Pre cat removal - a right pita
Discussion
Hi All,
I thought I would get stuck into removing the pre-cats as sorted a few hours spare. I want lower temps in the engine bay.
What a nightmare. I have a 94 4.0 HC, so I’m presuming the cats are 26+ years old? I wrongly presumed they would just break apart. 3 hours in, hands sore/ bruised & really getting nowhere. The cat was extremely hard and the more I hit it the harder tit seemed to get. In fact, it had moved back and was jammed and access was worse than when I started! Drill bits had broken; a flexible drill bit was going nowhere; my crow bar was making matters worse etc.
So, I had no option but to cut a window into the manifold. This proved a winner as I could peel the cat and finally get the bloody thing out. I didn’t mess about with the other one and it was out within 20 mins. The photos are of the second cat.
Both cats were in remarkably good condition. God knows how others got them out any other way as mine were rock solid and would not budge in any direction.
I thought I would get stuck into removing the pre-cats as sorted a few hours spare. I want lower temps in the engine bay.
What a nightmare. I have a 94 4.0 HC, so I’m presuming the cats are 26+ years old? I wrongly presumed they would just break apart. 3 hours in, hands sore/ bruised & really getting nowhere. The cat was extremely hard and the more I hit it the harder tit seemed to get. In fact, it had moved back and was jammed and access was worse than when I started! Drill bits had broken; a flexible drill bit was going nowhere; my crow bar was making matters worse etc.
So, I had no option but to cut a window into the manifold. This proved a winner as I could peel the cat and finally get the bloody thing out. I didn’t mess about with the other one and it was out within 20 mins. The photos are of the second cat.
Both cats were in remarkably good condition. God knows how others got them out any other way as mine were rock solid and would not budge in any direction.
Removing the precats is the biggest waste of time imo, some sort of perpetuated myth. Did mine with the manifolds off the car and it took many hours, made no noticeable difference to temps and left the empty manifolds now 'ringing' to the point were I had to cover them in exhaust wrap to try dampen it back down.
I agree with this ^^^^^
I think it might release a bit of hp at the top end, 5bhp maybe, but you’ll never really notice it.
If anything the main cat runs hotter.
And yes it effects the harmonics quite badly at cruising speeds so you now have an annoying booming that offers nothing useful.
I’d still prefer to run without the restriction so the only real answer is to replace manifolds for early de cat ones or a bespoke set up which is expensive but looks great and does offer better flow.
I think it might release a bit of hp at the top end, 5bhp maybe, but you’ll never really notice it.
If anything the main cat runs hotter.
And yes it effects the harmonics quite badly at cruising speeds so you now have an annoying booming that offers nothing useful.
I’d still prefer to run without the restriction so the only real answer is to replace manifolds for early de cat ones or a bespoke set up which is expensive but looks great and does offer better flow.
Edited by Classic Chim on Saturday 1st May 08:19
usually makes no sense to go that way, as the manifolds itselves often leak on the 4in1 joint and they often leack on the head-side flange.
so better remove them...do a proper job...
cutting-holes and re-welding it, will obviously put the focus onto the manifolds...so everybody opening the bonnet will immediately see what was going on....you may "cover" the weld by wrapping the manifolds.
so better remove them...do a proper job...
cutting-holes and re-welding it, will obviously put the focus onto the manifolds...so everybody opening the bonnet will immediately see what was going on....you may "cover" the weld by wrapping the manifolds.
I always intended on wrapping the manifolds and the rest of the exhaust afterwards and have done so.
Removing any cats has got to increase exhaust flow - I cannot see anything but a benefit with this. Also, when I removed my cats from my previous 4.5 Cerbera (located under the gearbox), the heat reduction was massive. Im already noticing lower running temps on the gauge which is a bonus. A right pig of a job but I'm pleased I did it. With the pre cats removed plus sleeving the centre muffler the exhaust noise is slightly louder with a more noticeable burble on tick over but nothing to write home about. I am quite disappointed actually.
Now to the main cat - I believe the noise will increase dramatically. This removal will be way easier but I will get this one welded by a pro as the "window" will be much biggerI don't want to sound like a boy racer but with no annual MOT checks here in WA it seems a no brainer again. I have already sleeved the centre muffler and still have a hot dog and some rear thin silencers remaining on each side of the exhaust so it shouldn't be too loud!
I removed mine as one of them was partially collapsed and that WAS interrupting flow. There was a slight difference in running and it crackled a bit more afterwards too. I wouldn't necessarily have removed them if there was no collapse and I agree with removing the main cat. Maybe start there first.
Just remember to wear a good mask/respirator while you're doing it. There are some nasty particles in there by all accounts...and yes, it's a pita job but worth doing properly.
Just remember to wear a good mask/respirator while you're doing it. There are some nasty particles in there by all accounts...and yes, it's a pita job but worth doing properly.
Wolvesboy said:
I always intended on wrapping the manifolds and the rest of the exhaust afterwards and have done so.
