it was good. I learned that I missed my chance a few months ago to see a HP increase by driving around when the eye of Hurricane Irma passed by, due to lowered atmospheric pressure.
me: gets pulled over cop: your vroom too loud! me: "my vehicle is operating at maximum efficiency, and reducing pollutants while increasing performance. *shows cop video* cop: understandable, have a nice day
@@netprowlerp he was making a joke. And you took it too seriously finally calling his audience 12 year olds without knowing the real ages. The only thing you should be telling your wife is organizing counseling cause you're way to serious.
Whatever you want to call it, if you have no back pressure at all, it sounds like ass. You need some kind of baffling and resonance to tune the sound and make it sound good.
It's amazing that people will not listen to a word you said because Cleetus at Smithys Muffler Shop tells them the backpressure of a Flowmaster will give them more power
@@CalebDiT No, he mentioned it and shrugged it off as if it was to complicated for us poor folk to understand. He never explained it. Also the title of the video is "Back Pressure is Bad!".
@@CalebDiT What he said was having a balance of velocity and restriction is ideal, not that having some back pressure is good. More restriction increases exhaust velocity but inhibits overall flow of exhaust, less restriction allows more exhaust flow but lowers velocity.
@@Talos_Valcoran87 You and the video maker seem to understand what is necessary, but you don't like the terms. "Back pressure is bad, but some calculated restriction is ideal." It's a contradiction to anybody truly listening.
*some guy at the auto part store says something about back pressure* EE: races home and starts writing furiously on a whiteboard while collecting valid explanations.
I think he knows his team have let him down, some of the stuff at the beginning of the video is very messy, not false, but over simplified and a a result not accurate. Back pressure is not air trying push back into the exhaust (and I think he knows this), it's the positive pressure built up by exhaust gases inside the exhaust system, the higher the engine rpm, the higher this pressure, which is why some high performance vehicles switch between 1 or 2 exhaust backboxes at specific rpms to alter the "back pressure" in the system to maintain higher performance and fuel economy throughout the rev range.
Nice work!!! And you are absolutely right, this is GOLD for all amateur tuners! My advise to budget track cars; Keep stock exhaust diameter, remove cat, get "straight through" resonator and muffler (with a tail/end dia' similar to exhaust dia' = no deep tone, pure race sound), this will roughly give you same performance boost as a expensive $1500, from headers and back, race exhaust @EE: if you don't take into account the Euro and newly establish similar US emission restrictions (completely disregarding the cat here) the backpressure is needed to recirculate some of the exhaust back into the intake, to burn unburned fuel, at given loads at specific rpms. So in modern cars it's needed to fulfill legal requirements ;) PS not all engines need this system, but if you increase 1st weight in your search terms and 2nd search increase engine volume/capacity and cross those you'll find it being implicated more and more
The guy who did my muffler delete on I4 said these engines need a bit of back pressure. I definitely felt a loss of torque at lower rpm. Also I’m surprised that so many mechanics think no tuning is needed after a muffler delete. My area doesn’t have that so yeah car sounds nice and loud with lesser torque which means loss in performance. ☹️ I do have a k tuner. Do you know if I can tune muffler delete by myself? And if so how? @Engineering Explained
@@Febreeze_Odor_Eliminator you believe that coming from a guy who chops mufflers off for a living? The only reason you “need” back pressure, is because it was tuned for it, from factory. So of course it “needs” it, but engines are just air pumps, why have a higher differential in pressure, when could just NOT
You have absolutely no idea how helpful your videos are. I just recently started trying to learn about my car and attempt to fix it myself. I normally troubleshoot radar equipment but when it came to my car, I was lost. No one could explain the theory to me very well so I found it very difficult to troubleshoot the symptoms I had. Your videos changed everything. Thank you.
Yea he's spot on, think of your exhaust and intake for that matter like sucking a milkshake through a small diameter or larger diameter straw. Or sticking your thumb over the end of a garden hose.
