Full Decat

I`m a newbie and want to do a full decat on my jspec mkiv tt. Car already has a aftermarket ss system from rear cat back (some jap make not sure which so downpipe only needed.

So, what's your question ?

suppose it depends on what size pipe you already have fitted i.e 2.5 or 3 inch.

A lot of the members have bought 2 sections (easy to replace 1 for MOT) off of Chris Wilson - who is also a member.

However i've just read this from a tuning company's website :

"We do not reccomend removal of the 1st catalyst (on vehicles using stock turbos) due not only to the legality issue but also the fact that the Twin Turbo Supra uses the cats as a method of boost control. Removal of both cats can lead to excessive boost levels and/or 'boost creep' (especially on Jap models) due to the vehicle being unable to control exhaust flow. Cat removal pipes are available that can sometimes keep boost pressures reasonably low but they need to be made from a relatively small diameter pipe (2.5") to still present a restriction to flow. In our opinon this is pointless and retaining the stock 1st cat and using the very large (3") HKS front pipe usually achieves a similar result at a cheaper cost, whilst still keeping the vehicle legal and guaranteeing that boost levels remain safe for the engine."

Sorry for the hijack but just wanted everyones elses opinions on this.

not an expert, but i know that many on the board have double decatted, and the difference IS worth it. the first cat is the most restrictive i think. regarding boost control issues, most people put in a restrictor ring to keep boost down to 1.2 Bar i believe

As rob says, a decat on the jap spec (running stock turbos) is fine but you must fit a restrictor ring to keep the boost at or below 1.2 bar. Then all will be fine. The best person to ask is Chris Wilson. He is a member on here. I have just had a pipe made up by him, will be here on Monday (thanks Chris).

So any questions its best to email Chris .

so what do i buy?

Well Chris Wilson makes 2.5" decat pipes, in two seperate pieces so you can put the second cat back on for MOT time.

Let him know what boost you want to run and he will make the restrictor ring to suit.

Email him, he will tell you all you need to know.

[email protected]

TRL VFCD .. to raise your fuel cut to 1.25Bar or 18psi.

Walbro Fuel Pump.

Decat pipes. .

Decent plugs ... Denso IK22's are good and last awhile.

Boost gauge to monitor boost levels.

Restrictor Ring.

Any of the traders will be able to source these bits for you.

cheers i`ll drop Chris a line

Thanks for the info

TRL VFCD .. to raise your fuel cut to 1.25Bar or 18psi.

Walbro Fuel Pump.

Decat pipes. .

Decent plugs ... Denso IK22's are good and last awhile.

Boost gauge to monitor boost levels.

Restrictor Ring.

 

Any of the traders will be able to source these bits for you.

Of course all the above bits will also be needed.

In our opinon this is pointless and retaining the stock 1st cat and using the very large (3") HKS front pipe usually achieves a similar result at a cheaper cost, whilst still keeping the vehicle legal and guaranteeing that boost levels remain safe for the engine.

Interesting quote...

whos website did you get that quote from?

So let me see if I understand this correctly.

Its better to stick with the restrictive first cat which probably has a bore size of LESS than 2.5" rather than go for a 2.5" straight through pipe (which CW says is good enough for cars upto 550 bhp)

I cant see the logic in going for a 3" 2nd decat pipe while leaving the restrictive cat in there...

Paul from Whifbitz decatted mine (removing both cats and fitted a restricter ring) - difference in response is amazing.

is the warlboro fuel pump really necessary too, i was under the impression that the standard was good for a little while longer to cover a BPU car?

Interesting quote...

whos website did you get that quote from?

 

So let me see if I understand this correctly.

 

Its better to stick with the restrictive first cat which probably has a bore size of LESS than 2.5" rather than go for a 2.5" straight through pipe (which CW says is good enough for cars upto 550 bhp)

 

I cant see the logic in going for a 3" 2nd decat pipe while leaving the restrictive cat in there...

 

Paul from Whifbitz decatted mine (removing both cats and fitted a restricter ring) - difference in response is amazing.

although i've not used them and purely going by word of mouth these people know what they're talking about...

http://www.tdi-plc.com/toyota_supraMk4.html

but make your own judgement.

although i've not used them and purely going by word of mouth these people know what they're talking about...

 

http://www.tdi-plc.com/toyota_supraMk4.html

 

but make your own judgement.

Not sure about the rest of you, my brother in law had a bad experience with his Pulsar & TDi (im using my words carefully here) - so I'll just ignore what they have to say.

thx for the clarification.

regards

fair play. As i say i've never used them.

also after reading it thoughly their mods look very optimistic too...

Stage 1 Exhaust 37 BHP

Stage 2 Air filter 49 BHP

Stage 3 Intercooler upgrade 54 BHP

Stage 4 FCD 112 BHP

Stage 5 Vein Pressure Converter 142 BHP

12 BHP from an air filter ??? i've been told the stock ones are better

15 BHP from an intercooler upgrade ???- didn't think they actually increase BHP just a safety precaution ???

What a load of rubbish! Lets just say TDi don't have a good reputation here.

Regarding the fuel pump, its not so much about the performance of the stock unit but that fact that its 10+ years old and will almost certainly be past it best. Like the boost gauge it’s an important safety mod.

The decat pipes from Chris are highly recommended, top quality and because they're 2 peice you can pop the mid cat pipe back in for MOT's (if you can't find a friendly MOT centre!)

The correct size restrictor ring, correct grade plugs and FCD (Thor do a very good one) and essential to make the car run properly after a decat.

Also, keep your stock air filter (if it hasn't been removed already), aftermarket ones will lose you power as they suck in hot air from the engine bay.

You should budget for around £800 to do a full de-cat properly (provided you can do the fitting yourself)

I find this MKIV.com a great resource of information in addition to this site.

Regarding the Induction kits, refer to Induction Kit test

What a load of rubbish! Lets just say TDi don't have a good reputation here.

 

Regarding the fuel pump, its not so much about the performance of the stock unit but that fact that its 10+ years old and will almost certainly be past it best. Like the boost gauge it’s an important safety mod.

 

The decat pipes from Chris are highly recommended, top quality and because they're 2 peice you can pop the mid cat pipe back in for MOT's (if you can't find a friendly MOT centre!)

 

The correct size restrictor ring, correct grade plugs and FCD (Thor do a very good one) and essential to make the car run properly after a decat.

 

Also, keep your stock air filter (if it hasn't been removed already), aftermarket ones will lose you power as they suck in hot air from the engine bay.

 

You should budget for around £800 to do a full de-cat properly (provided you can do the fitting yourself)

Would this include an aftermarket backbox etc and what sort of power gains could you expect after?

Would this include an aftermarket backbox etc and what sort of power gains could you expect after?

£800 is an accurate figure if you already have the exhaust system (Blitz/RSR/HKS). If your car is pretty much stock (like mine was) budget on £1200 for the bits ... then labour.

RSR = £500

Decat pipes and restrictor ring = £300

Walbro Fuel Pump = £100

Thor VFCD (2nd hand) = £60

DEFI Boost Gauge & Box = £200

Plugs = £60

Power gains ... dunno about Bhp or Torque figures. But you get a substantial amount. Turbo's spool up much quicker & boost pressure rises to 18psi or 1.2bar.

Stock is usually around 300-320bhp, after I did the bpu stuff to my car it went to 387bhp. You should see between 70 to 90 bhp extra, plus the car will feel much more responsive.

Once I added an FMIC this went to 429bhp (my side mount wasn't in the best of conditions). This is about as far as its safe to go without expensive upgrades (injectors, ecu, etc).