Scooby50WRX

...That's the sort of problem some french Subaru agents are speaking about and which have occured on turbocharged Subarus and can occur on ours.

They explain that the problem is coming specially when the motor runs without the first cat and that it's a better idea to use only an aftermarket backbox and nothing more !

For this reason, they don't want to modify the exhaust line of the STI 7.

So, quite of all of us use a decat line and we are a lot surprised to hear that. It will be very interresting to read your experience about that and also from professionals.

The only thing I can suppose (I'm not mechanic !) is that a decat line can produce a fuel setting not as rich as with a standard line. I say that because my STI 7 is running with a sport cat, a 63 mm line and a Magnex backbox and it seems that the exhaust tailpipe is not as black as it was with the standard exhaust line... apart that, the car is a stunning one with this fitting.

Any comments my friends ?

P.S. They say that the same problems of pierced pistons could appear if we use direct admission.

john banks

A change of the restrictor apparently cures the overboost that occurs. There was a big thread on this recently.

Scooby50WRX

OK for that, but there is not so big overboost on other cars than STI 7.

submannz

All the Twin Turbo Legacy's have that problem also, but tend to destroy the roller bearing turbo first.

Scooby50WRX

At this time, the two answers are about overboost.

Some experience about other source of problem ?

john banks

It certainly does not run lean on the MY99/00 with a decat. The EGT also remains cool.