325i dual exhaust to single conversion: How are people doing this?

[efficient]

thats real cool. welding is something id like to learn.

[phenryiv1]

I thought that I'd follow up to post how I got the 2-to-1 conversion completed. After running short on time, we took the pipe that had the oval-shaped end and went to an exhaust shop who basically flattened a 3" pipe and welded it to the oval-shaped outlet on the stock pipe. From there, I had them weld in a 3" to 2.5" reducer to make it easier to source parts and to route the exhaust.

Pictures:

[phenryiv1]

They should sell them in a 3 pack...

Hahaha!

[TheTacoMan]

I was going to use the same method TacoMan, but use oval 3" pipe for the subframe clearance. Crossing under using one of these http://www.spintechmufflers.com/oval...es/cat_51.html Then our Autocross venue instituted a 96db max with a 95db warning, so plans had to change.

Yea, even with a muffler this setup is extremely loud. Well over 96db at WOT

[Gary Horneck]

I was going to use the same method TacoMan, but use oval 3" pipe for the subframe clearance. Crossing under using one of these http://www.spintechmufflers.com/oval...es/cat_51.html Then our Autocross venue instituted a 96db max with a 95db warning, so plans had to change.

[TheTacoMan]

Y pipe into a full 3in.

[Gary Horneck]

Rallycross update

Are you concerned that the 2-to-1 muffler hangs so low? How does it compare to the height of the OEM system?

First Rallycross of the season this past Sunday, and the exhaust had no problems. I moved the tail section up a few inches, and used a heavy duty universal rubber, reinforced hanger. Never felt the muffler take a hit, and I was coming down on the bump stops hard. Muffler really is not lower than the lowest point on the headers, the pic I took sucked. Skid plate is the lowest point on the car, then the headers.

[Gary Horneck]

Worth trying. They are not very tough though. The only way I have found to make those HF pipe expanders work is to dismantle them first and polish the parts that make contact with the expanding cone. Then thin film of 90w gear oil. They should sell them in a 3 pack...

[DetailAddict]

I am considering a combination of the press idea, heat, and one of these to make the collected OEM pipe into a 2.5" almost-circle.

http://www.harborfreight.com/automot...der-69549.html

Thoughts?

[phenryiv1]

If I were to do it all over again, I would just put it on my press and press the outlet from 1.75" to 2.5" instead.

btw, I also put two vbands right before the Y to make things easier when we have to drop the exhaust for whatever reason.

I am considering a combination of the press idea, heat, and one of these to make the collected OEM pipe into a 2.5" almost-circle.

http://www.harborfreight.com/automot...der-69549.html

Thoughts?

[DetailAddict]

I am not very creative... so this is what i did... I picked up 2 x 1.75" 90° and cut right in the middle of the opening and weld the two pieces together to make a T. then take very careful measurements and rotate the two inlets 90° to make a Y. Last time I did this, I purchased a generic transition piece from 1.5" to 2.5" and had to cut down to 1.75" opening. If I were to do it all over again, I would just put it on my press and press the outlet from 1.75" to 2.5" instead.

btw, I also put two vbands right before the Y to make things easier when we have to drop the exhaust for whatever reason.

I have both of these to choose from as a starting point:



Now I just need to select a strategy on how to merge the 2 pipes.

[phenryiv1]

I have both of these to choose from as a starting point:



Now I just need to select a strategy on how to merge the 2 pipes.

[lcoleman]

I bought a y-pipe from a DSP competitor/forum member. Looks like it wouldn't be too hard to make, just a Magnaflow y on the stock downpipes with a homemade reducer to each inlet (think 1.5" welded to a section of 1.75" welded to a section of 2"...etc). I think this is better than beating a pipe into shape, for both flow and longevity. From there, mine goes to 2.5" all the way back. Big straight-through perf core muffler, big resonator. By big, I mean long...more surface area = quieter.

Plenty of clearance with ie3s. Borderline too loud for the street, but drone isn't what i'd call terrible. I say DO EET.

[Gary Horneck]

That ^ was plan #1. Our new site is very smooth and don't anticipate making any ground contact there. The old site... they used to kid me about my "air time".

[phenryiv1]

There is no way to get the muffler up any higher in that spot. The body of the muffler is only 1" bigger than the 2.5" pipe. My problem with Rallycross exhaust has always been breaking the mid-pipe to muffler union.

Gotcha. I was considering doing the union pipe at the OEM cat location and then putting a muffler in the OEM muffler location, just to keep things as tucked as possible in the middle of the car. I don't want my muffler to be the low point in the middle, if possible.

Still, 1" lower is not too bad...