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Driveline, Engine & DME Tuning
Talk about driveline improvements, NA tuning and DME tuning your E46 BMW here. This includes diffs, intakes, exhausts, chips, software and OBD tuning.

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Old 08-10-2012, 08:13 AM   #1
jared_wiesner
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Building a custom performance exhaust.

Well, the time is nearing when I'm going to have to put an exhaust on my car. The old exhaust has been patched a few times now and is starting to crack at other welds. I also need to have cats on my car in the next few months to pass emissions testing. I will be welding up cats after my headers but I don't want to weld them to my old exhaust and then have to do it again when the old exhaust breaks and its time for a new exhaust. I may as well get it all out of the way at once.

I know that aggie and a few others have messed around with custom exhaust and soon I'm going to try my hand at it. First, I wanted to get some opinions from the experience around here.

I'm currently toying with the idea of going dual 2.25 or 2.5. (depending on what I think will be the best compromise of flow vs velocity) The exhaust will be cats to xpipe and then straight pipes to a dual in dual out magnaflow 11385 or something at the back. This would basically copy the AFE exhaust that has supposedly made 13whp around 4000 RPM but I'd also add an x-pipe to the beginning to lessen volume and rasp and maybe help scavenging. The other option is to follow aggie and go with a single 3inch pipe. The problem with this is I would have to fit two cats ahead of the merge, my car has little ground clearance with an H&R race suspension and finally I don't know If I think a single 3 inch will make the most power on these cars.

I know aggie made a bit more than the magnaflow catback exhaust with his 3inch, but from the reading I've done, the magnaflow catback has a major bottle neck at the muffler because its two in one out (The outlet is a single out into a y tip). I think the 2.25 dual will keep velocity up compared to a 3inch. What do you all think?
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Old 08-10-2012, 09:02 AM   #2
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You don't want to put 2 cats ahead of the merge. The merge needs to be as close to the header flanges as possible. Burns actually wanted to weld the merge closer to my headers, but that just wasn't an option at the time.

You can possibly get away with a single 3 inch cat right after the merge.

Buy my Y-pipe
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Old 08-10-2012, 09:11 AM   #3
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Here's what I would do if I HAD to have a cat and I wanted a killer exhaust.

I'd build this same exhaust using the Burns pipe, but I'd use a high flow cat right after the bend. I would put a small muffler in place of the resonator that I have in place. I would also continue to run the Innovate LC-1 so that the car would allow me to run a very high flowing cat further downstream.

FYI, I was running H&R Race springs, too. Only on occasion did I scrape, the exhaust could be tucked up a bit more than mine was. Wouldn't have had a problem.

Also, if you decide to go 3-inch, PM me. I'll link you to a solution for the center hanger. I never had one because the exhaust is so light, but if you add in a larger resonator and cat, it might be a good idea.

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Old 08-10-2012, 09:21 AM   #4
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Hmm, until next year, my province tests at the tail pipe with a sniffer for emissions, so running a single 3 inch cat would not likely work.
I think the idea behind placing the merge close the headers is to put the hottest gas possible through the merge. Wouldn't a cat behind the headers would have the hottest gas coming out of it?
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Old 08-10-2012, 10:47 AM   #5
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Hmm, until next year, my province tests at the tail pipe with a sniffer for emissions, so running a single 3 inch cat would not likely work.I think the idea behind placing the merge close the headers is to put the hottest gas possible through the merge. Wouldn't a cat behind the headers would have the hottest gas coming out of it?
I don't see why that would be an issue.
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Old 08-10-2012, 11:06 AM   #6
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I don't think a higher flow 3 inch cat would clean up the exhaust nearly as much as 2 cats do. I seem to recall reading a thread somewhere at one point where it was pretty much stated that a single cat can never do the work of 2.

Edit* also, keep In mind that I have roughly 200 cc less displacement than a 330, this means that the importance of velocity weighs even more heavily (albeit by a slight amount) compared to a 330. (The 330 is pushing more through which naturally raises velocity)

I also just don't get why we aren't seeing companies, like AFE, coming out with a 3 inch exhaust if that was the way to make the most
power.

