My STi8 is booked for ECUTEK remap and I have got
a Magnex backbox and center decat.

How much power would be the result of Magnex backbox plus decat center along with a ECUTEK Custom map give me?

Or would a backbox and a decat downpipe with std center-catš+ ECUTEK give me more power, in that case how much more.

Which of these setups are more quite?

I realize that this is a question of estimates as the cars are slightly different...

/L-O

 

bttt

 

You really should be looking at changing your down pipe to get maximum effect, the standard pipe is very restrictive.

Milltek do a nice sports cat if you want to stay legal, or a de-cat pipe from the numerous after market suppliers.

 

Downpipe de-cat would give more power and drivability improvements than a centre de-cat. Sports cat downpipe and resonated centre would give good gains, whilst still remaining emmissions friendly.

Biggest difference to noise levels is in the backbox - fit a prodrive or remus or similar, it will be much quieter than say a Blitz or BPM, with very similar power figures.

If you really want to stay quiet, I'd recommend fitting a sports cat downpipe, resonated centre and stick with your existing backbox. Will be a few bhp down on a full de-cat, but pretty close, and not much louder than standard.

 

You could also just cut the cat out of the standard downpipe, and fit a hi-flow in the centre section.

Re. expected results - depends who tunes it, and how far they want to push. Are you changing your pump too? Without it, you're a bit limited above 6k - but that's no bad thing IMHO

Most of the cars I do, ~90% of the peak power gains come from the decat, I just work on fattening the torque curve.

Richard