Has anyone removed the small muffler directly following the catalytic Converter?

If so, did it have any impact on the engine performance?

Also, did it improve the exhaust sound?

Thanks

Softball60/Paul

1996 XJS 2+2 Conv, 1957 XK140 Drophead, 1989 560SL and every other British Sports Car known to mankind

 

V12 or AJ16?
A standard modification for the performance versions of the V12 (TWR, Lister) was to remove the centre boxes; it provides better breathing with a marginal performance gain and a much better sound; the sound is much louder and will be noticeable if you are doing a lot of highway miles.
If you are just looning around it is well worth doing because the noise is brilliant (my opinion, others will no doubt disagree).
The dog can hear me coming home 2 miles away.
I managed to luck into a set of genuine TWR quad tail pipes so the sound is quite, umm, unmissable.
Don't know about the AJ16 lump.

 

It is the AJ16 (6Cyl) and not the V-12.

Anyone with experience on the AJ16....Your comments are appreciated!!

Softball60/Paul

 

I don't have personal experience with AJ16 six cylinder engine but it might be worth contacting

HIGH QUALITY XJS EXHAUST SYSTEMS from AJ6 ENGINEERING / AJ6 Engineering

by email to ask their advice, even if you're not looking to buy their exhaust they may give an indication of power gains possible from deleting the muffler (silencer - UK)

Hope this helps.

PS in case you're not aware one of owner of AJ6 engineering was formerly employed by Jaguar in engine development position 'back in the day'

 

In the UK, it's technically possible to remove all the cats from the AJ16 (as long as you leave the lambda sensors) and it can still pass the UK emssions test for the annual MoT test. The AJ16 is that efficient as long as it can adjust fuelling based on lambda feedback.

The AJ6 straight-through centre pipes for 6-cylinder will fit the but you have to check that you've got the correct fittings as there are two types of connection after the cat downpipe. Some markets used the olive joint system and some markets used the slip joint system.

Good luck

Paul

 

If you leave the Lambda sensors....what are they connected to?

Thanks

Softball60/Paul

 

Paul,

They would be connected to the ecu as normal.

Apols if I've misunderstood.

Paul

 

Paul,

Did you ever remove the part of the exhaust after the cats and the o2 sensor?
I was curious how it sounds.

As far as removing the cats and wondering how to mount the O2 sensors, you can get a piece of pipe shaped to fit and have some bungs welded to it to mount the O2 sensors. A better approach might be to take off the cats and just remove the material inside. I did that on a 96 VW I had. It had a clogged cat and I wanted to make sure that that was the problem with the performance of the VW. All you have to do is stick a stout screw driver down there and knock it out with a hammer. Before you do that thought take a look in the cat after you have removed it. You should be able to see thru the honeycomb. If you can not it is clogged and hurting performance. The benefit to doing what I suggest is that for any casual inspection, the cat is there, just empty. By the way, this might/will set a cat efficiency code, either way you do this job. Hope this helps.

 

I removed the cats on a 1992 Series III V12 saloon, and I think it made no difference at all to performance or fuel economy. If they are not plugged, I would leave the cats.

My 1994 XJS V12 has the rear mufflers, the ones in front of the rear suspension, removed when we bought it. Doesn't really sound that different from a standard car, certainly not offensive on long highway drives. I've not driven a car with them in place, so can't comment on the difference in power (if any). Considering how the exhaust was bodged back in, I think any efficiency gains from removing the muffler were lost in the replacement piping. It's 6 different pieces of pipe cobbled together in 24", and more twists and turns than a drunken sailor.

 

It won't alter performance, because the cats are just half of that, what intervenes with the power. You can't simply dich the lambda sonds aka oxygen sensors, as the car needs them to determine the mix. A V12 without cats from factory has more power and gets better mileage... No cats, no O2 sensors, no issues...

Decatting is also a disgusting thing and people don't understand, before they stuff a screwdriver into the honeycombe, that the cats are worth good cash. Worn cats are bought up here for €50 min/piece if they still have the HC, no matter if molten, broken or in 1 piece..,

 

To be clear, I put in the European style downpipes with no catalytic converters, but welded in bungs for the O2 sensors; as my car originally had O2 sensors. I preserved that functionality.

V12's in non emission markets usually had higher compression, that is what gave the power boost, not the absence of catalytic converters.

 

I removed all mufflers and gutted the cats on my 6cyl and v12 cars, more so on the v12 with gutted free flowing exhaust the performance/mpg increase was astounding where as the 6cyl got somewhat better mileage and barely noticeable power improvement except on hard acceleration.

 

Gutting Catalytic converters is not a good idea, problem is the OEM cats are usually squared off at the ends and without the honeycomb inside this creates a restriction to flow. Only way to do it properly is to replace the cats with high flow units, these have tapered ends to aid flow, or gut the cat and insert a pipe through it.