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  1. #126
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    Default Re: Loss of torque with larger exhaust myth

    Quote Originally Posted by Jim Blackwood View Post
    Another data point to add to the discussion, one of the guys who recently built a 302 SBF conversion hit his target build HP goals exactly (400) using shorty headers (custom RV8 style). Looking at his exhaust system, he has 2-1/2" pipes and canister mufflers all the way at the end of the system, maximizing the reversion chamber volume. (The pipes go under, not over the rear axle so a bit shorter, and he has short glass pack cartridges just before the axle. Also an "H" tube.)

    I posted a question as to whether his mufflers have an internal baffle or are straight through type. There is no indication that he was knowingly building a reversion based system. Luck of the draw.

    The open end at the termination of a tube can also generate a reversion pulse but it would not be as strong as one reflected off a baffle. The rear end plate of the muffler could also generate a pulse. Also the glass packs will somewhat attenuate the pulse both ways. But the results do support the theory, and are noticeably better than that achieved with the more typical exhaust system. Makes me wonder if changing out the resonators on the MG-Roadmaster for canister type mufflers might improve the system, a cheap and easy mod. Perhaps we should do a before/after dyno test at the BritishV8 meet in Lewisburg next June. The results would be illuminating.

    I do think there would be a risk of placing the muffler too far back, particularly on larger cars. For instance, on a GS I doubt it would help and might hurt, to put the muffler back by the gas tank. At some point the phase shift is going to make the pulse out of phase with the valves again. But we really need far more data addressing this theory.

    That is why I felt the LT4 results might be relevant. Not because it makes 650 hp particularly, that has become considerably more commonplace. It's just that it is usually done with long tube headers. That is what I felt was relevant, that in this case it was not.

    I enjoy the deeper theoretical discussion but things like quantum physics and string theory are generally above the pay grade of most of us here, me included. Still, over time some of it does sink in. I'll make use of everything I'm able to.

    Jim

    With a few tricks, a lot can be done with less.

    Good post Jim, as usual.

    To the text in bold, there are a few here on the forums who swear by using ported manifolds and tricked out exhausts (smaller head pipe into a larger pipe, as described earlier, as well as an "X" pipe) and report outstanding results at the track.

    The point here I think isn't that (long tube and/or tuned) headers wouldn't be an improvement, but that you can get your factory iron manifolds, log style tube manifolds, or shorties to perform much better when the rest of the exhaust has a better draw on them.

  2. #127
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    Default Re: Loss of torque with larger exhaust myth

    Couple of comments on characterizing header types;

    Typical commercially available tri-y's most definitely fit the description of 'midrange' enhancing, and it might seem as if the dimensions of the pipes are what makes it so.
    Looking at a Nascar type tri-y header one will see a hybrid combination of 4-1 'long' branch (except they are 4-2) to even longer secondary tubes.
    If you think about it they are kind of tuned for dual peaks, with the header still acting like a 4-1 long tube with the exception being the out of sequence cylinder on each bank is paired 180* like the rest. Nobody is suggesting that these are low or midrange engines.
    Following the basic concept of multiple wave reflection within intake manifolds might suggest the same happens to some degree in a header, but in reverse.

    As far as what appears to be described as complicated system to attempt to fit into a car can be fairly easy.
    Take a 3rd gen f body as an example. Floor pan negates dual hump x member. I found a way to start with a set of shorties (the only practical way to fit a header) and chop the collector to make a 180* tri-y with stepped tubing and equal lengths, still maintaining math-correct collector dimensions, finally merging them to a large chamber where the cat conv. was, mimicking open atmosphere before going all the way back to a hypothetical no-loss system (to 700 hp). The Flowmaster transverse muffler was modified accordingly.
    The factory routing was simply followed. 2 pipes replace a larg-ish single off the former collectors. New collectors follow the original path to the big merge, which continues down the factory path.
    Anybody able to hang an exhaust system could duplicate it, starting with the pre-worked out dimensions, which would possibly fit the aforementioned magazine writer's convenient suggestions.

