Hi,

This has been covered in several other related threads but i thought i would post another to kinda confirm whats happening.

Basically its a 98sti in question. STill on std jap mapping.

I have been advised if i mess with the zaust i should get it remapped straight away.

I was trying to work out why decatting would mean the engine would run slightly off. The only explaination i could think of is:

The cats restrict the flow of zaust gases and so cause back pressure up to the turbo. Removing this back pressure will reduce the resistance on the turbo making it spin up easier, and faster when on full boost. And so more boost, which will mean all the ignition will not be perfect. Hence why a decat would require a remap.

I did consider perhaps back pressure to the cylinder is required. However im not sure why it would?

Now im curious. If the above is correct, i would then presume the majority of back pressure to the turbo would be caused by the first cat in the downpipe. Meaning i should be able to get away with doing a center decat and back box to make the car sound like it should, which may produce negligible performance increase.

Some people on here talk about reducing det. Is it common for people to record data from the knock sensor?

 

noone?

 

Not much help for you but i don't think you have a center cat (i know early imports only had 1 cat and that was in the downpipe).
My 93wrx is decatted (earlier spool up) and i was informed that the ecu could handle it but on the later cars the ecus were a bit fussier when it came to changing/removing bits.

As for your tech explanation i have no idea if that's right or wrong