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      03-18-2013, 05:24 PM   #1
philjw
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Advice please: New gears or new headers?

I know that there's a ton of info about these mods on this forum and others, and I've been trying to wade through it all. I am trying to figure out what makes more sense for a $2-3k investment for my '07 Z4M Coupe, which will see primarily street duty with perhaps a track day here or there. Also don't have the time or tools to do my own work, so have to factor labor into the equation...

Seems like headers are usually recommended as the go-to performance upgrade, but my car needs to pass OBDII readiness emissions tests, and I would need to have customer work done to relocate sensors or buy euro cats, and likely also need a tune, not to mention that some still seem to have issues? I like the idea of headers, as it would enhance the sound of the car as well, but seems like this could get very pricey and complicated, no?

Or, I've seen several happy endorsements for swapping out the rear diff for 4.10 gears? I don't care about the slight reduction in top speed or reduced mpg. Seems like an excellent idea for the $$$ from all I've read, but not sure why almost no one's done this but everyone here seems to be running non-stock headers?

Any input welcome! Thanks

Edit: Also would like thoughts about tunes (ESS/Evolve/Etc) with stock headers as not many seem to have gone that route. Worthwhile? Running AFE intake and SS Powerloop mufflers, otherwise stock.
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      03-18-2013, 06:14 PM   #2
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I've got both 4.10 gears and headers. The gears are definitely the way to go. Much more noticeable difference, because of the torque.

The big win with headers is the additional noise you get along with power, lots more growl and pops. The headache with headers is definitely smog issues. Although if you can pull off the relocate (or just buy euro section 1), you should be able to pass smog no problem. No tune necessary with the relocate or euro section 1.

BTW, I think the reason most people go with headers is that you can easily find a used set and then DIY install.
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      03-18-2013, 06:23 PM   #3
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Gears is where you want to go. That has been my plan for a very long time. Always something else come to divert my mod funds.

Beta passed smog with Euro headers and cat with flying colors. The best option is go with Euro cat. Less headache with O2/EGT relocation. The problem is finding one for sale. You are looking at 2k for headers and cat used plus $600 or so for installation. Any tune is not worth it if you are running stock headers.
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      03-18-2013, 06:57 PM   #4
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Quote:
Originally Posted by RobMCoupe View Post
Gears is where you want to go. That has been my plan for a very long time. Always something else come to divert my mod funds.

Beta passed smog with Euro headers and cat with flying colors. The best option is go with Euro cat. Less headache with O2/EGT relocation. The problem is finding one for sale. You are looking at 2k for headers and cat used plus $600 or so for installation. Any tune is not worth it if you are running stock headers.
Looks like DKF is getting closer to happening.
That will be my choice over cutting up the OE piece or finding that rare Euro section 1
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      03-18-2013, 07:17 PM   #5
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Quote:
Originally Posted by inTgr8r View Post
Looks like DKF is getting closer to happening.
That will be my choice over cutting up the OE piece or finding that rare Euro section 1
Forgot about DKF. Good point. The only thing I worry about is visual inspection. OP have concerns about passing smog.
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      03-18-2013, 07:21 PM   #6
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We get the sniff test here but dont have to worry about visual inspection ..
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      03-18-2013, 07:42 PM   #7
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Thanks for all the feedback. So far confirming my intuition that gears are my best bet if I'm going to choose between the two... Really excited about what this could do for acceleration and fun around town. Maybe headers could be next year's project?

For the headers and cats, not sure about the DKF option as I seem to recall the smog guys checking under the car with a mirror before hooking up the OBDII test last time I was there. Similar worries for any custom solution, and I also have concerns that the show would screw up and leave me with a useless section 1. Good to know that I wouldn't need the tune with the euro cats, but this just seems like so much money for what it is, no? Maybe this is a dumb question, but if I installed something like the Fabspeed headers here (VAC Website), could a tune trick the computer into not throwing a CEL and also returning a "readiness" state for all sensors? Can't seem to find the answer to that one.... Maybe I'm just missing something?
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      03-18-2013, 08:33 PM   #8
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Quote:
Originally Posted by philjw View Post
Maybe this is a dumb question, but if I installed something like the Fabspeed headers here (VAC Website), could a tune trick the computer into not throwing a CEL and also returning a "readiness" state for all sensors? Can't seem to find the answer to that one.... Maybe I'm just missing something?
Not a dumb question, this is often debated. As far as I can see, it's a definite maybe. Some seem to have no issues with the tune fixing the CEL. Others seem to have issues. For me, I'm still on the fence. I'm leaning toward the Euro cats just to be safe (look for Donovan on this forum as the source for euro cats - he has two now, by my count). But, I know I need to buy a tune either way for maximum benefit from the headers, so it seems worthwhile to try the tune first. I don't have smog tests down here, so I have one less concern.

