Mid pipe design and install...

[PaulMcA]

I have been thinking about getting my mid pipe bought and installed, but was wondering about design and possibly getting one built to my specs and this got me thinking.
Is there any reason why no one has manufactured a replacement mid section pipe that is a single 3-3.5" pipe design rather than the two. i.e. does away with the two branch runs and goes with just a single 3" or 3.5" design with minimal length two branch split to pair up at the DP end?

I have heard that some of the 135i cars preferred this design and have used this exhaust type setup.

Pros and Cons please?

[1911A145]

HPF have a single 3.5 inch exhaust

[vito747]

i guess it will drone a lot with no resonator

[1911A145]

Custom is also another route to go as well.

[Yellowceta]

From what I know, I believe the single branch to increase back pressure which hurts overall horsepower but will increase torque. These effects are small overall, but still effects. Maybe an x-pipe would help balance both branches, but there isn't much real estate under there. The 1M doesn't need additional low end torque. The VW GTI benefits nicely from a single pipe as an example.

[hmonay]

You only want backpressure with NA cars.

With turbo, you want the least amount of backpressure possible.

[PaulMcA]

Thanks for the info guys. Was looking at a little more technical input or from those that might have done this mod/change.
I have owned a few FI cars and fully aware that back pressure is a no-no. NA cars are certainly a bit different in their exhaust designs to create some 'pulse'.

[PaulMcA]

Originally Posted by 1911A145

Custom is also another route to go as well.

I think that is what I said in my original post. I am potentially looking at a custom design.

[robertm]

cross-sectional area:

3" pipe: 28.27 sqin
3.5" pipe: 38.48 sqin
twin 2.5": 39.27 sqin

The most volume is going to come from twin 2.5s. Berk and Maddad already make a great setup in that diameter. So why reinvent the wheel for less volume?

You can pick up a set of either used in the $300s and you won't have potential dragging issues like you will with 3.5" single. A custom single will be much more expensive and the only positive is slightly less weight. A few pounds at the lowest point on the car is going to make no difference though.

[PaulMcA]

Originally Posted by robertm

cross-sectional area:

3" pipe: 28.27 sqin
3.5" pipe: 38.48 sqin
twin 2.5": 39.27 sqin

The most volume is going to come from twin 2.5s. Berk and Maddad already make a great setup in that diameter. So why reinvent the wheel for less volume?

You can pick up a set of either used in the $300s and you won't have potential dragging issues like you will with 3.5" single. A custom single will be much more expensive and the only positive is slightly less weight. A few pounds at the lowest point on the car is going to make no difference though.

Thanks Robert... This is the kind of info I wanted Think you might be right.

[Texas F1]

I have a custom mid-pipe on my 1M. The pipes merge just downstream of the downpipes and there is also a small resonator just before the flange that connects to the cat-back exhaust. Seems to work great.

[robertm]

@Texas F1.

Wow very nice looking piece man! Welds are beautiful. Who did the work? How does it sound?

[Texas F1]

Originally Posted by robertm

@Texas F1.

Wow very nice looking piece man! Welds are beautiful. Who did the work? How does it sound?

COBB did the fabrication as part of several upgrades they did on my car while tuning the AccessPORT for various stages of hardware configurations. The exhaust system ended up with catted downpipes, this single mid-pipe, and an Eisenmann race cat-back exhaust. I like the sound--obviously more agressive than stock, but still reasonably quiet at crusing speeds.

[Em/1]

Originally Posted by robertm

cross-sectional area:

3" pipe: 28.27 sqin
3.5" pipe: 38.48 sqin
twin 2.5": 39.27 sqin

The most volume is going to come from twin 2.5s. Berk and Maddad already make a great setup in that diameter. So why reinvent the wheel for less volume?

You can pick up a set of either used in the $300s and you won't have potential dragging issues like you will with 3.5" single. A custom single will be much more expensive and the only positive is slightly less weight. A few pounds at the lowest point on the car is going to make no difference though.

Can't give you the exact numbers, but in a flow situation, single pipe will beat twin of comparable area to drag from the walls.

[Nugget]

Not a 1M but this car also has a 3.5" straight through exhaust.
http://www.1addicts.com/forums/showthread.php?t=852171

[PaulMcA]

Thanks again guys. I heard that the 135 track and race cars do prefer the single pipe. Good bits of information here. I am not doing it for any weight saving etc. Just though one big single pipe might have produced better results and sound.