Oh, and don't take this as me dismissing you guys. I genuinely want to dig into this and try and get everyone talking to see what will work best. Just trying to flare up the debate to hopefully get some good ideas coming.
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Old 08-10-2012, 11:25 AM   #7
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A single 3 inch would clean just fine. Heck my buddy's 300zx passes emissions with NO cats.

The velocity only has to be kept up through the merge. Anything after that is just candy.

FYI, the old HKS exhaust merged to a single, and then split to the end. It's all about sound. The single doesn't sound like what the average "enthusiast" wants on the car. It's just the characteristic of our I6. Dual exhaust helps with the rasp.

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Originally Posted by jared_wiesner View Post
I don't think a higher flow 3 inch cat would clean up the exhaust nearly as much as 2 cats do. I seem to recall reading a thread somewhere at one point where it was pretty much stated that a single cat can never do the work of 2.

Edit* also, keep In mind that I have roughly 200 cc less displacement than a 330, this means that the importance of velocity weighs even more heavily (albeit by a slight amount) compared to a 330. (The 330 is pushing more through which naturally raises velocity)

I also just don't get why we aren't seeing companies, like AFE, coming out with a 3 inch exhaust if that was the way to make the most power.
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Old 08-10-2012, 11:47 AM   #8
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A single 3 inch would clean just fine. Heck my buddy's 300zx passes emissions with NO cats.

The velocity only has to be kept up through the merge. Anything after that is just candy.

FYI, the old HKS exhaust merged to a single, and then split to the end. It's all about sound. The single doesn't sound like what the average "enthusiast" wants on the car. It's just the characteristic of our I6. Dual exhaust helps with the rasp.
Good to know, that does make me more torn about what I want to do. Noise does still factor in for me to some degree. The car does still function as a daily driver and routinely is used for 6-7 hour road trips. I had a friend who used to have a Subaru WRX with a 3 inch pipe, that thing was loud as hell and was not pleasant to drive in for an extended period of time... not that I may not be persuaded to take the plunge
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Old 08-10-2012, 11:49 AM   #9
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You just need to make sure you use good muffling. Cat will help, too.

Buy my Y-pipe.

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Good to know, that does make me more torn about what I want to do. Noise does still factor in for me to some degree. The car does still function as a daily driver and routinely is used for 6-7 hour road trips. I had a friend who used to have a Subaru WRX with a 3 inch pipe, that thing was loud as hell and was not pleasant to drive in for an extended period of time... not that I may not be persuaded to take the plunge
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Old 08-10-2012, 12:11 PM   #10
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Buy the Y pipe.
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Old 08-10-2012, 12:22 PM   #11
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Hmm, just listened to some 3 inch examples on YouTube of the m3, really like it, sounds really racey. It would cut a lot of my cost in half as well.
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Old 08-10-2012, 12:52 PM   #12
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And be lighter.
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Old 08-10-2012, 01:16 PM   #13
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Looking through Aggies NA thread again, it seems like he wasn't all that happy with the 3 inch and the burns has yet to be tested. He lost torque down low. I'm just not thinking this has been all that proven as an application yet. I'm also thinking that the pipe size into the merge is what will dictate power output. If that is the case, wouldn't staying with dual 2.25 be risk free and avoid the possibility of losing power through the merger. Man this is the most confused I've been on a decision yet.
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Old 08-10-2012, 01:42 PM   #14
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tuning becomes pretty important when changing the exhaust setup. you won't really feel the low-end torque loss, if you get the right software.


my opinion is also shared by aggie and iceman- a single, 3" exhaust is the best option for true performance and light weight on this platform. why do you need a cat? i don't think canada does tail-pipe sniffers, do they?

what you want (what i am also wanting) is a burns 3" merge (like the one aggie is selling).

then, have a muffler shop make a 3" mandrel bent mid-pipe, along with a high flow resonator or muffler mid-section. then, a high-flow muffler or resonator rear section. for me, i'd want twin pipes, just so it didn't look SO custom. it's not really a bottle neck, if it's a reputable muffler (burns makes AWESOME mufflers, too).

good luck. i may be in your shoes soon. i'm absolutely SICK of my stock exhaust note with catless headers. drives me nuts anytime i floor my car.
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Old 08-10-2012, 01:42 PM   #15
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PM'd Brady, I feel better about the idea after he offered his input. Bought the Burns piece. We'll see.

