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D shaped exhaust ports


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As part of the exhaust build I've found a company making flanges for the manifold. They have d shaped ports which they state are as per 'race engines' I've done a lot of reading on head modification for the 6 cylinder and haven't seen any mention of d-shaped ports. Could anyone shed any light? Ie when used, reasoning, any actually performance gain?




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I know nothing of the science of porting or gas-flowing heads, but will try a guess here: it that the maximum to which a head can be ported out without weakening it? So: if they make them this shape, then any shape or mod of head is likely to be within the d-shaped aperture they have cut? A sort of one-size-covers-all template for the flange?

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Of the Lucas Pi throttle bodies, the later CR versions had ports that went from circular at the butterfly to D-shaped at the injectors.     But they were properly shaped, with a vertical upright opposite the curve, not an arch like a church window.  But aside from ecclesiastical assistance, this was said to provide a restriction that accelerated the air past the injectors, improving atomisation.   

What you have, Dr.Kai, is an enlarged port at the manifold/ head junction.  That might improve flow, but they are identical on both inlet and exhaust, and I'm not convinced that one size, or one solution fits all.   And the whole port from there to the valve will need reshaping, AND the carb/throttle bodies AND the exhaust manifold primaries.   


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Those are the exhaust flanges.......

The ports in the head are squarish and angle downwards quite steeply.  If you look at the cast manifolds they match shape and angle pretty well - whereas the fabricated aftermarket ones tend not to.  Especially the angle.....

Pic shows flanges I made (by hand) a long while back where I was trying to  match this.  Still haven't got around to doing the manifold part.




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if there a lip on bottom edge, like wots shown on the flange / port pic

then this,l help a long duration cam work alot better at low revs

even better wid an ..inner pipe stub.. 


Janspeed used t,mek CV ex manis like this, an a ford or datsun engine was coming on cam 1000 rpms earlier


reason alot of ports ar D shaped is for space saving, that all.


this only ref i got of them, but give ye the idea,

its a little bit doon page





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