...recently had replacement decat downpipe .........and upipe also... .spool up much more progressive and earlier.But seemingly less power,im wondering if i could be imagining this or.........

 

Did you re-map after fittment? Because you should do

 

.....not as yet. ......do i specifically need to......or lose power? i need to replace original sti backbox soon not sure what else ....but may also have to sell shortly , sensibly

 

Map asap as car very likely to run lean without the cats. Up-pipe with allow more flow and less back pressure...remap only way to regain the loss of low power and gain more higher up!

 

Absolute B#llocks about it needing a re-map after a full de-cat,your car wont be running lean.Many people 'FEEL' they have lost some power due to the increase in airflow by removing the cats.I would try an ECU reset and see how it feels.

Its all down to less back pressure,giving the impression of less of a kick.

You dont say what MY you have but i have seen this happen on 01-02 cars and the reset helped it.

 

you don't run lean with more airflow. the OE ECU uses a Mass Airflow Sensor, it measures any increase in airflow and will adjust the fuelling to suit.

The main risk with a decat is that you upset the boost control parameters, and risk overboost. This can be adjusted with restrictor change on newer cars, although boost gauge may show all is well in this area too.

Paul

 

...Cheers for the varying opinions.Presumably overboost v .bad? car is 94 sti.....and, 1, reason i ask is that h and s upipe is wider that oe .and i recently read on here that could actually reduce power. i be diassapointed if this were so -but primarily dont want to do any damage- had what i hope was fuel surge moment today (but tank was nearly full ?) .I have no boost controller afr meter and only rudimentary boost guage . Having guys near me wire it up shortly to monitor+rocker gaskets renew

 

up-pipe will make very little difference on it's own to an older car. The newer cars have cats in the up-pipe so the replacement makes a huge difference to spool up. The H&S up-pipe is larger than the entry to the turbo, and the normal practive when fitting is to port out the entry to the turbo so the diameters match. If this isn't done I would say it's not such a great swap, but it certainly won't do any damage whatsoever.

Paul