Performance hike with decat only

Hi all,

I'm looking to push my TT Auto towards BPU in terms of performance, at present it has a Miami GT 3" cat back exhaust and aftermarket air filter, that's all.

Without wanting to spend a fortune at once and instead perhaps upgrade over a period of time, what would be the next logical step for me to take in terms of performance upgrades?

I was thinking that decatting was the next logical step, but what sort of performance increase could I expect by fitting a decat pipe instead and will I definitely need a FCD or can I run with just the decat pipe on its own whilst funds allow?

Jez

i was wondering the same tbh.... anyone?

As I understand it, if you remove both catts you need a restrictor ring to stop boost going above 1.2bar. You can leave it at that, but you will hit fuel cut at 1bar and your engine power will die suddenly. I have read some people do it, but seems silly to me. I would install an FCD too. Probs need cooler plugs also. What is the condition of your intercooler? might wanna check that now summer is on its way.

Hopefully you've seen the --> BPU

You MUST NOT decat without doing the prerequisite mods, otherwise it could be good bye engine. If you want to upgrade, do the other things first, then decat. You can't get something for nothing.

I had read the BPU article, it's very well put together - but it seems a hell of a lot of trouble and expense to go to for an extra 70-ish bhp. I may be (and probably am) wrong, only I was looking into ways of going BPU bit by bit as opposed to all at once to try and keep costs down a tad.

What you could do, is fit one or both decat pipes now with a restrictor ring to limit boost to less than 1bar.

You will get no performance benefits as such, but it will mean you don't need an FCD, fuel pump, plugs, boost gauge etc. Then buy and fit the other parts as you can afford them, finally once you have all teh parts then you can open up the restrictor ring to allow more boost.

I had read the BPU article, it's very well put together - but it seems a hell of a lot of trouble and expense to go to for an extra 70-ish bhp. I may be (and probably am) wrong, only I was looking into ways of going BPU bit by bit as opposed to all at once to try and keep costs down a tad.

+100 bhp and it only costs about £800 and will drive like that for 50k+ miles. Name one other car that can do that!

It's not so much the peak power though, its the delivery that changes significantly, in fact it changes the entire car. Have you ever been in a properly sorted BPU car?

Some of us spent £10k to get the next 100 bhp

The only other Supra I've been in is the one owned by gaz6148, which I feel sure is BPU but off the top of my head I recall he's had other modifications done as well. There was quite a lengthy period of time in between him taking me out for a spin and me buying my own that it's impossible for me to compare the two.

It sounds definitely like a no-pain no-gain thing, unfortunately whatever disposable income I have seems to disappear very quickly as petrol

Don't take this the wrong way fella, but if you can't spare £800 on a one shot modification package then a modified Supra is not for you. These things can surprise you with £1k bills every now and then (even for people like me that do most of the work themselves). If you can't budget for that then leave it alone

Totally agree Homer. last year had £1000 bill to fix Air Con system & replace failed water pump. Also spent £1000 on new shocks + fitting etc. Although I've got RSR exhaust and FMIC, I'm only running standard boost, as the car's fast enough 99% of the time and I really can't be doing with nasty surprises engine wise.

+100 bhp and it only costs about £800 and will drive like that for 50k+ miles. Name one other car that can do that!

Homer - +100 bhp? I have seen conflicting reports about what you can get on here. Are you saying getting up to 420hp with BPU is common place?

Also - what happens after that 50k miles? (Semi serious question, new engine time?)

James

As Homer said really, it does transform the car although I've never been in a stock TT, and yes I've been hit with nasty bills - some my fault, others the twathead previous owner.

As for 400bhp+ at the fly of course, this is certainly achievable with BPU mods, the additional ones too most likely like a BC to raise the boost above 1.2bar - dangerous if on stock tubbies though! Get a colder set of plugs, a Walbro Fuel Pump, FCD and Speed Delimiter if not installed already, an electronic boost gauge and I'd go one Decat with an 1.2 RR and see how that goes first before going full decat. You could always purchase a Boost Controller as mentioned above to raise the boost further but your EGTs will increase, once again risking your engine and turbos

Handy to have an AFR AEM Wideband in there too to keep an eye on fuelling.

As for the 50k+ miles, not sure exactly what Homer means, but my car did have another engine out in it only 2 years ago! Things just start to let go I suppose. BPU will put additional stress on your engine and I'd budget for other things to wear too - the turbos especially!

Thanks for the comments.

Mine is used daily for commuting so reliability is paramount, although I agree that the performance - cost ratio does make the Supra a superb candidate for upgrading.

so would i be alrite to pull my second cat pipe out and fit a 1.2 ring? im near finished the bpu stage just need to fit the fuel pump and boost controller

ps she is a j spec on stock tubbies

I would fit the fuel pump before taking out the 2nd cat and fitting the RR ( I did it that way, don't mean its correct)