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ok, i have an n/a integra with not much power. so therefore my exhaust b-pipe should be 2.25" now, as for a header and cat, do they also have to be 2.25" at the collector or flanges also?
 

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the headers usually come either with a 2 in. OD collector in the USDM headers or 2.5 in. OD for the JDM headers.

the stock cat has a 2 in. OD.

In exhaust sizing, you can use 2 different approaches:

1. have the same diameter all the way through.

2. have the diameters increase as you move towards the back or the muffler end. Most people say with our 1.8-2.0L displacement engine size, you want to increase or step up the diameter every 2 ft in length along the exhaust system. The increase in diameter prevents the reversion or backward exhaust wave from reaching the engine.

You never want to go from a larger diameter down to a smaller diameter as you go towards the back of the car.

since you have a 2.25 exhaust and they don't make 2.25 in. header collectors, you are forced to use the second method.

I suggest using a 2.25 in. aftermarket higher flowing cat so that you step up from the 2 in. at the collector to a 2.25 in. at the cat to the exhaust. You also want to cut out that 1.8 in. OD bottleneck at the exhaust Bpipe flange that connects the Bpipe to the cat.

cheers
 

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Mike....should he then go with a step up to the exhaust...just like you said...would that mean a 2.5' exhaust from the cat back?
Since the whole system should be stepped...


tim
 

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Michael Delaney on Aug/03/02 said:
I suggest using a 2.25 in. aftermarket higher flowing cat so that you step up from the 2 in. at the collector to a 2.25 in. at the cat to the exhaust. You also want to cut out that 1.8 in. OD bottleneck at the exhaust Bpipe flange that connects the Bpipe to the cat.

cheers
MD - according to what you stated above, he will be going from 2" OD collector -> 2.25" ID cat -> 2.25" OD exhaust. going from 2.25" ID cat to 2.25" OD exhaust would actually be "stepping DOWN," wouldn't it? 2.25" OD using 16 gauge is 2.12" ID. so effectively, he will be going from 2.25" ID cat to a 2.12" ID exhaust...
 

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dragontegz on Aug/05/02 said:
MD - according to what you stated above, he will be going from 2" OD collector -> 2.25" ID cat -> 2.25" OD exhaust. going from 2.25" ID cat to 2.25" OD exhaust would actually be "stepping DOWN," wouldn't it? 2.25" OD using 16 gauge is 2.12" ID. so effectively, he will be going from 2.25" ID cat to a 2.12" ID exhaust...
where did I use the term ID anywhere?
 

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i'm only asking because i was considering a comptech exhaust (which is 2 1/4" OD) until someone told me that cats are measured ID instead of OD.
 

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Space Boy on Aug/05/02 said:
Mike....should he then go with a step up to the exhaust...just like you said...would that mean a 2.5' exhaust from the cat back?
Since the whole system should be stepped...

tim
it depends on his hp goal and powerband location. A 2.25 in. may be fine, 2 3/8 in. exhaust may be fine, or a 2.5 in. exhaust may be fine depending on his needs.
 

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Michael Delaney on Aug/05/02 said:
Quote: dragontegz on Aug/05/02 i'm only asking because i was considering a comptech exhaust (which is 2 1/4" OD) until someone told me that cats are measured ID instead of OD.

that's fine. My dimensions are based on OD only....
so if i were to go with a 2.25" ID car sound cat, you would recommend a 2 3/8" OD exhaust? (16 gauge, of course.)
 

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Mike,
I just referred my brother to Dave about 2 weeks and I recall him quoting the cat as having a 2.25" inside diameter outlet to the b-pipe.
 

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~Cut and copied from my hotmail account~

My question:

SMSP
ATTN: Dave

I am a memeber of team integra.net and am researching getting a new cat for my 1998 integra LS coupe. Current mods are AEM cai, Comptech header and Comptech exhaust.

1. For a direct bolt on (straight swap) application should I go w/ the carsound 94065? I understand its the same length as the stock cat and has all the necessary O2 bungs and flanges already welded on there if I buy it from you guys. How much for it?

2. I was reading about the exhaust bottleneck that occurs from the cat flange > the b-piping of most exhausts. Mike Delaney (tuan) says you guys sell a flange that will fix it. Assuming I buy the cat from you guys, I would need a 2.25" inside diamter inlet (to mate up to the 94065 cat) with a 2.25" outside diameter (to hook up to the comptech b-piping). How much for this flange?
**Since the inside diameter of the comptech piping is slightly smaller than that of the cat will this be problem? performance wise that is?

P.S. do you guys have a website?

Thanks for your time

TI screen name: BlueTeg



Dave's response:

OBDII 2-1/4" Cat $166, includes hardware
2" donut $12
3 bolt gasket $4

The cat will have a 2-1/4" ID outlet and your B pipe should be about 2-1/8" ID. That isn't bad as compared to say a JDM header w/ 2-1/2" cat on an ITR which has a 2-1/2" ID on thecat outlet and a 1-3/4" ID on the B pipe. I don't know if I'd loose sleep over your set up. What you could do is just try to bevel the inlet of the B pipe flange with a round file so you get rid of the sharp edge.

The web site (www.sms-products.com) isn't up yet.

David Stadulis
SMS Products
4755 Ewell Rd.
Fredericksburg, VA 22408
The Alternative - It's Time You Paid Less For Performance
 

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Since I already have a 2.25" od exhaust would a 2.25" id cat mess up my flow?? Would I be better off getting a 2" id cat to mate up with my 2" od header?? That way it would be 2od>2id>2.25od
 

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Carsound doesn't make a cat w/ 2" ID. Nor does anyother aftermarket cat company that I know of for that matter.

I would say that 2.25" ID cat would be your best bet. This will restrict exhaust flow slightly....but to get a consistent diameter all the way through you'll have to get the 2.25" ID cat and buy a new 2 3/8" exhaust system.
 

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They actually have some 2" cats on the magnaflow webpage, which is made carsound.
 

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we are trying for more flow...please get the bigger diameter cat and hook up a proper exhaust diameter (i.e not smaller than the cat diameter) to it.

This whole ID cat issue has really clouded the way you set up the system. Just remember, the goal is to size the system to provide the right area (diameter) to support enough flow velocity out to get adequate scavenging. Never size the exhaust with a smaller diameter as you proceed to the back of the car or go too large.
 
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