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  • #91
    First off, we'll be testing several of the things that you guys are bringing up, including square vs round. We'll keep you posted on when, but it is coming.

    Second, the whole HVAC argument has no real bearing what soever. It's just stupid because hvac systems move similar cfm, but through much much larger "tubing". The speeds are much lower, etc, etc.

    If I was guessing I would say to do an oval who's area is an extra 25-50% larger than the same round tubing and see what happens. But, again, we'll be testing this to let you know exactly what is best.
    "A cross thread is better than a lock washer." Earl Lanning...My Grandpa

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    • #92
      Originally posted by BangShiftChad View Post
      First off, we'll be testing several of the things that you guys are bringing up, including square vs round. We'll keep you posted on when, but it is coming.

      Second, the whole HVAC argument has no real bearing what soever. It's just stupid because hvac systems move similar cfm, but through much much larger "tubing". The speeds are much lower, etc, etc.

      If I was guessing I would say to do an oval who's area is an extra 25-50% larger than the same round tubing and see what happens. But, again, we'll be testing this to let you know exactly what is best.
      that would be cool.
      every engine can learn from that.

      not to get caught up in TC thread robbing,
      but a vid channel like nelsons racing shows some extreme exhaust setups in normal chassis.

      he even called 4 inch a "stove pipe".

      the equation for square area of a circle can help determine what square can be used. The intake side of cars is even trickier when it comes to round and squares (although boosted can cheat all kinds of things).
      Previously boxer3main
      the death rate and fairy tales cannot kill the nature left behind.

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      • #93
        Dr. Gas was the only place I knew of that really had this stuff well defined and gave good advice and high quality products. I've received decent advice from SPD in NorCal and Burns in SoCal but they understandably don't want to give away their hard earned knowledge.

        Is there anybody else dealing in oval tubing and bends etc. that will help the back yard builder work this stuff out?
        Drag Week 2006 & 2012 - Winner Street Race Big Block Naturally Aspirated - R/U 2007 Broke DW '05 and Drag Weekend '15 Coincidence?

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        • #94
          Purple II Oval exhaust system, this was done for ground clearance though.

          sigpic

          Just an Old Drag Racer that still has dreams of going fast!

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          • #95
            those are great pix of a home made, low profile muffler and pipe setup-thanks for sharing...looks simple enough, other than having the welding skills to not make a hack of it which I would surely do

            for this year, I added the electric cutouts. Though I won't save the weight that comes with removing the rest of the exhaust, I'll at least bypass it on runs and not have to get under the car to do it.
            Last edited by Dignlif; August 3, 2012, 10:57 AM.
            Rich

            Drag Week Survivor 2009, 2011, 2012, 2013 - 2nd Place - Pro Street N/A, 2017

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            • #96
              Here are two links that I found pretty informative, first one is a calculator for determining exhaust size, second is an article on back pressure and the results from their testing... Interesting that 1.5 psi of back pressure was worth a 4-5% decrease in power over an exhaust system with 0 psi of back pressure.....

              Exhaust tubing calculator.....



              Back pressure article....

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              • #97
                Originally posted by Dignlif View Post
                those are great pix of a home made, low profile muffler and pipe setup-thanks for sharing...looks simple enough, other than having the welding skills to not make a hack of it which I would surely do

                for this year, I added the electric cutouts. Though I won't save the weight that comes with removing the rest of the exhaust, I'll at least bypass it on runs and not have to get under the car to do it.
                At idle when you open the cutouts what happens to your idle??

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                • #98
                  I believe the backpressure is a side effect of pulse wave tuning - not the primary reason for torque gains. It all depends on the application. I've seen engines that lose power with more open exhausts. But it's a LOT harder to get a tuned, optimized exhaust than most people think. You have to test it, you can't just do math and copy others' work in hopes you nail it.

                  When exhaust is tuned right, it's awesome. At Spectre we had an EFI 383cid Camaro that picked up +50whp at peak just by moving the X-pipe backwards maybe 2 inches.
                  www.realtuners.com - catch the RealTuners Radio Podcast on Youtube, Facebook, iTunes, and anywhere else podcasts are distributed!

