Mandrel Bent......?
 

Are there multiple types of piping bends or something? Isn't mandrel bent piping a piping that is bent without all the wrinkles like the pipes that places liek Meineke uses? I'm kinda confused. Is mandrel bent piping what I want?
THANKS
-James

Yes, mandrel bent tubing is without the wrinkles. It's a much freer flowing bend. So yes, that's what you want.

thanks
-james

You cannot get mandrel bent plumbing at a muffler shop, unless they buy the pre-bends.

There are several different types of tubing bending. You have the "wrinkle" bending.. . . heck if I know how they do that.

You have the typically muffler shop bender that uses a hydraulic bending die to bend/crush the tubing. This does not leave wrinkles but is NOT mandrel bent tubing. This type of bending reduces the inside diameter and shape of the tubing to make the bend. This equipment is inexpensive and is what almost all muffler shops have.

Mandrel bending is a very expensive process of constraining the inside diameter of the tubing while the tubing is bent. The end result is a tubing bend that has the same size and shape inside diameter regardless of where you cut the tubing. This equipment is on the order of 1/4 million to in excess of 1 million in cost. . . Not within the typical budget of a muffler shop. . . most shops and builders are force to buy prebent bends, or order large quantities of a certain bend configuration from manufacturers. . .

Enjoy,

ugh, i'll try to remember my fluids class here. this is gonna get ugly.:D

a larger diameter in the bends is going to reduce your flow velocity in the bend resulting in backpressure which you don't want.

yes, a bend, even of constant diameter, will result in losses but it won't upset the flow nearly as much as bends of different diameters.

Just to expand on Bryan Pendleton said, you can also buy prefab mandrel bends in a variety of sizes from many of the large domestic-oriented speed parts mail order houses, such as Jeg's or Summit. They are pretty inexpensive, and give you a way to obtain mandrel bends if your local muffler shops don't stock them.

FWIW I don't think that using crush-bent exhaust pipe is going to have a huge impact on a Protege's power output. The Protege has a fairly straight exhaust system compared to many other imports (looked under a Celica GT-S lately?) so the crush bends won't constrict it too much. The most restrictive part of the pipe is the U-turn over the right rear suspension, so I might buy some mandrel bends for that, but the rest of the system is so straight that IMHO large-diameter crush bends should be fine.

It will also create a really hideous situation if you try to transition back to smaller pipe after the bend. This creates tremendous turbulence that will add much more backpressure than a good crush bend will. :eek:

yup.

ah, i kinda miss fluids now.:D

In fluids you will learn a term call "head loss" It refers to viscous drag and flow losses through various configurations of tubing and pipe. Note that EVERYTHING suffers from viscous drag and flow losses. Even straight pipe has losses, due to viscous drag at tubing wall. Just an example but lets say you have 14psi at your turbo and a 1ft straight piece of tubing to the manifold. You will have for all practical purposes 14psi at the manifold. Now lets say for some UNGODLY reason you have 2 miles of straight tubing to the manifold. By the time the air flow make its to the manifold you may only have 2 psi at the manifold (could be more or less, this was just to illustrate flow loss).

Back to your question, if we are trying to reduce flow losses through the exhaust, then yes, larger diameter bends could help. Is say could, because now you have added two "transitions", one going from little to big and one from big to little, both of which cause more head loss that simple straight pipe alone. The "flow characteristics" of the exhaust have a very complex and dynamic relationship with the volumetric effeciency of the motor, so even though you may minimize flow losses through the exhaust, you cannot be certain you have maximized or even improved output of the motor.

An excellant collection of data was in the Turbo or SCC magazine here awhile back with about 12 different WRX exhaust. . . take a look at the outputs verse the various designs. . . . Whats good? Whats bad? Depends on the application.

Enjoy,

Don't 2strokes use this (tuned pipe) to draw exhaust out?
Why wouldn't the same work for a 4stroke.
I'm sure there's a reason, I just cant imagine what it is :D

Tuning the exhaust has a much larger effect on simple 2-stroke engines because they have no valves, and they rely on the momentum of the exhaust gas to pull the fresh intake air into the engine. The enlargement in the tuned exhaust pipe creates a low pressure area past the exhaust port, sucking more intake air into the engine and preventing the piston from pushing too much exhaust gas back up into the intake.

The exhaust valve(s) on a 4-stroke engine restricts flow out of the engine during the exhaust stroke, so exhaust tuning has a much smaller effect. Also, except for a very brief cam overlap period at TDC of the intake stroke, a 4-stroke relies on the downward travel of the piston during the intake stroke to pull fresh air into the engine.

BTW exhaust tuning has a much larger effect on power output on a rotary engine than a piston engine, and the reason is the similar- no flow-restricting, power-robbing exhaust valves.