Just a thought re de-catting headers

[The Prospector]

I have just been removing the cat from a set of second hand headers for my 2007 R1200GS (didn't fancy doing the originals till I see how it runs) and a thought struck me.....
Replacement cat free headers are quite expensive, removing the cat from standard headers gives you a 100mm diameter section of pipe, whether this adversley affects the gas flow I know not so....
Why does not someone market a Y piece that replaces the pressed section that contains the cat, you could cut the headers just in front of the weld where this section is joined to the header pipes join on the Y peice with a couple of stainless clamps, not beyond the realms of possibility is it. Charge around a £100 and I'm sure it would sell

 

[swissrob]

there was a post a while ago marketing this already

 

[Sgt Bilco]

Why does not someone market a Y piece that replaces the pressed section that contains the cat, you could cut the headers just in front of the weld where this section is joined to the header pipes join on the Y peice with a couple of stainless clamps, not beyond the realms of possibility is it. Charge around a £100 and I'm sure it would sell

Probably because it would look like a bodge with more connections in teh exhaust.

 

[Rasher]

Few of us have the tools / skills to cut and weld the pipes, most of us can wield a spanner / torx socket and swap the OE headers over (even me)

This would be a very small seller, plus if you have the skills to do the cutting and welding you could probably make up the link pipe yourself anyway.....

Then again you have already bought a second hand set to save doing a Frankenpipe job on your pride and joy, so by the time you have bough a second hand set of headers, paid for a link pipe, welded it all together would you be any better off?

Plus a decent aftermarket header set holds a 50%-70% resale value, I bought mine second hand for £100, and could have sold them 100 times over for the same price.

 

[Ali-bear]

The OP is correct - the price of aftermarket headers is extortionate.

All you would need to do is carefully cut the original headers before the cat and insert a length of link pipe.

 

[birdseye]

Why does not someone market a Y piece that replaces the pressed section that contains the cat, you could cut the headers just in front of the weld where this section is joined to the header pipes join on the Y peice with a couple of stainless clamps, not beyond the realms of possibility is it. Charge around a £100 and I'm sure it would sell

A pal with a 1200GS decatted his about 5 years ago and bought a Y piece to do so , so someone must make them.

Edit: sorry - it was his 1150 he had before the 1200

 

[(RIP) Miff]

If you are good enough at welding to weld in a "Y" piece, then you must be a good enough welder to cut the cat out and weld it back up.

 

[The Prospector]

Firstly - a welder I am not, I have removed the cat but need to get the pipe re-welded.
Coming to the BMW GS from more conventional Japanese multi's where it is common when fitting after market cans to obtain link pipes and replacement collector boxes not complete headers it just seemed logical to replace the cat with a Y shaped link pipe and keep your original headers instead of paying an extornate amount for something you already have.
After all if you are going to cut a set of standard headers to remove the cat ( be they second hand or not) you are not going to try to restore the cat at a later date are you.
I suppose what I am really getting at, is the 100mm diameter section of empty pipe left after removing the cat a detrement to the system or not.

 

[seahorse]

Firstly - a welder I am not, I have removed the cat but need to get the pipe re-welded.
Coming to the BMW GS from more conventional Japanese multi's where it is common when fitting after market cans to obtain link pipes and replacement collector boxes not complete headers it just seemed logical to replace the cat with a Y shaped link pipe and keep your original headers instead of paying an extornate amount for something you already have.
After all if you are going to cut a set of standard headers to remove the cat ( be they second hand or not) you are not going to try to restore the cat at a later date are you.
I suppose what I am really getting at, is the 100mm diameter section of empty pipe left after removing the cat a detrement to the system or not.

The OE pipes and collector which contains the cat is one piece so a Y piece is not really feasible. Many people have gutted the original cat, self included, and it works fine. You can also be sure everything fits no problem which is not always the case with aftermarket stuff.
Save £2-300 by not buying decat headers and spend it on something more useful would be my advice. Re-welding your collector is a piece of piss and shouldn't cost much even if you have to get a welder to do it.

