Mandrel bending versus regular

Discussion in 'Mopar Exhaust Systems' started by shadango, May 29, 2009.

Do you feel mandrel bending is really better than regular bending?

  1. Absolutely -- real world gains

    82 vote(s)
    78.8%
  2. Not really, but looks better

    17 vote(s)
    16.3%
  3. No way, not worth it -- no real-world gains

    5 vote(s)
    4.8%
  1. shadango

    shadango Well-Known Member

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    Do you feel that mandrel bending really makes a difference?
     
  2. rjsjea

    rjsjea Well-Known Member

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    Really depends on how good with a Tig you or your builder is.
     
  3. 7demon2

    7demon2 Registered User #1824

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    this is some good info that i just found to consider as well......

    Consider a straight plastic straw that you might use to drink a soft drink.
    If the straw is completely straight, it's very easy to blow air through the
    straw, as there are no restrictions. However, lets say you decide to
    bend the straw 90 degrees into an "L" shape. Now, blowing air through
    the straw will be very difficult, as the opening at the straw's elbow will have
    changed from a circle to a very narrow slit. This is exactly how the pipes
    in your car's intake and exhaust system work. Air is drawn through pipes,
    which, when "compression bent," become very restrictive to the flow of
    air. Mandrel bending is the solution to this problem. Mandrel bending
    works much like the flexible straws that you can buy in a grocery store.
    When the straw is bent, a flexible section of the straw expands to maintain
    the round opening no matter how much of an angle the straw is bent at.
    When an exhaust or downpipe is manufactured with mandrel bends, the
    steel is allowed to stretch on the outside of the bend and compress on the
    inside of the bend, maintaining the nominal pipe diameter. Exhaust gas
    follows fluid dynamics. You want to eliminate backpressure while
    maintaining exhaust gas velocity. Mandrel bending allows the hot exhaust
    gases to flow with less turbulence.

    2. Myth-You don't need mandrel bending unless you have a nascar running
    800+ horsepower.

    Truth-Mandrel bending alone will add 3-5% more horsepower and torque.

    3. Myth-Your motor is to small for mandrel bending to make any difference.

    Truth-It doesn't matter what size your motor is you will still get a
    3-5% gain in horsepower & torque. Obviously the bigger the motor, and
    the more horsepower you have, the larger the gains.

    4. Myth-We will only be making a few small bends so you don't need
    mandrel bending.

    Truth-(We will be using 3" tubing as our example) It doesn't matter if
    you bend a pipe 1 degree or 180 degrees you will still smash the pipe
    1/2 inch. A press bender will crush the pipe before it starts bending.

    5. Myth-We will only be putting 1 bend in the pipe so you don't need
    mandrel bending.

    Truth-If you have 3" tubing that is press bent it will smash 1/2 inch at
    the center of the bend. At that point you have 2 1/2" flow instead of
    3". It doesn't matter if you have one bend or five bends you still have
    2 1/2" flow.
     
  4. rjsjea

    rjsjea Well-Known Member

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    I agree with that last post based on a comparison to a factory type system, but a hot rod builders kit with an assortment or bends tigged together will flow better than a straw bent at a 90.

    I picked "looks better" for that reason
     
  5. AdamR

    AdamR Founder / Admin Emeritus

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    With all the low priced mandrel bent systems on the market now I see know reason for a compression bent exhaust.

    Summit, and Jegs are under $300 and Pypes is under $400 for stainless steel.
     
  6. crackedback

    crackedback FABO Gold Member FABO Gold Member

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    Putting a 3" exhaust on a 318 170hp engine isn't going to care if it's mandrel or compression bent. IMO, a general you'll gain x%, one versus, the other isn't really accurate if the tube isn't sized correctly at the start. Heck that 318 might just run better with a compression bent set up!

    So the question really is dependent on application.

    All things considered, mandrel is better because of restriction issues.
     
  7. Burntorange70

    Burntorange70 Well-Known Member

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    Mandrel. Looks better flows better and now a days is not very pricy at all.
     
  8. 72Swinger360

    72Swinger360 Well-Known Member

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    I agree with Burnt, my dad had a mandrel bent, stainless, dual, cat-back exhaust, complete with stainless Magnaflow mufflers and stainless tips, built and installed on his 02 Dakota with a 4.7 V8/Auto for $502.00 out the door at a local exhaust shop. They bent the pipes so they exit just behind the rear wheel at an angle. It looks great, sounds very agressive and I think it definitley helped in the HP department.

    Joe
     
  9. abodyjoe

    abodyjoe Well-Known Member

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    would love to see a real world comparrison of the two. i would think that mandrel would definatley flow better though. my 3" wasn't mandrel bent and it looks good until the tail pipes. it kinda flattened out over the axle and had a kink in it. after the new rear suspension was installed we bought 2 1/2" J bends and made tail pipes from them. the are mandrel bent and look a ton better and i would bet that the 2 1/2" flows as well if not better then the squished 3".
     
  10. 7demon2

    7demon2 Registered User #1824

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    there is about 9 to 14 hp and 10 to 15 tq difference between the 2 from what dyno results i have seen but it can vary depending on motor and setup....here is a chart on a chevy for an example.....

