catylst exhaust query
Discussion
I rang Tim at ACT with this query, but they all seem to be at the NEC at the moment so perhaps one of you kind and knowledgeable chaps could help me.
I have been reading with interest the various recent threads on the subject of modifying the exhaust system on a later Griff to improve the sound output.
With my 96 500 serp with catalysts the car does tend to sound muted and I can understand why so many of us owners with catalysts fitted look to make changes.
The thing I am unsure of and I could not find enough detail in the Bible to answer it is this - I think we have a three part cat system - 1 'pre'cat in each of the two manifolds coming from the heads just after they change from 4 to 1 and the main cat located in the system just after the 2 manifolds change to 1 pipe. (Please correct me if I have got it wrong)
From reading the various threads I understand that a number of owners have removed the 2 'pre'cats and even the main cat. Now I don't want re-open the debate on performance changes, but what are the 2 'pre'cats supposed to do and is it only the main cat that affects emissions (MOT).
My feeling (and I am no expert) is that as the exhaust gasses spend a lot of their time in just 1 pipe we will never truly achieve that V8 rumble that we hear on other cars without spending £££ on a sports exhaust etc.
Tell me I wrong please, and that I can get the sound of a V8 without breaking the bank or causing problems at MOT time.
Cheers, Paul
I have been reading with interest the various recent threads on the subject of modifying the exhaust system on a later Griff to improve the sound output.
With my 96 500 serp with catalysts the car does tend to sound muted and I can understand why so many of us owners with catalysts fitted look to make changes.
The thing I am unsure of and I could not find enough detail in the Bible to answer it is this - I think we have a three part cat system - 1 'pre'cat in each of the two manifolds coming from the heads just after they change from 4 to 1 and the main cat located in the system just after the 2 manifolds change to 1 pipe. (Please correct me if I have got it wrong)
From reading the various threads I understand that a number of owners have removed the 2 'pre'cats and even the main cat. Now I don't want re-open the debate on performance changes, but what are the 2 'pre'cats supposed to do and is it only the main cat that affects emissions (MOT).
My feeling (and I am no expert) is that as the exhaust gasses spend a lot of their time in just 1 pipe we will never truly achieve that V8 rumble that we hear on other cars without spending £££ on a sports exhaust etc.
Tell me I wrong please, and that I can get the sound of a V8 without breaking the bank or causing problems at MOT time.
Cheers, Paul
Hello Paul,the pre-cats are there only for cold idle emissions,and we dont test this as part of the mot in this country.If the engine is in good working order,then it will pass the mot with ease without them.It certainly sounds nicer without them i feel,so do most others.Theres no noticeable performance advantage or disadvantage to be felt after they've been removed in my experience(done two now).The benefits of removing some of the underbonnet heat alone,make removing them well worth it.
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