 

[Bobbin-Man]

OP, I assume you've read my thread here? I guess you're planning on doing the same ... so to answer your question the extra volume in the section of pipe that the cat's been taken from is not noticeably detrimental to the performance of the system.
In fact there's plenty that believe the link pipe at the front is important yet it doesn't exist on the majority of aftermarket headers, so retaining the link and having a 100mm bulge is really no problem. You could cut out the 100mm section and weld in a new short pipe which would save the job of removing the cat but probably it's the same work involved.
I notice you're based in Keighley you're not so far from Macclesfield so I would highly recommend JP Exhausts to weld your pipes back together

 

[Bendy toy]

My remus headers cost me £150. They fit perfectly with standard can, so why butcher the standard headers.

To cut out the standard cat section would need a new Y piece and probably new 2nd bends. All you save are top ends from cylinder head.

A pair of link pipes fitted from collector to silencers (for a 900 Diversion) cost me £80 from Xtreme Stainless. Add two more pipe, bends, welded Y and make it fit would cost a lot more than £150.

As others have said, fit used headers and keep the old cat headers so the bike can go back to standard.

 

[JFC]

Any issues with mot / emissions if you de- cat?

 

[Bobbin-Man]

To cut out the standard cat section would need a new Y piece and probably new 2nd bends. All you save are top ends from cylinder head

Er, nope, have a look at the post I referred to above. The o/e BMW headers are pretty good quality when compared to some of the after-market offerings, decatting them is definitely worthwhile. And, if a 2nd hand pair is sought to do the de-cat, they'll return at least the outlay when you sell the bike with the original system fitted.

 

[Bobbin-Man]

Any issues with mot / emissions if you de- cat?

Not part of the bike MOT test.

 

[Ali-bear]

My remus headers cost me £150. They fit perfectly with standard can, so why butcher the standard headers.

Current price of Remus headers on eBay is the wrong side of £375

 

[ncpierce]

Current price of Remus headers on eBay is the wrong side of £375

Grizzly - maybe you want to send me a PM I have a full Remus system sitting in the garage that I need to get rid of

 

[Bendy toy]

Current price of Remus headers on eBay is the wrong side of £375

Just wait around and some will turn up at sensible prices. Its not necessary to buy new.

Unlike most decat jobs, R1200s run leaner than before. The standard can is fine with decat headers, but a free-er flowing can might be too much. That's where IAT spoofing comes in.

 

[Ali-bear]

Unlike most decat jobs, R1200s run leaner than before. The standard can is fine with decat headers, but a free-er flowing can might be too much. That's where IAT spoofing comes in.

Thats the normal response to having a freer flowing exhaust.

 

[Bendy toy]

Thats the normal response to having a freer flowing exhaust.

I may be wrong but this is how I understand it

@Grizzly's comment is not the case on engines that use the O2 sensor to control the fuel air mixture. Most cars do this and I believe Japanese bikes running cats. Judging by how catted MotoGuzzis use fuel compared to the previous "dirty" versions they probably do as well.

All engines will flow more gas with the cat removed, but when fuelling is O2 sensor controlled, the cylinder mixture wont change. The O2 sensor wont know there is no cat - it simply signals exhaust gas O2 content ad the ECU feeds the fuel. The cat is supposed to burn off the excess hydrocarbons (HCs).

This is why a normally O2 sensor controlled engine will stink like a 1970s BL Maxi when decatted without a remap. Its also why catalysed engines use more fuel. They need the excess HCs to feed the catalyst itself.

However, Hilltop told me that the R1200 cylinder air/fuel mixture is controlled by the inlet air mass flow which begs the question - "why do these engine have O2 sensors?" (does anyone know BTW?)

The mixture is controlled by what goes in, rather than what comes out, so a free flowing exhaust will make it run weak. There is some limited compensation (more air going in needs more fuel) but it also explains why Inlet Air Temperature (IAT) spoofing has so much effect on the mixture and fuel consumption.

 

[Alan R]

Its also why catalysed engines use more fuel. They need the excess HCs to feed the catalyst itself.

Really? The above statement appears to fly in the face of both common sense and desirability from a fuel economy/environmental point of view - which after all was why catalytic convertors were introduced.

Until documentary evidence is available to prove otherwise, this for me is the leading contender for 'Complete internet bollocks' statement of the year.

Alan R