Getting rid of the pre-cats
Discussion
I'm thinking about getting rid of the pre-cats before the winter is over. I've read all about the difficulties, so I intend to take off the manifolds first and replace the gaskets at the same time.
Once back on the car, do I need to get the ECU re-mapped, or any other 'tweaks' if all I'm doing is removing the pre-cats?
Thanks in advance.
Once back on the car, do I need to get the ECU re-mapped, or any other 'tweaks' if all I'm doing is removing the pre-cats?
Thanks in advance.
I'm fairly certain that i did not change anything ecu wise when i removed my pre cats 
main cat then that's a different matter i seem to recall.
Any how its a good mod to carry out for the following reasons
1 Removing them reduces under bonnet temperature by a considerable amount
2 Will improve the exhaust note but not by a huge amount
3 will release approximately 3hp
They are a pig to remove as are the manifolds but as i say its well worth the effort just for the under bonnet temp reduction alone and also it has no bearing on the MOT test whats so ever so get cracking
main cat then that's a different matter i seem to recall.Any how its a good mod to carry out for the following reasons
1 Removing them reduces under bonnet temperature by a considerable amount
2 Will improve the exhaust note but not by a huge amount
3 will release approximately 3hp
They are a pig to remove as are the manifolds but as i say its well worth the effort just for the under bonnet temp reduction alone and also it has no bearing on the MOT test whats so ever so get cracking
All cats removed on mine. No ECU changes.
Just for your interest, below are temp readings before and after removing all three cats on my Griff.
Temperatures using IR thermometer: -
Before
NS pre cat area = 280c
OS pre cat area = 290c
Main cat area = 195c
After
NS pre cat area = 240c
OS pre cat area = 220c
Main cat area = 90c
Just for your interest, below are temp readings before and after removing all three cats on my Griff.
Temperatures using IR thermometer: -
Before
NS pre cat area = 280c
OS pre cat area = 290c
Main cat area = 195c
After
NS pre cat area = 240c
OS pre cat area = 220c
Main cat area = 90c
Your gonna have to shout if you do I reckon, I have removed precats and had the Offord sleeve conversion done and its loud enough but nice, with it producing a deep burble on tick over to a incredible roar when you get on the loud pedal. I`m toying with the idea of removing the main cat but have been told it sounds a bit "tinny" due to the large diameter of the pipe and will be that loud that it will attract a lot of attention from the B.I.B? 
Anyone shed any more light on the above mods and the resulting noise
?Right - seems no good reason to keep them then!!
Now I'll replace the manifold gaskets as a matter of course, but is there a special sealant or grease that I should apply to ensure a good seal? What about the bolts? Should I replace these too? Are they just standard off-the-shelf size or something special? Where is a good place to source these?
Any thing else I could do while I have the manifolds off?
I've finished my other winter projects and am now getting itchy. Can't have the car just sitting in the garage - need to either drive it (still got snow on the roads) or play around with it!!!
Now I'll replace the manifold gaskets as a matter of course, but is there a special sealant or grease that I should apply to ensure a good seal? What about the bolts? Should I replace these too? Are they just standard off-the-shelf size or something special? Where is a good place to source these?
Any thing else I could do while I have the manifolds off?
I've finished my other winter projects and am now getting itchy. Can't have the car just sitting in the garage - need to either drive it (still got snow on the roads) or play around with it!!!
No sealant required, New gaskets bolt it all back together,, Pre catts out & main catt removed defo not tinny at all. Really not sure about remove the box thou, To many saying they are to loud,
With Nick Smith making 8 oclock meets sunday mornings my neighbours will hate me,, Yes even more,, Dont forget about MOT if removing main catt..If you do when mot comes round i have a spare,,
With Nick Smith making 8 oclock meets sunday mornings my neighbours will hate me,, Yes even more,, Dont forget about MOT if removing main catt..If you do when mot comes round i have a spare,,
There seems to be a fair bit of confusion over the cats. On cat equipped cars there are three units fitted. There is a pair (One each side) where the four exhaust manifolds join into one , the main cat is located in the large cylinder after all the pipes have joined. The two smaller cats are allegedly there to cope with emissions during the warm up period for type approval. The main cat is needed to have any chance of passing the MOT emissions test. The “tune” the resistor alters the map allowing a richer mixture which the engine may prefer but is not compatible with running a cat. Catalytic converters only work in a fairly narrow mixture range so the lambda sensors measure the mixture reporting rich or lean back to the ECU so it can adjust as required.
There seems to be a good argument for removing the Pre cats as it does help reduce under bonnet temperature, removing the main cat however seems to me to be rather silly as there is very little to be gained unless it is blocked and the car will no longer pass the emissions test.
If you are taking the manifolds off get a decent set of bolts with smaller heads (ARP do some), makes it a lot easier to get a spanner on them.
There seems to be a good argument for removing the Pre cats as it does help reduce under bonnet temperature, removing the main cat however seems to me to be rather silly as there is very little to be gained unless it is blocked and the car will no longer pass the emissions test.
If you are taking the manifolds off get a decent set of bolts with smaller heads (ARP do some), makes it a lot easier to get a spanner on them.
yellowgriff said:
No sealant required, New gaskets bolt it all back together,, Pre catts out & main catt removed defo not tinny at all. Really not sure about remove the box thou, To many saying they are to loud,
With Nick Smith making 8 oclock meets sunday mornings my neighbours will hate me,, Yes even more,, Dont forget about MOT if removing main catt..If you do when mot comes round i have a spare,,
no cats and straight throughs With Nick Smith making 8 oclock meets sunday mornings my neighbours will hate me,, Yes even more,, Dont forget about MOT if removing main catt..If you do when mot comes round i have a spare,,
Mount Ventoux http://www.youtube.com/watch?v=_ESL1oWH
Testing lol http://www.youtube.com/watch?v=2TXYT9nMPS0
Loads more on here LINKY Including many other de catted 500s and original de cats
BB
obviously a car wont pass an mot very easily without the main cat, thats why you have a decat pipe, and refit the main cat for mot purposes, 2 hrs max work giving another 12 months glorious driving.
if you decat the main cat pipe by removing the cat itself, and still using the large dustbin sized pipe of course it will sound terrible,
if you decat the main cat pipe by removing the cat itself, and still using the large dustbin sized pipe of course it will sound terrible,
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