As mentioned above, some cars run fine with a decat and others struggle to control the boost.
The newage Sti in particular, or in more general terms any of the IHI turbo'd cars, will all run increased or unstable boost when the cats are removed, sports cats included.
This may not be immediately obvious, particulary if it is done on a mild day.
Once the ambient temperature drops and the turbo runs at higher efficiency the boost control system can get a bit upset, the knock on effects (no pun intended ) can be detonation and sub optimal air fuel ratios as the wastegate opens and closes surging the airflow rate through the engine.

Andy.

 

i've not yet had a remap and i've been running a decat since 1000mls on my '07 wrx (5000mls now) , also green air filter and intake resonator delete elbow (purely for the sound). i have a psi3 datamonitor and have had a cel showing overboost (felt like a jolt just as the light came on, i assume fuel cut?) on only one occasion, this was when i was redlining in every gear whilst using the BHP measure on the psi3, happened whilst redlining in 4th. after this i reset the ecu and the datamonitor peak settings, and now have had boost peak as 14.6psi over approx 4hrs of driving on about 8 trips with occasional foot to the floor in 1st, 2nd and a bit in 3rd as i tend to keep my road speed legalish (apart from my bhp test which was on a track). so a remap IS required to be safe, but provided you drive at road kinda speeds as opposed to track, then you'd prob be ok, but i would suggest either a remap or a monitor so you can keep an eye on things.

 

As Andy F mentioned the problem is more with the IHI turbo on the newage STi's rather than the Mitsi TD series on the WRX !!

Andy Supplied me with a front entry TD05 16G for my MY02 WRX ....great turbo ..but before that I ran a newage decatted bugeye WRX with no problems


John Banks (if memory serves me) worked out a fix drilling out the restrictor to try and sort out the STi boost problems when de-catted but I'd take Andy's advice and re-map if opting for a de-cat

Shaun

 

"you often find the newage sti will boost spike once decatted. the sports cat is more restrictive than no cat especually with regard to spool and boost spikes."


Simon

Our cat has a diameter that is 2 x that of the original system and roughly 1.6 x that of a 3" downpipe. Simple maths means that we've got 4 x the surface area or over 2.5 x in the case of 3" so how's that going to be restrictive?


To answer the original question, it may be OK, it may not. The only way to be sure is get it checked out. The general priciple though would be that if it's OK, the fitting the parts probably wasn't worth the effort. If it made any real difference then recalibrating it to suit would be needed.

Mike

 

I never said it wasn't good for a cat, but sorry it is still more restrictive than no cat at all.

Simon

 

I beg to differ!

As I pointed out previously, the cat has 4 x the surface area of the pipes either side (or 2.5 x compared to a nominal 3") and as it has a metallic substrate is less than 10% 'blocked' by it. Measuring the pressure pre and post cat shows no pressure drop across it and the backpressure measured post turbo is the same with and without a cat. Do the same with a std cat and you get very different results.......

Mike

 

so mike are you saying the prodrive cat as fitted in the ppp is realy no different than a decated d/p. Thats very interesting.

 

As Mike and others have said, if you have a newage car that appears to be running ok without remapping then the fact is it's probably not producing any better figures.

Therefore, IMHO, unless you are planing on getting a car remapped, decatting is not worth doing..!

Those of you with decatted/no map cars have obviously never been in or up against a similar well remapped car..!

Saying all this there are rare occasions when the odd car will perform well regardless, due to the wide manufacturing tolerances. Same reason why some cars, otherwise identical, perform totally different..! Similar to the fabled 'Friday afternoon' car..

 

Yep, did the same, limped it home, below 3000 RPM (engine management light still came on). Then had remap the next day.

I wouldn't risk it.

 

cheers guys, will get the decat pipe tomorrow hopefully then i wont fit it until just before mapping.