    The effect to the engine was well worth the fab time.
    It took a 400 inch, near 700hp engine with 270* @ .050" 105 LSA (@101 ICL) .640" lift beast and tamed the idle to that of a 280 to 292 cammed mild musclecar engine.
    An infrared gun at the primaries suggested that it wasn't overscavenging.
    Compared to the 4-1 larger tube headers it dynos with, it revs viciously with significantly improved response everywhere.
    The idle is downright nasty with the big 4-1's and has a definite sweet spot. It's temperamental and peaky, even if already ample.
    It would seem like the Nascar inspired system gives up nothing.
    I didn't dyno the fancy exhaust system to see the difference, it was well past it's goals already.
    The top end had a ton of flow bench time, math and computer sims before it's finished state.
    The engine was a copy of previously dyno'd packages.
    Anything accomplished to 'it' could be done with a Buick, take that for what it's worth.
    It could be copied in stainless for reasonable cost.

  3. #128
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    Default Re: Loss of torque with larger exhaust myth

    The point here I think isn't that (long tube and/or tuned) headers wouldn't be an improvement, but that you can get your factory iron manifolds, log style tube manifolds, or shorties to perform much better when the rest of the exhaust has a better draw on them.
    Again, without high overlap to jumpstart the induction system...the methods are different. It's a computer controlled car.
    Seeing too much scavenge requires going back and shrinking the exhaust port/valve and rethinking the whole thing.
    Thanks for highlighting Jim's line, it really clarifies the intent of the post.
    Different paradigms, both impressive results.

  4. #129
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    Default Re: Loss of torque with larger exhaust myth

    Seems the tri-y helped that engine to behave a bit better, as well as enhance performance all-around. I would think the better behavior would be desired over the relatively smallish power gains it gives (11 ft. lbs. average in that article on that engine, though actual results/gains would vary depending on the combination, of course) which would be what was felt by the seat of the pants and give a better driving experience (less finicky with more on either side of the peaks), and not so much the 11 ft. lbs., though the compounded effects of both would be noticeable for sure.

    Though when an engine already has 700 hp (or whatever arbitrary huge number), is 11 ft. lbs. (or 18 or whatever relatively smallish number) going to really make or break the combination? Sure, in a competitive environment such as drag racing, but for a pleasure machine, not so much. Again, everything's relative and dependent on intended usage.

    (((this could also be applied to parasitic loss from other components, making them relatively insignificant (as power levels increase to ridiculous numbers) as discussed elsewhere in the past, particularly when there are other factors that weigh in)))

    For engines with much less radical camshaft profiles I wonder if the tri-y would even be worth the extra fab time/expense though, when your vanilla 4-1 header design (or whatever else was used besides the tri-y) would achieve desired results/meet the power goal?

    Probably not.

    Though I'd say for max effort (or greater effort, however you wish to coin it), every trick you can muster is always good.

    It's always good too to expand the conversation to include various combinations and options that work well together.

  5. #130
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    Default Re: Loss of torque with larger exhaust myth

    Quote Originally Posted by 8ad-f85 View Post
    Again, without high overlap to jumpstart the induction system...the methods are different. It's a computer controlled car.
    Seeing too much scavenge requires going back and shrinking the exhaust port/valve and rethinking the whole thing.
    Thanks for highlighting Jim's line, it really clarifies the intent of the post.
    Different paradigms, both impressive results.

    You're quite welcome. Lest we forget, (if I may be permitted a little bit of 'pulling my own chain'), I have also brought up similar discussions in the past about this sort of thing, which weren't really met with much positive response, though I was always wondering if this sort of thing would ever be brought up again by other, more trusted sources, and it pleases me greatly to see this whole thing come to fruition.


  6. #131
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    Default Re: Loss of torque with larger exhaust myth

    My physical presence is required elsewhere, and so I must bid a brief farewell.

    Bis spter.

  7. #132
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    Default Re: Loss of torque with larger exhaust myth

    The part I honed in on reading the article link Sean posted wasn't the average gains, it was the 25+lbs or more at various parts of the curve.
    It's as inversely as important as when people state that headers added 5 hp over manifolds...at peak. Clearly it didn't need much help there or the combo was off to begin with. 25 lbs instant torque might as well be 20+ cubic inches, right where you need it.
    Those engines already have the benefit of much more development and parts choices, better top ends, blueprinting, etc. than the avg street and strip budget engine.

    Better than that is this aspect which is tough to quantify using a dyno the way they take their measurement, kind of like how lighter weight parts put more pressure against the driveline for acceleration and don't show up on the dyno, or even lower readings...a documented part of PS and Nascar development (You already said that, Gary).

