Pre cat removal
Discussion
I've heard/read that removing the pre-cats gives a nicer sound and a bit more welly. I'm thinking of having it done and have a few questions...
How much does it cost?
How much louder is it?
How noticable is the power increase in a 4L?
Does it affect insurance and if so by how much?
And all in all, is it worth it?
Can't afford the 4l->5l upgrade so I'm starting small
How much does it cost?
How much louder is it?
How noticable is the power increase in a 4L?
Does it affect insurance and if so by how much?
And all in all, is it worth it?
Can't afford the 4l->5l upgrade so I'm starting small
Can't remember what it cost, but it wasn't very much.
No noticeable increase in noise (but then I do still have the main cat).
No noticeable increase in power (maybe a few BHP but not enough to be obvious).
You need to inform your insurers, make sure they realize you have not removed the main cat, I would not expect any increase.
Worth it if your precats are loose or blocked, otherwise I wouldn't bother.
No noticeable increase in noise (but then I do still have the main cat).
No noticeable increase in power (maybe a few BHP but not enough to be obvious).
You need to inform your insurers, make sure they realize you have not removed the main cat, I would not expect any increase.
Worth it if your precats are loose or blocked, otherwise I wouldn't bother.
Interesting comments Peter - have similar situation myself.
I have an annoying manifold gasket type ticking noise, that has so far eluded many expert brains. Gaskets, rockers, lifters, manifold crack inspections etc, to no avail.
My theory is that there is a crack in between the 4 pipes where they meet at the first cat - therefore impossible to see.
If I change, my options are:
a) new manifold for left hand bank @ £lots
b) 2 stainless cat-free manifolds for about the same price as 1 standard manifold above.
c) 2nd hand std manifold for a fair bit less.
I quite fancy the s/s option, but am also interested in whether I'll get nicer sound or smoother/more power?
I'm also told that mine has manifold cats, NOT pre-cats (1997). I wasn't aware there was a difference, but there you go. I'm told pre-cats are just cones, and cats are, well, cats!
Of course the elusive ticking may still be something else, but I'm sure that's where it's coming from, even if no-one can see any exterior evidence.
Opinions gratefully appreciated........
I have an annoying manifold gasket type ticking noise, that has so far eluded many expert brains. Gaskets, rockers, lifters, manifold crack inspections etc, to no avail.
My theory is that there is a crack in between the 4 pipes where they meet at the first cat - therefore impossible to see.
If I change, my options are:
a) new manifold for left hand bank @ £lots
b) 2 stainless cat-free manifolds for about the same price as 1 standard manifold above.
c) 2nd hand std manifold for a fair bit less.
I quite fancy the s/s option, but am also interested in whether I'll get nicer sound or smoother/more power?
I'm also told that mine has manifold cats, NOT pre-cats (1997). I wasn't aware there was a difference, but there you go. I'm told pre-cats are just cones, and cats are, well, cats!
Of course the elusive ticking may still be something else, but I'm sure that's where it's coming from, even if no-one can see any exterior evidence.
Opinions gratefully appreciated........
[quote=V8 Kieran
I'm also told that mine has manifold cats, NOT pre-cats (1997). I wasn't aware there was a difference, but there you go. I'm told pre-cats are just cones, and cats are, well, cats!
Opinions gratefully appreciated........[/quote]
No The "pre-Cats" are the small manifold cats, I just prefer to call them manifold cats.
The cones are a modification done during decatting, all chimaeras left the factory with manifold cats.
the manifold cats are next to useless, many come loose or melt or a combination of the two, they are not required for the MOT test but you probably knew that.
I would recommend cones whether in new or used manifolds, and as a bonus you'll like the sound.
I'm also told that mine has manifold cats, NOT pre-cats (1997). I wasn't aware there was a difference, but there you go. I'm told pre-cats are just cones, and cats are, well, cats!
Opinions gratefully appreciated........[/quote]
No The "pre-Cats" are the small manifold cats, I just prefer to call them manifold cats.
