6.9 exhaust

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This was based on a minimum ID of 40.5mm (1.59”) for the 560. Minimum ID of 41.5mm (1.63”) for the 6.9.
 

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I was speaking to a mate who races a 450SE & his mods have been recommended by a well known racing team in V8SC. They specified an OD of 1 7/8” (47.63mm) and a minimum primary length of no less than 28” (711.2mm)!! Of course that’s in an ideal world with no space limitations.... So based on a wall thickness of 2mm that leaves an ID of 43.63mm. Not far off my calculations which were minimum sizes not taking into consideration size availability....
 

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I just measured the collectors of a Euro 6.9 , Aussie 560, 450 & 420. I can confirm they are all around 43mm!!

So basically the 420 has the same size outlets as the worlds fastest sedan (in 1975)!! And the 420 inlet (throttle plate) is actually BIGGER than the 6.9! The fact the 6.9 performed as well as it did seem to be purely down to CCs!
 

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Master
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I just measured the collectors of a Euro 6.9 , Aussie 560, 450 & 420. I can confirm they are all around 43mm!!

So basically the 420 has the same size outlets as the worlds fastest sedan (in 1975)!! And the 420 inlet (throttle plate) is actually BIGGER than the 6.9! The fact the 6.9 performed as well as it did seem to be purely down to CCs!
Note that figure is four into one (the collector) on each bank/side. Not to be confused with individual exhaust ports.... At not even 2” per side it can be seen that even changing an exhaust system from the manifolds back will not increase power or torque significantly unless the existing system is faulty or very poorly designed. The main result will be a change in note/tone/noise levels.
 

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Master
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By comparison, the Holley 750DP square bore which I believe was fitted to the XYGT used 4 x 1 11/16” (approx 43mm) barrels.
So the 6.9 uses an exhaust which has 1/2 the flow capability of a 5.8!!
 

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Master
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Something like this would be ideal however space is alway the enemy in this area!!
 

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Oversize

Master
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Not much room with these headers!! Twin 3” on a mates car but the collectors been crushed a fair bit to get around the steering box!! Driver’s side is very cramped. Makes you wonder how the fabricator managed to get it all in there without complete engine removal!! Food for thought...
F9C3FC87-9DDF-4C58-9DD0-DF05A8FD751A.jpegD10FEF1D-3A54-4D19-8F08-1485773EB4EF.jpeg3B6B5995-451C-4994-ACEC-9EA689D5F2BD.jpeg35073FCB-D888-49D2-AFFC-1C5AE68C18F3.jpegF7E542CF-9FD7-4125-859D-C2D425AFB6FA.jpegE089CC36-9A4D-4F6E-87A1-59D21EA41C20.jpegA42F2336-6DD4-4C50-9F53-BBD78A6F4CB9.jpeg
 

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