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my friend and I are going to build our own exhaust. and we were wondering how much power loss would we lose if we went with the "wrinkle" bends over mandrel bends? please dont tell me to get a cat back cuz im building it.
 

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I'd say go with tubing maybe 1/4 inch over your desired size. So, if you were thinking 2.25, go with 2.5 to compensate for any potential power loss from the standard bends.

Makes sense to me, I've never really heard folks talk about power loss by standard bends, but I figure just over compensate and you should be OK.
 

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yeah, i think the general work around is to use bigger pipe than you would intend with mandrel. the wrinkle bend really messes up the flow.
 

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Power loss depends on the severity of the bends. The farther you press bend something, the less internal volume you're left with. I cut through the middle of the bend on a 2.5in pipe that was press bent 90°. Just from eyeballing it, it looked like the effective size of the pipe was reduced to less than 2.25.
 

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the physical change in cross section in the bend isn't the main reason the wrinkle bend flows worse. the wrinkles themselves increase the resistance alot. the disturbances on the inside of the bend does not promote laminar flow (laminar flow is smooth flow, means it has a lower pressure drop thru the pipe)

this is why you need to oversize the wrinkle bent pipe, because the wrinkles increase friction and you need a larger pipe to make up for increased friction. of course this also decreases the velocity compared to mandrel bent pipe...maybe you should check into having some pipe mandrel bent, or if you are gonna weld anyways, get some mandrel bent 90's and cut the angle you need and weld away. just some ideas
 

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the wrinkles themselves increase the resistance alot. the disturbances on the inside of the bend does not promote laminar flow
Not by a long shot! But I didn't realize that wrinkle-bending was done on smaller pipes - I've never seen smaller adapters with the divits for wrinkles. The only wrinkle-bend adapters I've seen were for 3-inch pipe... learn something new everyday I guess. Press-bending is bad enough, I can't imagine wrinkle-bending anything.

the wrinkles increase friction
I don't want to sound like an ass, but you mean turbulence - we are dealing with flow.


if you are gonna weld anyways, get some mandrel bent 90's and cut the angle you need and weld away.
That's the way to go if you can weld. If you go this route remember, JCWhitney is your friend.
 

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I don't want to sound like an ass, but you mean turbulence - we are dealing with flow.
At normal atmospheric pressure (inside the pipe still counts), the flow of air can be treated as fluid dynamics, in which case, friction is the correct term.

Friction meaning that the air will hit the bend, encounter resistance, push back against the other flow and reduce the over-all amount of gas that is able to escape.

Friction n. Physics. A force that resists the relative motion or tendency to such motion of two bodies in contact.

/Physics geek
 

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the flow of air can be treated as fluid dynamics, in which case, friction is the correct term.
Regardless of what you treat it as, it's still air, not fluid. While the similarities between them from a physics standpoint are vast, and the two are in many ways comparable, turbulence is the appropriate word to use when discussing airflow.

Friction n. Physics. A force that resists the relative motion or tendency to such motion of two bodies in contact.

/Physics geek
So you're calling a stream of exhaust gas, a body? That's a stretch to put it mildly. It looks to me like you're just going out of your way to contradict me. But hey, whatever works for you.
 
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