Advice on partial decatting Chimaera?

[evo]

I've done the usual searches on decatting but would like to ask, can someone give me a quick advantages/disadvantages of partially decatting my Chimaera. I understand there are three cats on the Chim and reached the conclusion that it's best to just do a partial decat. I already have the rear silencers sleeved (I think this is the right way of explaining it) and I had the nice man at Goodwood stick the noise meter next to it and it came up with 92db on one and 97db on the other side.

The main qusetions I have queries about are will doing a partial decat make it run less smoothly than it does currently, will I need to have it on a rolling road afterwards and are there any longterm disadvantages with reliability? Also whats a "typical" cost of doing a partial decat?

Apologies if this topic has been done a million times.
Cheers,
JB

[siwes]

Hi
I have just had my Griff decatted completly, First if you have the manifold cats removed then that is a big job, to remove the manifolds you first have to get under the car, on the offside manifold the starter has to be removed for access, on the near side manifold the complete exhaust system has to be removed again for access.
If you are removing the main Y pipe cat that is easier and can be tackled from the engine bay . Ensure that the new Y piece is a good fit as there is not much give in the system.
My Griff has had all cats removed and even without the new ECU chip it performes better without doubt.
Most of all its the sound of a V8 burbling away it is awesome!
If a garage does the work it will cost you the best part of 160 pounds. Its worth it , e-mail me if you want some more advise.
regards Simon

[evo]

I didn't think that removing the manifold cats on a Chim was too difficult?

[wixer]

Removing the manifolds with engine in the car would be a real git. My engines out at the moment, so I removed the pre-cats, which took about 20mins a side.

[lateconvert]

I've just had new manifolds fitted (unweldable cracks)so decided to replace with pre-catless ones. No other changes necessary (ECU, rolling road session, etc). It certainly sounds better and maybe marginally more oomph, although so marginal it may be my imagination clouded by the healthier noise.

[docevi1]

I thought taking the cats of cars which they were fitted on was illegal?

[MOD500]

Morning

I had my precats taken out last year. The route I took was to buy exchange manifolds via Tim Lamont at ACT products. The manifolds have cones in them to aid efficient gas flow, venturi principle I assume, as when the pre-cats have gone there is a big empty space which can cause inefficient flow out of the manifolds.....I think anyway!

The result is abit more aggressive engine note and volume, and the car feels alittle more responsive.

The cost was £150 + VAT for the pair. If you do go ahead it is worth getting the thicker manifold gaskets to replace the thin TVR originals.

HTH

MOD.

Edited to say: Did'nt take the main cat out as was afraid of the spot checks for emissions they are doing around Yorkshire! Plus the big noise from de-catting is'nt my thing

>> Edited by MOD500 on Tuesday 10th February 07:41

[raceboy]

docevi1 said:

I thought taking the cats of cars which they were fitted on was illegal?

So's driving at 33 in a 30 I just love being a rebel

[Shotline]

Hi,

I have also wondered about the legality of de-catting. However, assuming that you have a pre July 95 TVR the MOT testers manual seems to say that the MOT test should be carried out as if the car is un-catted? See link:
www.motuk.co.uk/exhaust_emmissions.htm

Not sure if the above is correct as it depends on TVR not publishing emmission figures for the database. Of course your insurers would also have to accept the mods to your car.

Could anyone who knows shed more light?

[greenv8s]

I think in terms of the actual MOT test, taking the pre-cats out has no significant effect - apparently they're only there to improve the emmisions during the warmup cycle, whereas the MOT test is done on a hot engine. As long as you keep the main cat, I don't think removing the pre-cats will have any effect on the emissions.

[2 sheds]

GreenV8S is correct, no MOT issue if you remove only the pre-cats, you can do this yourself, or as mod500 said, you can exchange for prepared manifolds with internal cone, we also offer a stainless performance manifold with longer primaries, incase you're feeling "flush".
in reality when removing the manifold cats the performance increase is normally small 2-5 bhp(assuming the cats were in good condition), although most report that the car feels quicker after these mods.
Tim

[v8 racing]

Hi evo the pre cats as v8s said are only there as warm up cats and do nothing when warm, you did not say what size your motor was?? anything less than a 450 and they dont restict at all above that ie the 500 they do rob a bit of power, but i certainly would not remove the main cat in the y peice they will comfatably flow 350 bhp, and if removed you will have headaches every year getting it through mot's, around the £150 to de cat, but the manifolds that tim (act) can supply do work well with anti reversal cones to aid low down and mid range torque, maybe worth a chat with him???

[evo]

Thanks everyone,

Feeling a bit of a numptie, I had been told that the rear of my exhaust had been sleeved,I'm sure it's a bit louder anyway after a trip to Fernhurst in my lunch hour I now know I definately do not have a sports exhaust, what an incredible noise, thanks Fernhurst.

By next tuesday, thanks to my wife booking it in for me as a surprise I will have a proper sports exhaust

Would decatting, doing the partial decat make the noise unbearable?

Can't wait till next tuesday lunchtime......

[Shotline]

I don't think that a partial decat would be unbearable noise wise for me. Have seen a number of 500s with full decat and sports exhaust which may be unbearable on a long journey though. Problem is that there would not be much chance of doing many track days with the full decat unless additional silencing is added for the day.

Taking other points mentioned, I thought that a full decat would also remove the lambda sensors and require the closed loop control to be changed to open loop. This in turn should allow a more bespoke fuel/air mixture to be used. Coupled with improved breathing would this not release more power?