Re: 427 FE engine, under car 'street' exhaust system?

[Silversmith]

You guys know you can have custom NASCAR style flat rectangle pipe sections made for crossing under frame sections where needed a 1"X 4" = 4" pipe if you need that much exhaust. Or a 1"X 3"=3". NASCAR runs them from the header to the exhaust point & the flow is the same & so is the sound That is my plan; @ least under the frame points. But as usual, life's event have my conversion postponed. But I will get there one day soon. Just find a local muffler shop/ or just about any skilled fabricator/welder can make theses sections up for you with out huge cost either!

[DanEC]

On rectangular you have to go quite a bit bigger than that I believe. The cross section of a 2-1/2 inch pipe is 4.9 sq in. So you would need a 1 x 5 to get equivalent area. But to get equal flow I think you would need to go even bigger since the boundary circumference on a 2-1/2 inch pipe is 7.85 inches and a 1 x 5 rectangular pipe would be 12 inches - creating a lot of boundary drag and restriction in the rectangular pipe. Someone who remembers their flow mechanics courses better than me would need to figure out an equivalent size. Oval piping is probably a better approach where ground clearance is needed. .

[AC Ventura]

The area of a circle is diameter x diameter, divide that by 4 and multiply by 3.142.

Therefore the area of a 3" diameter pipe is 7.069 square inches.

That I am afraid equates to a much bigger rectangular section of 1" x 7" or 2" x 3.5".

However an oval section of 2" x 3.96" also equates to 7.07 sq in and is possibly the most practical alternative.......but very difficult to bend round a chassis.

What would really be beneficial, is for example with a 500hp big block, running 2" primaries, what is hp loss between 2.5 and a 3" collector pipes, if any?

[Buzz]

Its generally not necessary to bend the oval sections around the chassis. They only need to be used under the frame - maybe with horizontal bends in a flat plane - where ground clearance is an issue. Oval to round adapters can be used to transition to header connections and tailpipe sections that need to bend over the rear suspension.

[AC Ventura]

Originally Posted by Buzz

Its generally not necessary to bend the oval sections around the chassis. They only need to be used under the frame - maybe with horizontal bends in a flat plane - where ground clearance is an issue. Oval to round adapters can be used to transition to header connections and tailpipe sections that need to bend over the rear suspension.

With a car like mine, it's not possible to run 3" downpipes adjacent to the footwells. I just feel there's just not enough space for a practical and serviceable installation. With a 2 x 3 oval downpipe there might be, but no point if you can't get it to transition to under car, where it would have to twist.

I think it's 2.5" or revert (sadly) to some side action.....or run the headers forwards, then loop under the car, so no downpipes in footwells, Only downside I can see, is increased engine bay heat and odd looks. TVR did this with the Griffith and Chimaera, if they are known in the US.