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Triumph Spitfire - Exhaust design??

To improve ground clearance, is it possible to have a "flat" oval shaped exhaust under the car vs. a typical round pipe?
What size pipe do you think would be required? Say flatten a 4" pipe down to 1" tall and 5-6"wide?


The important issue is the area of a crosssection of the pipe.

If you currently have a 2inch pipe the area is pi x radius squared = 3.14 x 1 x 1 = 3.14 squre inches.

A 4 inch pipe flattened to 1 inch at the narrow diameter of the oval would still be larger than 3.14.

Some additional drag is added by increasing the area of the wall that the flow must 'rub' against - but, this should be negligible.

Go for 1.5 inches. A 4 inch pipe has 12.56 sq inches if crosssection when round. The closer you get to 0 inches, the smaller the cross-section.

Don Gardner

Sorry, Don, the diameter does matter, a lot.

Flow through a tube is determined by Poussieulle's Law, that says among other things that the resistance to flow is inversely proportional to the FOURTH POWER of the radius of the tube It is the narrowest radius that matters. In other words, halve the radius and the resistance goes up SIXTEEN TIMES (Fourth power of 2=16) Exhaust flow is pulsatile, which mutiplies the complexity so much that exhaust design is an art, not a science.
Jordan, I fear that a faltened 1" wide pipe would not be an improvement, but I doubt if you will notice much difference with the 4" one over conventional pipes. Once the primaries have joined, the silencer design has more effect that the pipe diameter, within reason - 1" would be rather small, but production cars had pipes little larger.

This thread was discussed on 01/04/2002

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