I was looking at the B pipe flange after I remove the cat and Comptech header to install my new JDM ITR 4-1 header and noticed the hole looked kinda small so I measured it and it measured 1-7/8", not 2.25" like the rst of the exhaust. I then proceded to remove the B pipe and I used my dreamel (SP?) to enlarge the diameter and match the B pipe diameter. The whole process took my a lil over 1 hr, not bad. I am going from a 2.5" header and cat to a 2.25" exhaust all the way to the muffler, instead of 2.5" to 1.875" to 2.25". I checked the rest of my exhaust flanges to make sure there was not another restriction and I could not find one, so i think I truly have a 2.25" exhaust now. I called Comptech to ask them why they built the exhaust that way and they said that the exhaust was menat to be used with the stock cat which is also 1-7/8". I'll buy that!. I think I might buy an adapter from SMSP soon, but that will involve cutting part for the B pipe and welding the adapter.
Has anyone else done something like this?
I have learned a lot and if I was to do it all over again, I would do a lot of things differently like NOT buying just because it is BRAND name that EVERYONE uses, but I would have my exhaust custom built or buy a SMSP exhaust for example.

 

YEp I did the same thing! I removed the flange on the b pipe soon after the Cat.
An adapter was welded in its place - a step down peice.
I also went alittle further and got the other flange removed from the rear side (where it bends towards the muffler) and also the flex joint. I made sure it was 2-1/4 all the way through. I used the mendrel bent pipe from the Comptech exhaust and had it welded onto a Magna flow street series muffler with the silencer cut out.
The work looks clean but I am alittle concerned with the Muffler intermediate piping. Although it is mandrel bent, the piping guy had to press it some more to fit exactly right without hitting the LCA. So I probably don't have a system that could flow its best.

As for the Magna flow 2-1/4 core, it sounds very similar to the Comptech Dynomax muffler. (Maybe 2 decible louder in the the car)

After spending some money on this ****, I realized a custom exhaust would have been key. Oh well!


-nick248

 

How much material do you have left between the flange and tubing? If you made this too thin you'll run the chance of it cracking. Do you have before and after pictures?

 

It's really a shame that the stock ITR exhaust is not a true 2.25" system......

 

SMSP - is that question directed to me or 1fastGSR?

 

1fastGSR

 

SMSP,
I don't have before/after pictures because I don't have a digital camera. I don't think I understand your question. The flange diameter was 1-7/8" so I used a dreamel tool to remove enough material off the flange until it was flush with the inside of the B pipe with is 2.25". I did not remove any material off the inside of the B pipe if that's waht your asking.

 

SMSP,
after reading your Q a 2nd time I think I understand your question. I have at least 3/8" between the outside edge of the flange and the inside of the pipe at the worst location. I only removed less then 0.20" all the way areound ((2.25"-1.875")/2=0.18"). I think I'll be ok, right? Soon I will buying an adpater from you anyways!

 

From what I understand the Comptech exhaust is 2-1/4" OD which makes it about 2-1/8" ID so I guess that should be around the limit that you should open that flange up unless you do it more on the inlet than near the weld line of the tubing to the flange.

Bottom line, you'll notice a difference in sound and response after you do the adapter.

 

I've got ya now! Now, I only removed enough material until I matched the inside of the pipe diameter. Darn, i did not measure the inside diamter of the Comptech pipe, but I was assuming it was 2.25"!!!!! I am discovering something new everyday!!! This sucks!