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Retired Mod
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Discussion Starter · #1 ·
This thread assumes you want to put an aftermarket header and 2.25" catback exhaust on your 7th gen D17 motor. This is the same for LX, EX, and you poor DX owners as well. This thread also assumes you bought an EX header. The last two things this thread assumes is that you want performance gains from your exhaust - not just extra noise - and you need to pass emissions.

First off, the 7th gen catalytic convertor is not the problem, it's the pre-cat pipe that is the issue. With an EX, you can get a header, you can get a catback exhaust, but the problem is still that pipe. It is a double-walled pipe. It looks like a 2.25" pipe, but actually has a 1.70" pipe hiding inside it. I'm not sure what the post-cat pipe on the LX looks like because I've never played with one.

Here are three shots of the Honda padded bra. The first shot is looking down the inlet, where the two bolt flange was that mates up to the header (I cut mine off). This starts at 53mm ID,aka 2.08", and then quickly tapers down to the doublewalled soda straw pipe you see in the second shot. The ID of that second pipe is 43mm, aka 1.70". You can see the cat element in the third picture and this double-walled pipe runs almost all the way up to the header flange. This pipe either needs to go away and a new piece welded in it's place, or just get a completely new cat/downpipe combo fabbed up.








Pretty restrictive. Bottom line is that unless you get rid of the stock EX downpipe, your 2-1/4" catback exhaust isn't going to do jack for you. The ass of the cat is also a problem. These are a couple shots of the stock exit flange on the EX catalytic converter. Because not only is there a 1.70" pipe in the pre-cat tubing, but the exit flange on the ass of the cat also shrinks back down to 47mm, aka 1.85".





Now I would recommend getting a new piece custom fabbed up. spending about $75 on a Magnaflow high-flow cat from Summit, a couple O2 sensor bungs, a 2.25" 3-bolt flange, a 2-bolt -1/4" flange, a 4-foot length of 2.25" tubing and 180-degree mandrel bend and have an exhaust shop make you a new downpipe. This way you will actually get gains from a header and catback on a 7th gen.

Take this list and let your fingers do the walking from two different stores:

Here's the P/Ns for all the stuff from Summit (www.summitracing.com)

Magnaflow cat: MPE-53005CA $67
2.25", 2-bolt flange: WLK-31885 $5
2.25" straight, 4-foot length: SUM-640022 $12

We're at $84 plus shipping right now.

Then head over to Mandrel Bending Solutions Ebay store (Click this), buy these items:

1 piece of 2-1/4" U-bend pipe - $12
1 three-bolt 2-1/4" flange - $4.25
1 two-bolt and 1 three-bolt gasket - $6 ($3/each)
1 oxygen sensor bung for your post cat sensor -$4
1 L-shaped hanger - $1.76

That's $33 plus shipping from Mandrel Bend Solutions. The whole new, truly 2-1/4" downpipe and real high-flow cat has just cost you $120 plus shipping for the parts. You will reuse those spring bolts already on your car.

Now, either weld this stuff up yourself, or take your new EX header, catback system, and box of exhaust parts to the nearest non-chain muffler shop. Point to the box of parts and then point to the car and say, "I want all this stuff on my car, and I want all the stuff that's currently on my car put in these boxes. I'll be back in two hours, here's $150." Buying the parts and having them welded up, while it may not be cheaper, will definitely eliminate the stock soda straw exhaust restriction, get you some gains from the exhaust, and still be 50-state legal for emissions.
 

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The Almighty
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nice read clint! too bad i already have 2.25 from front to back!!!
 

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The Almighty
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you guys should see the lx size is, its fucking tiny, i think its like 1.5 or 1.75" its waaaaay too small
 

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Wouldn't it be cheaper if I buy the Magnaflow high flow cat and ask them to fabricate the downpipe itself, instead of buying all those parts? I am thinking of upgrading my exhaust since I only got an axel-back (HKS). Also, I was thinking of buying ebay brand catback just for the midpipe/resonator and discarding the axel-back part and attaching my HKS on it. Would that be a better route instead of asking the muffler shop to custom make me an entire set up? Only reason why I wouldn't go through with the ebay route is because of the quality/sound it'll have when it's on, even though I got an HKS.
 

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The Almighty
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it cost me about 400 to have custom 2.25 from front to back at an exhuast shop, with high flow cat and high flow resonator, so u tell me
 

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Wouldn't it be cheaper if I buy the Magnaflow high flow cat and ask them to fabricate the downpipe itself, instead of buying all those parts?
That's exactly what Clint was talking about. You're not having them fab an entire exhaust setup, just the pre-cat piping.
 

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Retired Mod
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Discussion Starter · #10 ·
OK, yes you can buy the main components (cat, muffler, and resonator) and ask the exhaust monkeys to connect everything to the header with 2.25" mandrel bent piping. I live in England, and my exhaust monkeys are a lot dumber than US exhaust monkeys, so this thread assumes the worst - you buy everything you need, and since you can't weld, you take it to someone who can.

There are obviously an infinite number of ways to connect metal tubing to the front of your engine and make your car fart exhaust out of the rear, however you want to make that happen is up to you. The point of this thread is to say that you must do something about the stock catalytic tubing if you want any gains out an exhaust setup.

3" ftmfw! For real, I didn't even know what stock exhaust size was/looks like, lol.
No kidding man. I sent my stock catback down the road about a month ago and it looked sooo small!

you guys should see the lx size is, its fucking tiny, i think its like 1.5 or 1.75" its waaaaay too small
LOL - I gave my old Nopi N1 catback to Scott (guy who helped me yesterday) last month and he brought his ES1 over with it on there and I forgot how freaking giant that exhaust tip was. Fucking 4" monstrosity. Never again.

That's exactly what Clint was talking about. You're not having them fab an entire exhaust setup, just the pre-cat piping.
Woot! Thanks Jake!

Muchos grats for the compliments everyone else. Hope this thread helps folks in their decisions.
 

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K-Series Specialist
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you listed one o2 sensor bung for after the cat. does the cat already have a o2 sensor bung for the primary? also if you don't want a cat would you need to order 2 orders of "2.25" straight, 4-foot length: SUM-640022 $12" and a extra o2 bung?
 

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Good write up.:tup:

Just too bad the gains would be minimum......
 

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Discussion Starter · #13 ·
No James, the header already has the bung for the primary O2 sensor.

Yeah Matt, gains will still be minimal, but they will be actual gains vice just noise from bolting up exhaust and a header to the stock cat setup.
 

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good stuff i didn't know it was double walled. for the ex guys you could just pick up a random tech hi flow cat. and just bolt it on. ...more money of course. or ditch the cat and run a HP long tube race header. and yes you will feel the gain from that.
 

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i just bought a DC header and i measured the exit of the header. The ID is 2".

So how does it work. How do u bolt on a 2.25" pipe onto a 2" header outlet?:shrug:
 

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Retired Mod
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Discussion Starter · #20 ·
The donut gasket that goes on the the header takes up the space.
 
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