6.9 exhaust

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motec 6.9

Prodigal Son
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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
 

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Master
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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
 

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Master
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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.
 
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Master
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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

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

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Master
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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.
 

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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

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

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Master
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If you think you’ve finished, you’re not looking hard enough! ;):rolleyes:
 

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Master
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The more I think about it, the more I think a single 3-3.25" OD would be more desirable than a dual exhaust. It would weigh less, flow the same or better, would be easier to make, use less material and therefore cost less. It would also eliminate the need for a balance pipe.

I think dual exhaust was used due to ground (and other) clearance issues and the possibility 3" mufflers weren't common (or available)? There is also the possibility duel exhaust had the perception of power similar to quad exhaust now and 4 stacks on the old ocean liners!

So my next exhaust will be a single where possible, with a dual outlet.
 

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Master
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I would pay attention to the wall thickness too, since you don't want to select a pipe that has an OD that appears sufficient but the ID is below the minimum required for optimum flow.
 

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Master
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I may also consider having sections of larger pipe hydraulically crushed into an oval shape where ground clearance may be an issue!
 

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Master
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I haven’t used these guys but know others that have. If you’re after an amazing exhaust in VIC you can go past these guys. I’ll be getting them to do my next one...

2-D06765-C-9-A08-4490-A67-B-49-C339-F90-A4-F.jpg

846-BE716-4-EA1-4-C51-B4-D3-BEC32735-B2-A0.jpg

E14118-C3-2-C82-4159-ADB6-3-ABFE22-DFB0-B.jpg
 

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Master
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Some other M117 examples (very similar to the 6.9 & 6.3 layout) which are good, but NQR.

1-B3871-C4-99-B4-499-E-95-EE-BDFCC34718-E7.jpg

ACF08483-D366-444-F-9-E51-548-A41-A28268.jpg
 

motec 6.9

Prodigal Son
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Just put a polished rice boy 4 inch cannon on the back :p
 

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Master
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AMG original but obviously using old theories & ideas....

ADB7-BF46-864-D-4528-8063-4-DA843-E3267-C.jpg
 

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Master
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Up until recently I could still view the first series of pictures in this thread. Now I can’t see anything; what’s happened?
 

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Master
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I’ve just been doing some calculations & if you believe one school of thought, exhaust primaries should be a minimum length for optimum flow. Of course space is the biggest issue here, but by my math (using optimum diameter pipe), the minimum primary lengths are as follows:

560: 538mm
6.9: 632mm
 

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