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[Jim K]

For both 2.8 and 3liter na engines Bell gives 2.5" OD. Thats what I have on mine with two free-flow mufflers; no noise and no backpressure. If you're interested in headers, primaries 42mm OD, secondaries 52-55mm OD with the CSC lengths being correct for all around street/trackday use.
Jim K.

[Mats]

When I get home I will take a look and post some pictures. If Jim says a 2.5" pipe will fit then it will. However, it must be difficult, because I have three different Milano exhaust systems at home and all have 2.0" pipes that barely fit.

Greg

At least call me a liar to my face will you.

[Greg Gordon]

Mats I am not calling you a liar. I have no doubts you got a 2.5" pipe in there. I would just like to see it.

Greg

[Micke]

If I recall right the Q4 has 2.25" OE size. So, this must be enough for 232 hp.

[Mats]

Mats I am not calling you a liar. I have no doubts you got a 2.5" pipe in there. I would just like to see it.

Greg

Actually, I said 3".

Found some old scans, before digital cams...
Not very good but they show what you want.

[Greg Gordon]

Thanks Mats, that looks really good. I am going to try and shove a similar setup into a car soon. I didn't think it would fit.

Greg

[Mats]

It does. With a low car you will have some interference with the nut on the AR-bar but that is basically only when going over speedbumps and such excursions.
Keep the pipe close to the body and you need some stiff mounting points to keep it in check. It will give you some noise through the bodywork but I guess we're talking about a car that won't be used to go to the grocery store?

[Jim K]

I had the car up on the lift today and checked around the rear part of the 2.5" exhaust pipe. There is definitely room for a 3" pipe, no problem, without crushing at all. With a lowered car, both 2.5 and 3"pipes will be too low somewhere in front of the gearbox but a separate flat and wide section with conical ends (with the same area as the pipe) should take care of that. As Mats says, a somewhat rigid mounting arrangement is necessary to prevent the system from banging around.
Jim K.

[Mats]

Like this you mean?

2" pipe sliced along it's lenght and sheet metal added to keep the cross section equal to a 3" round pipe.

[Jim K]

Yes, something like that but with longer tapered sections before and after.
Jim K.

[Mats]

Never pleased, are you..?

[Flame]

One more photo of a 3" pipe over the de-dion on my gtv turbo, it fits whitout cuting and it dosent make contact whit body or caliper.

[killaz]

Whats the point of 3' pipe when car is n/a and has less than 300 hp? I was reading some articles related to build up of exhaust system and it clearly says that gases are cooled down enough just after 1,5 meters where you can switch to 2,5' pipe. And still, that would be enough for up to 300 hp.

Have a friend in Sweden that drives Saab with 3' piping, but his car is turbo and makes 400 hp / 500Nm.

[Mats]

Where did you get the impression that we were talking about N/A cars?

[Bruce]

... possibly by the O.P.