De-cat front exhausts

[mjheathcote]

I have a spare pair of standard front pipes, euro spec.
The lads are in the office tomorrow and they will have time to chop open the primary and secondary cats, gut them, and TIG weld them back up.
Plan was originally to gut the primary, and replace the secondary with less restrictive 200 cell cats, however I am feeling a bit naughty...
Okay it should fail the MOT, but can always refit the original pipes come MOT time, if necessary...

Questions:

1. With no cats, will the secondary Lambda sensor throw a warning light (assume so), and if it does will it effect the running of the engine/change the mapping?
2. Is the sole purpose of the secondary Lambda sensor just to ensure the exhaust is 'clean'?
3. Do those little mini cat 'foolers' that you can screw between sensor and lambda boss work to fool the Lambda?
4. Will my exhaust noise increase substantially, standard silenced middle X pipe, and Larini rear boxes.

and:

5. I assume the primary lambda sensor before the cats is there to anable the ECU to adjust the air fuel ratio, or is the system not that clever?

Ta.

 

[BennyD]

Personally, I would go with the 200 cell idea and then get an unsilenced 'X' or 'H' pipe instead of the standard centre box. That way you wouldn't have any potential management problems, it would be MOT legal and it would be louder as well.

 

[gingeh721]

I highly recommend you gut the primaries and replace the secondaries for 200 cell cats along with an un-silenced x pipe. I have standard rears.

Buy a SM x pipe off Benny for £200 then get a garage to gut your primaries and replace the secondaries.

For some reason I did get a cel a couple of times afterwards. I put 2 x foolers, that cost 20 odd quid, on and the cels never came back.

This mod increased power substantially, do it! Plus you can do it for less than 800 quid. Larini back boxes cost the earth and don't give you any bhp. 200cel cats and an x pipe also sound amazing and cost half as much!

 

[adam01]

I highly recommend you gut the primaries and replace the secondaries for 200 cell cats along with an un-silenced x pipe. I have standard rears.

Buy a SM x pipe off Benny for £200 then get a garage to gut your primaries and replace the secondaries.

For some reason I did get a cel a couple of times afterwards. I put 2 x foolers, that cost 20 odd quid, on and the cels never came back.

This mod increased power substantially, do it! Plus you can do it for less than 800 quid. Larini back boxes cost the earth and don't give you any bhp. 200cel cats and an x pipe also sound amazing and cost half as much!

+1

 

[mjheathcote]

My spare front pipes are now cat free.
We cut them, gutted them, and TIG welded them back up, you wouldn't know they were now empty!
The ceramic material was so brittle, a simple tap with a hammer and they crumbled away...I would be uneasy with US spec manifolds thats for sure.
Below internal shot of the squashed section, so managed to accurately measure the inside cross sectional area.
The conclusion is that the cross sectional area is 2/3 rds that of the main pipe diameter being 56mm inside diameter.
I would like to know the pipe diameter on the twin pipes used by Larini on there front pipes?
They would both have to be 40mm inside diameter to match the same cross sectional area as the 56mm inside diameter main pipe.
I suspect that they are most likely 1-1/2" outside diameter pipes (35mm inside diameter), so a little small to be perfect, but not far off. Am I right?

 

[CatmanV2]

Is it hard to get that section of the exhaust out?

Doesn't *look* too hard.

C

 

[philw696]

I have a spare pair of standard front pipes, euro spec.
The lads are in the office tomorrow and they will have time to chop open the primary and secondary cats, gut them, and TIG weld them back up.
Plan was originally to gut the primary, and replace the secondary with less restrictive 200 cell cats, however I am feeling a bit naughty...
Okay it should fail the MOT, but can always refit the original pipes come MOT time, if necessary...

Questions:

1. With no cats, will the secondary Lambda sensor throw a warning light (assume so), and if it does will it effect the running of the engine/change the mapping?
2. Is the sole purpose of the secondary Lambda sensor just to ensure the exhaust is 'clean'?
3. Do those little mini cat 'foolers' that you can screw between sensor and lambda boss work to fool the Lambda?
4. Will my exhaust noise increase substantially, standard silenced middle X pipe, and Larini rear boxes.

and:

5. I assume the primary lambda sensor before the cats is there to anable the ECU to adjust the air fuel ratio, or is the system not that clever?

Ta.

Wouldn't fail the MOT if I was doing it Mike that's for sure and its even better here as no emissions tests and the test is far simpler but you have to have reverse lights.
Cant believe the forum does not have any other testers ?

 

[mjheathcote]

Is it hard to get that section of the exhaust out?