I'm also trying to determine if the numbers justify the Fabspeed, AA or $uper$print headers over the euro. But maybe you solved my problem and ill just go for gears first
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      03-18-2013, 08:36 PM   #9
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Quote:
Originally Posted by inTgr8r View Post
Looks like DKF is getting closer to happening.
That will be my choice over cutting up the OE piece or finding that rare Euro section 1
Won't that only be for bypass, though? I was looking at this as a solution, but I need cats since I drive around topless all the time.
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      03-18-2013, 08:56 PM   #10
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Quote:
Originally Posted by GriffBrew View Post
Won't that only be for bypass, though? I was looking at this as a solution, but I need cats since I drive around topless all the time.
No...
It's for a section 1 with CATs.
There is an option c/w 100 or 300 cell CATS

The 300 should pass emissions,
........whether you're wearing a shirt or not

http://www.zpost.com/forums/showthre...8#post13611428
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      03-18-2013, 09:29 PM   #11
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Quote:
Originally Posted by inTgr8r View Post
No...
It's for a section 1 with CATs.
There is an option c/w 100 or 300 cell CATS
That's promising. Now we need a price nailed down. The old pricing is higher than used euro cats by a large margin. I'll also be interested in your experience with fabspeed headers to dkf section 1 with o2 bungs. Hopefully we're not derailing this thread, but broadening the options for OP to consider
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      03-18-2013, 10:28 PM   #12
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Quote:
Originally Posted by philjw View Post
my car needs to pass OBDII readiness emissions tests, and I would need to have customer work done to relocate sensors or buy euro cats, and likely also need a tune,
If you do headers, you'll WANT a tune. Not necessary, but definitely a good idea to get the most out of them. Getting a good shop to weld 3 bungs on to your existing Sec1 (if your not up to doing it yourself) is no big deal. Even with Euro cats, you'll still need longer O2's. So it's either buy them both ($$$) or use what you already have. Side note: Euro cats also have twice the material of ours, but any performance increase hasn't been proven yet as far as I know. Still...

Quote:
Originally Posted by philjw View Post
not to mention that some still seem to have issues? I like the idea of headers, as it would enhance the sound of the car as well, but seems like this could get very pricey and complicated, no?
You'll pass readiness tests if you utilize your sensors - so no issues and not complicated. Cutting, leaving them dangling, or removing them altogether (and relying on a tune to 'turn them off') is where you're asking for issues. ESS for instance, will ask you if your sensors have been relocated. If not, they won't provide the tune - too many problems. Other tuners will say they turn them off (which in actual fact is turned low, but not off), and presto. But users have reported a host of problems with this. $0.02
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      03-19-2013, 01:55 AM   #13
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Quote:
Originally Posted by philjw View Post
Maybe this is a dumb question, but if I installed something like the Fabspeed headers here (VAC Website), could a tune trick the computer into not throwing a CEL and also returning a "readiness" state for all sensors? Can't seem to find the answer to that one.... Maybe I'm just missing something?
I had headers + relocate section 1 and no tune, and everything was fine. No CEL and all readiness passed. Now I'm trying headers + stock section 1 + Evolve tune. So far no CEL, but I have 2 readiness issues. Still working with Evolve to try to solve this.
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      03-19-2013, 09:47 AM   #14
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Quote:
Originally Posted by philjw View Post
For the headers and cats, not sure about the DKF option as I seem to recall the smog guys checking under the car with a mirror before hooking up the OBDII test last time I was there.
Look into your state's laws concerning the visual inspection. They may be checking to see if the exhaust is totally OEM, or they may only be confirming cats are installed. In some states, aftermarket cats are acceptable.
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      03-19-2013, 02:23 PM   #15
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Thanks everyone! Lots of good input! So far no one has disagreed with my 4.10 gear swap idea, so that's likely where I'm headed for now. For the headers, it sounds like I need to either modify the existing cats, buy the DKF section 1 and cats, or buy euro cats to relocate the O2 sensors; or risk a tune not being able to return a readiness code. Also seems to be the consensus that while a tune isn't necessary with relocated sensors, I may want it nonetheless for maximum gains. Anyone disagree with that summary?

