I have an ECUTEK map plus a good few mods on a new age WRX. I have a full 2.5inch Hayward & Scott decat (inc up pipe), the back box is a H&S 3.5 inch rolled in tail pipe. I'm boosting to 18psi but as ive been a little unhappy with the relative quitness from the bb, so, i stuck on a H&S 4.5 inch jap slash and not only has the performace increased but ive noticed my boost gauge has increased from 2-3psi from time to time..........does anyone know why this may be the case or if another remap would be required???????

 

The boost has raised because your new backbox is less restrictive. As long as it is not hitting fuel cut, you should be OK - but check with whoever mapped it. Note that it will get much worse in winter

More boost is most of the reason for increased performance, not the decreased back pressure.

 

How does this happen, being thick here! I thought the boost was before it hit the backbox?

RR

 

Mee too , I thought that if there was any slight change at all the ECU would compensate accordingly?!?!?!??!

 

I could be wrong, but I can't see a backbox -no matter how "free flowing"- given you a boost increase. At the end of the day its the Cats that are the real culprits in the exhaust system.

I stand to be corrected though!

Ns04

 

EGBP has been reduced, increasing engine efficiency. It can do more with less. Boost control maps would have been optimised to provide target boost for the EGBP present at the time.

Exactly the same as going from a fully cat'ed system to a full decat - you get more boost, and sooner. Why? EGBP has been reduced.

A bad analogy - like you trying to play squash with a head full of snot after a cold, compared to same when being able to breathe properly

If cats were in place, you wouldn't notice it - but car has a decat.

ECU does try and compensate - but the EcuTek remap will likely have been done to provide the best boost control with the backbox it was mapped on (Subaru's stock effort of boost control is a little lazy, and can easily be improved on.....sacrifice is what you're experiencing now). Your just seeing an overshoot. To see if the map needs tweaking wait for a cold day and give it WOT on an uphill run in 4th - worst that can happen is you either hit fuel cut, or the boost will start to fluctuate up and down as the ECU tries to hit it's target. If you get neither of these things, I'd say don't worry. If you want it corrected, talk to the person who actually mapped it - and be aware that it may involve a charge For peace of mind, talk to the person who mapped it....it wasn't me

Richard