Hey Jason.👋 While some have mentioned the whiteboard looks a bit small and restrictive at times, my guess is that it has been engineered to just the right size for this application.👌 Much like your explanation in this video, everything on the board usually has a good, positive flow without feeling restrictive. We all know, knowledge is power and the power to weight ratio of the whiteboard is immense!💪 Great flow and power without undesirable drone... what more could we ask for? Thanks for a fantastic run in 2017 and all the best to you in 2018, sir. ✌😉
If you ever want to do a charity fund-raiser, take the current whiteboard that's been used in so many EE episodes, sign it in permanent marker, and stick it on ebay.
I live in the heart of NASCAR country, and the old time engine builders would bolt a straight pipe on the headers and run the engine up to 7k rpm, and where the pipe glowed cherry red, he'd cut the pipe and weld on a turn out. Said that little trick would add 5hp... This was back in the early 80's, so don't take any of this for gospel ;-) Excellent explanation Mr EE :-)
Very well said. Its a pet peeve of mine about back pressure. Its as if piston fighter aircraft arent a thing. No backpressure and scavenging is done via Bernoulli from airflow passing over the end of the pipe.
Great video and very easy to follow explanation. I work in automotive parts and it is constantly preached by many that "you have to have plenty of back pressure". No one knows why but they are certain it's true. Thank you for debunking this ancient rumor.
maybe it's no longer the case, but i was told a long time ago that back pressure protected the valves from burning. i took the exhaust off my bandit 400 16V and it was loud but all the way to 12K RPM just bonus grunt i loved it
I will explain to you the source of the backpressure myth. In the late 1970's carbureted cars were forced to run an extremely lean mixture. The older catalytic converters were quite restrictive. These cars were able to run so lean (without melting pistons) because the old catalytic converters created a form of passive EGR. If the exhaust on these cars is replaced with a less restrictive system the passive EGR was no longer present. These cars would run VERY lean, melt pistons and overheat UNLESS the carbs were replaced with pre-emissions carbs.Timing was not computer controlled and knock sensors did not exist. Hot engine, lean mixture, detonation... BOOM! It was a crappy system, there were 350 cu. in. V8's with less than 150 hp! So many vacuum hoses were required that underhood vacuum maps were quite detailed. Bad days for automotive tech.
So basically, early emissions systems were crappy and complicated, and were doomed to kill power unless there was an electronic babysitter to reign everything in efficiently? Big shocker.......
The 70's???? You've got to be kidding me. Or is that as far back as you remember? Because exhaust tech as you explained goes way back beyond the 70's vehicles.
D.E.B. B what he's saying is it really originated in the emissions days, which started very late 60s and came full swing in the 70s, that's when it really became an issue and the backpressure idea came to light
D.E.B. B - Catalytic converters became mandatory in the early 1970's. The tech was not the same in the 1960's. My first car was a 1967 Camaro one owner, low miles PERFECT...$1200; it was very simple (points, carb, drum brakes (all of them), and it had about 3 vacuum lines under the hood). My second car was a 1975 Monte Carlo. The Monte Carlo had dozens of vacuum lines, a cat, front discs, HEI ignition, AND IT WAS SLOW AS MUD. *Car tech changed drastically between 67 and 75.*
Catalytic converters did not become mandatory, it only seemed that way. Exhaust emission limit levels kept being reduced, and because of that, MOST auto manufacturers began using a catalytic converter in 1975 because they couldn't figure out any other way to meet the emission standards. That was the beginning of no lead gas,because the lead would supposedly coat the tiny platinum catalyst pellets inside the converter (I don't remember ANY cars using a cat con before 1975, and then all of a sudden, it seemed like all of them did). However Honda's CVCC engine (in Civics and Accords) was able to meet the emission standards WITHOUT a catalytic converter all the way until 1980 (except in California, I think that Honda needed cat cons there in '78). Exhaust tech did not change; as he mentioned in the article above, was just part of the science involved to get the engines to make certain amounts of power at selected points in the torque curve, while keeping the noise to a minimum. Short open pipes were usually used on vehicles that needed to make maximum power at high rpm's. Longer, smaller, more restrictive exhausts were used on street vehicles that had to be quiet. Somewhere in the middle were exhausts which were a compromise between the two. And for some bizarre reason, the aftermarket often did better than the OEM's; my Honda 750 bike with a Supertrapp exhaust made much better power than the stock pipe, yet was also relatively quiet (that was the exhaust where you could add or delete some discs to tune the exhaust). And yes, the vacuum line rats nest of some of those smog engines was enough to drive us nuts! One little crack in those rubber lines would make the car run terribly! I vividly remember taking polaroid pictures of the top of my engine, pulling off the Autolite carb and replacing it with a pre-smog Holley, plugging up all those little holes, and running it like that until the next emissions inspection when I'd reverse the whole shebang! Ahhh, the good old days!
