Just picked up this amazing 2001 XJR Jag a few weeks ago, and I'm looking to put an exhaust on it to hear that throaty V8. This is not to everyone's liking, but I like a pretty loud exhaust system. Was considering doing high flow cats and a cat-back exhaust. BUT, I was also thinking about doing no cats, (I live in a rural area, and we don't have emissions testing) and just go straight pipe. I know this may impact the ECU and/or alter the air/fuel mixture.
Would I need an ECU remap?
Any help on how this all works would be greatly appreciated.
P.S. Absolutely love this forum and have already learned a lot about Jag ownership!

 

Lots of info on exhausts in the XK forum, but general consensus, from what I've read, has been to remove the small middle mufflers. There are aftermarket options for the cats, but they're expensive, but because you have both pre and post O2 sensors, I couldn't guarantee you won't have issues if you remove them altogether.
Another thing to consider is replacing the first large central muffler with a proper cross or h-pipe, but there are pics out there showing that the original piece is basically an h-pipe already, so whether you get any real improvement is questionable

 

Hi
At the moment my exhaust system is out of the car. it is very loud but much much powerful. i thin 20% more powerful With traction control engaged you can not start at full throttle.
Tray to remove the middle silencer and check what i said If you like it use pipes from catalytic converter to the rear of the car, but you will be the only one happy your neighbor and the police they will be very angry.
Unfortunately i do not have a dyno in my town to check the power of the car without the silencer
Good luck

 

let me share my personal experience.

I cut off the middle portion and welded the straight pipe. Car sounded like a old school American muscle, loud and raw like a Harley. I was actually ok with that

but performance wise is the bigger concern . I could definitely feel a very unbalance of acceleration. I felt the car lost so much power at low RPM and once it hit 3k and Supercharger once kicked it, I had a very sudden back pushing feel. this is a SC V8 engine. most torque at lower rpm

it was not a very ideal set up

so later I went X pipe. It is much refined sound but still releasing the potential our SC V8 sound and I feel some power gain(at least feels like)

 

Consensus seems to be that you have to do some trickery with the downstream O2 sensors to run without cats. The easiest method seems to be standoff bungs that pull the probe of the downstream sensors a little further out of the exhaust stream, fooling them into thinking the restriction of the cats is still in place. Apparently this is worth some OK power gains when combined with a larger exhaust.

Your best bet would be to do a complete aftermarket exhaust. The exhaust on the XJR is very small for this powerful of an engine. It's nominally 2" all the way back, but there are several choke points where it goes below that. I would consider dual 2.25" a minimum for a nearly 400 hp engine, and dual 2.5" way better.

It seems that a tune is beneficial but not necessary if you leave the cats in place. It seems like you should get some gains without a tune, but quite a bit more with one. With an exhaust and catless downpipes, a tune is probably approaching necessity.

 

You don't need a tune. I have no cats with bungs on the O2 sensors and x pipe with 2.25 in, 2 magnaflows and 2 resonators to kill the drone. No ecu remap or errors

 

I put infinitely adjustable electric exhaust cut outs on my XJR right after the cats. The range of sound you can get is amazing, from luxury car quiet to full out race car and anything in between. No droning on the highway either.

The cost is reasonable too, depending on installation costs they run $400 DIY to $600-$800 installed by a pro.

This is without a doubt the best mod I have ever done to any car, ever, period.

Thread with pics of the install here: https://www.jaguarforums.com/forum/x...ut-outs-71960/

The pics are not in chronological order so you will have to use your imagination about how the install progressed.

This thread should be a sticky for anyone considering exhaust mods.
Vector

 

Hi Flow Cats installed, and that was enough for me. If I wanted my Jag to sound like an American muscle car, then I would buy and American muscle car..No thanks.