Loss of torque with larger exhaust myth

Discussion in 'Small Block Tech' started by sean Buick 76, Dec 16, 2016.

  1. sean Buick 76

    sean Buick 76 Buick Nut

  2. hugger

    hugger Well-Known Member

    You gonna upset Gary
     
  3. Gary Farmer

    Gary Farmer "The Paradigm Shifter"

    It's universally accepted that a dual 2 1/2" mandrel exhaust will support between 500-550 hp before a 3" system shows worthwhile improvements.

    On a big block producing well over 600 hp (such as the one in the video), the 2 1/2" system was restricting it, so it comes as no surprise that the 3" system will show gains everywhere except down low where the engine won't run at anyway (but a lesser powered one would).

    I've seen that video before, and it's very entertaining--in more ways than one.

    Cut the numbers in half for a single exhaust system, and it shows 250-275 hp would work fine off a 2 1/2" single before a larger one would be worthwhile (a 3" single supports up to 339 hp before back pressure starts to hinder it).

    Torque comes from cylinder fill, and higher revving, high scavenging engines will produce more torque than the 'grunt' engines that peter out before 4500 (considering similar displacements)...all with larger exhausts to support it.

    There's more to it than this, but it shows that things are relative.

    A low RPM engine with an exhaust setup that helps with lower RPM scavenging will improve torque this way. An exhaust such as this would utilize smaller diameter tubing, so again it is relative to where the powerband is.

    Another thing to consider is where the torque occurs and what your intended gearing and usage is going to be, which will matter more than what the raw numbers show.

    Another consideration is to ask yourself the question: how much do you really want/need? There is such a thing as too much, based on suspension, traction, and vehicle weight and intended usage.

    There are other things to consider as well, such as exhaust fitment, cost, noise level, ground clearance, moisture evacuation, and more. Not everyone wants to drive their car 1/4 mile at a time or stay at full throttle everywhere they go.

    Naturally Aspirated engines are more prone to backpressure woes than forced induction engines.

    I'm sure there's more that I forgot to mention.
     
  4. Mr. Sunset

    Mr. Sunset Platinum Level Contributor

    Interesting, I've been pondering exhaust size for a while now and this was the main question
    I'm not making much power 426 with open exhaust. I like the deep sound the 3" makes
    My concern was the back pressure. I would rather have the 3" so I can always build up.
    to a stage 2 engine and keep the back half of the exhaust.

    I had a Honda cr500 2 stroke dirt bike that absolutely required back pressure.
    ran like a scalded dog when the exhaust was tuned.
     
  5. alec296

    alec296 i need another buick

    Every engine and combo is different. Just because it works for one engine combo doesn't mean that it works on all . I have had duals give up alittle low end on a low compression small cammed engine. But have had huge pipes after a crossover open up top end .
     
  6. 8ad-f85

    8ad-f85 Well-Known Member

    Curious how this was proven?
    Honda's SAE papers do not support this.
     
  7. wovenweb

    wovenweb Platinum Level Contributor

    An ad for Viagra keeps popping up whenever I hit the link. I'm not sure how to take that.
     
  8. 8ad-f85

    8ad-f85 Well-Known Member

    I'd worry more about how your wife takes that :D
     
  9. Gary Farmer

    Gary Farmer "The Paradigm Shifter"

    Here's a 'follow-up' video of the same exhausts compared, only this time with a 345 hp Chevy 350, as well as a comparison between two muffler types.

    I won't spoil anything for you, so watch it yourselves. :)


    [video=youtube;bXQ-cXeri1Y]https://www.youtube.com/watch?v=bXQ-cXeri1Y[/video]
     
  10. sean Buick 76

    sean Buick 76 Buick Nut

    Thanks Gary I had watched that episode before I started this thread it's a cool video.
     
  11. alan

    alan High-tech Dinosaur

  12. Mr. Sunset

    Mr. Sunset Platinum Level Contributor

    Aftermarket FMF exhaust system.
    Spark arrestor got a hole wore through on the side, it would crap out mid range and top end.
    I took a beer can and some hose clamps and made a desert repair. (quality of repair is undisclosed)
    see quote above. also there is a supertrapp tuned exhaust system that increase and decrease back pressure.
    http://www.supertrapp.com/technology/index.asp
    http://www.supertrapp.com/product_sections/auto/index.asp (auto)
     
  13. 8ad-f85

    8ad-f85 Well-Known Member

    It's a timed pressure wave, not backpressure helping things in your 2 stroke.
    So, either 100 years and millions of dollars of engineering and testing are wrong compared to your findings or the pipe you attached isn't truly tuned to your engine.
    Maybe the damage disrupted a carefully balanced system that was thrown out of whack, then restored well enough to return your power.