I think the myth comes largely from very old cars, with extremely inefficient high back pressure exhaust systems -like original VW Beetles -if you fitted a free-flow straight-through exhaust to them, it would make such a dramatic change to flow / air:fuel ratio, that if you didn't change the carburettor settings at the same time, they often wouldn't start or would run very badly, historically motor manufacturers would tell mechanics and anybody that asked, that this is because you "needed back pressure" because they didn't want to encourage people to modify their engines, as they had other concerns like reliability, longevity and low noise.
I think it more comes from people putting oversized diameter exhaust on their vehicle and losing power/torque because the exhaust velocity has slowed down too much. They don't realize there is a difference between free-flowing and oversized.
Their carburetor was set up fora high back pressure exhaust and they put on a low back pressure exhaust and now it don’t run the same. That’s when they say they “ need back pressure”
Loss of power due to oversized piping is a bit more complex If the working routine of the engine is not modified, it will keep on kicking the same quantity of gas out for a given load, no matter what pipe size is used The loss of power is not due to the fact it looses velocity on getting out of the engine but on the pressure in the cylinders A bigger pipe allows more gas out so the cylinders will be emptied easier but If the cylinders feeding/emptying scheme is not modified, some of the mix supposed to ignite wil slip through the exhaust system before it is consumed, which turns out to leave less mix in the cylinders, giving that loss of power It's pretty simple Bigger exhaust implies better ignition timing
Learned the principles of exhaust tuning via the reflective and transmitted waves in vibroacoustics and have always jut shook my head when people talk about back pressure and why its needed in an engine (aka air pump).
Exhaust scavenging is even more important in small two-stroke engines, due to not having actual valves. In fact, when your two-stroke lawn equipment is "sputtering" and seemingly running badly at idle or under low power, that's exactly what's happening - there's not enough exhaust velocity to scavenge the cylinder effectively before the exhaust port closes and it tries to fire the next cycle. There's too much exhaust gas and not enough clean gas, and that cycle fails to ignite.
I have been applying this for years and it is nothing short of incredible how much torque can be found by building a proper exhaust system. not only length and diameter but collector and muffler design.
Many years ago, engines ran a fairly large amount of overlap (intake valve opened well before the exhaust valve closed) in order to scavenge all the old burned fuel out, with a large amount of muffler backpressure. If you ran straight pipes with no backpressure, the incoming (cold) air/fuel mixture would flow out the (hot) exhaust valve, and could cause the exhaust valve to warp. As muffler design has improved, we can get lower backpressure with similar noise dampening, so I believe the overlap is now shorter. So maybe valve warp would not be a problem anymore, but I don't know.
I'm a little suprised that anyone has even heard of this old piece of advice. Doesn't have anything to do with scavanging. Dates back to when vehicles were still carbureted. If you significantly changed a cars' breathing capabilities, you screwed up the carb tuning, and there was no computer to mod the A/F ratios. Every kid in high school would slap on open-element air cleaner and headers with straight pipes, but no one would bother to dig into the carb and change the jets and rods. The result would be that it would start eating gas and wouldn't really idle right, and you'd be throwing HP right out the tailpipe.
It's the same concept be it ecm or carb. If you change something to the car, motor intake exhaust etc, you have to tell the computer you made those changes otherwise it will keep doing what it was programmed too. Same with carb if you dont adjust or change the jets it will keep doing the same thing. Causing the idle issues, spitting unburned fuel air out the back, and other things
I have had this debate with a few friends. Something that helps to (erroneously) 'confirm' that backpressure is beneficial is that people sometimes do feel a power loss with the installation of a better exhaust, due to failure to finish the job. That is, proper jetting or EFI tuning. Most shadetree mechanics can change exhaust parts, many cannot accomplish the latter. Exhaust improvements are available for many engines, for which no carburetor jets are available, or which have virtually untunable efi. Many tolerate or are even unaware of their power loss, and enjoy the loud noise regardless.
