[Isaiah5411]

I'm absolutely insane for getting into this discussion, but...I need a distraction today (it's raining, my tune is in , and I've been driving all morning) and, other than working out, thinking about modding cars is the healthiest.

First of all, let me get this straight - our choices of combinations when it comes to headers are:

1) Catless headers (e.g. AA), retaining the secondaries
2) Catless headers, removing the secondaries
3) Catted headers (e.g. AFE), retaining the secondaries
4) Catted headers, removing the secondaries.

Not to jack the thread, but here are some questions (say in a car with 3 stage manifold conversion, Euro airbox, PE and AA tune):

a) Clearly, #2 would yield the most power, right? But by how much over #s 1, 3 and 4?
b) How much less power than the others would you get if you chose #3? In other words, is this a horrible choice if you're looking for some noticeable gains?
c) If you have the PE and you're already concerned about the sound it makes, should any of these even be considered without plans to modify the PE, such as put in a resonator (e.g. Vibrant) or a small race muffler (e.g. Borla) where the straight midpipe is?
d) If smell is a concern (e.g. you have a convertible), is #1 still an option or is #3 really the only choice?

Thanks! Talk amongst yourselves.

[andrey_gta]

Originally Posted by Isaiah5411

First of all, let me get this straight - our choices of combinations when it comes to headers are:

1) Catless headers (e.g. AA), retaining the secondaries
2) Catless headers, removing the secondaries
3) Catted headers (e.g. AFE), retaining the secondaries
4) Catted headers, removing the secondaries.

Not to jack the thread, but here are some questions (say in a car with 3 stage manifold conversion, Euro airbox, PE and AA tune):

a) Clearly, #2 would yield the most power, right? But by how much over #s 1, 3 and 4?
b) How much less power than the others would you get if you chose #3? In other words, is this a horrible choice if you're looking for some noticeable gains?
c) If you have the PE and you're already concerned about the sound it makes, should any of these even be considered without plans to modify the PE, such as put in a resonator (e.g. Vibrant) or a small race muffler (e.g. Borla) where the straight midpipe is?
d) If smell is a concern (e.g. you have a convertible), is #1 still an option or is #3 really the only choice?

Thanks! Talk amongst yourselves.

a)#2 most power - bad smell for daily car. Power gain of #3 catless I assume is like 5-10 whp 5-10 wTq more. This is based on Secondary deletes

b) based on my feel for these: up to 10 whp less than #1 Catless header + Secondary Catss. This is a main catalyc so its more restrictive or in a bad position. If the dyno surprises us and shows a power curve and top numbers similar to Catless + secondary cat then these are a great idea...

c,d I cant say

But I think question that needs to be asked is. For maximum power where should the Catalycs be: in the midpipe or on the exhaust manifold

[TheTallJS]

max power would be towards the exit, but then renders the cats pointless and might as well go catless.

[hassmaschine]

Actually, what matters more is in the primaries and in the merge. With the cat located right at the merge, there's definitely a loss of scavenging effect (although less than the stock manifold design). The secondary cat would create some back pressure, assuming it's really a restriction - but the scavenging effect of the AA headers will be better regardless of the secondary cat.

Now if you swapped the 2nd cats for a y merge, then you would be on to something. Otherwise, replacing them with straight pipie won't make a lot of difference.

Also, BMW cats last a long time. They should easily do 200,000 miles.

[Tom Droze]

Originally Posted by TheAxiom

Well?

If you are "welling" me, I gave it the old college try; in that I had everything disconnected and removed as per a header install write up TheSt|G had provided and I had three of the easier exhaust manifold nuts removed when I decided installing the headers really wasn't much fun, so I reassembled everything. However, I did manage to complete the secondary cat delete in the process. Part of my lack of enthusiasm is that I am only two days removed from having the flu for three days and I am still not feeling percent.

I will have the headers installed this week, I promise, as I know a good shop by my office with a few highly recommended BMW techs.

[Isaiah5411]

Originally Posted by Tom Droze

If you are "welling" me, I gave it the old college try; in that I had everything disconnected and removed as per a header install write up TheSt|G had provided and I had three of the easier exhaust manifold nuts removed when I decided installing the headers really wasn't much fun, so I reassembled everything. However, I did manage to complete the secondary cat delete in the process. Part of my lack of enthusiasm is that I am only two days removed from having the flu for three days and I am still not feeling percent.