Doesn't *look* too hard.

C

I'll let you know!

 

[maverick]

Be interested to hear how there sound, I am planning next Friday to cut and remove the secondary cats out but maintain the primary's , I have already modified the centre box removing the silencer part and I have different rear boxes on .just hoping for some more sound .

 

[mjheathcote]

Wouldn't fail the MOT if I was doing it Mike that's for sure and its even better here as no emissions tests and the test is far simpler but you have to have reverse lights.
Cant believe the forum does not have any other testers ?

I'm getting mine MOTed at the end of the month.
Plan is to then swop the pipes over.
I've known my MOT tester for nearly 30 years, always does my Stag (for nearly as long!) and whatever else I have, so will pop back over once fitted just to see if it would actually fail with no cats!

 

[CatmanV2]

Why are you doing it that way round, Maverick?

C

 

[mjheathcote]

Be interested to hear how there sound, I am planning next Friday to cut and remove the secondary cats out but maintain the primary's , I have already modified the centre box removing the silencer part and I have different rear boxes on .just hoping for some more sound .

I could also easily modify the centre box, however I already have larini's and with no cats, and also no centre silencing it would be too loud I fear!
This way, removing the cats, should help the gas flow (even retaining the squashed pipes) and thus help with the performance, as well as the noise.

I would like to know however how the silencing is achieved on the centre X pipe, so maybe it could be improved for better flow, with alternative silencing.

 

[philw696]

I'm getting mine MOTed at the end of the month.
Plan is to then swop the pipes over.
I've known my MOT tester for nearly 30 years, always does my Stag (for nearly as long!) and whatever else I have, so will pop back over once fitted just to see if it would actually fail with no cats!

I know when I removed the cat from my Celica GT4 rally car she still passed the emissions test.
Technically its a fail if fitted by the manufacturer and cats and dpfs removed.

 

[maverick]

Why are you doing it that way round, Maverick?

C

A couple of reasons really
I can do this my self and cost nothing ,I shouldn't have any problems with emissions(hopefully ) and also wouldn't have to move the lambor sensor by retaining the primary's .it would be nice to have more bhp but its faster enough as it is so just want a bit more noise.I'll try and get a before and after sound clip up .

 

[mjheathcote]

I know when I removed the cat from my Celica GT4 rally car she still passed the emissions test.
Technically its a fail if fitted by the manufacturer and cats and dpfs removed.

Would be handy if it passes emissions with no cats.
The way I've done it, the cat casings are still be in place, so you woundn't know they had been removed internally.

 

[MAF260]

Guys, don't get too over-excited by the thought of more power. The gains are not that significant when just changing exhaust parts. Read my thread on my exhaust mods, which were very thorough/extreme and the resulting measurements taken on a rolling road pre and post modifications. Manifold change/decat, removal of secondary cats, centre resonator removed. 200 cell sports cats added and h-pipe. Pre-mapping the gain was just 20bhp. The massive increase is in the noise!

 

[maverick]

Would be handy if it passes emissions with no cats.
The way I've done it, the cat casings are still be in place, so you woundn't know they had been removed internally.

I was toying with the idea like yours but getting a complete pipe mandral bent up , than making the flange and lambo sensor boss at work and welding them on ,was aiming for a less restricted squashed part but thought it would be to loud and I'll have emission problems don't need any more warning lights on the dash !

 

[mjheathcote]

Guys, don't get too over-excited by the thought of more power. The gains are not that significant when just changing exhaust parts. Read my thread on my exhaust mods, which were very thorough/extreme and the resulting measurements taken on a rolling road pre and post modifications. Manifold change/decat, removal of secondary cats, centre resonator removed. 200 cell sports cats added and h-pipe. Pre-mapping the gain was just 20bhp. The massive increase is in the noise!

Yah you are right, should spin up easier, however it does spin up rather well as stock!

 

[CatmanV2]

A couple of reasons really
I can do this my self and cost nothing ,I shouldn't have any problems with emissions(hopefully ) and also wouldn't have to move the lambor sensor by retaining the primary's .it would be nice to have more bhp but its faster enough as it is so just want a bit more noise.I'll try and get a before and after sound clip up .

Confused. I thought there was one pair of sensors in front of the primary cats (can't see any others on the Eurospares diagrams, although they are charmingly names lamda feelers

Everyone else seems to have take out the primaries with no issues. Just wondering what difference there is taking the secondaries instead.

C

 

[maverick]

There is one just before and one directly after the primarys , it not very clear on the diagrame and took me a couple of mins to find it . Item 6 before , I item 9 after . This is on the 4200 coupe search