Can I try to understand headers once and for all please?

[Adrian Thompson]

Can I try to understand headers on automatic cars please? There are dozens of threads on here and other places about EBay headers (North American term for tubular vs cast manifolds) or Manifolds (European term for all type, cast or fab) and I’ve reached brain overload here.

OK, from reading various threads I think the case is this.

North American 986’s have 4 catalytic convertors. One in each header/manifold and one in each link pipe for a total of 2 per bank, 4 per car?
Euro (RoW?) 986’s have just 2 catalytic convertors. None in each header/manifold and one in each link pipe for a total of 1 per bank, 2 per car?

Now, for a relatively cheap and simple upgrade there are dozens of both catless headers and catless ‘test pipe’s’ for 986’s. Consensus seems to be that the test pipes add maybe 2hp vs catless headers at around 5hp? Am I right so far?

Also the catless test pipes can throw a CEL whereas the catless headers don’t throw a CEL. Is this correct so far?

Next we come to the elephant in the room, automatic trans. No, it’s not ideal, no I’m not selling the car and buying a manual 2.7 or 3.2S, I’m keeping this one. Everything seems to say that the test pipe fits right in, but the headers don’t fit on autos. Here comes my confusion. I’ve seen some sources say the header fouls on a tube that can be bent or modified for clearance. Others say they foul on the trans casing. One seems easy to overcome, the other is essentially a nonstarter. Is this based on bad info, poor comprehension on my part or different parts and vendors?

I have no interest in chocking myself or others so I have no intention of going completely catless, but I believe the header cats are fast light off, and once up to full operating temp they are less important than the mid pipe, link pipe, test pipe whatever you want to call it. Ideally I’d like to fit a set of headers while the car is off the road over the winter, but I don’t want to waste time finding out I’m going down a blind alley.

The end goal is I’d be interested in pairing the headers with a ‘PedroSport’ style modified exhaust and de-snorkel for now. Then later a larger TB and the 996 Y pipe/plenum to suit. Should I pursue headers or drop that and go with test pipes instead?

Usage and expectations. The car is currently a 3 month daily driver. I know the standard response is ‘it’s not a race car’, ‘do a DE with the money instead’, ‘buy a different car’, but that’s not what I want. I haven’t been near an autocross or race track in at least 5 years now to the point my helmets are all out of date. No this isn’t a race car, no I don’t expect 30hp from these mods. What I want is a bit more pep at the top end without losing any of what little low end torque there is, and to enjoy that sweet sweet howl as I reach the red line, which tends to happen every day when in use. Yes I could do with more track instruction as I’ll never be a Hamilton, instead with practice I can be a mid-field racer, but that practice is long long out of date and not so much where my interests lie these days.

Can someone clear this up for me please?

[steved0x]

Originally Posted by Adrian Thompson

North American 986’s have 4 catalytic convertors. One in each header/manifold and one in each link pipe for a total of 2 per bank, 4 per car?
Euro (RoW?) 986’s have just 2 catalytic convertors. None in each header/manifold and one in each link pipe for a total of 1 per bank, 2 per car?

Northamerica 986 Boxster 97-99 have just 2 cats and they are in the link pipes between the exhaust manifold and the muffler.

Northamerica 986 Boxster 2000-04 have the same 2 cats as 97-99 and 2 additional cats integrated into the exhaust manifolds.

Originally Posted by Adrian Thompson

Also the catless test pipes can throw a CEL whereas the catless headers don’t throw a CEL. Is this correct so far?

On a 97-99 the catless test pipes will throw a code, because you are removing the only sets of cats from the car. But you can put a set of the eBay headers on these with no code, since you are just replacing the oem "header" with aftermarket.

On a 2000-2004, the catless test pipes will not throw a code, because that 2nd set of cats is not monitored by the OBDII system, only the initial integrated cats in the exhaust manifold are monitored. On 2000-2004 if you put an eBay header with no integrated cats, you will get a code since you would be removing the cat that is monitored.

I have a 2000 S 6 Speed with the 2nd cat delete pipes and like them. I can't answer your other questions about automatic transmission and clearances.

[Adrian Thompson]

Outstanding thank you. I didn't realize the early NA cars came with only two cats, that explains a large part of my confusion.

Now I hope someone can chime in on headers and auto's.

[busman65]

Adrian...I can't help you with the auto thing....I do run catless headers, 200 cell midpipes and a Dansk sport muffler....great sound and better power..I did have to have Softronic do a little "correction" to keep the 200 cell cats from tripping an efficiency code...the headers are from FVD and the cats are NPH.