Great video, this is for non-turbocharged vehicles though, with a turbocharged vehicle you just want the highest flowing exhaust after the turbo as possible. All the scavenging etc happens in the headers before the turbo
I think a turbo dampens out some of the pulsations that are important in a non turbo system making post-turbo more about big cross section and less about "scavenging"
He did not demolish anything, to much back pressure in an exhaust system and exhaust gas velocity is killed, to little back pressure in an exhaust system and velocity is killed, all these videos do is play semantics trying to say back pressure is a myth yet all properly designed exhaust systems will have back pressure. It is about exhaust gas velocity. Borla worked with John Lingenfelter and he built 600 horse power corvettes using 2 1/2 inch exhaust systems because that is what gave him the maximum exhaust gas velocity if a bigger exhaust pipe would have made Lingenfelter go faster he would have used it but a bigger exhaust pipe removed more restriction i.e. back pressure and killed the exhaust gas velocity. A 2 inch exhaust will only flow so much volume, a 2 1/2 exhaust will flow more volume than a 2 inch system and a 3 inch exhaust system will flow more volume than either a 2 inch or 2 1/2 inch exhaust system. What you are looking for is exhaust gas velocity if the 2 inch is to restrictive you kill exhaust gas velocity what is restriction, it is back pressure. If the 3 inch exhaust is to free flowing it kills exhaust gas velocity because it does not have enough back pressure. The 2 1/2 inch exhaust in this case has less restriction than the 2 inch system and has more restriction than the 3 inch system yet the 2 1/2 inch exhaust system has the highest exhaust gas velocity. Having said this what you have to do is design the entire exhaust system with the optimal size pipes to get the maximum exhaust gas velocity so it takes proper design to get maximum results, which is why Borla is the leader in aftermarket exhaust systems and they have won more races than all other aftermarket exhaust manufactures combined. All these videos are doing is using mental gymnastics trying to eliminate the word back pressure.
finally someone that get that the smaller factory exhaust exists to increase exhaust velocity. one thing though, for the scavenging section the intake valve opens at the end of the exhaust stroke while the exhaust valve is still open so that instead of creating a lower pressure in the cylinder, the cylinder is swept with fresh air removing the last bits of the spent air fuel mixture, this is called valve overlap. the factory exhaust system is designed to provide good drivability at lower engine rpms while providing reasonable performance at higher rpms. the reason to change to a larger free flowing system is to provide more performance in higher rpm ranges, sacrificing low rpm drivability.
I never believed in backpressure, but I wanted to watch this anyway. Care to elaborate on what methods manufacturers use for turbo applications? It's going to act as a restriction for sure but are there any tricks manufacturers use to mitigate this?
Generally for turbocharged applications, you simply want low restriction after the turbo, because you're no longer going to gain the benefits of scavenging from exhaust pulses. Leading up to the turbo, you want to keep routing short, and hot, so that little energy is lost from the exhaust valve to the exhaust turbine.
Engineering Explained To me that sounds like a short and fat turbo manifold leading into the turbine side of the turbo with a high flow cat right after it, and the absolute lowest possible restriction muffler after the cat to keep noise humanly acceptable. I am simply not psychopathic enough to needlessly pollute. Droning exhaust notes get old real quick.
Thanks for the laugh! I did a test on this on my car during the Spring of 1990. With no back pressure, the car had no bottom end power, meaning power picked up around 3500 RPM. But with back pressure the car could do burnouts. This car didn't have turbo. This was before EFI. A class to take is fluid mechanics in a pipe. Here again, no two engineers have the same solution.
Thank you, what you have are a bunch of people trying to eliminate the word back pressure when if you have to much pressure in the exhaust system you kill exhaust gas velocity and it you have to little pressure you kill exhaust gas velocity. It is all about finding the right sized pipe for the highest exhaust gas velocity. Where all the misinformation and confusion comes in is an exhaust system is not designed with back pressure, an exhaust system is designed by maximizing exhaust gas velocity. John Lingenfelter built 600 horse power Corvettes and Borla worked with him on the exhaust systems, John Lingenfelter used 2 1/2 inch exhaust systems because that is what provided the best exhaust gas velocity to make the most power, as Borla says if a bigger pipe would have made John Lingenfelter go faster he would have used it.