    I wouldn't assume that gains are scaled as seen by the article's 11 lbs avg, esp with less radical cams. I would expect the gains being higher as mild cammed engines are always air starved and can use all the help they can get. Even more from manifolds.

    My point with the tri-y's is that they are NOT complicated. Any 4 tube header can whack the collector and merge each pair in the same space the collectors would have occupied with 2 side by side tubes. You either get a short header donor or a long one. It should be considered a gift.
    We have already seen the Flowmaster merge pipes intending the same, but hey...they are quite expensive when you add them up.
    The CSOB would say, "Hmmm $20 worth of pipes and a chop saw...".

  8. #133
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    Default Re: Loss of torque with larger exhaust myth

    Carl posted this reference to BritishV8, I felt you guys would want to see it:

    Exhaust Scavenging and Energy Waves

    Inertial scavenging and wave scavenging are different phenomena but both impact exhaust system efficiency and affect one another. Scavenging is simply gas extraction. These two scavenging effects are directly influenced by pipe diameter, length, shape and the thermal properties of the pipe material (stainless, mild steel, thermal coatings, etc.). When the exhaust valve opens, two things immediately happen. An energy wave, or pulse, is created from the rapidly expanding combustion gases. The wave enters the exhaust pipe traveling outward at a nominal speed of 1,300 - 1,700 feet per second (this speed varies depending on engine design, modifications, etc., and is therefore stated as a "nominal" velocity). This wave is pure energy, similar to a shock wave from an explosion. Simultaneous with the energy wave, the spent combustion gases also enter the exhaust pipe and travel outward more slowly at 150 - 300 feet per second nominal (maximum power is usually made with gas velocities between 240 and 300 feet per second). Since the energy wave is moving about 5 times faster than the exhaust gases, it will get where it is going faster than the gases. When the outbound energy wave encounters a lower pressure area such as a second or larger diameter section of pipe, the muffler or the ambient atmosphere, a reversion wave (a reversed or mirrored wave) is reflected back toward the exhaust valve without significant loss of velocity.

    The reversion wave moves back toward the exhaust valve on a collision course with the exiting gases whereupon they pass through one another, with some energy loss and turbulence, and continue in their respective directions. What happens when that reversion wave arrives at the exhaust valve depends on whether the valve is still open or closed. This is a critical moment in the exhaust cycle because the reversion wave can be beneficial or detrimental to exhaust flow, depending upon its arrival time at the exhaust valve. If the exhaust valve is closed when the reversion wave arrives, the wave is again reflected toward the exhaust outlet and eventually dissipates its energy in this back and forth motion. If the exhaust valve is open when the wave arrives, its effect upon exhaust gas flow depends on which part of the wave is hitting the open exhaust valve.

    A wave is comprised of two alternating and opposing pressures. In one part of the wave cycle, the gas molecules are compressed. In the other part of the wave, the gas molecules are rarefied. Therefore, each wave contains a compression area (node) of higher pressure and a rarefaction area (anti-node) of lower pressure. An exhaust pipe of the proper length (for a specific RPM range) will place the wave’s anti-node at the exhaust valve at the proper time for it’s lower pressure to help fill the combustion chamber with fresh incoming charge and to extract spent gases from the chamber. This is wave scavenging or "wave tuning".

    From these cyclical engine events, one can deduce that the beneficial part of a rapidly traveling reversion wave can only be present at an exhaust port during portions of the powerband since it's relative arrival time changes with RPM. This makes it difficult to tune an exhaust system to take advantage of reversion waves which is why there are various anti-reversion devices designed to improve performance. These anti-reversion devices are designed to weaken and disrupt the detrimental reversion waves (when the wave's higher-pressure node impedes scavenging and intake draw-through). Specifically designed performance baffles can be extremely effective, as well as heads with D shaped ports. Unlike reversion waves that have no mass, exhaust gases do have mass. Since they are in motion, they also have inertia (or "momentum") as they travel outward at their comparatively slow velocity of 150 - 300 feet per second. When the gases move outward as a gas column through the exhaust pipe, a decreasing pressure area is created in the pipe behind them. It may help to think of this lower pressure area as a partial vacuum and one can visualize the vacuous lower pressure "pulling" residual exhaust gases from the combustion chamber and exhaust port. It can also help pull fresh air/fuel charge into the combustion chamber. This is inertial scavenging and it has a major effect upon engine power at low-to-mid range RPM.

