Hi. Had my STi mapped with a afterburner vortex no res cat back. I'm thinking of fitting a milltek no res cat back 2.75". Question is will the map be ok with the change of exhaust or will I need to get a tweek.
thanks John.

 

Are both exhausts the same bore?

 

I'm think the afterburner is 2.5" bore.

 

If your changing bore size then yes to remap tweek. Depends how bothered you are, some would say map it if you change your air fresher.

 

Just how much difference is there actually going to be to require a remap? If it was going from a standard system or decatting then it would be best to get it mapped, but going from one free flowing system to another, is there really any point? Since ive been on this forum this has always got me wondering why?

 

Yeah I can't see it really making much difference, just wondering if that extra 6mm in bore diameter would upset the car at all.
Surely the ecu would compensate for that small increase in bore size? Just want to make sure there's going to be no ill effects on the car if I don't get it tweeked in.

 

I would advise a remap, but in practice with my own car i have gone from 2.5" bore to 3" with no remap as yet, although it is on the cards. Car has been driven and drives fine acceleration is improved and no faults to speak off. To be honest there's loads of Impreza's out there that have had exhaust changes with no remapping. My first WRX had a decat and jap exhaust with no remap and never had any issues.

 

Worth getting at least AFRs checked,I run an AFR gauge,very useful.
Car might well be fine with a change of exhaust but,you always run a risk in any modification from standard,yes the ECU adjusts fuel but only in closed loop,ECU also adjusts for any knock but is limited.
Personally I would have the cable&software to check my own,so I have along with gauges to monitor,I don't fancy another rebuild(until I have the money for a forged stroker )

 

I needed a remap after changing my aftermarket 2.5" system with resonated centre section to a different 2.5" aftermarket system with un-resonated centre section. It caused my engine to breathe more freely and caused it to over-boost.


Keep an eye on your max boost levels, but in short, yes you might need a tweak.

 

That made me chuckle

 

I think I'll get the add checked after I've fitted it. The milltek I'm fitting is actually 2.75" bore compared to the afterburner 2.5" bore. Will be interesting to see how much it affects the afr.

 

I have got romraider, is there a way I can log the afr through that to check them rather than going some where else to get it checked.

 

You can check the LTVs which will tell you a bit of what's going on but to check AFR on WoT you will need a wideband O2 sensor,romraider will tell you how much the fuel trims change in closed loop and will show you if and how much timing is being pulled across the board.

 

I'm getting my standard downpipe on my Blobeye Widetrack changed to a 3 inch pipe with 200 cell sports cat. It's already has the 2nd cat delete with 3 inch system and mapped to suit. Would people recommend getting the map tweaked?

 

You may well need a tweak as the downpipe change could well free up the turbo and cause over-boosting. Worth data logging before and after to check.

 

Wise words

 

If you are keeping the down pipe then no tweek required.

 

With a 10% increase in bore diameter=more flow then I would be too sure.

 

Nah ,the fact he is keeping the down pipe where the back pressure isnt changing, then the boost wont start spiking, if he was going smaller id have a look at EGT`s, but not out of any real concern.

 

We dont get a remap tweek every time there is a 20 or 30 degree temp change in the weather, that will have more effect on our engines then this exhaust swap if honest.

 

The ECU compensates for temperature/air density in.
The ECU doesn't compensate for increase air out on load.
As per BPR post he changed from res to non res center pipe and that affected his car.
I've changed from a cobra to a revolution both 3" and I had to tweak for overboosst