How about an exhaust system primer?

[Copasetic222]

As a somewhat newbie with a self proclaimed lack of understanding, I've done some searching and pieced together some information. But, it would be extremely helpful to me, and I assume others, to have a thread that provides info on the possible systems, pros and cons, etc.

For example:
Why/why not add down pipes?
Cat backs vs axel backs?
What's the deal on straight pipes?
When do you have to change the rear diffuser?
What can you expect for warranty issues?
Are the higher end systems worth that much more money?
Which systems drone and which ones don't?

I'm sure there are a lot more questions as well.

Those of you that know a lot more about this, please chime in. Thanks!

[RPIpower]

Welcome, I hope I can help answer some questions about the exhaust for your M5! I’ll start with the topics you listed and everyone can build on this and go from there.
Why/why not add down pipes?
The factory downpipes on the F10 M5 contain the catalytic converters, which in terms of exhaust flow, causes a restriction. This restriction to flow prevents the engine from pumping the exhaust out, especially at higher rpm. Installing aftermarket downpipes that either delete the cats, or include high flow units, are able to make extra power with correct tuning. Just note that catless downpipes will leave you with a check engine light. Both options technically are tampering with factory emissions control devices and could present a problem for you if you are in an area of the country that requires emissions inspections of your vehicle. I won’t tell on you though!
Cat backs vs axel backs?
Cat back systems on the F10 M5 are the most popular option due to their ease of install, since you can unbolt the factory system right after the downpipe, and the ability to save your factory exhaust system in one piece. Axle-back systems will require cutting and either clamping or welding the new rear section to the existing factory mid pipes. There are many options out for both designs and it is up to personal preference which you should choose. Watch the many videos out there to make your choice.
What's the deal on straight pipes?
A very viable option on these M5s, either with stock or aftermarket downpipes, because the turbos themselves muffle quite a bit of the engine sound before it even enters the exhaust system post-turbo. On the M5, a straight pipe system has a very nice sound and will accentuate the pop/crack upon shifting and you will definitely hear the turbos after letting off. In general it has an extremely nice sound that I would imagine you're after since posting questions like this. Whether you install a straight through system with or without catless downpipes is a matter of how crazy you want the car to sound, and if you like your neighbors or not! It will be very loud on cold start with the downpipes and a straight pipe system.
When do you have to change the rear diffuser?
I am pretty sure that almost all of the popular options are designed to fit within the factory diffuser, and that the aftermarket diffusers are added for a cosmetic purpose. (Someone correct me if I’m wrong on this one)
What can you expect for warranty issues?
As far as warranty goes, the general consensus is that catback exhaust systems shouldn’t void your warranty, as they are installed after the emissions control features of the car (cats and o2 sensors) that being said, I’m sure there are dealers out there that will hassle you just because they can. It is very dependent on your particular dealer / service manager. Downpipes are going to be harder to get past them, and especially if you have to have an emissions inspection.
Are the higher end systems worth that much more money?
As with all exhausts, this is dependent on a few things. You may not want to spend that much on the system in the first place. You really won’t know how it truly sounds until you hear it in person, so just find high quality videos when trying to decide. They high end systems have a great fit and finish, but it is eventually going to get covered in road grit and most likely burned rubber from the back tires. It is an M5 after all. It is a matter of taste I would say, and potentially if you would like to have a valved system or not.
Which systems drone and which ones don't?
I have not heard all of the systems out there, but for the most part, the F10 chassis is very well insulated to sound and most of the catback systems produce a fairly low amount of drone, if any. (need others to chime in on this)

I hope this long mess of a message helps out some, and I hope others add to this as well.

