Decatting a UK TT6

Hi there,

Well my new Blitz Nur Spec will soon be on its way from Miami-GT, I'm contemplating decatting as both cats are currently in place.

I know you need to fit a restrictor ring on J-spec's, is the same true of UK-specs? I don't really want to run at increased boost as the car's been run standard up till now and I want to try and avoid any future engine problems!

Also what sort of power increase can I expect from a full decat? I've seen it quoted anything from 20bhp to 60bhp...

Are the J-spec and UK decat pipes interchangable? How much does Chris Wilson charge for one?

Finally how loud is it going to be on a Blitz Nur spec? I live in quite a built up area and don't want to piss of the neighbours more than I already do!

Cheers,

Francis

You wont need a restrictor ring like you have on JDM models, you need a boost controller to wind up the boost, it will be louder but not a great deal until you go WOT You'd be best to get it set up to run 1.2 bar This should be reliable.

im fully de catted uk car with nur spec, loud but it really sounds good, you will suffer boost creep, boost spikes, this is because toyota use the "pre cat" to control the boost levels, this WILL fuck the turbos, so tread carefully

I have a uk de-cat pipe for sale(replaces both cats), includes all sensor holes and is made of stainless steel.

Makes the car sound awesome, like a v8

As Rich says about the turbos, you may notice that your cars suddenly starts smoking afterwards, because the change in back pressure once the cats are off shows up worn turbo seals, mine did, thats y the cat pipe is for sale

Hmmm think I might keep it simple for the time being and stick with the cats... How much is your decat pipe though MPryde?

Your car does have 120k miles though right?

you can safely remove the second "large cat" with no probs at all, still will a performance gain, its when you remove both that you have to be careful

I'm getting my new blitz exhaust too and from this thread I guess it's best on my UK spec to removed the second cat only. Have any of you had to put it back for MOT? Another thing, are any UK specs running aftermarket induction and/or aftermarket BOVs?

no, yes and yes !!!!!!

I stand to be corrected here but I'm pretty sure you need a boost controller (or bleed valve) in order to achieve 1.2 bar on a UK car. The wastegate is larger so should control the boost much better than one on the jspec.

Edited to add - if you remove only one cat you are best off removing the 1st one (closest to the turbo) rather than the 2nd one, this will slow down heat build up in the engine bay.

its not the size of the waste gate that is the problem, it cannot react fast enough with all the cats out to effectivley control the boost,im running motec m800 and it takes care of everything for me !!

always leave the 1st cat in "nearest the engine" the second one is very restrictive and can be taken off safely

Homer is right, you won't need a restrictor ring on a UK car. You will probably need some form of boost controller to get the boost as high as you want. I like 30 quid bleed valves, others prefer 300 quid boost controllers. 1.2 bar is safe if the engines in good nick.

E-mail me direct if you want de-cat pipe pricing info. Cheers.

richardmee: im fully de catted uk car with nur spec, loud but it really sounds good, you will suffer boost creep, boost spikes, this is because toyota use the "pre cat" to control the boost levels, this WILL fuck the turbos, so tread carefully

Will the use of a boost controller prevent the turbos getting knackered ?

Hi I'm UKTT and have Nur spec and both cats out, currently running just under 1.0bar with MBC. Just had MOT last Friday and had to put second cat back in to pass emissions (no probs - 6 bolts, 2 for lambda sensor and two for each end of the pipe). No smoke at 86k (touch wood).

HTH

Rich

if both cats are out no, leave 1 st in, set the boost controller at the correct level for your engine tune and everybody is happy

if both cats are out no, leave 1 st in, set the boost controller at the correct level for your engine tune and everybody is happy

A majority of the tuners here would disagree with you.

OK thanx

i was told by my engine builder not to remove the 1st cat due to spikes, top man at option motorsport, your decision

Dude, mine is UK spec.

both cats in, boost was dead stock.

second cat out, boost dead stock

first cat out as well, boost still dead stock.

Without a boost controller, boost stays stock, the wastegate is properly sized on the UKSpec.

No need for electronic claptrap anyway, a £20-£25 ball&spring manual controller does the job admirably.

Off ya go.

Mine is a UK auto. Both cats out, RS*R, hitting boost-cut in high gear on motorway. The only obvious difference is that I have a 3" decat while most others have 2.5".

No need for electronic claptrap anyway, a £20-£25 ball&spring manual controller does the job admirably.

Where have you fitted the MBC John? Mine is on the hose to the wastegate actuator, and only seems to be affecting boost for no1 turbo, which is kind of out of its efficiency at 9psi I think

i was told by my engine builder not to remove the 1st cat due to spikes, top man at option motorsport, your decision

Perfectly true for J-spec cars. However UK-spec cars do not have this problem. I require a bleed valve just to reach 1 bar.

*start thread hijack*

Having a j-spec tt requiring a de-cat, are you saying it's not safe to remove the 1st cat? I was planning on removing both and using a restrictor ring or removing the 1st cat only and seeing how that goes.

>its not the size of the waste gate that is the problem, it cannot react fast enough with all the cats out to effectivley control the boost,im running motec m800 and it takes care of everything for me !!

dumb question, how does the motec help here? Do uprated actuators (that have been mentioned elsewhere) help the system react quick enough with the first cat out?

*end thread hijack*

Where have you fitted the MBC John? Mine is on the hose to the wastegate actuator, and only seems to be affecting boost for no1 turbo, which is kind of out of its efficiency at 9psi I think

During low-rev operation there are two wastegates operational, the 'bona fide' wastegate of #1 and the EBV

At high-rpm (over 4K) only the wastegate is operational. So if you only intercept the WG, you will only affect boost over 4Krpm.

Playing with the EBV has downsides though, beware. What is redirected away from turbo #1 is used to prespool #2. You can't get something for nothing.

As for the decat, I too have 3" and it STILL wouldn't budge a single psi without the boost controller. UKSpec wastegates rock