Anyone ever Decatted an XK8?

[MarkyM]

No real reason for me to have them since I'm LPG converted and one of my original CAT's (96) took a bashing from some road debris and has a small crack and needs to be replaced anyway.

Managed to get it through MOT with some judicious patching but that didn't last more than a couple of hours beyond the MOT. Given the price of a new CAT and fitting I could have both sides decatted for less.

What are the up and downsides?

Appreciate that with the following mods (I'm running at about stock BHP for a petrol):

Macleod X-pipe MkI
Cleaned and calibrated petrol injectors
Iridium plugs
Royal purple 5w30 fully synth
Bespoke Apexi intake in stock box

I'm guessing getting rid of the restrictive CATS will give me an additional 15 real-world BHP, and potentially improve economy?

Hope to hear from anyone with ideas!

Regards

Mark

[FELIX456]

Hi Mark
On a non-technical side of de-catting, my understanding of modern MoT's are that cats must be present if fitted originally to the car. However, not all testers physically check they're there, and some cars (though not Jags) actually have the cat in the exhaust manifold so it isn't easily seen on a test anyway.
If the car fails the emissions test, they will check for a cat usually to see if it is at fault.
De-catting may also effect the backpressure.
I have knocked the gubbins out of a cat box before, and the car still passed the emission test.
My suggestion would be adopt a tame tester (or bring some bribes to your next MoT!)
Sorry I'm no help on techi side though.
Ta
Tara

[J44EAG]

Would not there be a problem with lack of signal feed back from not having the oxygen sensors present or operative? How would the power train ecu cope with that?

Mike Kennedy S-type Co-ordinator

[FELIX456]

My response presumes the lambda sensors will remain on the car, the ECU would certainly get in a huff if they're removed!
I believe the lambda sensors are in line before the cats, and not after, so they don't necessarily know whether a cat is present. They MAY be able to read backpressure which MAY be effected by straight through pipes. As I mentioned, I had a Jag pass an MoT for emissions after I had emptied the cat box of the cat material, but whose lambda's were still there and still worked.
Forgive me if I am mistaken, I haven't checked under my XK8 to see exactly where the lambdas are, but on all other cars I have ever seen they are before the cats.
Am I any help at all?
Can someone else come with techi advice? I'm interested now, especially if the bhp goes up! Will the mpg go down?
Tara x

[mike020150]

I can't come up with a definitive answer to this one but since the emissions regs have become increasingly stringent and the MoT test procedure more comprehensive, I suspect that an XK8 would fail the test, probably on the high speed (3000 revs) part of the test procedure. The manufacturer certification procedure is very different from an MoT test and far tougher, which is why cars can sometimes pass an MoT minus one of several cats. A few years ago, LPG emissions were a lot cleaner than petrol emissions. However, these days the difference is much smaller so even on LPG, it's probable that the downpipe cats will need to be operational to get through the test. Mike.

[MarkyM]

My last emissions test (Dec 09) was

Description Limits Actual
CO <=0.300% 0.005%
HC <=200 ppm 11ppm
Lambda 0.970-1.030 1.010 (due to leaky CAT)

Fast Idle
CO <=0.300% 0.037%
HC <= 200ppm 18ppm
Lambda 0.970-1.030 1.028 (due to leaky CAT)

The MOT tester advised that it would fly through emissions once the decat pipes are fitted and both cats are leaking at the top joint (to the downpipe) in addition to one catalyst being holed. Also appreciate the current catalysts ARE coming up on 14yrs old...so he doubted they were actualy doing anything anyway!

Regardless once the decat pipes are fitted I am going to get it retested straight afterwards to see whether I need to save up for a set of sports cats when the next MOT comes around in 11 months.

Will let you know how it goes...EAPJ in Nottingham will be doing the work as I've been impressed with their work on my car in the past.

Mark

[mike020150]

We'll look forward with interest to the next instalment when the new parts are fitted. Mike.

[NormanD]

If you are changing the CATS how about a set of S/S free flow manifolds

As seen on eBay item 230428135929

[MarkyM]

Norman, wouldn't consider them at that price, am only going for the bypass pipes as less than half of what a set of sports cats would cost (supplied and fitted) and is unlikely I'll need CATS with me running on LPG.

Not really after performance gains since my car delivers 60-70 MPG based on me filling up at less than half the cost of unleaded (and the conversion having paid for itself 2yrs ago)

Would be 'nice to have' but I'd not consider at even half that price (given that fitting would probably be £300-£400)...and then only if they were thermally coated

Also seller looks slightly dodgy

M

[MarkyM]

Battery disconnected so could relearn.

OMG!!! coupled with my X-pipes the sound and acceleration are amazing.

Have yet to give it a really good seeing to...but am driving up to Sunderland from Somerset early hours of 23rd July for a 9am meeting....then on up to Edinburgh for another meeting at 2pm.

Not coming back until Sunday morning but should be a lovely drive.

Will report back on economy.

M
PS: passed LPG emissions test
PPS: now have a carbon dynamics air intake plumbed to the front grill for better cool air

[Nik]

Have yet to give it a really good seeing to...but am driving up to Sunderland from Somerset early hours of 23rd July for a 9am meeting....then on up to Edinburgh for another meeting at 2pm.

Not coming back until Sunday morning but should be a lovely drive.

Will report back on economy.

M

I guess you didn't make it back to report on the mods Mark

All the best ,

Nik

[MarkyM]

More than 8yrs on since my last post and car's still in my ownership.

Still getting 300 miles on a 60l fill of LPG at a cost of £30 that equates to 53mpg in monetary terms.

Cats weren't a requirement until 2015 when I had to buy a cheap set from ebay for £120 per side, flew through emissions and still does.

As all of my bushings were changed to poly some 10yrs years ago I've not had to change a single one since, was advised that the ride would be too harsh, but I still have all of my teeth.

Had to ditch the mcleod x-pipe as despite being ceramic coated it rusted away in less than 3yrs, went for a replacement with a lifetime transferable warranty from these people:

www.tonybanks.co.uk

[mike020150]

All interesting info. The latest (2018) MoT changes mean that testers are being primed to look for cats, so de-catting is not a practical option these days. Mike.