[phineasxx1]

I got a question so do i lose any hp or tq if i remove the muffler or the resonator ?
and if i remove the secondary cats do i gain any hp - tq or lose any ?
i see alot of people on other forum say that if u remove the resonator you lose 5-10 hp is that true?
i wanna go straight pipe on both car with secondary cats -Resonator and muffler delete the primary cats im not gonna touch that and if i remove any of those thing is the engine light gonna come on?
2006 530i 255hp 3.0 L 6 cylinder
2013 528i crash replace with the M5 big diff on power
2013 M5 560hp 4.4L v8

[EL Jeffe 5]

anybody removing any part of your exhaust and not installing better exhaust don't know much about back pressure
Back pressure is very important to the to whole engine a specially valves.
My advice is save money and buy good quality exhaust. Its BMW not a 1995 Civic

[STR8-6IX]

alright... there is lots of misinformation about this and let me set everything straight.

you are partially right about the resonator. you lose power from a res delete UNLESS you fit an x-pipe in the same place where the res used to be. otherwise, you lose roughly 2-4 ft/lb of torque and its not going to sound very good. you get about 3HP from a secondary cat delete but the throttle response is better and more engine sound coming from the sides of the car. no check engine lights from doing any of this.

the thing with backpressure is also not entirely true either. yes, below 2000RPM backpressure is good, but as soon as you reach 2500+rpm all its doing is restricting your engine from breathing and you do not need that restriction if you want a good performing, good sound automobile.

personally myself, I have deleted my secondary cats and installed a magnaflow muffler in place of the restrictive stock one. it sounds amazing and flows well. do not waste your money on a full catback system like the person above me mentioned. BMW's have a great exhaust system from the factory and it will sound + flow genuinely well as long as you remove the main restrictions. I know you mentioned you wanted to keep primary cats, but this is where all the power restriction lays. with a secondary cat delete and high flow muffler you get maximum 5hp and a couple ft/lb of torque whereas the primary cat delete, if you install good catless headers you will be seeing 10-15 hp and 15-20 ft/lb of torque with a tune so the difference is major.

anyways, be sure to keep your resonator. the ECU will also need to learn any sort of exhaust mods so wait 500KM after deleting your secondary cats before you install the new muffler. be sure to do lots of full throttle pulls as this will help your ECU learn better. I have videos of what my exhaust sounds like with secondary delete and magnaflow muffler if you want to hear, it sounds good. but yea.. be sure to keep your resonator.

so for your 530i: secondary cat delete + high flow muffler

for the m5 I would do a secondary cat delete, possibly replace the resonator with an x-pipe (or keep resonator does not matter) and install a downpipe. if you are worried about emissions get a catted downpipe and leave the mufflers stock. it will sound amazing when accelerating but stay quiet and make back pressure at low RPM cruising. if not, you can do a muffler delete on the m5 instead which should sound sick but will be very loud.

but remember, high flow muffler + secondary cat delete is a more natural, less annoying sound and better power then a simple muffler delete.