I will have the headers installed this week, I promise, as I know a good shop by my office with a few highly recommended BMW techs.

OK, you gave it your best shot and we'll let you off this time IF you can provide us with a photocopy of a doctor's excuse. Now, rest up and feel better...you've got 72 hours to git 'er dun!

[mmmnot]

Originally Posted by mlifxs

any drone before or after?

After the headers, not too bad - after the secondary cat delete, yes. I do not mind it. I was told by a friend it sounds like a modded E46 M3. I don't know if that's good or bad - considering it still sounds like a BMW and not a Honda, I'd say good

Originally Posted by Tom Droze

They are a thing of beauty!

Now, for the BIG question, should I attempt the install tonight? Hmmmmm. . .

Haha! Told ya' so!

Originally Posted by NJ Krish

Can't wait to see dyno with tune and IM. Great review! Also I agree with you on how awesome they look after the heat!

Also, shout out to CS majors haha

Thank you! They've stayed that color after over 3K miles.

Originally Posted by Eagle1oh7

I'm considering getting the aFe headers over the AA due to the emissions, but I'm still on the fence until such time when I do them later this year or next year.

Emissions has no concern with these, provided your state is NOT CA, where they are crazy strict with visuals.

Originally Posted by chris82

Nice review OP, they look as you say they do. I don't doubt AFE makes a great product



Very nice

Can't wait to see your results Tom Droze, I too have the N51

Thank you!

Originally Posted by andrey_gta

OP not to discourage you. BUt don't know if you will see a 250whp number after manifold plus tune. That is maybe real headers territory if I recall correct.
I predict something like 235-240whp based on intuition.


Which tune will you do: a off road header tune or a typical manifold only tune? Will a tuner like AA allow header tune on this? Because Header tunes differ than just turning off the CEL, wonder if the 300 CEL can handle it...

Yeah, I understand what you are saying. Either way, I'm very happy over the gains, performance and mainly low to mid end torque. I'll for sure update when I get a proper dyno done as the car sits.

I did not need the off road tune, as per my research this is mainly needed for catless headers. It was their standard tune, with some feedback from one of my datalogged interstate runs at WOT in 4th. I did note of the header mod to AA as well as it reflected in the data I've logged, then sent back to them for a second, custom tune.

Originally Posted by TheAxiom

Well?

Well, well, well!

[mmmnot]

Originally Posted by Isaiah5411

I'm absolutely insane for getting into this discussion, but...I need a distraction today (it's raining, my tune is in , and I've been driving all morning) and, other than working out, thinking about modding cars is the healthiest.

First of all, let me get this straight - our choices of combinations when it comes to headers are:

1) Catless headers (e.g. AA), retaining the secondaries
2) Catless headers, removing the secondaries
3) Catted headers (e.g. AFE), retaining the secondaries
4) Catted headers, removing the secondaries.

Honestly, IMHO - it just depends on your purpose of the car. If youre trying to extract every single pony, then ideally the most straight pipe would be ideal. Header back with a nice straight pipe towards the end or side of the fenders. Again, in my humble opinion based only on my random thoughts and logic. I just wanted a better flow, louder sound and a nice crackle and pop, which I was able to accomplish without compromising any emissions issues or future headaches.

Originally Posted by hassmaschine

Now if you swapped the 2nd cats for a y merge, then you would be on to something. Otherwise, replacing them with straight pipie won't make a lot of difference.

Speak more of this, would you? Does the Y pipe allow better flow? Any information/pics? Purdy please?

Originally Posted by Tom Droze

If you are "welling" me, I gave it the old college try; in that I had everything disconnected and removed....

Yeah, it's a real PITA. I did not even bother trying. I knew I'd just curse the time and pound my head against the wall. I hope you get it done at a good price. Again, it should be around 5 hours shop time.

[pinoye90]

The dyno graph on the AFE website states no tune necessary and will not cause a cel light. having the AA off-road tune would not be needed. The question is if AA can extract more power from this header? Someone local to FL should go and getter done!!!!

