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Decatting UK mkiv


Guest thechappers
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Guest thechappers

Hi everyone,

This is my first message on this forum. I've owned supras for ages, I had a mkiii for 5/6 years and I've had my mkiv for just over 2 years. (and a few supra toy models too if that counts!)

My supra is a UK automatic, and has no modifications except a badly fitted aftermarket exhaust (installed before me owning the car) and a Blitz turbo timer/LCD boost gauge (I installed).

The exhaust looks like some pipes welded together with a fancy end nozzle welded on, with no back boxes! Anyhow I've been planning to change it for ages and now the nozzle weld has come undone and its hanging. So its time to decat and sort it out properly!

 

I've had some minor experience with my mkiii DIY wise, but I have a few worries for decatting the mkiv.

 

1. I'm planning to get the Greddy BCC, which I believe is a device that is vehical specific, so will it work on the UK supra? Or is it just for the Japanese spec? Has any of the UK owners on the forum fitted the Greddy?

2. Is it ok to not install the cat o2 heat sensor on the UK spec? I presume having no cats means its pretty irrelevant, but perhaps it has some additional uses.

3. Has anyone been stopped/tested for emissions on the street or is my only worry the MOT?

4. Should I do a double decat with restrictor ring, or single decat?

 

I'm hoping to get whifbitz exhaust and pipes with the cat back being Blitz Nur Spec R. I'm also hoping to change the spark plugs.

 

I'm probably making a mountain out of a mole hill over this, but I'm aware the turbos are different on the UK and Japs, and so I want to make sure everything will fit and work together correctly.

 

Any advice on UK decatting would be gratefully recieved (I'm mainly finding US/Jap advice)

 

Many thanks to all!

 

the chappers

mkiv automatic TT 1995

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uk decats and j specs are diffrent so you cant change between them, if i was you i would buy a complete down pipe (replases both cats) and you dont need a restrictor ring for a uk car.

 

i would fit denso IK24 plugs to your car oh and the nur spec is a very good choise!! fit a walbro fuel pump and a FCD and your bpu and loving the power (thats if you arnt already)

 

and welcome!!

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fit a walbro fuel pump

 

DON'T fit a Walbro!

 

The UK pump is superior to the Walbro, it's quieter, it will last longer and it flows more - it's also a lot more expensive. If your current one is working OK leave it alone, if it needs replacing fit another UK one.

 

Otherwise what the gent above said is spot on, UKs are far easier to take to BPU thanks to them having proper fuelling already but you'll more than likely need a boost controller to raise the boost as the decat alone won't do this like it does on the J-Spec.

 

They need the restrictor to lower boost, we need something to raise it.

 

Lots of info on this in the tech sections, welcome to the forum and let's see some photos of your machine!

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Welcome Chappers :)

 

This link has a lot of good info http://www.mkivsupra.net/vbb/showthread.php?t=94705

 

The second sensor on the UK's is an O2 sensor so should really be fitted. If you buy decat pipes made for the UK spec it will have a boss on the 2nd decat pipe allowing you to refit it. On the J-Spec's the sensor is just a cat temp sensor which can just be tied out of the way.

 

You can get 1 piece decat pipes or two piece. The two piece decat pipes make it easier at MOT time as you will have to refit you second cat to get through the emissions test.

 

Another option (to spend money lol) when fitting the FCD is to buy a replica fields harness, that way you won't have to cut into the loom. It will also help in the future if you decide to add anything else.

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1. The Greddy BCC got some bad press a few years back so, I went with the TRL unit http://www.thor-racing.co.uk/Fuel_Cut_Defencer-VFCC.asp Pete Betts, who owns Thor designed and built this and he has had a MKIV supra for a long time. I know that HKS do one as well. So, you are not restricted to just one unit to buy.

 

2. If you buy UK spec decat pipes i.e. Chris Wilson's then they come with the boss ready for the o2 sensor.

 

3. Only at MOT time - So, IMO it's best to buy two decat pipes over one large one. (Easier to swap the #2 pipe out with the cat come MOT time).

 

4. Double decat.

 

you'll more than likely need a boost controller to raise the boost as the decat alone won't do this like it does on the J-Spec.

 

I did, I got upto 0.91 bar which, put a big smile on my face at the time. But, yes, you will need a BC to up it further.

 

 

 

i would fit denso IK24 plugs to your car

 

No need IMO, unless he does up the boost to more that what a double decat and exhaust will do. (Unless he gets a missfire)

 

It depends on his budget.

 

I agree with Michael about the Walbro though!

 

Anyway, Welcome to the club and get some photo's posted up of your cars. :thumbs:

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Guest thechappers

Wow, thanks everyone. Some useful and much needed advice there!

 

1. I'm glad to hear the greddy will work for the UK spec, although I hadn't heard about the bad press associated with it. What was that about? The HKS FCD I've heard isn't so good for midrange (or so I read!) so I'm leaving that out of mind for the time being. But the Thor unit is new to me, does it work like the Greddy (Clamping the signal?!), or like the HKS (reducing by a fixed percentage).

 

2. I was looking at the Whifbitz decat pipes, but I believe they don't have the o2 sensor input. If Chris's does then thats good, I shall investigate. Does Chris Wilson's pipes come in 2 parts?

 

 

I'm not intending on buying a boost controller just yet, partly money, but also because I'm fairly happy with the power I have at the moment. I can stretch the budget for new plugs, as they were last replaced in 2003 and I'm not sure what they are (it was before my time). But if there is no need, I might put that on hold.

 

Thanks again!

 

P.S.

I'm now a paid up member, :) and I have put a few pictures up :D

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I don't remember the issues, it was ~5 yrs ago :)

 

Some useful info here:

http://www.mkiv.com/techarticles/index.html

 

Your plugs have not been changed for ~4yrs - how many miles have they done ?

 

In anycase, if you double decat & exhaust you should see a slight increase in boost and responsiveness of the turbo's. You might not need the FCD if you are not upping the boost anyfurther, well, you might hit fuel cut on COLD days but, I had the FCD fitted at the same time so......

 

If you do the above and get a missfire, you will then need to change the plugs.

 

Yes, CW pipes are in two parts.

 

HTH

 

Oh, love the photo of the soop on the beach :cool:

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