Im cuurrently running
Mugen 4 - 2 -1 with 2.5inch outlet
some piece of crap free flowing cat
Stock B pipe
Mugen twinloop modified to fit the stock B pipe.

Having the bottleneck is mentally killing me, so I want to clear it up by.

1.Replacing the cat with a 200 cell cat.
2. Replacing the B pipe to something that flows better.

So my options are to keep the stock b pipe, and just upgrade the cat.
or to buy a new Mugen twinloop and B pipe for 800, then sell my twinloop for bout 500.
Or to get a custom B pipe for roughly 600 - 650.

So what do you guys think of the Mugen B pipe, would it be as efficient as getting a straight through 2.5inch B pipe custom made, is the mugen B pipe restrictive ?

I have read the old threads, but thought I would seek some advice.

 

Something to consider when you're looking at the Mugen Bpipe is that the section right AFTER the cat, it is something ridiculously tiny like 2.0 or maybe 2.25 (waiting for other current Mugen TL system owners to clarify)

However, most people don't seem to find it much of a restriction, but others like BigPhat R eventually opted for a custom 2.5 due to the fact that his mods outgrew the system.

And yet, there are others like B19coupe whom I believe runs the entire Mugen TL system but makes some intense numbers with his setup.

Whatever your reasoning may be from here on in, I personally would run a better cat plus a whatever 2.5 midpipe (T1-R etc) as I didn't like how the Mugen TL midpipe would drag virtually EVERYWHERE since it hangs so damn low (even on stock ride height).

 

I had the same dilemma some time ago. To make the long story short, I went with a JDM 4-1 header with the 2.5" collector, T1R test-pipe, T1R 2.5" B-pipe, and Mugen TL muffler. Its almost a full 2.5" setup from header collector all the way to the muffler. It works extremely well (my ITR is making 206whp) and is very quiet.

At the collector side, the Mugen B-pipe is just over 2.25" and progresses up to 2.5" at the muffler side. This works well and produces good torque but is not so good when you add cams, headwork, high compression, etc.. and need a free-flowing exhaust. With the complete Mugen B-pipe and muffler setup I would not break 200whp. Once I went with the T1R parts, I solved that problem.

So, my suggestion is .. keep the Mugen muffler and get a 2.5" B-pipe.

Here's a few pics of a comparison I made between an ITR OEM exhaust, Greddy EVO2, and Mugen TL. I don't have pics of my T1R on this comparison, but at least you can compare Mugen vs. OEM. Hope it helps.
First, all three side-by-side

Muffler side connection..

Header collector side..

Mugen header to b-pipe connection:

ITR OEM header to b-pipe connection:

 

i replaced my mugen b pipe with T1R b pipe which is 2.5 " diameter.. i beleive
it had bottle neck but i modified it and removed it

i didnt see that much of gain for me to notice. if you dont care .. i'd just leave it.

i did it cuz i'm building up my motor.. n/a

 

Wow, some great replys.

I wonder why the mugen is designed the way it is, it just doesn't seem like the best way of getting high flow.

 

Mugen designed to give the exhaust a velocity or turbulent flow. It is pretty well designed. Proved from dyno and flow charts. It was designed like that for a reason.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by typer_696 &raquo;</TD></TR><TR><TD CLASS="quote">Mugen designed to give the exhaust a velocity or turbulent flow. It is pretty well designed. Proved from dyno and flow charts. It was designed like that for a reason.</TD></TR></TABLE>

so do you think it will effect the flow of the system if i have full 2.5 " instead of whatever it was. 2.25~2.5? whatever it was?
it was pretty skinny in some spots

 

600-650 for a custom b pipe? seems a bit steep to me. I have one made by a local shop and it only cost about 100(no resonators, 2.5", I would recommend atleast 1 small resonator or else youll get the buzzzzzz ricer effect).

get a better cat, custom b pipe and call it a day.