6.9 exhaust

[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]

Originally Posted by s class

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.

[motec 6.9]

Yes the outlet on the back of Stock cast headers on the 6.9 is less than 2 inches so very restrictive its main reason for my extractors

[Oversize]

And I’m guessing that’s the reason why this one is so quiet even with NO mufflers??? Or could it also be due to the lower CR of a US version? Or poor audio on the recording?

Do this on a Chev 427 & im sure you’d be rather deaf for some time....

https://youtu.be/ECoKrh5ueUg

[motec 6.9]

Not a bad note if I do say so myself https://www.youtube.com/watch?v=kk3LrogTT1c

[Oversize]

Finally I have the ability to add real figures to this thread! By my calculations the following should be adopted for optimal performance. Oh and these sizes are MINIMUM ID (NOT OD as pipes are normally specified). Include lots of bends (and not straight-through mufflers) in your design and you should go even bigger....

6.9

Twin system (ea): 59mm (~2.5")
Single: 70mm (2.75")

560

Twin system (ea): 58mm (2.25")
Single: 69mm (~2.75")

PS I had to take an average port size on the 560 since they're oval and not round. Hence there's not much difference due to the port sizing.

[Oversize]

Originally Posted by motec 6.9

Yes the outlet on the back of Stock cast headers on the 6.9 is less than 2 inches so very restrictive its main reason for my extractors

Outlets on the headers should be AT LEAST 59mm (2.31") for a 6.9 and 58mm (2.25") for a 560. That's each side....

[motec 6.9]

That's why I went 2.5 inch duel exhaust . And extractors are 2.75 at collector from memory

[Oversize]

Sweet! The LH bank headers are a compromised design with the firing order but I’m struggling to see how it could be done any better.

[c107]

Have you seen the Carobu 560 system they have recently started advertising?

http://www.carobu.com/hb-sport

Same principles could probably apply to the 6.9.

[Oversize]

Well isn’t that an interesting development!! Seems others are also supporting these models since they’re gaining in popularity & value...

I like their dedication & the diameter of the primaries is good but I still see opportunities for improvement! I’ll have to make my own with the help of some mates in the trade.

[motec 6.9]

My 6.9 extractors were made with correct sequence for firing order for 6.9.