De-Cat is it worth it ?

[SyncroS8]

AFAIK, you can run an extension on the post lambda sensors. They're only looking for a delay in signal from the gas going through the CAT.



However, you won't easily pass your MOT without CATs. The only way I could think of doing this would be to add an exhaust pump as per Porsche 928s to get the emissions down to 0 at idle.

MG

[adjuster]

What's the air injection pump doing at idle? (On the 40v V8's, there is an air pump in the air box that is hooked up to the exhaust system, injecting air.)

If it's not always on, it could be switched on at idle, and that would absolutely lower the reading from the tail pipe.

[ainarssems]

Originally Posted by adjuster

What's the air injection pump doing at idle? (On the 40v V8's, there is an air pump in the air box that is hooked up to the exhaust system, injecting air.)

If it's not always on, it could be switched on at idle, and that would absolutely lower the reading from the tail pipe.

Thats for cold starts only

[S4Phil]

Secondary air injection heats the cats when they're cold by pumping fresh air into the exhaust to heat it quicker. (hotter cat = more efficient cat)

If you're de-catting probably best to cut out your old cats and keep them, then adding in some v-bands or similar to make replacing the cat with the straight pipe easier

[ainarssems]

Originally Posted by S4Phil

Secondary air injection heats the cats when they're cold by pumping fresh air into the exhaust to heat it quicker. (hotter cat = more efficient cat)

If you're de-catting probably best to cut out your old cats and keep them, then adding in some v-bands or similar to make replacing the cat with the straight pipe easier

It does help cats to heat up quicker but primary objective is to reduce emissions during warmup as engine is running rich on cold starts and unburned fuel, CH and CO go into exhaust and extra air is needed to burn them off to reduce pollution.

[ainarssems]

Originally Posted by SyncroS8

AFAIK, you can run an extension on the post lambda sensors. They're only looking for a delay in signal from the gas going through the CAT.



However, you won't easily pass your MOT without CATs. The only way I could think of doing this would be to add an exhaust pump as per Porsche 928s to get the emissions down to 0 at idle.

MG

Not delay, they are looking for lower O2 content then before cats. What you see in the picture is bringing it out of the flow. Less flow= slower reaction= lower voltage so ECU thinks cat is working OK.

I have also seen small incision made in exhaust just before lambda and small piece of metal sheet welded in to do the same thing.

[SyncroS8]

Originally Posted by ainarssems

Thats for cold starts only

The 928's I've worked on have had the air-pumps running constantly. They pump air into the exhaust manifold so that the emissions drop.

This causes all sorts of problems within a modern MOT so we ended up disconnecting them for the MOT as the lambda reading wouldn't pass... it thought that there was a leak!

MG