Too big ???

[67 455 Bird ragtop]

Looks like I'll finally be able to get back to work on my car. Looking at me exhaust system I picked up an exhaust system a while back off a Winston Cup road course car. It's complete with mufflers and x-pipe. Looks like it was raced maybe two or three times. But when I arrived I noticed the pipes were pretty big. pipes are 3 1/2" at the collector and transition to 3 1/2 oval, 2 1/2 x 4". I can get a transition that goes from my 3" header collector to a 3 1/2 oval. But I'm wondering if this system is too big for the combination listed in my sig. Any thoughts ?? I'll post a pic later.

[65 drop top]

Very general range, in my opinion.
2 1/2" up to 500 h.p
3" up to 700 h.p.
3 1/2" up to 900 h.p.

[67 455 Bird ragtop]

Very general range, in my opinion.
2 1/2" up to 500 h.p
3" up to 700 h.p.
3 1/2" up to 900 h.p.

Thanks for the feedback.

[sccacuda]

All the mags have done test before and ALL revealed that the larger pipes did not hurt HP or Torque on anything tested.

That oval tubing doesn't have the same flow characteristics as round. It's less. The oval tube sales sights have the flow comparison listed as a size comparison, i.e. 3 -1/2 oval equals 3" round (just an example, not fact! but it is significantly less).

[67 455 Bird ragtop]

All the mags have done test before and ALL revealed that the larger pipes did not hurt HP or Torque on anything tested.

That oval tubing doesn't have the same flow characteristics as round. It's less. The oval tube sales sights have the flow comparison listed as a size comparison, i.e. 3 -1/2 oval equals 3" round (just an example, not fact! but it is significantly less).

Thanks. Looks like I may need to do a little more research.

[67 455 Bird ragtop]

Found this post on the "math" between oval and round. Was pretty interesting. Did a quick double check of the formulas and didn't see anything wrong.

"It's been a while since I've done any fluid dynamics, but here's a brief rundown for you:

Flow is based on a number of factors, but the primary one dealing with shape is Hydraulic Radius, which is calculated by Rh = dA/dP.

Given the Area of a Circle = pi*r^2, Perimeter = 2*pi*r
And the Area of an Ellipse = pi*a*b, Perimeter = pi(a+b)K, where a and b are the long and short radii, and K = (1 + 1/2m^2+1/64m^4...), where m=(a-b)/(a+b)

Set the perimeters equal (same size initial pipe to be used for circular and elliptical cross sections), so 2*pi*r = pi(a+b)K, which reduces to d = (a+b)K.

Therefore Rhc (circle) = (pi*r^2)/(2*pi*r) = r/2 or d/4
Rhe (ellipse) = (pi*a*b)/(pi(a+b)K) = a*b/d (remember our nice substitution earlier)

If we look at the numbers proposed:
4" circular - Rhc = 4/4 = 1
2 3/4 tall and 4 3/8 wide - Rhe = (1 3/8 * 2 3/16)/(2d) = .7519

3.5" circular - Rhc = .875
2 1/2 tall and 4 wide - Rhe = .625

In both of these cases, the hydraulic radii are decreased by going to an elliptical shape, which would, all else being equal, mean the elliptical pipes flow less than their circular counterpart. This, however, is best determined experimentally, as a number of other factors, such as temperature and pressure differentials, turbulent or laminar flow, friction of the pipe, fittings, etc. all greatly impact the real world dynamics of fluids in a pipe. In other words, depending on other factors, the advantage may go to the elliptical pipe.

Ultimately - in the situation you're looking at, either pipe would provide ample area for the exhaust of an LS1, so I wouldn't worry much about it. Just use what you've got that works."


So if you add in a 3" and a 2 1/2 " round you get .75 for the 3" and .625 for the 2 1/2. So the 2 1/2 oval is the same as the 3 1/2 oval. Still plan on doing some more research between round and oval.