good luck on your quest. Just be aware on diminishing hp returns on $ spent.
1. headers options, ranked in approx cost hi to low
Supersprint, ARMAspeed, MMW, MXP, diy cut out cat
User mapleridge is also working of a new set
2. Exhaust- you will se gains if you remove the secondary catalytic converters. Other options are mostly for looks & sweet sound.
AA has one tune,used to be called stage 2
Othe companies are Eurocharged, OEtuning
They are all kinda equal for a car without the DISA manifold based on all dynos
128i Sport 6MT converted to Euro 130i spec, tuned by evolve ~220 whp 207 wtq(ft-lb) SAE
In-progress: n54 ssk, m3 trans mnt, e36M lip Wishlist: m3 susp, n55 eng mnt, headers, LSD, finn dif e60
"The 1-series is the last car that BMW engineered before the Germans, as a car-making culture, fell out of love with driving." - R&T 2013 135is