V8 Downpipe, one or two cats?

[Reggieroo]

I've been told two different things regarding the down pipe cat. One chap has said that it only has one cat & the other side is a a silencer & another chap has said what I thought that it has two cats one either side.

My thinking is that you can't have one cat on one side & not the other on a V8 down pipe as one side will be more restricted than the other + it has two lambda sensors, one on each side.

Does anyone know for sure then answer to this question?

[cluffy]

two cats

[craig_midz]

yep as above 2 cats but cut em out ya v8 will love ya for it mine does an it passes its emissons as it still got lamba sensors in

[Reggieroo]

I've already cut one out, thats why I was asking as I was told by one guy I only need to do one  :?

[craig_midz]

what i did was buy a rangie 3.9 downpipe without the cats in an found 2 nuts that the lanba sensor would screw into drilled 2 holes in downpipe an welded nuts onto downpipe looks orginal then an never had a problem all it did was give me a bit more of a growl out of exhuast an a few extra ponys

[Jonny Boaterboy]

Now that's interesting! I have got cats that are rattling and have been wondering what to do. I have been told by the MOT place that if The Range Rover was made after a certain date (1990 I think) it falls into a lower emissions bracket, hence the cats to bring the emissions down to that level. I have been told that you can remove them but still have to be below the emissions level which is only achievable with a good tight engine...... well I'm up to 160,000 miles now and don't think I would get away with it.... that said I don't burn any oil and the engine seems good, and at every MOT test the emissions have been really low.

My other concern is altering the back pressures in the exhaust. I was told that if you want your Land Rover V8 to run smoothly you need to stick with a genuine exhaust. If you fit an oversized stainless steel exhaust minus a silencer to get more BHP you only achieve this if you have the ECU remapped. How true is this? Can you just cut out the cats and still have it running smoothly? 

[craig_midz]

all i know is i have cut the cats off my exhuast an kept middle box in for back pressure an it does seem to give it a bit more poke an a better exhuast note an mines done 102k an its a 1996 disco an it flys through the emissions but a tip to get ya car through emissons if its just over is turn on ever eletrical item on in your car as it draws power will lower the emissions sounds daft but it works ;)

[JIMBOBLY]

definatly 2 cats mate,as i have already cut mine out,if you leave the lamda sensors where they are it will automatically adjust everything,ie the mixture timing etc,thats what the sensors do,i left the cat boxes empty,but i have done some for other people,and they dont like the noise,so you can either cut the whole lot out,or discuise it,by cutting the side of the cat that buts up against the chassis,knock the guts out,weld a pipe in the centre,then weld the bit you cut out back in,that will stop the resinating noise you will get,so if anyone got underneath and had a look,they'd think you still had cats in,and what the other chap said,if everything is in good working order,it will still scrap through the test,mine has twice now,with quite a bit to spare on the emission limit :dance:

[Range Rover Blues]

Now that's interesting! I have got cats that are rattling and have been wondering what to do. I have been told by the MOT place that if The Range Rover was made after a certain date (1990 I think) it falls into a lower emissions bracket, hence the cats to bring the emissions down to that level. I have been told that you can remove them but still have to be below the emissions level which is only achievable with a good tight engine...... well I'm up to 160,000 miles now and don't think I would get away with it.... that said I don't burn any oil and the engine seems good, and at every MOT test the emissions have been really low.

My other concern is altering the back pressures in the exhaust. I was told that if you want your Land Rover V8 to run smoothly you need to stick with a genuine exhaust. If you fit an oversized stainless steel exhaust minus a silencer to get more BHP you only achieve this if you have the ECU remapped. How true is this? Can you just cut out the cats and still have it running smoothly? 

Change the oil before the MOT. makes a big difference.

ECU, it can adjust itself to cope with a free flow exhaust and K&N but no more, so bigger engines, naughty cams all need a new ECU but de-catting iot should cope with, after all you can tell the ECU there is no cats with the TSR anyway.

[Reggieroo]

Mines on LPG so should go through the MOT anyway. I haven't even got the ECU plugged in as the petrol system doesn't work since I flooded it in a ford  :shock: I wonder if the running will be affected without the cats then?

[Jonny Boaterboy]

O.k My cats have had it they are getting nosier by the day. I want to cut them out. Can I just cut streight through the exhaust pipe either side of the cats and replace with a straight bit of pipe slightly bigger that the external diameter of the exhaust pipe slotting over and clamping? Do you need to remove the section of exhaust with the cats in to do this of can you do it in situ.

Happy new year!

[Reggieroo]

O.k My cats have had it they are getting nosier by the day. I want to cut them out. Can I just cut streight through the exhaust pipe either side of the cats and replace with a straight bit of pipe slightly bigger that the external diameter of the exhaust pipe slotting over and clamping? Do you need to remove the section of exhaust with the cats in to do this of can you do it in situ.

Happy new year!

Well I done mine by cutting out the cats one at a time make sure that the exhaust is bolted to the manifold when you put in the replacement pipe so that the flanges all meet up in the right place otherwise when you come to bolt it back together it won't fit right. Use a piece of pipe larger than the exhaust as a friend of mine thought it would be a better way to do it with the same size........................what a pain in the arse that was. I did the other side with a piece larger & it was l a lot easier.

[Jonny Boaterboy]

I did the other side with a piece larger & it was l a lot easier.

