Disadvantage on 2.5inch all the way exhaust?

[TheSaint]

2.5 is too big for a "dc2" (assuming its a vtir with the usual mods....) full stop.


IF you have heavy work , or supercharged etc 2.5 is great. But the usual intake/header mods do not justify a larger than say 2.25inch system

Noted that the cat-back piping should match the outlet size of the cat itself - which should also match the collector size of the header too.

IMO if it must be a 2.5 inch , use a standard ITR muffler or similar to tighten the sound and aid throttle response both down low and mid range. Back pressure is real and is needed on smaller engines.

i on my D15b7 have ebay 4-2-1 headers, magnaflow cat and 2.5" stainless catback with one resonator and an xforce 2.5" s12 twinloop
runs great - i was a true beleiver of the whole 2.25 over 2.5 for n/a honda - but after i got that system put on the car i was like ... eh almost no difference between that and 2.25
the header collector size is still the same - it than bottlenecks OUT to the cat after a bit of piping - perhaps this is why

[dougie_504]

So do we agree that the happy medium is.....2.25"? I'd have put 2.5" on my brother's dc4 but unfortunately nobody really makes that size, only 2.5. Seems to work fine though and we can probably use it when he goes turbo. But I always thought 3" was best for F/I.

[rhys.l]

I'm not sure if you can group all 2.25 or 2.5" systems into the same boat. The piping diameter in some systems ( such as spoon?) steps down at the axle back flange (like with the stock dc2r system), and this is designed to create some back pressure (which another 'straight through' 2.25 or 2.5" system wouldn't)

[Evok]

Hey guys, great info. So im guessing i should just go for it...its just custom exhaust with custom headers. 2.5inch piping with stock cat. asking cause i got a good offer.....i mite have to mod it later cause i think its guna be too loud ...the engine has no work to it at the moment to clear things up... so should i still go for it?

[MWAKU]

lol

1. dont mod for the sake of modding it
2. lol my vote is no. whats the point, go buy a hi flow cat. comes out of headers, then gets restricted again. if its going to be too loud. dont get it, just for the sake of it, unless its something u plan on really wanting. if u can do without it, do without it. sometimes its better to just save that money even if its cheap, rather than bolting on shitty loud exhausts
3. 60mm is what most jap branded exhausts use for their piping, this would probably be the best?

[bennjamin]

Another variable is the piping design itself - whether it's mandrel bent ( same sized ID at straights and bends) or crush bent ( tapers slightly in bends).
Also most bolt on Japanese cat backs have tapered restrictions at every joint !

[GSi_PSi]

sigh, this is why the US honda scene will always be ahead of us in terms of outright power.....

everything past the headers is a restriction anyway....2.5 vs 2.25 you will be making more hp overall..
you might lose a bit of torque downlow,

[Jccck]

sigh, this is why the US honda scene will always be ahead of us in terms of outright power.....

everything past the headers is a restriction anyway....2.5 vs 2.25 you will be making more hp overall..
you might lose a bit of torque downlow,

People seem scared to try the bigger size.
Plenty will say "But that's too big i'll lose power" or "No way that'll be too loud"
Nonsense, and use a better muffler.

But you're right, alot of the USA runs with the motto "Go big or go home" for most things.. Haha

[khoannaDA9]

yo i got a non vtec b18a stock and im running 4-2-1 header and 2.5 inch all the way through. from my personal experiences so far. its loud as hell when u gun it and u can feel the power when ur at high revs. so when mine hits about 5 - 6k revs, u can feel the car pull. but thats just my 2 cents. i also did a lot of research but i just went with the 2.5. goodluck with ur choice mate.

[curtis265]

I got 2.25 on my H22 and it gives me a fair bit more midrange (untuned)
I still reckon that I probably should have got a 2.5..

I'd probably recommend the same for an integra

[TheSaint]

lol

1. dont mod for the sake of modding it
2. lol my vote is no. whats the point, go buy a hi flow cat. comes out of headers, then gets restricted again. if its going to be too loud. dont get it, just for the sake of it, unless its something u plan on really wanting. if u can do without it, do without it. sometimes its better to just save that money even if its cheap, rather than bolting on shitty loud exhausts
3. 60mm is what most jap branded exhausts use for their piping, this would probably be the best?

thats some very good advice there - listen to the man

sigh, this is why the US honda scene will always be ahead of us in terms of outright power.....

everything past the headers is a restriction anyway....2.5 vs 2.25 you will be making more hp overall..
you might lose a bit of torque downlow,

this ^^
i had the same ifs and buts when i got a lightened flywheel
lost a teeny tiny bit down low - but the car builds revs so much better/quicker and revs a hell of a lot smoother now too
so at the end of the day - piping size 2.25 to 2.5 wont really matter - but i would suggest getting something quality with no bottle necks
and make sure u get a desent cat to go with the system as well

[rhys.l]

Depends what you want out the car. If it's outright dyno power, I'm sure 2.5" (or bigger) is the way to go. However, I spend 99% of my time below 4.5k rpm so I would prefer something that is a bit more responsive around this rev range. I'd say that is where a 2.25" system or even stock (if we are talking dc2r) would have the advantage.