Thread: Downpipes..... CONFUSED !!!!

Ok, so now that all you have helped me with my whole exhaust and intake stuff, I have some questions about Downpipes and testpipes. Ive been looking at Megan Racing Downpipes and I noticed that the GSX pipe is 3" inlet and 3" outlet, but the GST pipe is 2.5" inlet and 3" outlet; why is that ? Is there going to be a performance difference between the two ? So this might sound like a newb question, but does the down pipe connect to the exhaust manifold or something else? And if so, how big is the outlet on whatever it connects to? Does inlet size of the downpipe matter? I think im very confused. haha. I hope someone can catch on to what im tryin to ask. :? Dont get mad at me, my previous car was a honda. :(

Made sense for the most part. So why is the GSX downpipe 3" ?? Is the stock GSX o2 3" ?? As far as Megan Racing goes, have you guys heard much about their parts ? Are athey any good ? Also, if im not gonna use a cat, do i jus have Marco Muffler do 3" from the downpipe to muffler, or do i need to get a test pipe, or r they the same thing ? Thanks again for all the help.

No the o2 housing is identical between the GSX/GST. I would have guessed the inlet/outlets of MR's downpipes were also identical regardless of model. I hear they've done some redesigning, but my MR downpipe necked down to something like 2.75" inlet & outlet.

Material and welds look good, but I am not happy about my MR downpipe. Fitment stinks on my car; I'm going to have to pull it off and redo it.

In addition to what boostedAWD said, if you don't get a tubular o2 housing with a wider outlet and wider bolt spacing, getting the downpipe bolted to the stock o2 housing is a pain in the a$$.

As far as the test pipe, most downpipes have them built in--it's just a pipe where the cat would be. As I'm sure you're aware, this is a big no-no for emissions.

So then it would be a good thing that the GST MR pipe is 2.5" inlet with a 3" outlet correct? Cuz then it will bolt directly up, or at least it sounds that easy. The o2 is 2.5" right ? As far as emissions, im fully aware that this is a BIG no-no. :twisted: So if i get the MR downpipe, i wont need to buy a testpipe or hi-flow cat? I like the sound of that. Have any of you had ur o2 ported ? If so, where is a good place to get it done? I appreciate all this feedback. I am quite a newb to the whole turbo scene. So yeah, Thanks again. pCe

I'm pretty sure the outlet for the o2 housing is smaller than 2.5 inches. If I had to guess, I'd say that it's closer to 2.

I really don't know if the GST MR downpipe is any easier to bolt up to the stock o2 housing. The problem is the 2 studs on the stock o2 housing are so close together that there is no room between the downpipe and the nuts to get a socket on and tighten them up. Again, the GSX MR downpipe necks down to about 2.75" so it may still be close with the GST pipe.

As far as the test pipe goes, think about it this way:

Stock exhaust = Stock downpipe -> cat -> catback exhaust

If you were to just get a test pipe it would be:

Stock downpipe -> test pipe -> catback exhaust

Most DSM aftermarket downpipes (including the MR) replace the entire stock downpipe and cat section:

Aftermarket downpipe -> catback exhaust

No need or place for a test pipe here. If you want a high flow cat in this situation, you will need to get the downpipe modified to accept it. And guess what the leftover part of the downpipe could become.

Time to spend some time at vfaq.com. :)

So if the stock o2 is 2.25", no matter what DP i get, itll be a hassle cuz they r all 2.5"+?? Hmmmm, what to do what to do...

Here's a link to a discussion about the Megan downpipe:
http://dsmtuners.com/forums/showthread.php?t=129317

I have the downpipe on my car right now and have no complaints...hopefully it'll stay that way for a long, long time.