niceperson709
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| posted on 10/6/09 at 03:44 AM |
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running with out a cat
Ok guys I have a simple question on my car i have the standard double cat set up from the Nissan Pulsar donor (there is a cat in the exhaust manifold
and a second one just before the first muffler.) Now I am considering deleting the second one when I rebuild the car in a couple of weeks and
replacing it with a new section of 2 1/2 stainless tube that I just picked up at my favourite scrap metal place.
I am unconcerned about increased emissions because there is no annual testing where I live but I do wonder if it will make any difference to the
tuning ?
Any ideas or experience out there?
I just think that since I am making a pretty new body
for the car that I should have a better looking exhaust as well.
[Edited on 10/6/09 by niceperson709]
Best wishes IAIN
life is not the rehearsal , it's the show so don't sit there thinking about it DO IT NOW
http://iainseven.wordpress.com/
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A1
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| posted on 10/6/09 at 04:51 AM |
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when i took the cat and silencer off my car it ran better, the throttle response was noticeably sharper and it seemed to accelerate faster.
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l0rd
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| posted on 10/6/09 at 05:17 AM |
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If i was you, I would remove both. Specialy the one in the manifold.
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smart51
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| posted on 10/6/09 at 07:08 AM |
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Is there a lambda sensor after the second cat? No? Then the electronics won't know it has been removed. In which case I'd have thought
it would be OK.
As for an increase in emissions, I doubt it. Cat converters change CO and partly burned fuel into CO2 - one form of pollution into another. The
total volume doesn't change. Removing the cat may even reduce your fuel consumption slightly, reducing overall emissions.
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niceperson709
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| posted on 10/6/09 at 07:50 AM |
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Thanks guys what you have been saying matches what I have been thinking.
Smart 51
the lambada sensor is on the exhaust manifold so as you suggest the engine won't notice the difference.
l0rd
I would think about removing both but I am not quite ready to make an entire exhaust manifold 
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l0rd
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| posted on 10/6/09 at 07:51 AM |
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After having a discussion with my mechanic about improving the performance of my Laguna 1.8 16v, He adviced me to change the manifold to a 2.0L one
and also to stick a bar through the manifold cat.
The only worry will be when you do an emission test, in order not to fail, you need to have the car warmed up and the normal cat should be perfectly
all right for the test.
I have seen on a Dyno, a Renault Megane II 1.6 (115HP factory claim) that produced 123HP without the manifold cat and 128HP with an unbranded
induction kit.
I am not saying that you can do that. I am not to be held responsible if anything goes wrong. This is what i was told and what i have seen.
[Edited on 10/6/09 by l0rd]
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l0rd
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| posted on 10/6/09 at 07:53 AM |
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quote:
Originally posted by niceperson709
Thanks guys what you have been saying matches what I have been thinking.
Smart 51
the lambada sensor is on the exhaust manifold so as you suggest the engine won't notice the difference.
l0rd
I would think about removing both but I am not quite ready to make an entire exhaust manifold
I din't say make an exhaust manifold. If you can get a spare one, you can just remove the cat and check the diference
[Edited on 10/6/09 by l0rd]
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niceperson709
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| posted on 10/6/09 at 08:10 AM |
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l0rd
I had not thought of getting handy with an iron bar to the cat matrix in the manifold but it would reduce restrictions in the exhaust without altering
the appearance.
so thanks fro the idea
Best wishes IAIN
life is not the rehearsal , it's the show so don't sit there thinking about it DO IT NOW
http://iainseven.wordpress.com/
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l0rd
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| posted on 10/6/09 at 08:24 AM |
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Just try to get hold of a second one if possible. You do not want to get any ECU errors.
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mark chandler
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| posted on 10/6/09 at 09:09 AM |
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I had a MR2 turbo, broke the cat up in situ within the manifold, it made the car much faster, turbo spooled up really quickly and made no difference
to the ECU.
Regards Mark
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smart51
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| posted on 10/6/09 at 09:25 AM |
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quote:
Originally posted by niceperson709
Smart 51
the lambada sensor is on the exhaust manifold so as you suggest the engine won't notice the difference.
If your car has 1 lambda sensor and it is before the cat then removing the cat shouldn't affect it. Some cars have 2 sensors, one before and
one after the cat. It uses the second sensor to fine tune the fuelling. You'd probably need to leave it alone.
My understanding is that you can change anything after the last sensor and the ECU won't know any different.
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MikeRJ
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| posted on 10/6/09 at 09:43 AM |
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quote:
Originally posted by smart51
Some cars have 2 sensors, one before and one after the cat. It uses the second sensor to fine tune the fuelling. You'd probably need to leave
it alone.
This is found on OBDII equipped cars, and is to tell the ECU how well the cat is working, i.e. it's purely for emissions warning than fuelling.
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smart51
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| posted on 10/6/09 at 10:15 AM |
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quote:
Originally posted by MikeRJ
quote:
Originally posted by smart51
Some cars have 2 sensors, one before and one after the cat. It uses the second sensor to fine tune the fuelling. You'd probably need to leave
it alone.
This is found on OBDII equipped cars, and is to tell the ECU how well the cat is working, i.e. it's purely for emissions warning than fuelling.
Are you sure? I'm fairly certain that Euro 4 and 5 cars fine tune their fuelling for aggressive emissions limits by looking at the excess air
both sides of the cat.
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Peteff
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| posted on 10/6/09 at 12:20 PM |
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My Kia failed on emissions last year and when I took the front pipe off it was completely hollow. I replaced the cat and can say it has not made a bit
of difference to performance or noise (it's still noisy and slow )
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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MikeRJ
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| posted on 10/6/09 at 01:59 PM |
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quote:
Originally posted by smart51
Are you sure? I'm fairly certain that Euro 4 and 5 cars fine tune their fuelling for aggressive emissions limits by looking at the excess air
both sides of the cat.
Quite sure. The only useful information that can be gained by an oxygen sensor after the cat is how well the cat is working. The ECU looks at the
difference between the pre-cat and post-cat oxygen sensors, a similar reading on both indicates the cat is not doing it's job.
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mark chandler
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| posted on 10/6/09 at 04:02 PM |
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Failed emmisions without a cat is usually down to a lazy lambda sensor, they should be replaced on a regular basis but just get left alone.
Regards Mark
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niceperson709
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| posted on 10/6/09 at 10:47 PM |
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Emissions is not an issue Mark because they do not test for that here.
Thanks to all here for your help, it looks like one cat will go in the bin and the other will be getting the iron bar treatment
Best wishes IAIN
life is not the rehearsal , it's the show so don't sit there thinking about it DO IT NOW
http://iainseven.wordpress.com/
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andkilde
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| posted on 11/6/09 at 12:54 AM |
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quote:
Some cars have 2 sensors, one before and one after the cat. It uses the second sensor to fine tune the fueling. You'd probably need to leave
it alone.
If you're saddled with an OBD II system you can purchase O2 bung "extenders" which take the one of O2 sensors out of the exhaust
stream to fool the ECU into thinking the cat is functioning properly as well. You might be able to fiddle the signal with a resistor as well.
For the most part, a "bad" or missing cat will throw a Check Engine code without causing the engine to run poorly, the 1st O2 sensor is
the one used to measure mixture for closed-loop operation, the second is just an emissions system health indicator. In this case, the
"fault" can be cured with gaffer tape or wire cutters 
Some cars may be programmed to go into "limp" mode with any fault though.
Cheers, Ted
[Edited on 11/6/09 by andkilde]
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