Removing any cats has got to increase exhaust flow - I cannot see anything but a benefit with this. Also, when I removed my cats from my previous 4.5 Cerbera (located under the gearbox), the heat reduction was massive. Im already noticing lower running temps on the gauge which is a bonus. A right pig of a job but I'm pleased I did it. With the pre cats removed plus sleeving the centre muffler the exhaust noise is slightly louder with a more noticeable burble on tick over but nothing to write home about. I am quite disappointed actually.
Now to the main cat - I believe the noise will increase dramatically. This removal will be way easier but I will get this one welded by a pro as the "window" will be much biggerI don't want to sound like a boy racer but with no annual MOT checks here in WA it seems a no brainer again. I have already sleeved the centre muffler and still have a hot dog and some rear thin silencers remaining on each side of the exhaust so it shouldn't be too loud!
Dont cut a window, mark the orientation accurately then cut the entire top off with a thin blade hacksaw just under the weld seam, much easier to get the cat out. Then tig weld it back together again to ,make it look pretty. I prefer to use a saw rather than a grinder with slitting disc as you can easily go off track with a slitting disc and it will end up looking a right pigs ear if you're not careful.Removing any cats has got to increase exhaust flow - I cannot see anything but a benefit with this. Also, when I removed my cats from my previous 4.5 Cerbera (located under the gearbox), the heat reduction was massive. Im already noticing lower running temps on the gauge which is a bonus. A right pig of a job but I'm pleased I did it. With the pre cats removed plus sleeving the centre muffler the exhaust noise is slightly louder with a more noticeable burble on tick over but nothing to write home about. I am quite disappointed actually.
Now to the main cat - I believe the noise will increase dramatically. This removal will be way easier but I will get this one welded by a pro as the "window" will be much biggerI don't want to sound like a boy racer but with no annual MOT checks here in WA it seems a no brainer again. I have already sleeved the centre muffler and still have a hot dog and some rear thin silencers remaining on each side of the exhaust so it shouldn't be too loud!
caduceus said:
I removed mine as one of them was partially collapsed and that WAS interrupting flow. There was a slight difference in running and it crackled a bit more afterwards too. I wouldn't necessarily have removed them if there was no collapse and I agree with removing the main cat. Maybe start there first.
Just remember to wear a good mask/respirator while you're doing it. There are some nasty particles in there by all accounts...and yes, it's a pita job but worth doing properly.
I have only used a long SDS drill bit and patience to break them out previously , but Spitfires advice is sound Just remember to wear a good mask/respirator while you're doing it. There are some nasty particles in there by all accounts...and yes, it's a pita job but worth doing properly.
also agree with Caduceus above it dont take much history of a misfire to get them moving or worse collapsing/melting the common result is they then go on to shear off the 02 sensor tips IME or restrict gas flow causing further aggravation and cost if not diagnosed correctly spitfire4v8 said:
Dont cut a window, mark the orientation accurately then cut the entire top off with a thin blade hacksaw just under the weld seam, much easier to get the cat out. Then tig weld it back together again to ,make it look pretty. I prefer to use a saw rather than a grinder with slitting disc as you can easily go off track with a slitting disc and it will end up looking a right pigs ear if you're not careful.
Thanks for the advice - I have already done them now. I found welding a patch over the window was way easier than attempting to use the original cut out. Ok, my method will look a lot messier but exhaust wrap hides it perfectly! Does the main cat removal make 'that"much of a difference to the sound?
Just adding my 10cents worth. I did the precat removal with manifolds on. A very scary exercise indeed knowing that getting any cat pieces back into the engine would be curtains. I used a very long drill bit and then a variety of other improvised tools to get the cats out... one was already loose. I also used a Garden leaf sucker to Vacuum out the pieces as I went. End result was, in my opinion, a better exhaust note and more pops and crackles. For zero outlay, save my nerves, it was worth it. If I had other reasons to take the manifolds off I would have done it that way. I’ve no intention of removing the big cat.. don’t fancy the truck like sound.
I never would but then I'm a believer of s
t can happen so lower the odds I cant really notice a massive difference in the exhaust noise with pre-cats removed. It is probably a smidgeon louder at the front end. Then again I still have a "hotdog" and a smallish silencer on each exhaust pipe out the back. I definitely don't get any pops and bangs or anything like a decent exhaust note still.
I have manifolds similar in style to those sold by ACT as performance manifolds and despite being smaller than the TVR ones they make a huge difference to sound I guess as there's no restrictions until the silencer. I don't get pops and bangs like a teenagers mapped mini put I do get a few partly I think due to having a leaking manifold at the mo.
Edited by indigochim on Saturday 15th May 11:49
Wolvesboy said:
I cant really notice a massive difference in the exhaust noise with pre-cats removed. It is probably a smidgeon louder at the front end. Then again I still have a "hotdog" and a smallish silencer on each exhaust pipe out the back. I definitely don't get any pops and bangs or anything like a decent exhaust note still.
Do you have a picture of your silencers on your tail pipes as that’s an after market thing I assume? Your unlikely to get pops and bangs with extra mufflers damping them out I’d have thought.
Try slowing down with a bit of trailing throttle at around 2000 revs or below, that should provoke pops and bangs.
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