    [sorry about the dead gif. it showed the flow go out and the sound wave reflection time itself to both help arrive back to the cylinder to pull as well as trap cylinder pressure]
     

    Attached Files:

    Last edited: Jan 3, 2017
  14. Jim Blackwood

    Jim Blackwood Well-Known Member

    2 stroke exhausts are known as "extractors" because they suck. Those engines won't hardly even run without one.

    Jim
     
  15. Gary Farmer

    Gary Farmer "The Paradigm Shifter"

    Nomenclature and semantics aside (as well as condescension), very educational.

    Notice no power (torque) was lost with either exhaust, as long as it was sufficient to evacuate the system, until a restrictive muffler was introduced.

    The cheaper Thrush muffler was a 'turbo' design, and so the restrictions inside it using reduced diameter tubing were less of a hindrance than the abrupt ending into the baffle, then redirecting this way twice (for a three tube (common) turbo design) and was the real reason it lost power.

    This engine would have made the same numbers with a 2 1/4" press bent system on 345 hp. The real 'secret' here is the headers, which are doing all the real work.

    This is why the Dynomax super turbos are better than regular turbos, in that they have curved deflector plates welded to the baffles to help redirect the gasses around the curves as opposed to the waves crashing into the flat baffle surface and finding their way around inside the muffler, which costs power no matter which exhaust is used--proven by the huge 3" system which was overkill many times over.

    Another option would be to use longer mufflers, or a series of them, or even a pair of resonators in conjunction with 2 large straight through mufflers to help reduce the rasp or loud droning of a straight through design (Magnaflow), which is a top-notch muffler for flow.
     
  16. Mr. Sunset

    Mr. Sunset Platinum Level Contributor

    What supertrapp Technology states:. decrease flow, will increase backpressure, will increase torque. and vise versa.
    It also states a change in fuel/air mixture and this may be the cause of poor performance on the two stroke honda.
    I would submit that the volume of escapable exhaust plays a vital role on performance and the needs of each application.
    If it's an increase in torque you require, restriction is necessary. For top end, open it up and let the big dog eat.
    According to supertrapp the exhaust is a tunable application and effects desired performance.

    [TABLE="class: cms_table"]
    <tbody>[TR]
    [TD]A signature feature of SuperTrapp exhaust systems is the diffuser disc technology, created and patented for the XDUSOR, the first motorcycle exhaust product sold by Moller in 1971. This technology allows the rider to adapt their bike, or ATV, to a specific riding environment. This is accomplished through a series of discs with a precisely aligned diameter that form the exhaust outlet. By adding or subtracting discs, the rider can tune the powerband and sound of their machine in just a few minutes with basic hand tools.

    Removing discs decreases the exhaust opening and increases backpressure. This effectively decreases the powerband to create more low-end torque. It also decreases exhaust tone and enriches carburetion.

    Adding discs increases the exhaust outlet and decreases back pressure. This widens the powerband at the top end. It also increases exhaust tone and leans out carburetion.

    All SuperTrapp systems come with installation instructions that indicate the recommended number of discs for each application.
    [/TD]
    [/TR]
    </tbody>[/TABLE]

    [​IMG]
     
  17. 8ad-f85

    8ad-f85 Well-Known Member

    Rather than submit any arguments towards flow or backpressure, I encourage a quest of books and Googling into the basics behind Pipemax type programs and why they do what they do.
    Sound wave reflection and acoustical tuning goes well beyond the effects of backpressure and flow.
    Single cylinder engines and their peculiarities of depending on wave reflection are a significant tangent to how I see the thread helping people learn.
    One would have a tough time arguing with the top level of motorsports about the benefits of backpressure.
    No condescension intended.
    I appreciate the time and effort that went into copy/pasting marketing nomenclature.
    The numerous books to both the hobbyists/hot rodder types as well as students headed towards OEM careers and product development would be an excellent starting point to continuing the thread's progression.
    :)
     
  18. Mr. Sunset

    Mr. Sunset Platinum Level Contributor

    Before picking up a book, I will first google the words "nomenclature", condescension" and "tangent". as I am but a simple contractor and your intellect and vocabulary skills surpass any understanding I may have of these.
    For the copy and paste comment..Could you have been a bit more patronizing in your intent to insult. I will say your welcome and to you sir "you have a nice day". I will consider you to be like an opinion, everyone has one.
     
  19. 8ad-f85

    8ad-f85 Well-Known Member

    I apologize for how that came across.
    Some use the engineering or skills for their profession.
    It isn't offered accurately to sell products.
    My skills lack tact and politeness at times.
    It was an attempt to offer an educational direction and inspiration to a mostly opinion based information sharing forum.
     
  20. UNDERDOG350

    UNDERDOG350 350 Buick purestock racer

    Of course Supercrap says their stuff is great, they sell it. Truth is you can do the same "tuning" by crimping your tailpipe shut with some channel locks. I've used the disc system on bikes and it is crap.
     

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