The cones are a modification done during decatting, all chimaeras left the factory with manifold cats.
the manifold cats are next to useless, many come loose or melt or a combination of the two, they are not required for the MOT test but you probably knew that.
I would recommend cones whether in new or used manifolds, and as a bonus you'll like the sound.
The term pre-cat often causes confusion.
Cars which were built before cats were introduced (in 1993) are called pre-cats.
The RV8 cars fitted with cats have three cats: the main cat at the front of the engine bay, and a smaller cat inside the 4:1 collector in each exhaust manifold. The smaller cats in the collectors are called pre-cats. It is a common modification to take out these pre-cats and put a non-reversal cone inside the collector instead, leaving the main cat unchanged. This is entirely legal and shouldn't cause any trouble at MOT time, but you would need to advise your insurers. There is no need to get the car remapped if you don't want to.
A more extreme modification is to replace the whole exhaust manifold and Y piece with one without any cats in. This what is normally meant by the term 'decat'. It is unclear whether this is legal, my understanding is that it is legal but others disagree. It will certainly make it extremely hard or impossible to pass an MOT. Again, you would need to advise your insurers. Since the catless manifolds normally won't accept the lambda sensors, you will have to have the car remapped in open-loop mode. Even if it does accept the lambda sensors, changing the whole exhaust makes such a big difference to the engine tune that it would be sensible to have it remapped.
Cars which were built before cats were introduced (in 1993) are called pre-cats.
The RV8 cars fitted with cats have three cats: the main cat at the front of the engine bay, and a smaller cat inside the 4:1 collector in each exhaust manifold. The smaller cats in the collectors are called pre-cats. It is a common modification to take out these pre-cats and put a non-reversal cone inside the collector instead, leaving the main cat unchanged. This is entirely legal and shouldn't cause any trouble at MOT time, but you would need to advise your insurers. There is no need to get the car remapped if you don't want to.
A more extreme modification is to replace the whole exhaust manifold and Y piece with one without any cats in. This what is normally meant by the term 'decat'. It is unclear whether this is legal, my understanding is that it is legal but others disagree. It will certainly make it extremely hard or impossible to pass an MOT. Again, you would need to advise your insurers. Since the catless manifolds normally won't accept the lambda sensors, you will have to have the car remapped in open-loop mode. Even if it does accept the lambda sensors, changing the whole exhaust makes such a big difference to the engine tune that it would be sensible to have it remapped.
Hi Jimothy, my experience is with a 5.0
If the noise is the main thing, get the exhaust sleeved, £120 at an independant, sounds great, no power / torque benefits.
If the pre-cats are in good condition, I understand removing them may improve the torque a little, no real power benefit, sounds a bit louder again. The main cost is the time it takes to remove / replace manifolds, AFAIKS.
And the noise... don't forget it still sounds better to the onlookers than the drivers! I believe one or two ppl have been disappointed. If you live near a tunnel, on the other hand, you will be just fine!
If the noise is the main thing, get the exhaust sleeved, £120 at an independant, sounds great, no power / torque benefits.
If the pre-cats are in good condition, I understand removing them may improve the torque a little, no real power benefit, sounds a bit louder again. The main cost is the time it takes to remove / replace manifolds, AFAIKS.
And the noise... don't forget it still sounds better to the onlookers than the drivers! I believe one or two ppl have been disappointed. If you live near a tunnel, on the other hand, you will be just fine!
Podie said:
So if you remove the pre-cats (or manifold cats) then you should replace them with cones..?
I assume this is to maintain some sort of pressure in the system..?
How much are the cones…? … and why can I feel my credit card melting…
Hi Podie, having mine done at the mo in Peninsula.....pre-cats removed and non-reversal cones fitted: better back pressure/sound and performance (so I'm told by RS there) and the main box gutted and s/s/ sleeves fitted also.
As for cost, I think all the exhaust work is around £350, but I'm having other work done as well (new MC2 cam) £AAHH! So at the time they will have easier access to all the gubbins and may well be cheaper than if just doing exhaust mod alone.
deeen said:
Hi Jimothy, my experience is with a 5.0
If the noise is the main thing, get the exhaust sleeved, £120 at an independant, sounds great, no power / torque benefits.