    There are other factors that further complicate the behavior of exhaust gases. Wave harmonics, wave amplification and wave cancellation effects also play into the scheme of exhaust events. The interaction of all these variables is so abstractly complex that it is difficult to fully grasp. There does not appear to be any absolute formula that will produce the perfect exhaust design. Even super-computer designed exhaust systems must undergo dyno, track, and street testing to determine the necessary configuration for the desired results. Last but not least, the correct choices and combinations of carburetor, air cleaner, cam shaft, ignition, and exhaust used in the proper relationship to each other for the intended riding application will always produce the finest quality results. Most important of all, is to do your research prior to purchasing the combination of products and equipment best suited to your individual style of riding.

    Original reference lost.

    [www.zggtr.org]

    Also
    http://www.chevydiy.com/chevy-small-...haust-systems/

    No info on what happens when the pressure wave goes up long tube headers though.

    Jim

  9. #134
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    Default Re: Loss of torque with larger exhaust myth

    No info on what happens when the pressure wave goes up long tube headers though
    Scavenging.
    (Sorry, couldn't resist )

  10. #135
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    Default Re: Loss of torque with larger exhaust myth

    Quote Originally Posted by 8ad-f85 View Post
    The part I honed in on reading the article link Sean posted wasn't the average gains, it was the 25+lbs or more at various parts of the curve.
    It's as inversely as important as when people state that headers added 5 hp over manifolds...at peak. Clearly it didn't need much help there or the combo was off to begin with. 25 lbs instant torque might as well be 20+ cubic inches, right where you need it.
    Those engines already have the benefit of much more development and parts choices, better top ends, blueprinting, etc. than the avg street and strip budget engine.
    I would consider the gains as a percentage rather than static integers when considering the overall performance of an engine, since static numbers can be a bit misleading on what would actually be felt (not necessarily measured), but again this is relative and dependent on the intended usage. It's commonplace to use average gains across the entire powerband when considering the same for the improved general behavioral characteristics of the package as a whole.

    Even so, 25 ft. lbs. would mean a lot more to an engine that only produced 375 ft. lbs. to begin with, while that same static number means less when you're talking 575 ft. lbs. (for example). It would be noticeable at the track for sure, but everywhere else probably not so much.

    This is not intended to belittle 25 ft. lbs. by any means (no matter what it's applied to), but rather (as I said in my previous post), that what matters more than this is the overall improved behavior of the entire engine as a whole (better manners above and below peaks), and would be more noticeable than a relatively small percentage gain in power, especially when the '25 ft. lbs.' (arbitrary number used) is only seen in a very small window, with the average increase over the entire powerband holding more meaning, which is a considerably smaller number, and even this can fluctuate depending on other circumstances such as atmospheric conditions, etc. putting the behavior improvement way ahead of the power gains. (IMO) --sorry for the sentence length. lol

    Its meaning and purpose is still quite significant, of course.

    Better than that is this aspect which is tough to quantify using a dyno the way they take their measurement, kind of like how lighter weight parts put more pressure against the driveline for acceleration and don't show up on the dyno, or even lower readings...a documented part of PS and Nascar development (You already said that, Gary).
    Much of this I already addressed in the above statement, though I wanted to point out that I have never read any documentation from these sources, so I guess it's nice to know my brain is on the right track. Clarification is always welcome and even encouraged.

    I wouldn't assume that gains are scaled as seen by the article's 11 lbs avg, esp with less radical cams. I would expect the gains being higher as mild cammed engines are always air starved and can use all the help they can get. Even more from manifolds.
    Would it be reasonable to expect the percentage of gain to remain similar (or even increase) with increased airflow then, or does the dyno (or other means of measurement, such as track results) show different? If the gains are so vast when using tri-y's, it would only show that the combination had issues elsewhere or was not running as optimally as it should, as previously communicated by you. The dynamics can be pretty complex, and so I suppose it would depend heavily on the combination itself, rather than to attribute it all to the implementation of specific header design.

    Bold: 'Tis true; more clarification on my assertions. Thank you.

    My point with the tri-y's is that they are NOT complicated. Any 4 tube header can whack the collector and merge each pair in the same space the collectors would have occupied with 2 side by side tubes. You either get a short header donor or a long one. It should be considered a gift.
    We have already seen the Flowmaster merge pipes intending the same, but hey...they are quite expensive when you add them up.
    The CSOB would say, "Hmmm $20 worth of pipes and a chop saw...".

