I wish I could confirm this but on 'other' M power cars I have lost upto 10 bhp on a dyno (rear wheel figure) with Eisenmann. I am not the only one who has seen this on M power cars.Hello.
The muffler you mention will have no negative effect in my view, assumimg that
the rest of the system is present & working.
Due to this mufflers different internal baffle arrangement & material, it will be louder,
but little else, & that is what some owners want.
The F/I stuff I have tested on the same cars from them and other manufacturers gives around the same gains. H&S is far from anything special.Very Interesting, have to say i've never had a problem with the F/I stuff they have done for me, but they have never done any N/A stuff for me.
Considering the Eisenmann system is only slightly more expensive, that might be the way to go, but i'm not convinced by the exhaust tips, really want some that look completely standard.