6.9 exhaust

[s class]

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.

 

[s class]

THE INSTALLATION

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













Very nice, thank you.

 

[s class]

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.

 

[s class]

THE COST :

All-up, the equivalent of about US$ 370 including the custom silcencer fabrication. Nice.

 

[Michel]

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

 

[SELfor50]

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.

 

[Styria]

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

 

[SELfor50]

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..

 

[Styria]

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

 

[s class]

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).

 

[Styria]

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

 

[TJ 450]

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

 

[Styria]

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

 

[WGB]

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

Bill

 

[Styria]

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

 

[Oversize]

Thought I'd revive this thread and ask a question regarding extractors. One of the inhibiting factors to effective 6.9 modifications is the cost. This is despite the fact that the pride of the MB fleet (in the late 70s anyway), is now quite affordable.

Has anyone considered taking a set of their custom extractors to any of the well known suppliers (eg Genie) and checked them for similarities? Could it be that they're very similar to something commonly available, which could then be slightly modified for use on a 6.9; at not-so-crazy prices?

Obviously this would mean that the rest of us would have a large cost advantage over someone who's already laid down some hard-earned cash for custom extractors. I for one would be prepared to reimburse some of their costs (Motec?), if it meant I could have extractors at a reasonable price....

To give you an example of costs, I replaced the entire exhaust system on my Fairmont Ghia V8 (including brand name extractors & high flow cats, pipes & muffler, stainless dual tips & fitment) for $1800..... Far less than just extractors on a 6.9!

Seems to me that many contractors double their fees (or more), as soon as you mention MB (or 6.9). Heaven forbid if they're ever mentioned in the same sentence!! We should all stick together and try to keep at least some loose change in our pocket (and I thought poverty was owning a horse)!!

 

[motec 6.9]

Hi Mark the cost of the extractors was $2500 and yes it is a tight fit spacing is close to windsor of exhaust ports but problem is drivers side i have investigated making copies just not sure how many would be interested i have purchased a t51 turbo so if i go down that route i am sure Cam would put up his hand for the extractors

 

[Oversize]

This is the thread that I was referring to when I asked a question about twin throttle bodies. I've heard quite a few people say that a largish single pipe (2.5"-3") flows better than two smaller 2" ones. When I was replacing my Fairmont exhaust, I was told to stay away from the twin XR8 system, which I thought should flow better. I went with their advice & couldn't be happier; less kickdown, more power & a glorious note! Some of this would be attributed to fitment of aftermarket extractors & high flow cats (I suspect the old ones were partially blocked). The theory that a large single is better that two smaller ones appears well known as I've never heard of anyone replacing a twin 2" system with a single 4" one (usually it'll be 3").

Oh & I believe spending big on stainless is a waste of money, unless the car is only used occasionally, or you care about finish quality (ceramic coating mild steel may be dearer than going stainless in the first place).

 

[Oversize]

I still love this thread... interesting that my Ford is now quieter that when the exhaust was first installed. I’m not sure if it can be attributed to deposits coating the internal surfaces of the exhaust, or the loss of power since she’s now covered over 440k km (yes she’s tired now). Where there once was a true bark on over-run (which I regret I never captured on video), it’s now muted.

I can see that it’s desirable to go with a twin system, since clearance is an issue with a single pipe. A twin is less efficient since there’s more surface area thereby more friction and probably the reason why a single 3” flows the same or better than twin 2”.

Interesting too that the combined exhaust outlets are way larger for the exhaust (compressed gases) than the tiny 70mm for the inlet (atmospheric pressure). Weird....

 

[Oversize]

The ID at the outlet of the manifolds is 42mm, well below ideal.

That’s just criminal! Crazy considering the advertised performance aspirations of the model.