2.5" outlet on headers mated with 2.25" catback on b16?

[djt]

Would this be bad in anyways in terms of performance? Reason i ask is my mate is selling 2.5" headers and another mate is selling a 2.25" catback for an ek4.

Thanks

[dougie_504]

Not a good idea IMO. You don't want to bottle-neck your exhaust (IE go from larger to smaller). Always want a consistent or increasing ID.

Some people say you can put whatever size exhaust on whatever engine because there is no evidence of back-pressure issues, but IMO I still think the best size for a N/A D16 is 2" or 2.25" max. Most D and B series engines run a 2" header outlet anyway, as long as the cat and cat-back is the same size or a little bigger.


So if I were you I'd consider the 2.25" catback but not the header. Consider a 2" header (Ebay, seriously) and match that to a 2.25" high-flow cat converter, then put on the 2.25" catback.

[djt]

ok, thanks mate. Guess gotta look for new headers

[shepparton]

i have tried put the stock civic gli exhaust (2" size?? ) on 2.5" header and i can felt the performance was really bad.
To be honest my eg h22 got spanked by stupid kia because of that lol

[u mad?]

2.5 collector with 2.25 catback should be fine.

[dougie_504]

i have tried put the stock civic gli exhaust (2" size?? ) on 2.5" header and i can felt the performance was really bad.
To be honest my eg h22 got spanked by stupid kia because of that lol

GLi (and all D's I think) are about 1.75" standard lol. Total crapola. 2" is great for D's.

[lil_foy]

Not a good idea IMO. You don't want to bottle-neck your exhaust (IE go from larger to smaller). Always want a consistent or increasing ID.

Some people say you can put whatever size exhaust on whatever engine because there is no evidence of back-pressure issues, but IMO I still think the best size for a N/A D16 is 2" or 2.25" max. Most D and B series engines run a 2" header outlet anyway, as long as the cat and cat-back is the same size or a little bigger.


So if I were you I'd consider the 2.25" catback but not the header. Consider a 2" header (Ebay, seriously) and match that to a 2.25" high-flow cat converter, then put on the 2.25" catback.

You know a jdm dc2r runs a 2.5" collector to a 2.25inch~ catback right?
And 90% of good jdm headers are 2.5" collector.

OP, it will be fine, your cat will act as a taper to the catback.

[dougie_504]

You know a jdm dc2r runs a 2.5" collector to a 2.25inch~ catback right?
And 90% of good jdm headers are 2.5" collector.

OP, it will be fine, your cat will act as a taper to the catback.


So why do people upgrade their cat-back then? Because they want to lose power? lol


We're talking about a B16, not a B18CR.

[lil_foy]

So why do people upgrade their cat-back then? Because they want to lose power? lol


We're talking about a B16, not a B18CR.

Well aftermarket jdm systems are generally 60mm (2.36inches) so theres still a taper down.
Fyi I run a 2.5" collector into a 60mm system and my b16 feels good, chrips 3rd gear easy enough.
Headers are where alot of power is made, and a cat will be a long enough tapering surface to smooth the flow to 2.25".

[dougie_504]

Well aftermarket jdm systems are generally 60mm (2.36inches) so theres still a taper down.
Fyi I run a 2.5" collector into a 60mm system and my b16 feels good, chrips 3rd gear easy enough.
Headers are where alot of power is made, and a cat will be a long enough tapering surface to smooth the flow to 2.25".

You're not telling me anything I don't already know mate, this is just a matter of opinions and preferences. I have a jdm catback, I know 60mm is a common size etc etc.

But IMO going 2.5" down to 2.25" isnt ideal if you making your own setup. If it were me I'd want a 2.5" cat as that the most restrictive point in the exhaust, so why not taper after the cat rather than with it? If you're buying you own components just make it simple - equal or progressively larger ID.


And I seriously doubt your 2.5" header, cat and cat-back are making so much power in your b16 that it chirps into 3rd. Most likely it's to do with your front suspension setup + tyres.

I have a full head build with I/H/E on my b16a running healthy comp of 215/210/215/220 and I dont chirp 3rd at 9,000rpm. Toyo R1R 195/50/15. Bilstein coilovers 8kg front.


If its a cheap header sure go for it, but for me I'd be going same size or getting larger towards the back to prevent bottlenecking.

[mocchi]

i agry re:tire aspect.

4-1 header good for b16a right? so buy it here
http://www.ozhonda.com/forum/showthread.php?157106-4-1-SS-header-for-B18C-B16A-2.5-quot-collector


http://www.ozhonda.com/forum/customavatars/avatar28865_10.gif

[lil_foy]

You're not telling me anything I don't already know mate, this is just a matter of opinions and preferences. I have a jdm catback, I know 60mm is a common size etc etc.

But IMO going 2.5" down to 2.25" isnt ideal if you making your own setup. If it were me I'd want a 2.5" cat as that the most restrictive point in the exhaust, so why not taper after the cat rather than with it? If you're buying you own components just make it simple - equal or progressively larger ID.


And I seriously doubt your 2.5" header, cat and cat-back are making so much power in your b16 that it chirps into 3rd. Most likely it's to do with your front suspension setup + tyres.

I have a full head build with I/H/E on my b16a running healthy comp of 215/210/215/220 and I dont chirp 3rd at 9,000rpm. Toyo R1R 195/50/15. Bilstein coilovers 8kg front.


If its a cheap header sure go for it, but for me I'd be going same size or getting larger towards the back to prevent bottlenecking.

Where do I or OP say anything about having a 2.25" cat?
I personally run a 2.5" cat with a 60mm flange on the catback side, zero problems with it. If it was that detrimental to keep a consistant ID then im sure more jdm companies would, no?

B16a2+tb,im,headers,cat,exhaust running 205 50 15 rsr + mfactory coils(16/12) (in low 900kg eg), keeping in mind that this was on track (I barely drive the car on the street) so the tyres were well and truely up to temp, I do run a fair bit of camber for track though but its hardly huge. But hey what would I know, right?

[senna]

The smaller diameter isn't as much of an issue if you have the reduction further back in the system - as the exhaust gasses get further away from the motor they are getting cooler and as a result require less space - so if the axle back is smaller than the header merge its no real issue, however if the cat flange is smaller up against the header flange it will be less than ideal...

BTW lil_foy, you're probably chirping 3rd because of your 16kg springs, not much give there

[djt]

So is it ok to go through with it or still no good?

[senna]

Sure you can do it, but you may not get the maximum potential out of the headers...

[djt]

ok, great, aslong as i dont lose power lol. Thanks peoples ;)

[honda4444]

i run stock dc2r headers to dc2r mid pid pipe with a high flow cat and a 2.25 axel back with a mugen twin loop muffler quiet as all hell now but sounds crisp in vtec i run this in my ek4 b16a2.

[mugen_ctr]

Can anyone back up the claims of using smaller diameter from the header backward has any real performance downers or woahs vs 2.5 all the way? Dyno read outs with back to back testing and real world results would b nice :D

Keen on real proof... as ive only really seen ppl do back to back test on turbo cars with exhaust sizes an not N/a boys ;)

[CRXDEL501]

proof? no proof needed.
common sense. why go from 2.5 to 2.25.
cmon guise

[GSi_PSi]

Lol at B16 chirping 3rds as a way of determining performance.
It's more to do with tire pressure , tyre grip and your clutch type .
On my stock b16a delsol with worn tyres and heavy duty clutch I could chirp 3rds all day everyday lol z
Heck my gsi b18b2 used to chirp 3rd and that thing was a turtle