I got lucky with my 77 1/2 ton 4 bolt 350. yanked the fucktory choking manifolds, slapped a pair of headers on, cut a drive shaft in half that was thee same size as the collectors then chopped and gutted a pair of old glass pacs, took 2 1/2" cyclone fence posts and cut slots in a spiral pattern from end to end, used my air hammer with point bit and drove into each slot causing it to swirl the exhaust as it passed through, welded it all together and damn what a sweet sound not to mention large improvement over the entire rpm range. couldn't believe how much it did for it
Martin Varela Unless you're a diesel guy in which case you gotta run a compounding turbo setup for each cylinder just to be safe. So one turbo per turbo per cylinder.
You forgot to mention firing orders where the Pistons are in varying states of the 4 cycle process, most firing orders keep one piston exhausting one after another, continuously pushing the exhaust flow out. Reversion waves are kept at bay, sometimes they never reach the cylinder. The other is, for those old timers who remember, cast iron log type exhaust manifolds, were also called "heat stoves" sometimes had a spring loaded gate the would close the exhaust flow n would open up when the motor was accelerated more exhaust. This device to an extent would increase back pressure, n therefore also increase "heat" which is energy. Keeping the exhaust manifold, "heat stove" hot or hotter would increase "energy" and also exhaust "scavenging", one of the reasons hot rodders "wrap" their header pipes with exhaust wrap, which is not only to keep from burning yourself, which most people think, but it's to retain "heat" which is energy... So, a little bit of back pressure is beneficial, as you say, you have to find a happy medium in exhaust pipe diameter to get the best velocity, and in doing so, you are introducing a bit of back pressure. Also depends on engine size, stroke, n displacement...
Here's my personal hands on experience by feel not by dyno. Vehicle: 89 f150 2wd carbureted 351w 4spd manual. Engine mostly stock with long tube headers, electric cutouts in front of 10 series single chamber mufflers. With cutouts closed and running exhaust through mufflers, strong pull, but hesitates at first. With cutouts open, smooth response but feels like it isn't picking up speed. As said before, this was all based on the feel not the dyno sheet. Never went to dyno because it was a beater with enough pep to have fun on your drive to work. Also had a passenger that confirmed the feel.
Nounours2627 you want that pressure wave to be as consistent as possible drawing maximum air out of the engine as possible. Ie maximum velocity with minimal resistance to keep the turbo spooled higher.
No back pressure you lose power because fuel is going out of the chamber... What does the backpressure is to keep the fuel inside the chamber before the piston goes up.
a lot of people dont realize that while an engine may have no need of exhaust backpressure, the way an engine is tuned is usually accounting for some back pressure, and depending on how smart the ECU is, it is possible for an engine to run worse or have other adverse side effects from simply removing exhaust backpressure. looking at you newer dodge gasoline trucks!
This explains why low rpm at high load causes denotation. Some hot exhaust gases are still in in the cylinder on the intake stroke due to lack of scavenging.
I swear, I feel like if you really wanted to and actually paid attention ...all you have to do is watch all of his videos and you’d be able to tune your car at home without the help of these expensive shops.
Yeah, I know that. But with the knowledge provided, it’d be cheaper to do it yourself than pay someone else to do it (in the long run and depending on what vehicles you prefer) if cars are that big of a part of your life.
It's my impression there are important acoustic effects after the collector, and the length of the exhaust pipe from the collector to the "resonator" is important, and removing the resonator but maintaining the total exhaust length can negatively impact performance.
I’ve always heard that exhaust valves could deform due to heat if you went with too low of a back pressure such as straight pipes or just headers. Your explanation was great. Lower velocity due to less restriction means the hot exhaust gases are lingering causing heat issues. I understand velocity and pressure (PV/nrT) but it still seems counter intuitive sometimes. That’s why I’m an Electrical Engineer ;)
Dolly DeHart can somebody confirm this? I run my 05 wrx with a 3" straight pipe after the downpipe which is 2.5" (stock) and I was told I would deform the valves sooner or later....is this actually true?
