Runs worse with decat.
 

I've been running a Toyosport decat pipe for a little while, and never really liked the change in power delivery when it was fitted, so I've returned to the original catalyst downpipe.
With the decat, there was a huge midrange hit (around 3500rpm) that just seemed to go flat as the revs increased. With the catalyst back in place, there's no midrange surge, and the power delivery feels a lot more linear.
The car's a MY95 WRX with standard turbo, Fujitsubo cat back system, ESL daughterboard (that's optimised for a full decat, I believe), Green panel...
Are the symptoms that I'm seeing expected, or should I be looking for a problem that's causing a big boost spike with the decat (although I never hit fuel cut and boost is normal, reaching 1.1bar and tailing off to 1.0bar at around 5500)?

What Toyosport decat you are fitted?

Are you fitted Up pipe,if yes this Up pipe is oversized and this can cause bigger lag than with OE up pipe

Or if you fitted 3" exhaust from Toyosport,which is bit overkill on yours,would say 2.5" will be best for your needs and stay clear from the Toyosport exhaust/up pipe


Jura

Ah, yes it was a 3inch downpipe. So you're saying that it flows too much?

Make sure you have the car mapped for the exhaust that's on the car!

3" exhaust is recommended above 400bhp,but some running above that 2.5".

All depends from exhaust and sometimes from manufacturer

When you are fitted this DP(downpipe),car has been mapped for this change?

If not this can be your problem,decatted exhaust flow more than catted exhaust


Jura

I see. So the short of it is that the downpipe is over-specc'd for the job.
The chip is a "one size fits all" daughterboard that is suited to a decat downpipe and front mount. I know the older style chips are frowned upon when compared to a bespoke remap, but I'm monitoring mixture, knock, etc. and don't want the extra outlay of an ECU/ remap at this time.
My question was really to try and understand why the downpipe didn't appear to offer better breathing at the top end, when the midrange increased so dramatically...

That might just be the way the chip is programed but it will be because you fitted the cat back on. I don't think the fact that its 3" pipe causing the problem as i am running a 3" Turbo back (toyo sports) and have 330bhp.