car. 2.5 inches converted to mm = 63.5. So either the x-pipe came 2.5 inches or the pipes on the 4.6is are smaller. Doesn't make sense.

I've looked under both cars and they look exactly the same to me. Any knowledge is appreciated!

IIRC, 3.0i and 4.4i both have 2.25" stock diameter piping.
Would also be interested in 4.6is and 4.8is info on this subject!

If it helps,I can confirm that the 4.8is has 2.5" O/S diametre pipe going to rear silencers,as I fitted them on my 3.0 D ,which only has 2.0".

So breakdown as follows:
3.0d - 2.0"
3.0i - 2.25"
4.4i - 2.25"
4.6is - 2.5"?
4.8is - 2.5"
Could someone confirm all the #s

OP I've seen several people run 2.5" xpipe on their 4.6is and no fitment issues whasoever. I'm going to take a wild guess that stock catback piping on 4.6is is same in diameter as on 4.8is which is 2.5".

What's interesting is the piping between the cats and the center resonator (for the V8s). As it turns out, the 4.4's from '00 to '03 had a 50mm (2 inch) downpipe on both sides. The 4.4's from '04 to '06 (N62 facelift) had 55mm downpipes (2 1/8 inch). The 4.6is interestingly had a 55mm downpipe on the driver side and 50mm on the passenger side! The 4.8is had 60mm (2 1/4 inch) downpipes, hence the throatier sound.

From the resonator back, it seems that 3.0, 4.4, and 4.6's all had the same diameter pipes (55mm I think). The 4.8is had 60mm pipes to the rear mufflers, again, hence the throatier sound. As an example, Supersprint makes one part number for the 3.0, 4.4, and 4,6is mufflers. They make a different part number for the 4.8is mufflers with bigger pipes. Eisenmann makes the same part number for 3.0 and 4.4 but different for 4.6is.

So the question is, if I were to find a cheap set of mufflers from a 4.8is, would they bolt onto my 4.6is resonator flanges? Or are the flanges on the 4.8is exhaust bigger than on my 4.6is resonator?

Well can anyone answer this longstanding question regarding the install of 4.8 mufflers on a 4.6?

4.8 mufflers won't bolt onto a 4.6. The flanges are different and "clocked" differently. Others habe done it, but it requires cutting off the flanges and adapting.