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6-cylinder exhaust design

craigdiver - 30/4/17 at 08:17 PM

I have just read the contents of the internet on exhaust systems but still don't have a clue!

Engine is the BMW dual-vanos 2.5 6-cylinder.

My initial thoughts are that I want to bring the 6 pipes (1 1/2" ) straight out the side of the car below the top rail, then each one 90 degree bend down then joining into a main horizontal 2" pipe using 45 degree bends. This would be TIG welded and then chromed. Then into a cat, a silencer and finally tail pipe.

The other issue is that the engine currently has four oxygen sensors, two before cat and two after (original exhaust was 6-2-1). The two after will be deleted when ECU reprogrammed but what can I do with 6 individual collectors and two oxygen sensors? (Can I just put them in two of the 6 pipes or both in the single 2" pipe next to each other before the cat?

I would really like to have the 6 pipes on show and realise I might loose a little power but anybody understand exhaust systems and can comment?

Cheers

Craig

[Edited on 30/4/17 by craigdiver]

[Edited on 30/4/17 by craigdiver]

rodgling - 30/4/17 at 08:33 PM

I'd think you need a 6-2-1 system to get the lambdas to work properly? This is what I have, which does the job. I do have a second silencer under the fuel tank, as I can't get it quiet enough for track otherwise.

craigdiver - 30/4/17 at 08:41 PM

quote:
Originally posted by rodgling
I'd think you need a 6-2-1 system to get the lambdas to work properly? This is what I have, which does the job. I do have a second silencer under the fuel tank, as I can't get it quiet enough for track otherwise.

I could still bring the 6 pipes out and into two horizontal (where lambdas would be mounted) then into a 'Y' to a single pipe, or keep it as two horizontals but would mean having to buy 2 x cats and 2 x silencers but would look good!

ettore bugatti - 30/4/17 at 09:39 PM

Could you not place the 2x pre sensors opposite each other and the 2x post as well, but still relative correct position to the cat?

You might need a big cat to cope with the 6x exhausts.

craigdiver - 1/5/17 at 08:13 AM

quote:
Originally posted by ettore bugatti
Could you not place the 2x pre sensors opposite each other and the 2x post as well, but still relative correct position to the cat?

You might need a big cat to cope with the 6x exhausts.

The original cats were not too big, looking at the original exhaust again might need to make exhaust 6-2

SteveWallace - 1/5/17 at 08:25 AM

However you make your exhaust look, if you keep the BMW ECU then you will need to preserve the 6:2:1 configuration and the two pre-cat lambda sensors. The ECU interprets each sensor as being from a specific set of three cylinders and the engine will run rough if you mix them up. If your lambda sensors are outside of the engine bay though, make sure that they are positioned so as not to fail the IVA radius test.

A single Magnaflow 200 cell sports cat should be sufficient for your engine, there are a couple of cars on here including mine that have 2.8 straight 6 BMW engines that have passed IVA with these.

craigdiver - 1/5/17 at 08:36 AM

quote:
Originally posted by SteveWallace
However you make your exhaust look, if you keep the BMW ECU then you will need to preserve the 6:2:1 configuration and the two pre-cat lambda sensors. The ECU interprets each sensor as being from a specific set of three cylinders and the engine will run rough if you mix them up. If your lambda sensors are outside of the engine bay though, make sure that they are positioned so as not to fail the IVA radius test.

A single Magnaflow 200 cell sports cat should be sufficient for your engine, there are a couple of cars on here including mine that have 2.8 straight 6 BMW engines that have passed IVA with these.

Thanks Steve, going to have the EWS delete, along with removal of the post-cat lambdas and the air pump. is there a photo of your exhaust system on the forum? And, does it sound good? :-)

SteveWallace - 1/5/17 at 08:48 AM

This is probably the best photo that I have, but have a look in my photo archive as well. I went for the understated approach of only having two pipes coming out of the engine bay. Yes, it sounds great, but it is loud and I was right on the edge of the IVA noise test, so be careful with choice of silencer or use a DB killer for the test.

I also have a de-cat pipe, but I prefer the sound with the cat in place.

If your going to have the ECU remapped then have the limp home mode engine map replaced with the same map that you use for normal running as your final build will have so many sensors missing (e.g. ABS) that the ECU is almost bound to go into limp home. By changing the map it will make no difference.