    Snap1.jpg
     
  11. Prine

    Prine A-Body Fanatic

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    Mandrel bent pipe flows FULL FLOW everywhere because it maintains its inner volume throughout the bends, whereas a Press-bent Pipe is restictive and causes drag on the exhaust gases.....this is a well documented fact on Turbo Cars....and every horsepower is crucial to a already disadvantaged 4 cyl. vehicle.

    Is it worth it? The real question, Is It Worth it TO YOU? When trying to extract the most power from a particular engine combination, everything is important. (At least to me) 1hp, here and there adds up....and can be the difference between Winning/Losing a challenge.

    If anyone is interested, I have a box full of Mandrel Bent Mild Steel 2.5" 90*'s, and some 3" 90*'s....I would let go of them cheap.

    Mandrel Bends > Press Bends: Hands Down
     
  12. AdamR

    AdamR Founder / Admin Emeritus

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    If the bent it on site its not mandrel bent most likely.
     
  13. Prine

    Prine A-Body Fanatic

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  14. richard tarbox

    richard tarbox Active Member

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    from what i've read on this site witch i am conserend putting big block or hemi in a dart or b block once you dent that header to get it to fit doesnt much matter
     
  15. Mrmopartech

    Mrmopartech Well-Known Member

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    Richard,when installing a large motor into a car and clearance is a factor,there are two rules of thumb.1)fit the part to the car.2)fit the car to the part.Now this becomes a big issue if you have just spent a G note on a set of hemi headers to fit a dart,and have to refit them to clear,Don,t ask why I know this.You have a custom painted engine bay that you just spent how much on and now its down to a redo of the bay or banging up a set of custom headers,and there is no time to get a nother set as the car has to be at a show,really niece choise,right,mrmopartech
     
  16. shadango

    shadango Well-Known Member

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    Can you provide teh name of the local shop? Industry is a bit of a haul for me to go without an exhaust on the car....

    Seems that no one near me does mandrel bending, or at least doesnt advertise it.

    One other issue is getting the car to a shop. The shop near me I am considering can flat bed me down and back for $30.

    I just cant seem to find any better alternatives locally.....

    As for buying a kit, I guess I could....but I have heard some horror stories about the kits fitting like crap and being a real PITA to install....and I would still have to take it somewhere to be welded up....

    These care came stock with standard bent tubing, and did pretty well on teh streets. But I get it -- mandrel bent *may* mean a little extra power....if the local guy did it I would go that route,....
     
  17. green1

    green1 Well-Known Member

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    what I would like to know: Why don't they fit? Good money was paid.
    It seems that they tried a test fit on a Duster; tweaked ithem, and before test fitting again- sell them for multiple applications.
    All people that make headers should be forced to install them, for the same price.





















    i
     
  18. lenweiler

    lenweiler Well-Known Member

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    I run a 3" custom welded, compression fit system. It's formed exactly to the cars' underpinning needs. If the technition knows what he's doing, I dare say there'd be little gain. I'm looking at 10.2's likely, down the road with my full compression system. I ran 12.8's with a '69 Bee, little more than a stock 440-6 setup, with a compression bent 2-1/2" system. And no hedders..........
     
  19. duster340

    duster340 street racer

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    i prefer mandrelbent for alot of reasons but im biased since i run a mandrelbender every day at work, but the endresult looks so much better and for sure it will flow alot better also. and nomather how i look at it i just cant see why anyone would want all that weight and sound of a 3" system without also having the flow..
     
  20. shadango

    shadango Well-Known Member

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    I ended up going with a Magnaflow 2.5" mandrel bent system.......the shop that installed it the second time (long story) did have to compression-bend a bit here and there to get it to work.

    The kit is NOT a bolt-on!

    But I think it sounds good and looks pretty good too.

    Itwas $351 at performancepeddler.com and $120 to install.
     
  21. moper

    moper FABO Gold Member FABO Gold Member

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    I know mandrel flows better. But the ready made stuff frankly isnt bolt on in many cases. Plus, the weith offsets some gain especially witha smaller engine. So a back to back, non magazine real world test would be cool. Have compression bent 3, run it, cut off at track and bolt in whats available and run the mandrel 3
     
  22. shadango

    shadango Well-Known Member

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    There shouldnt be a weight difference, between mandrel and crush bent, should there?
     
  23. duster340

    duster340 street racer

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    there could be a kind of small diference in weight depending on tubing used, i dont know about the wallsizing in inches but you need about 2mm of wallthicknes when bending with a compresionbender (i only have experience with a HUTH bender) or the tubing will deforme horribly while a bandrelbender can bend tubing being alot thinner, i like to mandrelbend tubing with 1.5mm of wallthicknes it usuly bends nicely and the pipes will be noticeable lighter than with 2mm, atleast with 2½" and 3"
     
  24. Fstforward

    Fstforward Barracuda Freak

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    Where did you get it installed, I am going to need a custom bent system when I get my car together.

    FF
     
  25. 64conv65hard

    64conv65hard FABO Gold Member FABO Gold Member

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