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  1. #1
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    Default Loss of torque with larger exhaust myth

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    My book called Small Block Buick Performance covering the V6, 215, 300, 340, and Buick 350 engines will be released soon.

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    1970 Buick Skylark Turbo 350 street/strip

  2. #2
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    Default Re: Loss of torque with larger exhaust myth

    You gonna upset Gary
    70 stage 1 Back under construction
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    Shooting for 1khp at the tire and 5.50s

    .

  3. #3
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    Default Re: Loss of torque with larger exhaust myth

    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. #4
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    Default Re: Loss of torque with larger exhaust myth

    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.
    $$$* 1967 Buick GS 400 *$$$

    Joe M.

    1967 GS 400 sport coupe, frame off restomod BBB
    1967 Skylark sport coupe 340 peg leg. (has been laid to rest)
    1987 K5 Blazer Silverado 4x4,
    new 4 bolt main 350 , 700r4. restored for hunting only
    1999 GMC Sierra, 6.0 The work truck
    2015 Camaro 2SS, black on black. 426hp stock

  5. #5

    Default Re: Loss of torque with larger exhaust myth

    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 .
    Andy bridgeview,il
    65 special v6 daily driver-this needs to go faster possibly a 380 stroker.
    82 gn clone 455 12.50's on pump, soon trishield 464
    84 gn
    72 skylark convert#2 ,N-25

  6. #6
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    Default Re: Loss of torque with larger exhaust myth

    I had a Honda cr500 2 stroke dirt bike that absolutely required back pressure.
    ran like a scalded dog when the exhaust was tuned.
    Curious how this was proven?
    Honda's SAE papers do not support this.

  7. #7
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    Default Re: Loss of torque with larger exhaust myth

    An ad for Viagra keeps popping up whenever I hit the link. I'm not sure how to take that.
    Brian
    San Antonio, TX

    1970 Buick Skylark Custom Convertible
    1970 Buick GS 455 Convertible(project)
    1968 Pontiac Firebird 400 coupe
    1968 Pontiac Firebird 400 convertible

  8. #8
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    Default Re: Loss of torque with larger exhaust myth

    I'd worry more about how your wife takes that :D

  9. #9
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    Default Re: Loss of torque with larger exhaust myth

    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.



  10. #10
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    Default Re: Loss of torque with larger exhaust myth

    Thanks Gary I had watched that episode before I started this thread it's a cool video.
    __________________________________________________ __________________________________
    My book called Small Block Buick Performance covering the V6, 215, 300, 340, and Buick 350 engines will be released soon.

    http://www.v8buick.com/forumdisplay....rformance-Book
    __________________________________________________ ____________________________
    1970 Buick Skylark Turbo 350 street/strip

  11. #11
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    Default Re: Loss of torque with larger exhaust myth

    Just in case someone hasn't seen this. (header bash)

    Not exactly on topic but still exhaust related.


    https://www.youtube.com/watch?v=azPKIjxmmdU


    Tuning probably has much more to do with it all than just size.
    alan

    It isn't what happens to you that matters most, but rather what you choose to do about it.

    '73 Estate wagon - Best ET 11.74, best MPH 117.13

  12. #12
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    Default Re: Loss of torque with larger exhaust myth

    Quote Originally Posted by Mr. Sunset View Post

    I had a Honda cr500 2 stroke dirt bike that absolutely required back pressure.
    "ran like a scalded dog when the exhaust was tuned".
    Quote Originally Posted by 8ad-f85 View Post
    Curious how this was proven?
    Honda's SAE papers do not support this.
    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_se...auto/index.asp (auto)
    $$$* 1967 Buick GS 400 *$$$

    Joe M.

    1967 GS 400 sport coupe, frame off restomod BBB
    1967 Skylark sport coupe 340 peg leg. (has been laid to rest)
    1987 K5 Blazer Silverado 4x4,
    new 4 bolt main 350 , 700r4. restored for hunting only
    1999 GMC Sierra, 6.0 The work truck
    2015 Camaro 2SS, black on black. 426hp stock

  13. #13
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    Default Re: Loss of torque with larger exhaust myth

    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 Images Attached Images
    Last edited by 8ad-f85; 01-03-2017 at 01:22 PM.