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                  • #99
                    Originally posted by dieselgeek View Post
                    I believe the backpressure is a side effect of pulse wave tuning - not the primary reason for torque gains. It all depends on the application. I've seen engines that lose power with more open exhausts.
                    Was the A/FR held constant? My anecdotal suspicions (mostly from running open headers with insufficient collector length) is that power losses on "more open" exhausts are the result of either lean outs or wrong collector lengths (resulting in rarefaction waves that "clash" with (or fail to support) the pulses from the primary tubes. e.g. resonate a disparate frequencies).

                    I tend to agree with the numerous technical writers (Vizard, A. Graham Bell, Jeff Hartman, Julian Edgar, etc.) that logically conclude backpressure is the enemy of power (that is unless the "backpressure" is doing some useful work powering a turbine . . . .) Thus, systems that rely on backpressure to "work" have some other design/tuning defect that backpressure merely covers up.

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                    • Originally posted by dieselgeek View Post
                      I believe the backpressure is a side effect of pulse wave tuning - not the primary reason for torque gains. It all depends on the application. I've seen engines that lose power with more open exhausts. But it's a LOT harder to get a tuned, optimized exhaust than most people think. You have to test it, you can't just do math and copy others' work in hopes you nail it.

                      When exhaust is tuned right, it's awesome. At Spectre we had an EFI 383cid Camaro that picked up +50whp at peak just by moving the X-pipe backwards maybe 2 inches.
                      In my experience on my friends '69 Chevelle that has a 11.5:1 402(.060 over) putting exhaust on the car caused a complete change in the way the car idled..... I rebuilt the carb and we started the motor with open headers, the engine fired right up and idled at 1000rpm with no other adjustments to the carb. Then a few weeks later he put an exhaust system on it that was dual 3" pipes going into one 5" single chambered Flowmaster and then it exited before the rear tire on the passenger side with a 5" pipe. He went to start the car and the car would no longer idle..... The problem was he had 3 1/2" collectors and then went to a 3" exhaust, that is a 1/2 reduction right at the end of the collector where exhaust speeds are still pretty high, it basically caused a restriction and thus created some back pressure which disrupted the air flow through the motor, so not as much air flow means not as much power at idle to keep it running..... Or at least that is the way we looked at it....... Back pressure effects two valve events, one is when the exhaust valves first starts to open, second is during overlap, I always knew about the effects it had on overlap, but I just recently learned of it's effects when the exhaust valve opens.... In both instances back pressure disrupts air flow through the motor and will cost you HP........ It was enough on my friends motor to whether it would idle or not.........

                      And yes we did disconnect the pipes to see if it was them not letting it idle and not a problem with the carb and with the pipes disconnected the motor ran fine again. I guess we never thought that with what we consider such a "huge" exhaust system that it would effect the idle like it did.............
                      Last edited by TC; August 3, 2012, 01:14 PM.

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                      • Back pressure sucks.

                        If back pressure causes an increase in power, it means that the engine combination isn't properly scienced out. Finite amplitude waves can be used, both in the intake and the exhaust to enhance power production. But it takes both modeling and testing to work out the best solution.

                        Bigger is not necessarily better. We swapped a smaller diameter set of headers, with a longer collector, onto the EMC engine and picked up 54 hp.

                        After the amount of testing that we've done over the last few years, I can say unequivocally that generalizations are exactly that. (for those that need an explanation: generalization = generalization ) Without doing the math and the testing for your specific engine combination you will not reach an optimal solution.
                        Last edited by Bob Holmes; August 3, 2012, 12:49 PM.
                        I'm still learning

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                        • Originally posted by BangShiftChad View Post
                          First off, we'll be testing several of the things that you guys are bringing up, including square vs round. We'll keep you posted on when, but it is coming.

                          Second, the whole HVAC argument has no real bearing what soever. It's just stupid because hvac systems move similar cfm, but through much much larger "tubing". The speeds are much lower, etc, etc.

                          If I was guessing I would say to do an oval who's area is an extra 25-50% larger than the same round tubing and see what happens. But, again, we'll be testing this to let you know exactly what is best.
                          First, you're welcome for giving you an idea about an article.