Just theory to consider here. Assume the header was tuned to perfectly scavenge the remaining hot gasses from the cylinder at peak torque as demonstrated in the video. It's pretty easy to see why this ideal, you would get a boost in peak torque. So imagine the result if you removed what was scavenging the last bit of hot gasses from a combustion chamber. A little bit of that hot mass lingers there when chamber pressure reaches equilibrium with atmospheric. I think this would create a hot spot on the head that the cooling system wouldn't be able to deal with. After the energy (heat) has been extracted and turned into mechanical work via spinning a crankshaft or driving a turbine, it's just causing issues by hanging around. Once it's useful life has ended inside of an engine it needs to be returned back to mother nature as quickly and efficiently as possible so the cycle can repeat.
I+Dolly DeHart - it's not the pressure, but the slow flow. Low velocity is what helps burn valves - it allows the hot gasses to sit around the valve longer. That is the exact point of this video - the common misconception is that people use 'backpressure' when they mean 'low velocity'. Look closer at the top right of the whiteboard in the video - that's talking about pipe diameters. Too small gives you high velocity, but high pressure. Too large a pipe does the opposite - low velocity (cook valves) but low pressure. There is a sweet spot for each engine, but it's more about power generated percylinder. Power = airflow, and it's true in the exhaust as well. You can calculate how much exhaust gas a cylinder will produce for a given power level - then you need to find the sweet spot for that flow in pipe diameter.
"Back pressure" is just a term people who read too many car magazines and think themselves engineers use to overly simplify the very complex fluid dynamics involved in the tuning of an internal combustion engine, which real engineers use computers to simulate extensively before they build anything because the problem is so mathematically complicated that it's literally impossible to solve analytically.
remove the back pressure on any non racing vehicle and you will loss low to mid torque and your fuel usage will go up (race cars run at high rpm and fuel use is not an issue). never listen to people that say back pressure is not needed on street vehicles and that info comes from a transport engineer with over 30 years experience. it doesnt mater what type of engine you have you MUST get a tuned exhaust to suit or it WILL cost you money in the long run. ps. unless you are a lead foot putting a tuned exhaust on can save fuel and give you a nicer sounding exhaust
Even on race vehicles, they have some exhaust. Even dragsters don't just have bare exhaust ports at the heads, they have exhaust tubes, and even though they are only 30" long and no muffler, those tubes are carefully selected to control the velocity, even though they have a big blower on top.
Had a brand new 93 Mustang with 2.3 4cyl engine auto trans. Bought a dual exhaust kit with ;single "2 to dual " 2-1/4 exhaust pipe ;2 - "2-1/4 inlet x " 2-1/4 outlet turbo mufflers; 2-"2-1/4 LX tail pipes. Had muffler shop install while I watched. Car was only 3 months old only had 5K miles on odometer. Sounded good but never ran right from install!! It wouldn't shift into OD at correct speed ! Always hunting/jerking at OD speed RPM. I ended up trading it in on a proper brand new 93 5.0 5speed manual LX Mustang a few months later. I was told the computer didn't sense correct rpm BECAUSE OF LOWER BACK PRESSURE !!! Hence hunting/jerking of AOD lockup !!!!
Alex Gunner my I-64 Southern Indiana hills Dyno said the same thing when I put a dual exhaust on a 318 Magnum in a 99 Ram, after gaining considerable torque from Gibson truck headers. Didn't lose all of it, thankfully.
If you don't have an exhaust pipe properly tuned to your engine, with the correct length headers, you're actually going to increase back pressure, because the natural tuning of the pipe is opposing the volumetrics of your engine. A larger pipe is not actually always going to produce better flow. If you think that pipes are only going to be tuned for a small range of RPMs, you're absolutely correct, which is why a perfectly tuned exhaust and a "perfect" cam is going to have one hell of a power spike at one RPM, making the power curve a lot less usable. A certain amount of detuning is essential to make a car drivable (and not horribly anemic up until 4,500 RPM, at which point it peels the rubber off your tires).
