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cat bypass / decat

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Old 09-29-2008, 05:03 PM
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Default cat bypass / decat

Anybody removed their catalytic convertors with a pair of straight through pipes here?
I've noticed that there's two O2 sensors (before and after the cat) in the std pipe and was wondering if it would throw any error codes.
(any links to decat suppliers would be good too)
 
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Old 09-29-2008, 05:05 PM
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Default RE: cat bypass / decat

yes youll throw codes, theres a UK company that sells performance bolt on cats
 
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Old 09-29-2008, 09:45 PM
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Default RE: cat bypass / decat

Milltek
 
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Old 09-30-2008, 02:57 PM
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Default RE: cat bypass / decat

thanks. I'll take a look at their site.


 
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Old 10-01-2008, 06:29 AM
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Default RE: cat bypass / decat

The car might runokay with the cats removed, but the downstreamO2 sensorwill set a PO420-430 code that willl not go out. You would not pass vehicle inspection most places with this done. Anotherissue of this is that there will be an unknown change in exhaust backpressure that the mixture trim sensorsmay not have the range to handle. It will be an experiment.
 
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Old 10-06-2008, 03:31 PM
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Default RE: cat bypass / decat

Ok thanks.
I'd change the cats back in again come MOT (vehicle inspection) time and could quite happily live with the code so the only concerning issue would be fueling.
I've got a Wideband O2 I can use to check the mixture too so I think I'll see about getting a pair made up in the next couple of months and see how it goes.

 
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Old 10-06-2008, 04:31 PM
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Default RE: cat bypass / decat

Why would you want to remove the cats? I highly doubt you would notice any significant HP gains.
 
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Old 11-07-2008, 06:55 AM
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Default RE: cat bypass / decat

Cats are restrictive and you will see worthy performance gains on an XJR by replacing them with straight through pipes.
 
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Old 11-07-2008, 07:47 AM
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Default RE: cat bypass / decat

you need to use spark plug anti fouler to try and eliminate the code for inefficient cats, they do work but Ive seen people have to use 2to 3 to get the desired result which is to move the downstream 02 out of the exhaust stream enough to think theres a cat there thats cleaning the exhuaust. Because its only looking at the reading variance between the up and downstream readings to determine cats are working properly.
 
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Old 11-12-2008, 11:07 AM
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Default RE: cat bypass / decat

If you have an XJR, wouldn't be more effective to work on the supercharger and pulley combo?
 
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Old 11-13-2008, 01:49 PM
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Default RE: cat bypass / decat

Really, if you know SO much why are you asking these questions in here? The engine was designed to run with the cats in place, what makes you think that taking them out is gonna make any NOTICEABLE difference in output? Have you seen a dyno graph indicating this or is it seat of the pants feel?
 
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Old 11-17-2008, 01:09 PM
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Default RE: cat bypass / decat

Just something to think about, if thebackpressure is reduced, the fueling map needs to be adjusted to prevent leaning from too much scavenge. Unless you have access to an engineer that can remap for you, the risk is a car that runs more poorly than stock. Messing about with sophisticated cars like this without engineering talent can be a frustrating exercise. The alst thing you need is a burned valve, and this is possible if the sensors do not have compensating range.
 
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Old 11-17-2008, 01:58 PM
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Default RE: cat bypass / decat

No Cats = No Backpressure
No Backpressure = Reduced Compression
Reduced Compression = Less Torque
Less Torque = NO FUN!!! [:@]

You may pick up 3-5hp on a N/A car and 5-10 on a S/C, but by doing this you significantly decrease the amount of torque your car will have by decreasing the backpressure too much which in turn will drop your compression... If you own EuroToys and you can Retune your ECU yourself and adjust your air/fuel, advance, and swap your cams, then hell have at it.. but considering that most of us here don't own our own Jaguar performance shop.. your much better off leaving well enough alone..


HOWEVER... if your cats are clogged or destroyed from dumping gas into them from a misfire or running too rich and your picking up a catalytic converter operating below efficiency type code, then go for it..
 
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Old 11-26-2008, 06:01 PM
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Default RE: cat bypass / decat

I have not checked but I think the fronts are wideband and the rears are narrow band.
 
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Old 12-02-2008, 07:56 PM
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Default RE: cat bypass / decat

Your cat is getting decatted.... more like a declaw.. with the loss of compression....


your kitty will wimper. MEOW!
 
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Old 07-12-2018, 12:56 AM
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10yr old post but will reply regardless

My XK8 was decatted for a total of 5yrs with a straight through exhaust with NO silencers, dyno'd at Noble's at running 18% higher BHP and 11% stock on the torque curve throughout the band

But my car also ran:

BMC carbon dynamics intake
Royal purple 5w30
On lpg/propane 95% of the time

It sounded awesome (esp through tunnels!) The bypasses still look brand new and had two holes each for 02 sensors (my car only had one a side so one is bunged

Oh and I never had a fault code
 
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Old 07-12-2018, 02:31 AM
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Though now it would be an MoT fail.

And it was not legal anyway as it's not allowed to tamper with (let alone remove) emissions-related devices.
 
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Old 07-12-2018, 05:56 AM
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Nice information to have, for later. Over here, after 25 years, your days of E check are finished. So if nothing really complex needs to happen, other than places correctly spaced for the 02 sensors, why not? Do the cats really increase back pressure much at all? If not, wouldn't your computer adjust things as far as the trim numbers without any real issues? If so, better performance, without a decrease in fuel economy, or EXCESSIVE exhaust noise, seems to be what we are all looking to accomplish.
 
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Old 07-12-2018, 08:04 PM
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I have an 05 XJR, My first exhaust mod was to remove the center resonators and replace them with an X-pipe. This improved the exhaust a note some and I don't recall much of a performance gain. My next step was to replace the converters with strait pipes that I made myself with O2 simulators. The car was way too loud. I installed a magaflow X muffler in place of the X-pipe and the exhaust note was more tolerable. The car is louder than most of Jaguar purist would like, but It sounds good to me. I do get the occasional check engine light, but I can reset it. I may try to add some spark plus anti foulers like Brutal to the simulators to see if the keeps the check engine light from coming on as often.

The car runs strong, but I don't have access to a chassis dyno near me to check the HP. The car also has a 3 LB Pulley, Caldoofy intake, Mina Gallery cone air filter and upgraded inter-cooler pump.
I get a 20 MPG on the interstate. Could be a little better if I kept my foot out of it. we don't have MOT or emissions testing in Kentucky.

Woofard XJR
 
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