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MECHANICALS With a 30 year-old automobile, there will always be discussion here - maintenance, modifications and mechanicals.

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  #1  
Old 29th November 2008, 05:32 PM
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Default 6.9 exhaust

THE DESIGN :

Trusty rusty has for some time run with the original spec 6.9 exhaust borrowed from the red car. The time had come for trusty rusty to get its own system now.

I did detailed measurements and design, and I provide them here for anyone else who may be interested.

Some calculations show that for a 6.9 euro, intended for street use, around 52.5mm ID is ideal (two of). For track use, something a little larger could be used.

The original piping is 50mm OD, which benefits low end torque at the expense of ultimate top end power. I intend to go to the next size up, being 57mm OD, 53mm ID - very close to ideal. (This is quality thick wall (2mm) 308 series stainless).

I measured the original silencers, and modified the designs slightly to accomodate 57mm tubing.







In general, an X-box or balance pipe is desirable on a V8, but the consensus seems to be that 6.9's never had them. So I did not have one fitted (in the interests of originality) though in theory it should give a useful performance benefit.

Last comment - as is well known, the 6.9 header arrangement is far from ideal. Given the space constraints, there's not a lot that can be done about it. The ID at the outlet of the manifolds is 42mm, well below ideal.
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'80 W116 280SE euro - the ride
'76 W116 6.9 euro - trusty rusty
'78 W116 6.9 euro - the AMG
'74 W116 350SE euro - the stand-in ride
'82 W126 500SEL euro - full hydraulics - the limo
'83 FORD XR3 - the beast

0 benzes on stands, 5 RUNNING
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  #2  
Old 29th November 2008, 05:33 PM
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Default Re: 6.9 exhaust

THE INSTALLATION

THis week I received the custom silencers, and had the system built.













Very nice, thank you.
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'80 W116 280SE euro - the ride
'76 W116 6.9 euro - trusty rusty
'78 W116 6.9 euro - the AMG
'74 W116 350SE euro - the stand-in ride
'82 W126 500SEL euro - full hydraulics - the limo
'83 FORD XR3 - the beast

0 benzes on stands, 5 RUNNING
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  #3  
Old 29th November 2008, 05:35 PM
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Default Re: 6.9 exhaust

THE VERDICT :

I'm very happy with the large standard size silencers. The final outlet is a pair of polished 63mm pipes. Sound is deep but subtle at idle, and is almost dead quiet above 1500rpm - as with the standard system.

Interestingly, no real performance difference that I can tell, though admittedly I haven't been out on the freeway yet.

All in all, I'm happy. The lessons I think can be learned - the offensive booming and droning usually associated with free-flow stainless systems can be mitigated or even eliminated by using thick walled tubing, and decent sized silencers.
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'80 W116 280SE euro - the ride
'76 W116 6.9 euro - trusty rusty
'78 W116 6.9 euro - the AMG
'74 W116 350SE euro - the stand-in ride
'82 W126 500SEL euro - full hydraulics - the limo
'83 FORD XR3 - the beast

0 benzes on stands, 5 RUNNING
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  #4  
Old 29th November 2008, 05:36 PM
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Default Re: 6.9 exhaust

THE COST :

All-up, the equivalent of about US$ 370 including the custom silcencer fabrication. Nice.
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'80 W116 280SE euro - the ride
'76 W116 6.9 euro - trusty rusty
'78 W116 6.9 euro - the AMG
'74 W116 350SE euro - the stand-in ride
'82 W126 500SEL euro - full hydraulics - the limo
'83 FORD XR3 - the beast

0 benzes on stands, 5 RUNNING
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  #5  
Old 30th November 2008, 06:57 AM
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Thumbs up Re: 6.9 exhaust

Quote:
Originally Posted by s class View Post
THE COST :

All-up, the equivalent of about US$ 370 including the custom silcencer fabrication. Nice.
By Australian standards that would be classified as 'CHEAP'.....

Well done
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1978 W116 690SEL # 3312
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  #6  
Old 7th December 2008, 02:16 AM
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Cool Re: 6.9 exhaust

Great detail and design S Class! A very good read.

Did you assist with the fitting also at the workshop? Looks like a quality job..

As Michel's said, 370USD for a custom job like that is pretty bloody good!!!

Great work...

Cam.
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1978 W116 - 450 SEL - Finally locked
1979 W116 - 450 SE 6.9 - New Ticker
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  #7  
Old 7th December 2008, 03:23 AM
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Default Re: 6.9 exhaust

Hi S-Class, at that price, one is giving the system away. Obviously, I have noted from some of your previous posts, the cost of labour, if not for parts, is certainly in the bottom basement category when compared with Aussie prices.

