The Decat / up pipe / confused thread
 

Guys, need your help. im looking to have my standard Bug WRX release a couple more horses, but......

Ive heard alot of talk about up pipes and decats but its spinning my head out on what im supposed to get before i get the remap done. ive already got a HKS panel filter and an aftermarket exhaust in place.

I would want something that i dont need to change over once a year because of MOT emissions failure.

So the question is, what the hell am i supposed to do ???

Prodrive sportcat, second cat delete, Harvey up-pipe, sti pink injectors, STI I/C and undertray and VF35. That ll get you over 300bhp easily.

What is the difference between the 2nd cat delete pipe and an up pipe

Wrx has 3 cats, one in the up pipe that feeds the turbo, one in the down pipe that comes out of the turbo, and one more in the mid section of the exhaust.

The up pipe with cat feeds the turbo and the 2nd cat comes well after it.
The stock primary cat will pass an MOT, you can shove it back on once a year and run with a decat. (Many do!) Failing that, fit a sport cat.
Only the WRX has all those cats.
As per amazing tech drawing below.. :lol1:

http://i49.photobucket.com/albums/f2...effery/cat.jpg

I have just replied to this thread whom is in the same boat as you:
https://www.scoobynet.com/general-te...et-300bhp.html

You wont go wrong with the harvey's set up, but it depends on what power and spool you had in mind?

Pete has highlighted the cats out, and just so your aware the STI only has 2 cats, there is no cat in the STI up pipe, this is what makes the WRX struggle to be honest as well as the TD04 depending on purpose. changing to a STI up pipe would be a good start, but to be honest I would change the TD04 for something with a little more punch such as VF35.

Rob

The second cat delete is the mid section after the downpipe, as stated above.

Do the guys at Haynes know about your diagram skills. :thumb:

Cheers for all the info..... as a first step to you think a 2nd delete pipe would be ok for a sucsessful remap

Personally I think the up pipe cat needs to go mate, your looking at moddifying your car for more power, but the up pipe cat is sooo restrictive. Lets not forget this is pipe that feeds the turbo that is currently catalytic restrictive that then makes the blower do its job.

Rob


EDIT - analagy, if you have a stream of water which powers a water wheel, if you were to put a filter in the stream prior to the wheel, this will slow down the rate, thus the wheel will turn slower, so big changes post the wheel wont make much difference to the rate the wheel turns if you dont do something about the rate prior the wheel. JESUS I hope I made sense there lol, ive just settled down with a cider.

Good thinking batman..... the serch begins for an up pipe.

Anyone selling on cheep ???

Yep :norty:

Subaru fitted the cat in the up pipe to restrict the bhp the Bug produced (so as not to reduce interest in the Bug STI.) Removing it will improve spool up.The VF35 from a UK STI is cheap and will provide far more mid range and top end grunt over a TD04. Removing all the cats will give you the maximum performance gains with a remap. You will pay around £25 per annum for refitting the exhaust at MOT time

Maybe I manybe no :lol1: :norty:

Just so the OP is aware the Cat in the Up pipe will not need to be refitted due mot time.

Rob

I have a two-part, slip-jointed H&S one that's been mildly ported, which I don't need...

Measures 40mm dia. which I understand is optimal for spool-up, up to around the 400bhp mark.

Bah Alan all that time you have to make a flash piece of modern art, yet not reply to my PM ;)
and the OP is the only one who found it all abit confusing to start off with heh :d
im hoping to drop one cat from my STI to free a few ponies along with a remap

i guess if the WRX loses the up pipe cat it'll still need a remap

Rob you got pm fella

How much work is involved in changiong the up pipe?

2 hours maybe with the right tools and some skin missing of your knuckles