The misconception comes from two stroke gasser engines which use the scavenging of the fuel air mixture coming into the cylinder to push out the exhaust gases. Since the is no valve to close the exhaust port some mixture leaves to the exhaust pipe without combusting and you use the resonator to redirect it back inside the cylinder to ignite it. But that process uses the sound shockwave in front of the exhaust gases not the actual back pressure.
My lecturer at university said that you do want a small amount of back pressure for N/A engines because the residual exhaust gasses left in the cylinder effectively increase the compression ratio as you are compressing a larger volume of gas into to the same volume at TDC. With forced induction engines you might not want this as you can make up the difference by forcing more air and fuel into the cylinder
Residual exhaust gases can be beneficial from an emissions standpoint (this is what the purpose of EGR is), but if you're displacing air in the cylinder with spent combustion gases, there's less room for fresh air & fuel.
Fair point, for power that would make sense but if you wanted to an engine to be efficient then having that small amount of residual exhaust means you can have a higher compression ratio and use less fuel
AstonMan NOx forms primarily when a mixture of nitrogen and oxygen is subjected to high temperature, the lower combustion chamber temperatures caused by EGR reducesthe amount of NOx the combustion generates (though at some loss of engine efficiency). ... For example methanol is more tolerant to EGR than gasoline. Adjusting timing and fuel mixture is the answer to efficiency and power and Optimum combustion temperature. EGR exhaust gas recirculation only reduces nox it is beneficial for nothing else.
With n/a 4 strokes it doesn't hold as true. Shorty pipes can ruin the engine, and in a midget car my grandpa just welded a full straight exhaust to the back for looks and destroyed every race. Every race they would tear down his engine thinking he was cheating and all that was changed was a longer pipe
I remember way back in the 70's when Nascar team owner Junior Johnson's race car went to equal length exhaust headers and gained some hp on the competition. It completely changed the sound of the engine, sounding more like a 6 cylinder than an 8 cylinder.
My car has a 2-stroke sooo, my cars exhaust needs reflective sound waves :D but yeah planing to put in a 4 stroke and then that dose not matter anymore and i have to remove the components that are tuned to the 2 Stroke. ^-^" your videos help understanding what i have to consider with the conversion - keep it up your a big help :) kind regards Lara
back pressure will severely harm the performance of a 2-stroke here again you are confusing back pressure with the reflective sound waves as it works the same way in a two stroke.... reflective sound waves are much more critical for the performance of a two-stroke to keep the intake from escaping the exhaust port. these are not my words but the words of Pop Yoshimura the greatest tuner of all 2-stroke engines there ever was and the inventor and designer of Honda's first two stroke engine
He did break it down and describe it pretty good. You do need a certain amount of pressure, not necessarily back pressure, but enough pressure to keep the escaping exhaust from slowing down and not escaping fast enough. Yes pressure can create higher velocity. Think of it like a garden hose, if you install a 4" garden hose on your house faucet, the water velocity will slow down due to the size of the hose because the water pressure can not fill up the hose fast enough to create a pressure to push it out fast enough, and it will escape slowly, but if you use a standard size hose, it will have greater velocity and escape faster. Now, if you connect that 4" hose onto a Fire Hydrant, then you will have a good flow. So size everything to your engine. Primary Size, Collector Size, Header Type (4 into 1, 4-2-1), Exhaust Tubing Size, The bends in the primaries before it gets to the collector, the collector design, muffler type, and so on, will all have an affect on performance based on your engine and how much CFM each cylinder can produce.
You kind of skipped the 101 version and went straight to 102 class. The 101 version would have been a better explanation. Back pressure exerts force back into the cylinder requiring use of some horsepower through another cylinder firing exerting force on the crankshaft to physically push gas out. The more back pressure the more horsepower is used up in rotating parts and not making it to the driveshaft and propelling the vehicle. Your explanation of pressure waves is more towards tuning of intake and exhaust timing and design differences of header lengths and exhaust sizing. EI was more about exhaust design then about back pressure being bad. I know they are interrelated but feel you really did leave out important info.
Fish R Relaxing well when you explain back pressure like that it sounds like version 100. If there is back pressure on a cylinder then it will take power to push it out. Bam the videos done. Take care see you next week.