Description

Nickp - 1/5/17 at 09:47 AM

I used a pair of manifolds similar to these-

DIRENZA STAINLESS STEEL EXHAUST MANIFOLDS FOR BMW 3 SERIES E36 320 323 325 328

I turned the rear one upside down and brought it over the top rail then joined them at the side of the car before the cat.

craigdiver - 1/5/17 at 11:25 AM

quote:
Originally posted by SteveWallace
This is probably the best photo that I have, but have a look in my photo archive as well. I went for the understated approach of only having two pipes coming out of the engine bay. Yes, it sounds great, but it is loud and I was right on the edge of the IVA noise test, so be careful with choice of silencer or use a DB killer for the test.

I also have a de-cat pipe, but I prefer the sound with the cat in place.

If your going to have the ECU remapped then have the limp home mode engine map replaced with the same map that you use for normal running as your final build will have so many sensors missing (e.g. ABS) that the ECU is almost bound to go into limp home. By changing the map it will make no difference.

Description

Limp mode will be gone, great advice, cheers

Nickp - 1/5/17 at 12:10 PM

quote:
Originally posted by SteveWallace
This is probably the best photo that I have, but have a look in my photo archive as well. I went for the understated approach of only having two pipes coming out of the engine bay. Yes, it sounds great, but it is loud and I was right on the edge of the IVA noise test, so be careful with choice of silencer or use a DB killer for the test.

Description

Mine sneaked through the noise test at 97dB IIRC, using this silencer-

https://profusionexhausts.com/silencers/round/6-inch-152-mm/2-50-inch-6-x-6-round-27-inch-polished-stainless-steel-profusion-universal-exhaust-812640. html

Volvorsport - 1/5/17 at 02:23 PM

I don't see why you couldn't do a 6-1 manifold

Nickp - 1/5/17 at 02:33 PM

quote:
Originally posted by Volvorsport
I don't see why you couldn't do a 6-1 manifold

And where would the lambda sensors go?

Volvorsport - 1/5/17 at 02:37 PM

In the collector

Nickp - 1/5/17 at 02:56 PM

quote:
Originally posted by Volvorsport
In the collector

But they work in 2 banks of 3. One lambda sensor is used for a bank of 3 injectors.

Volvorsport - 1/5/17 at 03:20 PM

Can the sensors and collector not remain paired ?

Nickp - 1/5/17 at 03:30 PM

quote:
Originally posted by Volvorsport
Can the sensors and collector not remain paired ?

Not sure what you mean by that. The lambda sensor needs to sense the mixture in the manifold that the 3 injectors it is paired to. It won't run right if it sees the mixture of all 6 or just 1.

Volvorsport - 1/5/17 at 03:46 PM

Lambda only measures a portion of exhaust gas. I can see a fault occurring if the gas changed and it couldn't see any mixture change. All they would be is further down the pipe.

Nickp - 1/5/17 at 03:55 PM

It's effectively set up to run as two seperate 3cyl engines on the fuelling side. How can it accurately adjust the fueling for each of these 3cyl engines if its reading the mixture of all 6cyls?

Volvorsport - 1/5/17 at 04:10 PM

If the lambda range was in value . Why would it be wrong ?

Nickp - 1/5/17 at 04:41 PM

quote:
Originally posted by Volvorsport
If the lambda range was in value . Why would it be wrong ?

Ok, so why do they run rough if you connect them the wrong way around?

Volvorsport - 1/5/17 at 06:42 PM

Do you swap the tail lambda at the same time?

Nickp - 1/5/17 at 06:48 PM

quote:
Originally posted by Volvorsport
Do you swap the tail lambda at the same time?

Tail lambda? After the cat? Mine doesn't have those. Sounds like the later twin vanos (TU) one does but he's having that deleted along with his remap.

craigdiver - 2/5/17 at 05:33 AM

I think, being sensible, and wanting the lambdas under the bonnet, I will stick with the 6-2-1 configuration - probably :-o

However, the original exhaust system has two cats, might still consider bringing two exhausts horizontally along the car with 2x cats and 2x silencers giving a 6-2 configuration. Would need to downsize pipes slightly to keep exhaust gas velocity up.