Exhaust help!!!

[TECDUP]

Hey guys i dont know if this is noob enough so move it if needed...
I have recently just received my JDM 5Zigen header and JDM ITR Cat fresh from jap thanks to edw-r(Max-Hondapower)...now i know the cat is shorter and will not match up to my oem catback on my vtir dc2.
My question is what would be the best to do without buying a JDM Catback as im not flush with cash atm?

Flange the 2.5' JDM Cat straight to the oem 2'(i think, correct me if im wrong) catback...my question in doing this is would it cause to much back pressure in the air flow or anything that could do damage? I am hoping that all it does is just restrict the flow a little and not allow the header and cat to put out its full performance potential, i would be able to handle that as it is only a temp instalation for a fujitsubo RM01A ......or


Should some kind of bottle neck be used on the oem catback that can move smoothly from the 2.5' Cat into 2'(again correct me if im wrong) catback???

If you have any other suggestions on how i could have it installed and also cost if it is from experience, please let me know, but any advise would be helpful
Thanks
Robert

[TECDUP]

some one must be able to help me out
bump!!!

[CUL8R]

ok from reading the post i think is the cat 2.5" where piping is 2"???
idealy would be best to have same size, but in this case it cannot be avoided so i would say try and kind of creat a smooth transition between the pipe to cat and back out to pipes again.
when theres a sharp edge, instant 2"-2.5" transition ,air behaves alot liek a liquid and will form eddies which will cause a loss in energy in the form of heat which will in tern slow the velocity of the air being pumped through. u dont want this because it is a turbulant zone.turbulance is bad coz its a restriction.

i dont know if its the time, or whether the first post is just witten badly but from what i can read is that u will be buying a cat back exhaust soon enough. just wait till u get that, go to an exhaust store with cat and exhaust and discuss what options you have because putting a cat on a stock setup will do u nothing, so dont waste the $$$ right now and try and do them both at the same time. it would be better for the hip pocket and better for the cat as u wont be welding then cutting then welding again.

like i said, i may have missed the point all together, just trying to help out with what i knew.

[Paul1985]

You do not want a bottleneck!
You are just wasting money and not getting the performance upgrades you are paying for.
I reckon you should just save up and wait until you can finish the rest of the exhaust system. Makes no sense to me adding a 2.5" cat to a stock system which is smaller, even if you have new headers. If adding a 2.5" header (if its this size?) to a smaller system, it will not be getting all the performance that it can due to bottlenecking.

bottlenecking would be when you have a 2.5" header going into a smaller system.

If you think about if, your exhaust is trying to remove 2.5" worth of emissions from the header (if using a 2.5" header + stock exhaust). It gets through the header to the exhaust where its less than 2.5" and it cant remove all the emissions as quickly. You want a free flowing exhaust, this is not free flowing..

its like this:

Header (2.5")
___________________ Exhaust (2" for example)
...............................\______________
Gases in here, cant
all fit through here ---> _____________
____________________/

Hope this helps a little, not the best diagram lol.
Search bottlenecking on google.com or howstuffworks.com for better answers. I agree with the reply above though. Just wait until you can afford the rest of the system (b-pipe + muffler). You might need a custom 2.5" pipe from the collector on the headers to the cat, im not sure, maybe not.

[Limbo]

they can flare the 2" catback to fit into the 2.5" cat. That way when you do get money you will change the catback to a better system, which i am sure you are doing anyway. You will get a slight bottleneck but it is still better than not putting the items on.