If the pre-cats are in good condition, I understand removing them may improve the torque a little, no real power benefit, sounds a bit louder again. The main cost is the time it takes to remove / replace manifolds, AFAIKS.
And the noise... don't forget it still sounds better to the onlookers than the drivers! I believe one or two ppl have been disappointed. If you live near a tunnel, on the other hand, you will be just fine!
The loudness isn't my main concern (but its a nice by-product
). One of my friends has a Scoobie and he was told that removing the Pre-Cats on that gives 40bhp more, so it was the power increase thats got me thinking. I can't afford anything more drastic yet so a little bit to enlarge my normal TVR smile would be nice.V8 Kieran said:
Interesting comments Peter - have similar situation myself.
I have an annoying manifold gasket type ticking noise, that has so far eluded many expert brains. Gaskets, rockers, lifters, manifold crack inspections etc, to no avail.
My theory is that there is a crack in between the 4 pipes where they meet at the first cat - therefore impossible to see.
Kieran, get a length of silicon pipe approx 5mm inside diameter (silicon is heat resistant) and put one end near your ear and poke the other end down the gap between the 4 pipes. If there is a crack there the ticking noise will get louder the further you push it in .
Following on the lines of Podie's question then, do the Peninsular s/s manifolds come with cones, or do I need to specify etc? (I suppose the answer is "call 'em", but thought I'd ask)
Thanks Peter for the CAT lesson. I agree with you in that my understanding is cars must be sold with cats, but it is not a legal requirement to have them - you just need to pass the emissions test.
Although I'm not really a bonnet-up guy, s/s manifolds also look cool!
Thanks Peter for the CAT lesson. I agree with you in that my understanding is cars must be sold with cats, but it is not a legal requirement to have them - you just need to pass the emissions test.
Although I'm not really a bonnet-up guy, s/s manifolds also look cool!
else said:Thanks Andrew.
Kieran, get a length of silicon pipe approx 5mm inside diameter (silicon is heat resistant) and put one end near your ear and poke the other end down the gap between the 4 pipes. If there is a crack there the ticking noise will get louder the further you push it in .
Castle did similar to confirm noise coming from that area, but I might try sliding the hose up and down to see if I can find the crack..... (How long can you resist Podie?
)
Podie said:
So if you remove the pre-cats (or manifold cats) then you should replace them with cones..?
I assume this is to maintain some sort of pressure in the system..?
How much are the cones…? … and why can I feel my credit card melting…
I'm told the cones make a noticable difference in power. I can't believe they cost that much to insert, the pricey bit is removing the manifolds and cutting the cat section out.
Ian A.
V8 Kieran said:
Interesting comments Peter - have similar situation myself.
My theory is that there is a crack in between the 4 pipes where they meet at the first cat - therefore impossible to see.
If I change, my options are:
a) new manifold for left hand bank @ £lots
b) 2 stainless cat-free manifolds for about the same price as 1 standard manifold above.
c) 2nd hand std manifold for a fair bit less.
I quite fancy the s/s option, but am also interested in whether I'll get nicer sound or smoother/more power?
Opinions gratefully appreciated........
Hi, just to say both my manifolds cracked in the weld where the four go into one, so you could well be right.
Mine were removed, cut for access, leak welded, then access cut welded.
I was quoted 4 hrs to remove and replace both manifolds, 4 gaskets, and one or two hours welding per manifold. Had the pre cats taken out, included in above. No cones - don't understand cones.
Once the manifolds are off it's easy to check for the leak, I guess.
One person who does stainless manifolds is ACT. I believe his design smooths out the gasflow a bit and he does claim HP benefits, don't know if this assumes remap or RR setup though.
Jimothy - I was told nothing like those horsepower gains removing pre-cats on healthy 500, in fact I was told to expect no power gain but an improvement in torque, but also that they do come accross blocked pre-cats from time to time.
>> Edited by deeen on Tuesday 1st February 14:09
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