Mandrel bent exhaust

[jaybee]

Mandrel bent exhaust tubing obviously looks really good, with consistent shape and area through the bends.  What about performance?  Yeah, I know the bends in a conventional tubing bender reduce the cross sectional area some, but I suspect for most applications it's like saying slotted and cross-drilled rotors deal with outgassing of brake pads.  Technically correct, but you can't possibly push a street car hard enough for it to actually happen.  A 2 1/2" exhaust with crossover should be able to move a bunch of exhaust, so I suspect the bends don't produce a significant restriction.  Very large or high-revving engines might be a different story.  If I'm right, mandrel bending is primarily an aesthetic consideration for most applications. In that case conventional muffler shop bends would save a few bucks if you can't look up under the car or the look of the exhaust just isn't an issue for you.

Does anyone here know how much "conventional" bending impacts the flow rate of the exhaust, and if it's an issue from a performance standpoint?

[Fat Cat]

Mandrel bent exhaust tubing obviously looks really good, with consistent shape and area through the bends.  What about performance?  Yeah, I know the bends in a conventional tubing bender reduce the cross sectional area some, but I suspect for most applications it's like saying slotted and cross-drilled rotors deal with outgassing of brake pads.  Technically correct, but you can't possibly push a street car hard enough for it to actually happen.  A 2 1/2" exhaust with crossover should be able to move a bunch of exhaust, so I suspect the bends don't produce a significant restriction.  Very large or high-revving engines might be a different story.  If I'm right, mandrel bending is primarily an aesthetic consideration for most applications. In that case conventional muffler shop bends would save a few bucks if you can't look up under the car or the look of the exhaust just isn't an issue for you.

Does anyone here know how much "conventional" bending impacts the flow rate of the exhaust, and if it's an issue from a performance standpoint?

Boy you are asking me to go way back in my work career. From what I can remember in most cases the conventional bends create a restriction of about 1/4" in pipes up to 4". In other words if you use a 2 1/2" pipe and bend it with a crush bender you will in effect have a 2 1/4" pipe in the area of the bend. While that is a restriction of sorts in the average street engine it will not be noticeable, especially if you install a crossover. That said you will end up with what effective operates as a 2 1/4" exhaust even though you are using 2 1/2" pipe because the flow is restricted to that volume in the bends.

If you want an example of how it will operate take a piece of 3/8" clear tubing and slip a piece of 5/8" clear tubing over one end then put another piece of 3/8" tubing on the other end of the 5/8" tubing. Now pore some water into the top of one of the 3/8" section and watch how the water travels through the 5/8" section. You will notice that it will flow in a spiral pattern through the tube until it fills up completely, at which point it becomes invisible but is still happening. The water never flows more than the 3/8" tubing can flow in or out of the 5/8" section. It will just hold more volume in the 5/8" section.

Mandrel bent tubing does not have the same restriction as crush bent tubing but does suffer slightly from the ridging created inside from the mandrel ball being drawn through the pipe. But it is very minimal and the increase in pipe volume offsets the vortexes or turbulence that the striae create in the flow patterns.

[jaybee]

Very well written, and just about what I expected.  If a 2 1/2" pipe effectively becomes a 2 1/4" that's not so bad.  If the restriction were more equal to a 2" or 1 3/4" that would start to become a more serious issue.  I guess I see it a bit like stock or "economy" A arms on an MII suspension.  If it's a car where the suspension is fairly visible then a better looking piece is more appropriate.  If the suspension is very difficult to see at all then why not put that money in a more visible place or maybe some additional creature features.