Sunday nov 11
Hi everyone,
It has been a few months since I was in this forum. good to be back.
I have a 1995 XJ6 VDP with 91K miles
It seems that one of the two catalytic converters is more or less totally plugged and this "bothers" the engine.
I am in NC where a 1995 car does not need the "emission" test for car inspection.
Therefore I am thinking of removing the two cat's and replace them with some kind of other mufflers.
has anyone done such a thing,
I would most welcome your experience in this matter (like also removing the oxygen sensor and so on)
Thanks a million

Claude
1995 XJ6 VDP

 

I assume you are talking about removing the catalysts in the downpipes, not the undefloor catalysts. You could remove the downpipes from the car and knock out the metalic substrate, but it won't be easy. You should re-fit the sensors afterwards, otherwise you won't have proper fuel control. However, removing the catalysts will probably cause the check engine light to turn on, because the engine ECU should detect that the signals will be identical from the sensors that are upstream and downstream of the location where the catalaysts used to be.

 

No I meant the two "muffler" like catalysts

 

What is the reaction of the ECU of a European model X300, with only downstream sensors ?

 

my car is a Australian spec X300 XJR
I have custom headers and exhaust system my model has 2 sensors just bellow the front cats when I did the exhaust system I put my new cats under the floor my car doesn't illuminate any dash lights
If I was repairing the original system I would just remove all the cats and put a single large diameter cat under the floor then a single resonator then split it into the twin system most economical way to do the system and if the old cats have dropped some rubbish into the old resonators you have bypassed the problem just use of the shelf magnaflow stuff its readily available
If you keep the front cats just remove the rear ones and add a single resonator splitting into 2 again very easy mods

The reason I did a full system on my car where my cats where 220,000 k,s and 17 old also the car had an over enriching problem which wouldn't have done the cats any good also my header pipes have cracked 3 times just decided to replace the whole lot got sick of the cost of repairs

I also sell the headers for X300 cars made out of 304 stainless steel they have no provision for front cats that way they are true tuned length that's why I put my cats under the floor in my car

If I was doing my car again or another car I wouldn't have used 2 cats under the floor or 2 resonators just one High flow cat and a long single large bore resonator of the shelf like they say you learn as you go along with these cars

 

Did you have an exhaust shop build this from scratch? Anyway of duplicating? How much power did this create? I have an x300 xjr, and just want it to be the happiest it can. Thans for any info.

 

I actually make and sell the headers they are a proven design as you can see in the pic's for my car and below I replaced the full system on my car as the car is 18 years old the original cats would be pretty full by now

With my headers they have no up stream cats making them true tuned length but have oxygen sensor threaded bungs
The headers are designed to be a direct replacement to your standard pipes which means you could just replace the headers fit the oxygen sensors and be going for just the cost of the headers remember these cars are getting old and the standard headers are prone to cracking

If I was doing a system again and had these headers available I would replace the section under the car where the underfloor cats are and underfloor mufflers as the pipe from the headers is a single pipe which splits in to 2 underfloor cats and mufflers
I would install a single same diameter as the single front pipe magnaflow high flow cat and a single resonator with a single input pipe and duel output pipe that would be the most cost effective way to release the power from the engine

My full system made 18 HP at the wheels but gave better low down torque and slightly better fuel economy
With a open air system and exhaust mod and either a remap or timing advance bracket from (XJR engineer) there should be 25 HP in the whole set-up doesn't sound like much but it does make the car perform better

Then a diff ratio change I.E. from the standard XJR 3,23 to 1 to the N/A cars 3.54.1 makes the car substantially quicker
I can hold my head up high against some of the modern cars instead of getting left behind
If you want more info or details private message me

 

That's a work of art! Beautiful work Doc! Where were you 2 months ago when I spent $1K ordering two exhaust manifolds from England?

Can you clarify something: you say your header has an 02 sensor threaded bung, but then you recommend a single cat underfloor. I thought the 02 sensor needed to be downstream from the cat? Aren't they downstream of the factory downpipe-cat not underfloor-cat?

We have no emissions testing here either. Would the engine management system run properly if the car had a new exhaust system with no cat(s) at all?

 

We have emission testing here just not regularly they do spot roadside testes
The 02 sensors are only heat switches when the mixture is lean they sense the heat variation and richen the mixture and vice versa like a switch
The later wideband style 02 sensors are more like a potentiometer /volume control I.E. give a more finite control unlike ours that just switch

My car runs sweet as no fault codes has an awesome note but a very costly exercise for the cost of the prototype headers and full system I could have bought a brand new daewoo that's why if I was doing it again I would do it like I said my system is overkill it comes out of the header into a single 3 inch pipe uses a super slim Subaru specific stainless resonator then splits into twin 2,1/2 inch pipes with 2 cats 2 resonators again overkill 1 cat and one resonator would be more than enough in the end its the tuned length of the headers and front engine pipe that make the power the rest is to shut it up and stop droning

I intend to keep the old girl for a long time

I got sick of the crap cast headers cracking tried for years to buy a set finally bit the bullet 2 years ago had a full exhaust made for my car and prototyped these to sell to enthusiasts that also got sick of cracked headers as
I live in Australia our cars only have 2 02sensors at the front of the car
I also removed my air pump as it is only used to heat up the rear cats my new cats are in the place of the underfloor cats and I used 200 cell metal substrate cats Metal Cat - High Performance Metal Cat 2.5"
these type of cats heat up very quickly no need for the air pump and are street legal

 

Thanks for the information Doc. I'd love to hear how it sounds.

 

I need to put it on the dyno again I did it before and left my phone on video behind the car but the sound is pure distortion but before doing anything I have to drive it she has been sitting since October we have had the worst weather floods rain cyclones so I am just leaving her under the carport I want to get the damage from when I hit the gatepost fixed but want to wait till its dry and cool something it has not been for 5 months
I now understand why people in the UK get moppy when the sun doesent shine for a while we have only had one sunny day in a month let alone this summer what summer normally the sun shines all the time LOL

 

Do you still make the headers for an X300?