fiestaturbo.com

[Syorme]

which exhaust would be best fo a Si 16v.
mongoose silenced 3.5 from the end of CAT back or
or a magnex 3 or 4 inch system.

and what does the cat by-pass do

[xander7]

i can't vouch for the magnex, but i can safely say the mongoose is IMO superb. excellent quality, superb fit and looks pukka. heres a pic of a 3.5" rolled cat back system on my si



it isn't overly loud, suprisingly quiet on idle, and more than bearable under normal driving, and really gets noisy when you floor it

cat-by-pass, simply means removing the catalytic converter from the exhaust system, and replacing it with a straight through piece of pipework, namely a de-catpipe. it will improve performance, and be less restrictive, but you'll increase emissions so it'll fail an MOT with it on, so the cat would need to go back on come MOT time

HTH

xander