De-catting please!!
Discussion
I know this has been discussed recently but I could do with info from anyone who has actually done it.
I am lead to believe there are 2 pre-cats and a main cat. Where are the pre-cats, are they removed from the manifolds? I assume the main cat is in the dustbin shaped Y section. Does the welded joint need to be split and re-welded?
Is the only change to the ECU to swap the resistor to 470 ohms?
What realistic benefits has anyone seen with the mod? Are there any downsides (aside from the obvious legal ones!)
I dream of loudness, flames and more power!!
I am lead to believe there are 2 pre-cats and a main cat. Where are the pre-cats, are they removed from the manifolds? I assume the main cat is in the dustbin shaped Y section. Does the welded joint need to be split and re-welded?
Is the only change to the ECU to swap the resistor to 470 ohms?
What realistic benefits has anyone seen with the mod? Are there any downsides (aside from the obvious legal ones!)
I dream of loudness, flames and more power!!
I had mine done by a dealer, on my Chimaera 500.
The pre cats are in the large (4") pipe section into which the four headers merge - one each side obviously.
I had the manifold and Y piece sections replaced entirely, mainly because I wanted to be able to put it back how it was. TVR have separate parts without the cats, externally no difference whatsoever. Large bill though, 1.2k.
There was some "chipping" involved, and I think the timing might have been altered to get max benefit from the cat removal.
I had it done for the sound basically, and was not dissappointed (though it is still NOT a wedge!). Performance is subjectively better, but that could just be because it sounds faster!
One drawback is that at idle the car does sound like it has a leaky gasket - the large cat(-less) chamber makes quite a racket now. I don't think fuelling on mine is 100% as the tickover became erratic to non-existant.
Popping and banging on part throttle is fun! Give it some gas, then back off to part throttle at 4000 rpm and bang! Not sure if explosions as ferocious as that can be good for the car though!
Phil
The pre cats are in the large (4") pipe section into which the four headers merge - one each side obviously.
I had the manifold and Y piece sections replaced entirely, mainly because I wanted to be able to put it back how it was. TVR have separate parts without the cats, externally no difference whatsoever. Large bill though, 1.2k.
There was some "chipping" involved, and I think the timing might have been altered to get max benefit from the cat removal.
I had it done for the sound basically, and was not dissappointed (though it is still NOT a wedge!). Performance is subjectively better, but that could just be because it sounds faster!
One drawback is that at idle the car does sound like it has a leaky gasket - the large cat(-less) chamber makes quite a racket now. I don't think fuelling on mine is 100% as the tickover became erratic to non-existant.
Popping and banging on part throttle is fun! Give it some gas, then back off to part throttle at 4000 rpm and bang! Not sure if explosions as ferocious as that can be good for the car though!
Phil
My Griff 500 is de-catted and was done by the previous owner.
Disadvantages:
Makes the car modified so the insurance company needs to know. No increase in premium as the engine was seriously tweaked as well.
Makes the car loud enough to get banned from most track days. I have to use additional silencing.
The ECU needs to be re-chipped as the replacement manifold bits do not have any lambda sensors and the ECU needs to be converted from closed loop to open loop. Reprogram not a resistor change.
Won't pass the MOT emmissions test so you need to refit the cats to get it through.
The flames eats through the silencer making replacement an expensive and more common occurance.
Leagality still not clear.
Advantages:
Breathes a little bit better.
Slightly crisper sound.
Would I do it if it had not already been done? No.
Regards
Steve
Disadvantages:
Makes the car modified so the insurance company needs to know. No increase in premium as the engine was seriously tweaked as well.
Makes the car loud enough to get banned from most track days. I have to use additional silencing.
The ECU needs to be re-chipped as the replacement manifold bits do not have any lambda sensors and the ECU needs to be converted from closed loop to open loop. Reprogram not a resistor change.
Won't pass the MOT emmissions test so you need to refit the cats to get it through.
The flames eats through the silencer making replacement an expensive and more common occurance.
Leagality still not clear.
Advantages:
Breathes a little bit better.
Slightly crisper sound.
Would I do it if it had not already been done? No.
Regards
Steve
quote:
I know this has been discussed recently but I could do with info from anyone who has actually done it.
I am lead to believe there are 2 pre-cats and a main cat. Where are the pre-cats, are they removed from the manifolds? I assume the main cat is in the dustbin shaped Y section. Does the welded joint need to be split and re-welded?
Is the only change to the ECU to swap the resistor to 470 ohms?
What realistic benefits has anyone seen with the mod? Are there any downsides (aside from the obvious legal ones!)
I dream of loudness, flames and more power!!
You can knock the pre-cats out with no other mods at all, the power gain is between 5/10 BHP which is enough to measure but not really enough to feel any difference. You do have to dismantle the exhaust to take the precats out but I understand it doesn't involve cutting/welding etc, just unbolting. (Had mine done, but didn't do it myself.)
No effect on MOT, the emissions during cold start will be a lot worse but they don't measure that.
Cheers,
Peter Humphries (and a green V8S)
Edited by Greenv8s on Thursday 20th December 21:49
They are cheaper than buying a new PAS steering rack... 
If you are at all worried, don't remove them. It is not mandatory to remove cats. As I said in Sprint on trade up vs modify, virtually any modification will be done at the owner's risk. If something goes wrong, the owner is repsonsible. If you take out the pre-cats and run a main cat and it fails... then who knows. If it is under warrenty, then forget it, you may have a very hard time getting anywhere. If it is out of warrenty, you pay if it fails anyway so there is no choice.
Steve
www.tvrbooks.co.uk
If you are at all worried, don't remove them. It is not mandatory to remove cats. As I said in Sprint on trade up vs modify, virtually any modification will be done at the owner's risk. If something goes wrong, the owner is repsonsible. If you take out the pre-cats and run a main cat and it fails... then who knows. If it is under warrenty, then forget it, you may have a very hard time getting anywhere. If it is out of warrenty, you pay if it fails anyway so there is no choice.
Steve
www.tvrbooks.co.uk
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