Ok that sounds good...... where do I find the pipe? Can't think of anywhere that would sell that sort of pipe can you give me a few pointers!

Tar

[Range Rover Blues]

If you are binnning the cats Jonny then do as suggested above and fit a 3.9 pair of downpipes, they are slightly better gas flowed to give smoother running.  Just cut the Lambda sensore out and weld it into the new pipe (well the nut for it).

[Reggieroo]

I did the other side with a piece larger & it was l a lot easier.

Ok that sounds good...... where do I find the pipe? Can't think of anywhere that would sell that sort of pipe can you give me a few pointers!

Tar

You will have to try & source that sort of thing locally as we did, my friend got the first bit of pipe that was the same diameter & I got a bit of stainless pipe that had the ends opened up to fit over, this I got form a local tyre & exhaust place that does performance exhausts.

Unless somebody on here has any floating about.

[Jonny Boaterboy]

O.k I have brought a 2m section of flexable exhaust pipe. £27.98 it's galvanised mild steel (not too sure how long it will last! decided to go with that RRB rather than paying £60 for new down pipes as I want to change the whole system for a stainless one in the future so did not want to spend too much on this repair) will there be any problems having flexable exhaust pipe instead of the ridged steel pipe i.e. no support excess noise, poor gas flow as it's got ridges inside??

I've cut the cat out and had a look inside and there were a few bits of lose ceramic in there but not much...... I thought that the whole of the inside of the cat would have had a ceramic matrix in there? if it should have, were has it all gone? not so worry about passing the emissions now as If it passed with the cat in the state, should have no problems without them!

Is it worth using stainless steel bolt to refit to the manifold or just stick with steel?   

[Range Rover Blues]

I've tried with stainless bolts, they still get rusty.

Can't comment on the flexu pipe as I've not tried it, I'd have suggested looking for decent secong hand downpipes if they don't have to last you too long, they don't suffer form excessive rust that far foreward.

[Jonny Boaterboy]

Well I have done it! What a pain in the arse the whole Job was! getting to the manifold down pipe nut's and bolts was difficult and long winded, and then fitting the flexi pipe was just as hard as they were a tight fit, I had to put 4 slots in the exhaust and crush it down to get it to go on! Worth the hassle though, sound is alot nicer, slightly deeper but not too noisy I have added some photos to my gallery, cut one of the cats open.... have a look at the photos

[Range Rover Blues]

Err, how do I get to your galery these days :-k

[Rossko]

Just to clarify a few points raised along the way.

The Lucas injection system on 3.5/3.9/4.2 EFI will NOT adjust the ignition timing to suit modified exhausts ... it has a conventional distributor, after all.

If the injection system has oxygen sensors, yep as folks say do keep them even if removing cats.  It gives better efficiency (i.e. power and economy) than "retro-converting" to sensor-less configuration.

The use of oxygen sensors does indeed allow the Lucas injection system to self-adjust to an extent to cope with significantly free-flowing exhausts, K&N filters, etc.  BUT only at light loads, steady state conditions.   They do NOT allow any self-adjustment when running full throttle.  Everything works off a fixed map then.  This system is not smart enough to use long-term fuel trim techniques.  So if you are obsessed with max performance you would need a remap.   In real life very few people would bother!


When messing with the exhaust, take the oxygen sensors out first and put back last.   You might not think it, but they can be very fragile inside.   Welding or hammering the exhaust with them fitted will more than likely destroy them internally.

cheers, Ross K

[Range Rover Blues]

He's right you know ;) the hot-wire system is only self-tuning with s full set of sensors and although early UK models came without lambdas sensors and had a different tune select resistor this put the ECU into fixed-map mode.

The big problem with tuning the system is the air flow at full throttle is higher than "normal" or more importantly the air flow the ECU perceives as maximum is reached at a lower throttle opening which will make the system less economical.

With a heavioy tuned engine another limiting factor is that the injectors are "on" most of the time and unlike other types of injector turning up the fuel supply pressure doesn't overcome this, it takes more power and fractionally more time to open them against the supply pressure.

Typical, another Lucas Prince of Darkness speciality elektrik system.

[Rossko]

Typical, another Lucas Prince of Darkness speciality elektrik system.

Did you know it was a bought-in Bosch design, same as used on BMW of the period, and Lucas version also used on SAAB etc.?

It does what it does, simply and effectively.  And as it turns out fairly reliably after twenty years service.  It's not Lucas fault if folk want to mess about with it  ;)

[Range Rover Blues]

Typical, another Lucas Prince of Darkness speciality elektrik system.

Did you know it was a bought-in Bosch design,

I didn't.  I do know there were better alternatives available using full multi point technology but as usual it was built down to a cost.

Like you say it work well in factory trim and is very reliable.  Very few EFi systme cope well with "timnkering" because full throttle air flow is one of the parameters that has to be programmed in.

[Jonny Boaterboy]

Very interesting stuff you boys know a thing or two! any way here's my botch of cat removal!!

http://www.mud-club.com/galleries/Jonny+Boaterboy

[Range Rover Blues]

Crikey mate, it's clean under there.

[Jonny Boaterboy]

Probable because I have a hatred for rust  :twisted: everything under there is covered in grease, waxoil old engine oil anything that will slow the rot down. It's messy to work on though, but I don't mind too much! I want the Range to go on for years and as rot is a big killer I'm at war with it!