[justpete]

Originally Posted by mmmnot

Does the Y pipe allow better flow? Any information/pics?

That's what's going into my car after the cams, a Y collector followed by a 3" thinwall 304SS straight pipe exhaust with a low back pressure muffler or two, Coast Fabrication 17" glass packed with V-band clamps to make changing the packing easier every year. I _think_ Burns Stainless makes a Y collector with the correct spacing for the headers so it's a bolt-in but the rest of the exhaust has to be fabricated, typically by mitering and MIG welding the pipe so it angles back under the car to the stock tailpipe location. Then it's dropped, TIG welded together, and reinstalled.

No bends and minimum departure from a straight line line maximizes velocity, I think, and that's really all that matters. We'll be adding another type of Y adapter at the end so a couple of pieces of the 3" pipe can be added to duplicate the look of the PE tips but the usual termination is a single pipe with a slight turn-down to help with noise to meet track requirements.

[Taskmaster]

The biggest part of the exhaust system is going to be the Y pipe and the placement of it. Everything after it makes little to no impact on power.

[justpete]

Originally Posted by TheAxiom

The biggest part of the exhaust system is going to be the Y pipe and the placement of it. Everything after it makes little to no impact on power.

Well, not necessarily. If not using a low back pressure muffler it's difficult to optimize flow velocity. Pipe diameter matters as does whether it's mandrel bent or mitered, etc. although it's not terribly critical. The Y-collector determines scavenging timing at the head so yes its placement is more critical than the others but its effectiveness can be reduced by poor downstream design choices, I think. You and hass know more about it than i do, I'm going by the results the guys at the shop have found by dyno'ing many many different exhaust configurations on their NA and turbo race cars.

[hassmaschine]

Right, it can be restrictive. But the stock cats are sized for the engne, so whatever flow restriction is present is minimal. It's no different than putting in an intake, the stock one is already pretty good so gains are minimal.

Headers make more power because they improve scavenging, have better merges, longer primaries, etc. If the only difference was the lack of cats, you could cut them off and make the same power as headers. While it will make a difference, headers still make more power.

[Isaiah5411]

Originally Posted by hassmaschine

While it will make a difference, headers still make more power.

So...in your opinion, is it worthwhile to replace stock with the AFE catted headers while leaving the secondaries? (Note: I have the PE on my convertible and don't want it much louder.)

[Taskmaster]

Originally Posted by Isaiah5411

So...in your opinion, is it worthwhile to replace stock with the AFE catted headers while leaving the secondaries? (Note: I have the PE on my convertible and don't want it much louder.)

That's up to you - we haven't seen a real dyno proven increase, but they can/should add power. Otherwise those secondaries removed and that exhaust will probably be louder than you have now - Even with the AFE headers.

[pinoye90]

If I already have secondary delete with PE, adding AFE header would make it louder? I don't think it would be anymore louder than it is already. What's funny is after upgrading to stage 3 manifold the PE+secondary delete did get just a bit louder but tolerable.

Anyone have vids on PE+secondary+AFE header?

[Benan]

The look mighty nice, but the arnt much diffrent to the OEM?
Or do US and Euro have diffrent headers? Mine look like this:

[TheSt|G]

Was it my DIY you referenced? If so, you should have felt free to PM me if you had any questions. AFE headers most definitely do not fall into my "tough shit you bought China junk" rule.

[jc5988]

Originally Posted by Benan

The look mighty nice, but the arnt much diffrent to the OEM?
Or do US and Euro have diffrent headers? Mine look like this:

yes, US has different and more restricted header design, AFE uses euro design but with 300 cell cat.

[TheSt|G]

Originally Posted by jc5988

yes, US has different and more restricted header design, AFE uses euro design but with 300 cell cat.

Euro version was also only used on pre-facelift euro cars.

[hassmaschine]

isn't the euro N52 rated at the same HP output as the US N52?

[TheSt|G]

Originally Posted by hassmaschine

isn't the euro N52 rated at the same HP output as the US N52?

That's a pretty broad question, but to what it is relevant here, the N52 in Europe lost 6-7hp in the facelift when those headers changed to the worse US spec design.