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

[phenryiv1]

I am on the final steps of my 325e to 325i conversion for rally cross and I am looking to do something with the exhaust. I have components from several stock "i" exhaust systems (down pipes and all of the pipes between the cat and the muffler) around from past builds/partouts, but I really want to save the weight versus the heavy OEM setup.

I don't need a cat and don't need the actual "muffling" functionother than to cut out the pure obnoxiousness of straight pipes- the car is not street-driven.

I am on stock manifolds and have the stock downpipes from the "e" still on the car, but would rather switch to the "i" downpipes for the increased diameter.

I have read conflicting reports on the stock diameter of the dual pipes- 1 3/4" and 1 7/8" come up with just about equal frequency.

I would like to do a dual-to-single conversion, which I see on here all of the time, but I never see what people are using for a merge/collector pipe.

I looked on Vibrant's website, on eBay, on Columbia River Mandrel Beinding, etc. I see NOTHING that converts 1 3/4" or 1 7/8" to a single 2.5" pipe.

So what are people using for the single-to-dual conversion?

[ak-]

You shape/manipulate your single pipe to take shape and form of the first collector near the downpipes and weld.

edit: or maybe it was the second collector?

Squint your eyes, but here is an example:

[Northern]

ebay headers + a Y pipe? they're both pretty cheap.

[phenryiv1]

ebay headers + a Y pipe? they're both pretty cheap.

I just dropped over $1000 on safety gear. I am pretty tapped out right now and the season starts in 4 weeks, so I need to get a move on.

I did not see any "y" pipes for the e30 on ebay. I was looking for collector/merge pipes for the appropriate size(s) and came up empty. If you have a link I'd appreciate it.

[Gary Horneck]

This is what I did for my Rallycar. Just finished the system this weekend. I used eBay stuff and ended up with a nice light system for just over $100.

Stainless Steel Performance Muffler Magflow 2258 PP2258-1 - $40 It has dual 2" inlets and a 2.5" outlet. Installed right after the bend on the mid-pipes.



then 2 1/2" Exhaust Flex Pipe 2.5" x 4 Heavy Duty Steel 4"OL -$18



2 - MANDREL BEND 45 DEGREE 2.5 inch ALUMINIZED STEEL 16ga - $9.95 each (they kick it past the lower subframe).



Glasspack resinator Muffler Glass Pack straight 2 1/2" in & out 3518115 / 621825 - $17.64



Then a 8" long tailpipe with a turndown on the end.

Hung the system with these - Exhaust hangers universal w/ gromments 5 pack HA7542-5 $13.75



Some connectors from your local parts store... a slip fit at the mid-pipes, then weld it all together.

[phenryiv1]

This is what I did for my Rallycar. Just finished the system this weekend. I used eBay stuff and ended up with a nice light system for just over $100.

Stainless Steel Performance Muffler Magflow 2258 PP2258-1 - $40 It has dual 2" inlets and a 2.5" outlet. Installed right after the bend on the mid-pipes.



then 2 1/2" Exhaust Flex Pipe 2.5" x 4 Heavy Duty Steel 4"OL -$18



2 - MANDREL BEND 45 DEGREE 2.5 inch ALUMINIZED STEEL 16ga - $9.95 each (they kick it past the lower subframe).



Glasspack resinator Muffler Glass Pack straight 2 1/2" in & out 3518115 / 621825 - $17.64



Then a 8" long tailpipe with a turndown on the end.

Hung the system with these - Exhaust hangers universal w/ gromments 5 pack HA7542-5 $13.75



Some connectors from your local parts store... a slip fit at the mid-pipes, then weld it all together.

I can't weld, but paying a welder to do it should not run too much.

The mangaflow is listed with dual 2" inlets- was that an issue with the 1 7/8" or 1 3/4 OEM piping?

I really appreciate this thurough post!

[Gary Horneck]

Well... I could not weld either. Still can't. But a Harbor Freight 90 amp welder for $89, and some old pipes to learn on, and 3 hours later I had an exhaust system. The welds are not pretty, but functional. Still came in under $200 for everything including welder. I used a 2" exhaust pipe connector off the mid-pipe, the inside diameter was just a loose fit, but welded up fine. And, it sounds great. Not too loud till it gets to 4k, then the perfect wail.

[phenryiv1]

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

[phenryiv1]

In case someone else has the same questions, I did find this as an option for a merge/collector pipe.

2" duals to 2.5" but if a dual 2" muffler works, so would a dual 2" "Y" adapter.

http://www.amazon.com/Magnaflow-10748-Stainless-Exhaust-Y-Pipe/dp/B000CC9C3W

[Gary Horneck]

There is no way to get the muffler up any higher in that spot. Its up higher than my skidplate, so should be good. 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.

[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...

[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".

[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.

[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.

[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.