[Copasetic222]

Originally Posted by RPIpower

Welcome, I hope I can help answer some questions about the exhaust for your M5! I’ll start with the topics you listed and everyone can build on this and go from there.
Why/why not add down pipes?
The factory downpipes on the F10 M5 contain the catalytic converters, which in terms of exhaust flow, causes a restriction. This restriction to flow prevents the engine from pumping the exhaust out, especially at higher rpm. Installing aftermarket downpipes that either delete the cats, or include high flow units, are able to make extra power with correct tuning. Just note that catless downpipes will leave you with a check engine light. Both options technically are tampering with factory emissions control devices and could present a problem for you if you are in an area of the country that requires emissions inspections of your vehicle. I won’t tell on you though!
Cat backs vs axel backs?
Cat back systems on the F10 M5 are the most popular option due to their ease of install, since you can unbolt the factory system right after the downpipe, and the ability to save your factory exhaust system in one piece. Axle-back systems will require cutting and either clamping or welding the new rear section to the existing factory mid pipes. There are many options out for both designs and it is up to personal preference which you should choose. Watch the many videos out there to make your choice.
What's the deal on straight pipes?
A very viable option on these M5s, either with stock or aftermarket downpipes, because the turbos themselves muffle quite a bit of the engine sound before it even enters the exhaust system post-turbo. On the M5, a straight pipe system has a very nice sound and will accentuate the pop/crack upon shifting and you will definitely hear the turbos after letting off. In general it has an extremely nice sound that I would imagine you're after since posting questions like this. Whether you install a straight through system with or without catless downpipes is a matter of how crazy you want the car to sound, and if you like your neighbors or not! It will be very loud on cold start with the downpipes and a straight pipe system.
When do you have to change the rear diffuser?
I am pretty sure that almost all of the popular options are designed to fit within the factory diffuser, and that the aftermarket diffusers are added for a cosmetic purpose. (Someone correct me if I’m wrong on this one)
What can you expect for warranty issues?
As far as warranty goes, the general consensus is that catback exhaust systems shouldn’t void your warranty, as they are installed after the emissions control features of the car (cats and o2 sensors) that being said, I’m sure there are dealers out there that will hassle you just because they can. It is very dependent on your particular dealer / service manager. Downpipes are going to be harder to get past them, and especially if you have to have an emissions inspection.
Are the higher end systems worth that much more money?
As with all exhausts, this is dependent on a few things. You may not want to spend that much on the system in the first place. You really won’t know how it truly sounds until you hear it in person, so just find high quality videos when trying to decide. They high end systems have a great fit and finish, but it is eventually going to get covered in road grit and most likely burned rubber from the back tires. It is an M5 after all. It is a matter of taste I would say, and potentially if you would like to have a valved system or not.
Which systems drone and which ones don't?
I have not heard all of the systems out there, but for the most part, the F10 chassis is very well insulated to sound and most of the catback systems produce a fairly low amount of drone, if any. (need others to chime in on this)

I hope this long mess of a message helps out some, and I hope others add to this as well.

Thank you for the great answer! Exactly what I was hoping for.
I hope others will also chime in, as you suggested.

One additional question: would you, or someone else, please explain about valves? Also, can you open/close the valves from the cabin in some systems to change the sound?

Thanks again.

[straightpipeguru]

Totally awesome write up !! RPIpower

I have the RPI GTM (Straight pipe) system on my ride and totally love every minute of it, (yes cold start might wake up my neighbors but they are cool with it!!)

the downpipes will definitely give you gains and will be louder, it will trigger the check engine light but there is software out there to erase it.

[MCarsFan]

Great system RPI GTM - great exhaust write up you should look at OP

http://f10.m5post.com/forums/showthr...=823271&page=3

one of the top sticky threads for this section.. Mild to Wild - this is a great summary of your options.

@RPiM5 put this thread together years back and it was the best source of deciding which exhaust to choose in 2013.

[gdavis]

Great write up!!

[ur20v]

Just be carefull, most systems and axel backs drone to some extent, will depend on your tolerance, I for one seem to have little tolerance compared to most on the board. I am in my forties and have a great family and niegbours so don't like pissing them off or giving myself head ache- I must have good hearing still lol!

I had a axel back and changed within a couple of months due to drone then went Agency Power Ti system, super light, nice tone and a nice step up in volume with NO DRONE!... winner for me.

You also need to deside what you are going to do with the car, DD, cars and coffee,drag strip or 2nd/3rd gear road pulls with mates (racing), if DD and just plonk your foot down when you feel the want you don't need to gain 10hp from downpipes and straight pipes and suffer the drone and very loud noise etc but on the drag strip on drag radials you may want every last HP- note our cars are traction limited so you need to use DR's to use the extra power over a tune (piggy or flash or both, your choice!).