Exhaust upgrade question

[SharkInfested]

So I'm in need (want) of a complete exhaust overhaul on my 88 M6. Since I don't have emissions restrictions, I'm thinking of new pipes off the manifold going, uninterrupted, to a new muffler (possibly a SuperSprint or Magna Flow - suggestions are welcome).

My question is, if I do this type of set up, I believe the O2 sensor would no longer have a place on the system. What are the implications or should I maintain a resonator, which I believe the O2 is connected to?

I know that without a res, the exhaust would be louder, but not sure how much. I definitely want to free up some horsepower, but don't want it to be obnoxious in the process.

A muffler specialist I spoke with said he could merge to a single pipe coming off the manifolds into one well before it comes to the muffler, but would this impede the purpose/performance of the adjustment ports for each cylinder located on the manifolds? Or any other performance implications?

Your thoughts, guidance would be appreciated.

[1SGDHORN]

Word of caution when looking at replacing your OEM M6 exhaust.... Not much out there is an improvement, performance wise, over the stock system. And if a local shop is advising you about going with a single tubing system my first question would be what size exhaust tubing will he recommend. I have read that it takes a surprisingly larger size exhaust tubing to equal the flow of the factory dual set-up. There is a lot of science involved, way more than I have knowledge of, but I have read a lot on this as I too was looking into replacing my M6 exhaust and my research showed that I would only be gaining a louder exhaust note. If you want more Horsepower it needs to come as a complete engine system being cam upgrades, port work on the head, better breathing headers, ECU remapping and then an upgraded free flowing exhaust. Additionally, so I have read, removing the catalytic converter makes the car's exhaust smell much worse.

I have come to the conclusion that for me, the stock exhaust and the M6 in general, was very well engineered by BMW.

"IF" I did replace my exhaust it would not be done by some local shop. I would go with a reputable aftermarket vender who has experience with the 635/M6 engines. Just my two cents.

Hopefully others with more first hand experiences will lend their opinions as well.

- - - Updated - - -

Look into Billy Boat and Supersprint which are cat back systems. These are two popular choices with the 6er crowd. Ireland Engineering as well but, I'm not sure they sell a system for the M cars. I only see one listed for the 635s.

A couple others options could possibly be Dinan or Korman.

[dwal95008]

+1 to the above.

The main restriction on these cars, M or otherwise, is usually in the engine cylinder head. You can increase efficiency by chipping, and some under-drive pulleys for the accessories, but when it comes down to real power gains you need boost or aggressive engine work.

The s38 equal length "bundle of snakes" tubular headers flow perfectly well up to a LOT of horsepower. If you go bigger and less diligently engineered you will lose low end and not gain much at the top. I have heard recommendations of greater than 3" for a single pipe and even then dont do anything to the headers.

[SharkInfested]

This is really good insight guys, thanks.

For now, I'm leaning back to a BMW stock option for pipes, resonator and muffler. It's a pricey option (about $1200), and I'm all for keeping the M6 stock, but if anyone else would like to chime in, I'd be happy to hear your thoughts.

As for a power boost, chipping is an option, but messing with the heads is not something I'm prepared to do right now.

The point made about no cat leading to a smelly exhaust made sense. I want a throaty sound, more power, but not at the expense of smelly drive-bys.

[Badgas]

A local shop that serves the hot roders would likely do a great job of bending and welding a custom exhaust that closely matches the stock exhaust. A bung for the O2 sensor can be welded into the exhaust where ever needed. I did such a system a while back and posted details and pictures. I also posted a dyno run so you can hear what it sounds like. It is an alternative. (Mine is a bit loud but there are quieter muffler/resonator combinations out there)

FYI, It only takes a single 3" diameter pipe to match the flow of (2) 2" diameter pipes. It's all based on area of the pipe cross section, Area = pi x r squared.

[master6]

I do not understand the desire to make a louder exhaust and delete the Cat Converter.
This was engineered by great people, and our cars are luxury Grand tourers designed for the Autobaun.
Not a noise machine.
Have you ever driven behind an older car, and were forced to smell their exhaust, gross.

[SharkInfested]

Thanks for your insight. The desire is to make greater horsepower. With a non-obnoxious sound, but still gain a throatier note. I respect German engineering a great deal, but this technology is 27 years old and there are many German-respecting providers that can achieve the goals of today's owners and hold true to a grand tourer that want more horses. This forum is a great place for owners to gain more information from peers, which is exactly the purpose of my original question. As for smelly exhaust, see my last post.

If any others would like to chime in, please do.

[DaHose]

Here is a link to my first exhaust build.

http://bigcoupe.com/phpBB2/viewtopic.php?t=22606&postdays=0&postorder=asc&start=0

Here is a link to audio of the exhaust.


https://www.youtube.com/watch?v=0I1Wb0P9B8g&feature=youtu.be

Here is a link to my most current version of that exhaust. I am still going to tinker a bit more, but that will have to wait until I have more time.

http://bigcoupe.com/phpBB2/viewtopic.php?t=24489&highlight=tig+jose

Jose

[1SGDHORN]

DaHose, just finished reading your exhaust thread and am more convinced than before to buy an exhaust for my M6 that someone else has designed and crafted. Thinking Billy Boat (though maybe too loud) or Supersprint. And I agree with master6, old non catalytic cars really smell badly and would sacrifice a few lost horsepower not to have to smell that smell. And with todays high flow/high performance cats I bet you wouldn't even lose power.

[DaHose]

The catalytics didn't feel like they made a difference in power, but they did help remove the low rpm drone. Take a look at the VSR1 (vsr1.com) middle section for the M6. It's pricy at $850, but beautifully made. It might also bolt directly to the Magnaflow E28 rear section. That could make for a very nice combination.

Making your own exhaust is DEFINITELY a ton of work if you don't have a nice high lift and a mandrel bender. Even just having a mandrel bender would make it SO much easier.

Jose