Discussion
Removing manifolds and using a 300 mm long masonry style SDS drill bit to break them up and easily remove them. Some say you can do it in situ but there’s always a risk you suck some honeycomb back into engine when you next fire it up. Using a vacuum cleaner as you break them up might help but I just removed manifolds to be sure.
They are thin so be careful if using chisels or you could easily distort them.
They are thin so be careful if using chisels or you could easily distort them.
I did it off the car with a similar method. I'd bought a spare set of manifolds to do it on rather than spoil my original set. My tip would be to check they don't leak before going to the effort of digging out the cats. These ones I bought leaked at the junction of the 4 pipes into the large one. Fill them with water and see if they leak (Obviously off the car) As it happened one of these spares I had one pre-cat just fell out and the other was a pig to dig out with a selections of pry bars and old chisels.
dogbucket said:
I will chip in with my usual reply and say unless there is something wrong with them leave them alone. It is a pig of a job and I found the now hollow manifolds then 'ring' and sound terrible afterwards.
Well there is that. I totally agree now I come to think about it.
I removed my pre cats because people mentioned the less under bonnet heat ( true) and about 5 hp more from your engine. Both true but 5 bhp you can barely feel it!
Back in the day when it seemed the only thing that mattered on here was your hp figures I did it thinking it was a good thing to do. Totally ruined the sound of my car and I was very disappointed as a result! That boom is very annoying and takes away some sophistication from the car, about the only bit of sophisticated thinking the car possessed
Having pre cat or stainless manifolds now that’s a different matter
Edited by Classic Chim on Tuesday 18th January 13:37
No guarantee you will get the dreaded boom removing pre-cats but possibly will 
I removed mine over 15 years ago due to a pre-cat moving and shearing the tip of one of my 02 sensor 
(possibly down to a previous misfire before my purchase etc) put up with the boom for years but no more since fitting the long primaries ACT manifolds and less ringing to boot
I removed mine over 15 years ago due to a pre-cat moving and shearing the tip of one of my 02 sensor (possibly down to a previous misfire before my purchase etc) put up with the boom for years but no more since fitting the long primaries ACT manifolds and less ringing to boot I bet they put the pre cats in because the later style manifolds with shorter primaries caused boom at certain revs. My very powerful 450 engine makes this problem even worse Simon 
Ok they put the pre cats in for better emissions and my engines not that powerful
I think you might be right about some cars and not others, I’m sure I’ve driven a number of cars decat and never noticed it like l do on my own. It’s got to be down to all that grunt my engine posses Simon
the decked block and compression seems to make it louder out the pipes which does make mechanical sense,,, I think
Or that’s all a load of old tosh
Ok they put the pre cats in for better emissions and my engines not that powerful
I think you might be right about some cars and not others, I’m sure I’ve driven a number of cars decat and never noticed it like l do on my own. It’s got to be down to all that grunt my engine posses Simon
the decked block and compression seems to make it louder out the pipes which does make mechanical sense,,, I think Or that’s all a load of old tosh
Edited by Classic Chim on Tuesday 18th January 15:17
Nope your right Alun more radical cams,bigger CR better breathing, bigger CC's etc all add to the issue IMO, my boom became unbearable after the engine work 2.5k RPM ish and the ex note is still too loud for me and my silencer is stock I think a re-pack may be in order a job for spring no fault of the new manifolds but the silencer itself
more radical cams,bigger CR better breathing, bigger CC's etc all add to the issue IMO, my boom became unbearable after the engine work 2.5k RPM ish and the ex note is still too loud for me and my silencer is stock I think a re-pack may be in order a job for spring no fault of the new manifolds but the silencer itself Did mine in situ today.
A long frustrating job, but not difficult. A much deeper exhaust note and sharper throttle response.
Use a long 10mm masonry drill bit, and don't be too gentle. A small pry bar and cold chisel are very useful. Allow at least three hours. But worth it in my opinion.
Just mind the lambda!
I vacuumed out that dust. Thought I'd got it all. Fired her up on just the manifolds, dust everywhere! And some flame!!
A long frustrating job, but not difficult. A much deeper exhaust note and sharper throttle response.
Use a long 10mm masonry drill bit, and don't be too gentle. A small pry bar and cold chisel are very useful. Allow at least three hours. But worth it in my opinion.
Just mind the lambda!
I vacuumed out that dust. Thought I'd got it all. Fired her up on just the manifolds, dust everywhere! And some flame!!
Hi,
I did mine nearly a couple of years ago in the 1st lockdown.
I took the manifolds off, the manifold gaskets needed replacing anyway.
Whilst off I replaced the engine mounts, easier with the manifolds off.
Mot has never been a problem, passed the emissions with ease.
Easy job, just takes a bit of time and patience.
There was a bit more of a ringing noise but nothing to write home about.
Good luck.
I did mine nearly a couple of years ago in the 1st lockdown.
I took the manifolds off, the manifold gaskets needed replacing anyway.
Whilst off I replaced the engine mounts, easier with the manifolds off.
Mot has never been a problem, passed the emissions with ease.
Easy job, just takes a bit of time and patience.
There was a bit more of a ringing noise but nothing to write home about.
Good luck.
Tyre Smoke said:
NOT an MOT fail.
Not what the MOT tester handbook says for any car later than 1994."On vehicles that qualify for a full cat emissions test, check the presence of the catalytic converter."
https://www.partinfo.co.uk/files/VOSA%20Inspection...
Hi Hans 
I bought some 18" spiders and hub conversions from you some years back (crikey, those were the days). I had ACT do mine with some 'non-reversal' cones put in place to help with exhaust gas speed and scavenging. I thought I'd just do it best I could as I was having them ceramic coated in and out at same time. Overkill maybe for some but it was part of my long term plan so was a little different and I can't knock what others have done. Anyway, good to see you're still around.
I bought some 18" spiders and hub conversions from you some years back (crikey, those were the days). I had ACT do mine with some 'non-reversal' cones put in place to help with exhaust gas speed and scavenging. I thought I'd just do it best I could as I was having them ceramic coated in and out at same time. Overkill maybe for some but it was part of my long term plan so was a little different and I can't knock what others have done. Anyway, good to see you're still around.Gassing Station | Chimaera | Top of Page | What's New | My Stuff