Pressure bending vs. Mandrel Bending

Ok, I want some input. Got into one of those never gonna end arguments with some tard on another board over exhaust bending methods. He says mandrel bending is a placebo and a total waste of money. Who agrees disagrees??

 

I would disagree, you are decreasing the diameter when you pressure bend the pipe, instead of making it equal through out like mandrel bending does. It would be similar to bending a straw in half and trying to blow through it, although it would not be that extreme you get the idea. I mean if all you had was one bend it would not make a big difference, but an exhaust system usually requires multiple bends.

 

I guess it depends on how much the diameter of the pipe is reduced by the pressure bending. The mandrel has the same diameter throughout, therefore a smoother flow. I don't see it making a huge difference, except maybe on really tight bends, but i'd say mandrel bending is better if you're trying to get every bit of horsepower you can. Just my two cents.

 

a waste of time is NOT having mandrel bends! muffler bent trash equals smaller diameter. i cant tell you how many times i have seen guys take their 2.75" stock fbody exhaust replaced for hundreds of dollars with 3" muffler shop bent exhaust. with the bends they have to do it is SMALLER than stock! so their exhaust got worse. whoever says the opposite is just plain ignorant about physics and racing combos. anything more than a 45 degree angle and your exhaust is in ROUGH shape. also turbulance plays a major role in exhaust SCAVENGING, the real point of exhaust systems.

 

Big problem with that kind of bend is that it is in the inside of the turn, and thats where fluid (yeah gas follows fluid dynamics) likes to travel.

 

magazine ( cant remember which one ) did dyno tests
and proved that mandrel is superior - esp on high HP motors
less tubulence, flows more air.....

 

You get what u pay for.... Why does a new mandrel bender cost 40k, and real nice pressure bender go for 6-8k? W/ mandrel bends you have no wrinkles/buckles= ....better flow. A pressure bender wrinckles= restricted flow. Still looking for mandrel bender..........

 

Mandrel is superior no doubt. How much power loss are you talking depends on how far the motor is built and such. I have a press-bent exhasut on my F150 and while I know I'm losing power...my stock E7 heads are costing WAY more than the exhaust is.

It's going to be relative...

 

I think everyone here can agree that like bend for like bend the mandrel bend is less restrictive.

A cross sectional view will illustrate the short side of the bend is actually a different usually more tight bend and the long side becomes flattened in the stretch. Both of these characteristics alone make for poor laminar flow due to the dramatic change of gas velocity but more over the change in velocity causes turbulence in the form of "tumble." This creates backpressure. Now in some cases this may prove to be benficial if the diameter of pipe selected is too large, but in cases where tubing size is optimal you have created a restrictor.

It is often times difficult to simulate exhaust flow dynamics exactly how they exist with only a flow bench or through fluid dynamic simms as they really don't address the variable of thermal dynamics. Heated gases react very differently than simple pressurized air molecules and more over such things as flow benches have a difficult time in general with simulating the true character of exhaust gas pulses. Often times people settle for near approximations for costs sake. All in all i feel its true that these things may only net small changes in flow/power and may cost tremendous amounts of money on testing and tooling to create or recreate but thats the nature of this kind of topic ... ideals.

Back to the crush thing ... Often time it is misconstrued that the crush bent 3" pipe system is making the same power as a 3" mandrel bent system simply because the 3" system was too big to start with and maybe a 2 3/4" mandrel system would have performed more optimally. As an extreme case and point you will often see small displacement import type vehicles equiped with 2.5-3" tubing for purely for marketing purposes but once you investigate the internals of the muffler you may find, diffusers, chambers, smaller diameter internals or even restictor plates whose sole purpose is to make the large tube "act" smaller. In any case you may get an equally tuned system but through different means.

BTW- it is not ucommon to pay 150k-200k for a CNC mandrel bender ... not exactly chump-change. Good parts cost good money.

 

Ummm...I think that sums it up right there. Good work Oxidizer.