Thanks for the encouragement bryce
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Old 08-10-2012, 03:04 PM   #16
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Looking through Aggies NA thread again, it seems like he wasn't all that happy with the 3 inch and the burns has yet to be tested. He lost torque down low. I'm just not thinking this has been all that proven as an application yet. I'm also thinking that the pipe size into the merge is what will dictate power output. If that is the case, wouldn't staying with dual 2.25 be risk free and avoid the possibility of losing power through the merger. Man this is the most confused I've been on a decision yet.
Eeehhh, yes and no. Brady's issue is that he didn't have a proper merge collector, and it caused a major pressure drop and as a result, stagnate exhaust gasses. That's why he was experiencing low end power loss, you want to merger to promote scavaging from the exhaust.
You're not doing yourself any favors by running 60mm pipes, as the piping after the merger is insignificant. The worst that can happen is the exhaust doesn't flow enough and becomes a bottleneck.

Quote:
Originally Posted by bryce-o View Post
tuning becomes pretty important when changing the exhaust setup. you won't really feel the low-end torque loss, if you get the right software.


my opinion is also shared by aggie and iceman- a single, 3" exhaust is the best option for true performance and light weight on this platform. why do you need a cat? i don't think canada does tail-pipe sniffers, do they?

what you want (what i am also wanting) is a burns 3" merge (like the one aggie is selling).

then, have a muffler shop make a 3" mandrel bent mid-pipe, along with a high flow resonator or muffler mid-section. then, a high-flow muffler or resonator rear section. for me, i'd want twin pipes, just so it didn't look SO custom. it's not really a bottle neck, if it's a reputable muffler (burns makes AWESOME mufflers, too).

good luck. i may be in your shoes soon. i'm absolutely SICK of my stock exhaust note with catless headers. drives me nuts anytime i floor my car.
You honestly probably won't need a tune (but I would get one, as higher flow could lead to a change in the A/F ratio...potentially) but as I mentioned to Aggie, the biggest changes should be in power under the curve, not just peak.

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Old 08-10-2012, 03:30 PM   #17
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Eeehhh, yes and no. Brady's issue is that he didn't have a proper merge collector, and it caused a major pressure drop and as a result, stagnate exhaust gasses. That's why he was experiencing low end power loss, you want to merger to promote scavaging from the exhaust.
You're not doing yourself any favors by running 60mm pipes, as the piping after the merger is insignificant. The worst that can happen is the exhaust doesn't flow enough and becomes a bottleneck.



You honestly probably won't need a tune (but I would get one, as higher flow could lead to a change in the A/F ratio...potentially) but as I mentioned to Aggie, the biggest changes should be in power under the curve, not just peak.
Great stuff, really makes me happy I went this route.

I'm not too worried about my tune, we'll see on Tuesday, but It feels great, I don't imagine this could throw it off that much.
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Old 08-10-2012, 04:12 PM   #18
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You honestly probably won't need a tune (but I would get one, as higher flow could lead to a change in the A/F ratio...potentially) but as I mentioned to Aggie, the biggest changes should be in power under the curve, not just peak.
well, judging from how my other bmw's responded to exhaust work (not deleting the cats, those were gone on day 2 of ownership lol), i would always get re-tuned or adjust the settings on the tune (if you have a laptop and are comfortable adding/subtracting fuel and adjusting ignition set points).

my 335i needed a lot more fuel in the low-end to compensate for the higher flowing exhaust. this was post-catless downpipes and retune by the way.

my e46 has needed special tuning to get the most gains from the headers. i expect similar tuning once i settle on an exhaust to use.
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Old 08-10-2012, 04:14 PM   #19
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Great stuff, really makes me happy I went this route.

I'm not too worried about my tune, we'll see on Tuesday, but It feels great, I don't imagine this could throw it off that much.
two options:


-maximize gains from a free-flowing exhaust

-not have your tune "thrown off too much"



it's your car, do as you please (of course). me, i am getting re-tuned once i find an exhaust solution.
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Old 08-10-2012, 04:31 PM   #20
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Well I can always have the tune updated, but Given I'm just having the tune files sent to me from epic tunes, I'd have to see if they would really do anything different with the exhaust, I'm sure they would if they could dyno tune it, but worth asking anyway.
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