More importantly, does anyone think I should prioritize the header swap over the diff? If so, why? I may do both eventually, but not this year...
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      03-19-2013, 02:55 PM   #16
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I agree with the summary. Priority of headers vs. diff? Coin toss there. Finding a good shop to do the diff is the key. Do you have that resource?
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      03-19-2013, 03:16 PM   #17
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Quote:
Originally Posted by Finnegan View Post
I agree with the summary. Priority of headers vs. diff? Coin toss there. Finding a good shop to do the diff is the key. Do you have that resource?
I don't... If anyone knows of a good shop in the Portland, OR area, please let me know. Otherwise I'm planning to just buy a rebuilt diff from Turner, Dinan, etc.
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      03-20-2013, 10:03 AM   #18
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I remember seeing a full diff with 4.10's already installed going for $1800 (no core charge) over on one of the other 3 series forums. If you can't find it with Google, PM me.
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      03-20-2013, 10:13 AM   #19
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Quote:
Originally Posted by philjw View Post
I don't... If anyone knows of a good shop in the Portland, OR area, please let me know. Otherwise I'm planning to just buy a rebuilt diff from Turner, Dinan, etc.
Note that I don't believe that the hard part is the physical R/R of the diff itself, but rather setting up the gears properly, ensuring the gears have the proper backlash and all that other fun stuff.. If it's not setup properly, you will have a noisy diff and could fail early. There are shims that are used to ensure proper backlash.

I don't think you necessarily need a tuner shop to do install the gears, rather you just need someone who's experienced setting up differentials. All differentials are basically the same, regardless if it's GM, BMW, Nissan, or Bugatti.

Anyone should be able to do the R/R of the differential in the car, if you get a complete one and not just the gears.
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      03-20-2013, 01:22 PM   #20
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4.10s are not just going to give you acceleration. They will make the gear changes shorter, so you will be shifting more and the car will feel tighter (more like a motorcycle if you have experience with those). Just want to make sure you understand the change, as it does change the way it feels and how you drive it.

As for the diff. Find a good diff builder. Doesn't have to be bmw or any brand. Just look around until you find a diff builder with stellar ratings, even if you have to travel. Best most cost effective way of doing this mod is to buy the gear and pinion and have it installed in your own diff, but you need an excellent diff builder.

Look around for offroading / hot rodding / etc. as they tend to do this kind of work. Look at this thread for more details.
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      03-20-2013, 03:40 PM   #21
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Quote:
Originally Posted by elwesso View Post
I don't think you necessarily need a tuner shop to do install the gears, rather you just need someone who's experienced setting up differentials. All differentials are basically the same, regardless if it's GM, BMW, Nissan, or Bugatti.
Quote:
Originally Posted by beta View Post
As for the diff. Find a good diff builder. Doesn't have to be bmw or any brand. Just look around until you find a diff builder with stellar ratings, even if you have to travel. Best most cost effective way of doing this mod is to buy the gear and pinion and have it installed in your own diff, but you need an excellent diff builder.
Look around for offroading / hot rodding / etc. as they tend to do this kind of work. Look at this thread for more details.
Thanks, guys. And if anyone happens to know of such a shop in the Portland or Seattle areas, let me know! I know we've got a lot of off-road enthusiasts here, so maybe I'll figure out where they go...

Beta, I understand what you're saying about the mod, and that sounds like exactly what I'm looking for. Looking at the thread you linked, I realize that you literally just installed your 3.91 last month? Any updates since then? Have you made it through the break-in period and had some fun?
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      03-21-2013, 12:25 PM   #22
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Originally Posted by philjw View Post
Beta, I understand what you're saying about the mod, and that sounds like exactly what I'm looking for. Looking at the thread you linked, I realize that you literally just installed your 3.91 last month? Any updates since then? Have you made it through the break-in period and had some fun?
Still in break-in period, but at this point I'm not too worried about it since my gears were shot peened and REM polished so I've started opening her up. Honestly it's a great mod and I'm happy I did it. It makes our already short gearing just a little shorter, so I feel I"m always in the power band.

It also is "the poor man's supercharger" as sometimes if you're just highway driving, you don't have to downshift to power out, you always have just a little more torque than you used to.

On the downside, it does make the car a little harder to drive, a little more raw, and you end up shifting more in regular driving (I use 4th now when putzing around town). But for me these are pros, as I think it fits the character of a raw sports car with creature comforts perfectly. Every mod I do I try to increase performance without decreasing comfort (or increase comfort without decreasing performance), as I love what the car is, so I'm just trying to make it more of that
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