2010-02-01 Exhaust Manifolds

2010-02-01 Exhaust Manifolds

I've ordered all the tubes + bends I think I'll need to make the exhaust manifolds for the V6 in the manta. But, I need to order the manifold flanges.

Previously I designed some manifold flanges to suit 1 3/4" primaries. However, having consulted the book Four Stroke Performance tuning and going through some sums it looks like I need to go a bit smaller on the primaries. The American company that I ordered the tube through does 1 5/8" tubing and that works out pretty much spot on, so I ordered stainless tubing, mandrel bends and collectors in that size. The collectors are 3:1 and 1 5/8" inlets and 2" outlet.

So, I need to work out the external circumference of the tube + make this the circumference of the holes in the exhaust flange (Plus some clearance!)

The od of the tube is:

1 5/8" * Pi = (1.625 * 25.4) * Pi = 129.7mm

The current cutouts in the exhaust flange are obrounds with a radius of 15mm and an external horizontal measurement of 55.5mm. Thus the circumference of that cutout is:

((15 * 2) * Pi) + ((55.5-30) * 2) = 94.25 + 51 = 145.25mm

(I never remember the order of precedence for operations so I've just parenthesised it well)

I need a couple of mm of clearance, but not 15mm! So I will instead use an obround with an overall horizontal dim of 50mm and a radius of 13.75mm

((13.75 * 2) * Pi) + ((50-27.5) * 2) = 86.4 + 45 = 131.4mm

I've uploaded a quick reference drawing of the design. I should upload a DXF too as this makes life a lot easier. It's too complex to fully dimension the PDF!

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