Exhaust Flow Dilema

[JohnnyJohnJohn]

Hey OH!,

Well I've got abit of a dilema thats doing my head in, I've tried searching around abit but can't get an exact answer. Ok so I have an EH9 Civic Sedan with a dead stock D16A8, when I first bought the car it was a total wreck, one of the problems was a rusted and blown exhaust system.

So I got the exhaust fixed, so from the Headers -> Cat is basically dead stock, unreplaced piping and what not, but from the cat back was replaced with a 50mm(2") exhaust system with a 2" tip. Keep in mind that the stock pipe diameter is smaller, not exactly sure 1.5"? 1.65"?

Exhaust Layout:

| D16A8 |---Stock Headers--->| |---Stock Cat--->| |---Stock Pipe--->| * |---2" Pipe--->| |---New Hotdog Muffler--->| |---2" Pipe--->| |---New Rear Muffler--->| | 2" Tip |

*Stock & New pipe welded together

Picture of the bit which im having problems with:


Ok so the problem is I didn't know at the time (Stupid me) that the pipe right after the cat and right before the 2" pipe was not replaced but just welded together, I was quoted $50-$70 by the guy at the exhaust shop to get that actual pipe replaced with the flange to the cat and brackets welded on, but he said there won't be any difference interms of performance so theres no point. Which confuses me and now seeking some others opinions.

Does it really make a difference? is this pipe bottlenecking the system? what are the cons of this setup? keep in mind that the car is an Auto and a daily beater, aimed for quietness as to it being an auto but with abit of extra performance. Planning on getting N*Power headers in the long run, will keeping the stock cat and the pipe hinder this upgrade? Due to the fact that the car basically has crap all for torque anything under 3000-4000rpm.

Any info and comments is greatly appreciated,
Thanks!

[dougie_504]

Since it gets larger towards the back, and not the other way around, there shouldn't be any bottlenecking. It's a pain that it's less than 2" though - 2" is perfect for 1.6L D-series for a bit more pep, and also quiet.

N*Power header is a good buy, and I would recommend getting a high-flow cat (100cel) and making all of the piping 2" to match

[Lukey]

getting headers without upgrade the cat and any existing stock exhaust pipe is wastefull.

[mooshie]

You got nothing to worry about there. listen to the exhaust shop guy, it would be a waste of money.

Change it when you upgrade the header and cat.

[JohnnyJohnJohn]

thanks for the advice, I had a hunch this was the answer I was gonna get which is good. I guess ill save up for a new cat, but regarding the hi flow cat, it would obviously need to be 2" inlet/outlet correct? and the lower the cel the better the flow? if so any recommendations on which to get or are the ones on ebay perfectly fine?

[bennjamin]

getting headers without upgrade the cat and any existing stock exhaust pipe is wastefull.

Majority of any gains or change of powerband , are
Found in replacing the header itself. With economy cars such as ANY d series - replacing just the cat and cat back will result in loss of power everywhere except perhaps peak and result in a farty noise. Replacing just the header with a known proven item will scavenge more torque and give the car more pep. Best to replace the header and get a cat and cat back to match the headers collector size. 2 inch maxxxx. Get a magnaflow 2 inch cat
From eBay - us sellers will send it cheap too

[JohnnyJohnJohn]

Majority of any gains or change of powerband , are
Found in replacing the header itself. With economy cars such as ANY d series - replacing just the cat and cat back will result in loss of power everywhere except perhaps peak and result in a farty noise. Replacing just the header with a known proven item will scavenge more torque and give the car more pep. Best to replace the header and get a cat and cat back to match the headers collector size. 2 inch maxxxx. Get a magnaflow 2 inch cat
From eBay - us sellers will send it cheap too

yea i plan to get the N*Power headers for the D16 as so many ppl say they are great especially for the price, next will be a 2" cat but once the funds come rolling in that is. Just want the car to be a great cruiser for those drives here and there as theres no point for me modding an auto D series lol. when you say just replacing the cat back will result in a farty noise... I was seriously gonna ask why my exhaust sounds like a cannon or so type muffler with a massive silencer in it lol its driving me nuts sounds so bad! I was hoping replacing the pipe would prevent this but now i know why lol, so when you say replacing the headers and cat would that make it sound stock with no air farty noise? or would it be worse?

p.s. any chance anyone knows what the size of the N*Power headers are? aren't they 2" althroughout?

[bennjamin]

the noise is created by the cat-back or muffler. Larger size , different material , less resonators ( mid mufflers ) etc all add to this. This farty noise is basically the exhaust pulse filling the extra void and its you loosing power. A summary is a nice header and high flow cat will make more power / feel than a larger cat-back and muffler.

[GSi_PSi]

should of started with headers first , then do the cat and catback. something to think about for next time
lot less messy too

[JohnnyJohnJohn]

the noise is created by the cat-back or muffler. Larger size , different material , less resonators ( mid mufflers ) etc all add to this. This farty noise is basically the exhaust pulse filling the extra void and its you loosing power. A summary is a nice header and high flow cat will make more power / feel than a larger cat-back and muffler.

Sounds spot on there mate! Will definitely keep this in mind!

should of started with headers first , then do the cat and catback. something to think about for next time
lot less messy too

I wish I did but I had no choice as I couldn't drive the car with a blown exhaust, if I could I would of upgraded I/H/E all in one go, but short in cash thats the cons of being a uni student it's like being on the doll but your parents are proud.....