I also see that you have at least some sort of flange fitting for the system. About three years ago, I had my system modified by:

1) Fitting a genuine 350 (107 SL/C) as the first muffler, and

2) Fitting flanges alongside the bell housing connecting engine down pipes and the first set of pipes leading to the 350 muffler, and

3) Fitting flanges behind the 350 muffler and the front pipes of the rear silencer.

All in the name of "easy" maintenance whenever required. The sound is a little different from standard - perhaps a little more 'snarly', but hard to describe. Regards Styria
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Old 7th December 2008, 03:37 AM
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Default Re: 6.9 exhaust

So you have 350 pipes on Gleaming Beauty styria??

My beast came alread with a 2" system pretty much straight through with a muffler at the back.. In coming months I'll probably just remove the rear muffler and have it straight through all the way.. I 'may' upgraded it to 2.5".... depends on whether the exhaust man takes 'cash'.

I've already accepted that custom extractors will never happen due to cost and engine bay restraints..
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1978 W116 - 450 SEL - Finally locked
1979 W116 - 450 SE 6.9 - New Ticker
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  #9  
Old 7th December 2008, 04:29 AM
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Default Re: 6.9 exhaust

Hi SELfor50, only the muffler is 350. I don't think that I altered the system or increase pipe diameter in any way. The rear muffler, if anything, has probably smaller outlets than standard 6.9.

I am not really sure how Gleaming Beauty stacks up powerwise with other 6.9s. I think it is pretty good, taking a line through bb's, 6.9 forever's, plus a few others, but it is really only a dyno test that would reveal it all accurately. Regards Styria
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  #10  
Old 7th December 2008, 05:14 AM
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Default Re: 6.9 exhaust

I would think that the 350, 450 and 6.9 might likely all use the same middle silencer anyway. I only have one set of flanges - over the rear axle.

I had originally intended to take your advice and have another set near the gearbox somewhere, but I was talked out of it on clearance reasons.

I am actually so happy with this system I'm going to order another set of these custom silencers for the red car, and another middle one for the 280SE (its present one is rusting out).
__________________
'80 W116 280SE euro - the ride
'76 W116 6.9 euro - trusty rusty
'78 W116 6.9 euro - the AMG
'74 W116 350SE euro - the stand-in ride
'82 W126 500SEL euro - full hydraulics - the limo
'83 FORD XR3 - the beast

0 benzes on stands, 5 RUNNING
Reply With Quote
  #11  
Old 7th December 2008, 05:57 AM
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Default Re: 6.9 exhaust

Hi S-Class, the 350 muffler is quite a bit smaller than the standard 6.9 unit - very flat, quite wide - wish I had a picture to illustrate. Regards Styria
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  #12  
Old 7th December 2008, 11:10 AM
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Default Re: 6.9 exhaust

Flanges are good, as long as they are not installed in low clearance areas.

IMHO, having a flange up the front, unless it was up near the manifolds, would be a questionable idea. One of my mates had a BMW with such flanges, it is very easy to get them snagged and rip the whole system off, as happened to him while I was in the car.

Tim
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  #13  
Old 7th December 2008, 12:27 PM
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Default Re: 6.9 exhaust

Well no, Tim, in this case - the flanges are right alongside the bell housing, and out of harm's way. No chance in the world would they get snagged on any obstruction. Again, wish I had some pics.

I can relate though, having flanges to the engine down pipes, certainly assists in taking the heads off - obviously, on the o/s it is of no assistance, but on the other, you can actually remove engine down pipe and head as one unit. Regards, Styria
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  #14  
Old 7th December 2008, 01:44 PM
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Default Re: 6.9 exhaust

Almost any driveshaft or transmission work requires dropping the exhaust sytem - so the easier the better.

Bill
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  #15  
Old 7th December 2008, 04:09 PM
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Default Re: 6.9 exhaust

Hi WGB, the entire exhaust system, when slip fitted as it originally came from MB, is extremely difficult, cumbersome and heavy to manoeuvre unless of course you have a hoist (as you do !) and a gearbox jack (as you do ! - I am jealous). Thus, it can be a real boon where you only have to undo some nuts and bolts to remove sections of the system.

When I had this done, the exhaust place charged me about $180.00 (from memory), but it was money well spent. Regards Styria
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