  14. #14
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    Default Re: Loss of torque with larger exhaust myth

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

    Jim

  15. #15
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    Default Re: Loss of torque with larger exhaust myth

    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. #16
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    Default Re: Loss of torque with larger exhaust myth

    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.

    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.

    $$$* 1967 Buick GS 400 *$$$

    Joe M.

    1967 GS 400 sport coupe, frame off restomod BBB
    1967 Skylark sport coupe 340 peg leg. (has been laid to rest)
    1987 K5 Blazer Silverado 4x4,
    new 4 bolt main 350 , 700r4. restored for hunting only
    1999 GMC Sierra, 6.0 The work truck
    2015 Camaro 2SS, black on black. 426hp stock

  17. #17
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    Default Re: Loss of torque with larger exhaust myth

    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. #18
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    Default Re: Loss of torque with larger exhaust myth

    Quote Originally Posted by 8ad-f85 View Post
    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.
    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.
    $$$* 1967 Buick GS 400 *$$$

    Joe M.

    1967 GS 400 sport coupe, frame off restomod BBB
    1967 Skylark sport coupe 340 peg leg. (has been laid to rest)
    1987 K5 Blazer Silverado 4x4,
    new 4 bolt main 350 , 700r4. restored for hunting only
    1999 GMC Sierra, 6.0 The work truck
    2015 Camaro 2SS, black on black. 426hp stock

  19. #19
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    Default Re: Loss of torque with larger exhaust myth

    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. #20
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    Default Re: Loss of torque with larger exhaust myth

    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.
    Steve Caruso
    Maker of reproduction N-25 exhaust hangers, chrome rally wheels, 68-72 Firewall grommet, MBM brake parts dealer.

    72 GSX clone. Pure Stock 350 13.45@ 100mph
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  21. #21
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    Default Re: Loss of torque with larger exhaust myth

    Quote Originally Posted by UNDERDOG350 View Post
    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.
    is the product crap or the whole theory of being able to dial in the optimum backpressure/exhaust velocity at the tail pipe with adjustable orifices and or different size tips?
    1971 LeSabre Custom 4 door hardtop
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  22. #22
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    Default Re: Loss of torque with larger exhaust myth

    Quote Originally Posted by UNDERDOG350 View Post
    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.
    How could they be bad - Jeremy Clarkson had four of them on his Buggy in the last episode of The Grand Tour?jeremys-v8.jpg
    Steve E.

  23. #23
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    Default Re: Loss of torque with larger exhaust myth

    The engines we are discussing do not benefit from backpressure.
    Sizing, velocity, wave reflection? Sure.
    Not looking to create conflict here, just bring the discussion 30 years forward.
    Not bashing any products either.

  24. #24
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    Default Re: Loss of torque with larger exhaust myth

    Ok, this thread seems to be working fine now. Deleting the other thread that pertained to this one being broken to eliminate clutter.

  25. #25
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    Default Re: Loss of torque with larger exhaust myth

    Also consider that a 2 cycle engine pulls the gasses through in a much different way than a 4 cycle engine does.

    First of all, NO VALVES and NO CAM...which means all the theories of back pressure and what's needed to help control the fuel/air moving through the engine that relate to 4 cycle engines is pretty much irrelevant.

    Back pressure can in fact control air flow and reduce detonation, as well as provide better moisture evacuation (among other, usually negative things).

    If people aren't worried about losing 25 hp over larger transmissions, but nickel and dime 10-15 hp here and there, including some lost from back pressure, spending 100's or even 1,000's of dollars to gain what a simple (and CHEAP) trans swap could offer, well where does one draw the line and keep from looking ridiculous?

    There will ALWAYS be some back pressure, even if it's just in the heads themselves (yes, it's there), and is relatively short lived, but when you work with it, it can be turned around to provide benefit depending on what you're talking about.

    Sometimes, there's a fine line between having optimal velocity and approaching too much back pressure.

 

 
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