    There's a few ways to skin this cat, true.

    The cost of creating a custom set of tri-y's would depend on how much skill one had, or money to pay a skilled fabricator. Even though there are short-cuts or 'head starts' that are indeed useful, most professionals don't want to give their services away for free, as well you know.

    Without specific tuning techniques, would creating a set of tri-y's be worth the hassle/expense (even though it's not that complicated, but all things are relative depending on the skillset of the implementer), and would/could it be detrimental to the engine's performance should one not do it correctly...there is such a thing as creating a "Y" merge that would hinder performance instead of enhancing it, as we've seen suggested previously in this thread.

    Important questions and thoughts.

  11. #136
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    Default Re: Loss of torque with larger exhaust myth

    Much of this I already addressed in the above statement, though I wanted to point out that I have never read any documentation from these sources, so I guess it's nice to know my brain is on the right track. Clarification is always welcome and even encouraged.
    Dyno engineers would be able to do a better job of explaining this but the way I understand things is that rather than a variable load to control a sweep rate, a set load is applied and the time it takes to accelerate the rpm sweep is timed. It negates the common way dynos measure power and translate to a standard. At least that's my understanding.
    So the way it had been explained to me was that the dyno might show a reduction in power, yet the vehicle might accelerate better.
    (The often heard, "we don't race dynos or flowbenches")
    Throw that into the mix here
    [Edit. Documentation is tough to come by as most of the hot rodding world uses a dyno method that's different. There's your conspiracy theory of the day]

    I don't think there's any way to scale improvements accurately.
    It would depend on what you were working with and where you want to end up.
    Keep in mind that (budget) circle track is extremely rule bound.
    I would guess the limits would be mean best torque, BMEP, VE, etc. that limit out to displacement accordingly.
    The way I understood the higher level engine development was that the effectivity of the header and scavenging is what allowed them to reduce exh. valve size, header size, and make the intake bigger.
    Rather than continue to shorten exhaust duration and profiles to reduce overscavenging, they went the other way.
    Seems like it would help any engine biased towards the intake side, such as an LS or help tame a combo with a tad too much top end.

  12. #137
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    Default Re: Loss of torque with larger exhaust myth

    Good stuff, as always Tony.

    I enjoy the dialogue here.

    More later when time permits.

  13. #138
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    Default Re: Loss of torque with larger exhaust myth

    To continue the discussion, I found another video from Engine Masters, which shows log style manifolds vs medium length headers vs full length headers, and felt it was relevant to this thread.

    Though this isn't exactly a Buick 350, it does show the differences between each setup using the same engine without any help from the exhaust system (no merges/crossovers to aid the manifolds or med-length headers), so the full length headers would be at a clear advantage here based solely on this aspect, regardless of other aspects of exhaust flow.

    It also shows that a free-flowing engine (obviously) needs a free-flowing exhaust.

    Also not considered was a tri-y header.

    I strongly suspect, that even though the log manifolds did surprisingly well, would have done much better with the aid of an effective exhaust system behind it.

    That's my opinion, of course.

    Knowing that more needs more and less needs less, something as simple as a cam swap (or even using an engine that flowed less and/or made less power) would have made a significant difference in how each one of these three compared items would have done without anything else considered.

    Take it for what you will, here it is:


  14. #139
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    Default Re: Loss of torque with larger exhaust myth

    The one thing they touched on for just a moment is valve overlap.
    A camshaft with more overlap may be more sensitive to scavenging than a cam with less be it a difference in LSA or just the cam size in general.

  15. #140
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    Default Re: Loss of torque with larger exhaust myth

    Predictable outcomes for the bolt on market.
    Glad to see better iron manifolds being made, kind of like Pontiac stuff in the 60's.
    Curious of the measurements... actual tube ID, collector ID, effective collector length.
    Would have liked to have seen the torque curve with a more suitable collector diameter for the rpm range/cylinder size.
    Not that it would have been in the nature of a 'test' video intended for the mass market bolt on crowd to have thought of this forum in which to contribute valuable data...

  16. #141
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    Default Re: Loss of torque with larger exhaust myth

    Yes indeed gentlemen.

    There are still valuable lessons to be extracted from even this generalized information.

 

 
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