                          Second, why are you guessing? you don't know either - and I really doubt you have any idea of what pressures are in an HVAC system; so to make a general assertion without anything support seems a bit.... let's see... what's word.... oh yeah, Chadish If anything, what happens at low pressure helps understand higher pressures.... the difference is HVAC generally doesn't see waves of pressure from exhaust valve timing.

                          Third, don't care about oval, it has the same problem as round - just without the vertical resistance strength (pre-squished)

                          my bet - a single plane (meaning moves only in one direction) will have higher flow with less static pressure (fancy HVAC term for how much, snicker, drag is in the pipe vs. the air flow). I also bet the only real to square is its storage of water vapor in the corners - in short - it'd rust faster. The way air flows, it has a high pressure core then radially has less and less pressure because of the static pressure created by the enclosure. In a square tube, that means the air in the corners moves slower then the air in the center. In round pipe, it doesn't make much difference because the water can only collect in areas of high pressure, but that position (such as the inside of a radius) is untenable because of its mass - meaning it moves then gets sucked out at the pressure equalization point.
                          Last edited by SuperBuickGuy; August 3, 2012, 12:54 PM.
                          Doing it all wrong since 1966

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                          • Huge swings in power from exhaust can reflect how the engine is set up (for with or without exhaust) and how well its set up for the one chosen. Back pressure is made with Camshafts and exhaust ports, why would someone use a exhaust to make back pressure? Back pressure added by the exhaust is really saying I am changing the pressure recovery of the cylinder with something besides the camshaft and exhaust ports set up which if it was made to run open headers then you missed the mark and left power on the table. If you want it to run with full exhaust then it needs to be factored in from the start with exhaust port and vavle timing. This is why lash looping and camshaft valve timing are such big things, guys that quote camshafts out of Jegs and such have no idea other than it worked in mine or at least I think it did.
                            2007 SBN/A Drag Week Winner & First only SBN/A Car in the 9's Till 2012
                            First to run in the .90s .80s and .70's in SBN/A
                            2012 SSBN/A Drag Week Winner First in the 9.60's/ 9.67 @ 139 1.42 60'
                            2013 SSBN/A Drag Week, Lets quit sand bagging, and let it rip!

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                            • Originally posted by Bob Holmes View Post
                              Back pressure sucks.

                              If back pressure causes an increase in power, it means that the engine combination isn't properly scienced out. Finite amplitude waves can be used, both in the intake and the exhaust to enhance power production. But it takes both modeling and testing to work out the best solution.

                              Bigger is not necessarily better. We swapped a smaller diameter set of headers, with a longer collector, onto the EMC engine and picked up 54 hp.

                              After the amount of testing that we've done over the last few years, I can say unequivocally that generalizations are exactly that. (for those that need an explanation: generalization = generalization ) Without doing the math and the testing for your specific engine combination you will not reach an optimal solution.
                              I missed this as I posted mine! A-Men give that man a Love offering of $20.00 there is no magic numbers. This is why its so important to do not just read.

                              Back to my Ol Buddie Yogi Berra


                              "In theory there is no difference between theory and practice. In practice there is. "
                              Last edited by JeffMcKC; August 3, 2012, 02:23 PM.
                              2007 SBN/A Drag Week Winner & First only SBN/A Car in the 9's Till 2012
                              First to run in the .90s .80s and .70's in SBN/A
                              2012 SSBN/A Drag Week Winner First in the 9.60's/ 9.67 @ 139 1.42 60'
                              2013 SSBN/A Drag Week, Lets quit sand bagging, and let it rip!

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                              • my favorite saying - the thing that most annoys the people who say it can't be done is when someone interrupts them by doing it.

                                practice is awesome if you play baseball, but has no place in physics.

                                Its great that you've achieved so much, Jeff, but what's it worth if it can't be duplicated? or worse, discussed?

                                **I've edited this twice now to try to make it non-confrontational, and sounds confrontational - but it's not intended to be
                                Last edited by SuperBuickGuy; August 3, 2012, 02:49 PM.
                                Doing it all wrong since 1966

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