Rexin Oridle. As in a vacuum pump? Potentially beneficial but compared to a compressor on the inlet you are pretty limited in what you can expect in terms of improved output.
Rexin Oridle I think you would find that the benefits gained from better exhaust scavenging would be more than offset by the weight and power consumed by the exhaust fan/supercharger so you would actually achieve a net performance loss.
I was about to write a lengthy comment commenting on the problems with your idea when I had the image of a mechanically or belt driven turbo device with compressor wheels that simultaneously create pressure and vacuum in both inlet and exhaust sides of the engine. I guess if it used fans as supposed to a roots type supercharger it could work.
Actually, there have been some passive exhaust extractors used in Formula racing whereby the exhaust tip is placed in a high velocity area (think above the rear spoiler or outside the firewall) with an integrated radial venturi to create a lower than atmospheric pressure at the exhaust tip. Operates similar to the venturi in a carburetor -- it sucks better! Most effective on a short exhaust with naturally lower flow resistances/losses. Also, on very short exhausts the exhaust pipe can be flared to broaden the scavenging RPM range (similar to velocity stacks on carbs). Analogous to impedance matching in the RF world.
Been a tech for over 20 years. I’ve seen many check engine lights caused by aftermarket exhaust that lower back pressure. Many cars were even designed with back pressure transducers to operate the EGR systems.
With need for a lower external pressure for exhaust gasses, do manufacturers consider aerodynamics of where the exhaust is placed to maximize vacuum or are the fractions of an atmosphere negligible?
Negligible unless you’re running serious drag car power That said top fuel cars create about 5-600 lb of downforce from their exhaust just because they move so much air Same reason pro mod drag cars will run bull horn style exhaust. Every little bit counts. But honestly in passenger cars you’re more worried about the physical exhaust route than you are the gasses coming from it. Same goes for “low” hp cars
It makes a difference on motorcycles as their aerodynamics are crap. For example changing the direction of the exhaust tip can mean that you increase back pressure and harm horsepower by trying to make the gas escape into a high pressure zone. Or moving it a little bit can mean having the exhaust gases exit into a low pressure zone and helping with the scavenging effect. They can't be measured on a dyno. Unless your dyno is also in a wind tunnel
You get a shock wave with a p0/p1 ratio at about .52. that's certainly something you want to avoid. So the lesson is try to cool that exhaust as much as possible before it hits atmosphere. Pressure drop can be modulated by expanding the exhaust size and channeling it though passages to even out and cancel sound waves. P0 = P1 + .5pV*V
You're absolutely almost right. there are engines in the motorcycle industry that have unique cam timing and overlap that makes them so sensitive to exhaust pressure control that "opening 'er up" with straight pipes will make them run like ass. Suzuki VL1500 comes to mind. And yes, as 30yr veteran of the industry, I've been seen plenty of examples. This is the point where someone replies about carb jetting or injection tuning.... sorry, save yourself some typing
those of you saying you have lost power, you may well have. Horsepower is a function of torque. You can tune where your peak torque RPM is by changing your header pipe cross section. The formula Torque Peak RPM= primary pipe c/s area x 88200 / volume of 1 cylinder. So if you put something really big on your engine, then you moved your torque peak way up in your RPM, meaning your engine will have to scream to reach that point. You can use a variation of that formula to find what size exhaust you should run for a specific RPM: Primary Pipe c/s area= volume of 1 cylinder x RPM peak / 88200. This way, you can set your torque peak at an exact point of your choosing, and find the header pipe size that is perfect for that. Those of you that mentioned racers having multiple header sets are correct. they use them to tune the engine based on the demands of the track. An oval track where they can maintain a high RPM they can use a large pipe. If they are going to have to do lots of acceleration and wide changes in RPM, they will probably use a smaller pipe to move that torque peak to a lower RPM so that they have power to accelerate. Lots of math when building an engine for racing.
It's exactly the same except the scavenging effect is even more useful as there is more unburned fuel after the initial powerstroke. The take from this is that backpressure is the wrong term.
So back pressure bad, but scavenging is good. I don't have any interest in doing more work on my gas engines than necessary replacing a stock exhaust, but it is nice to have a good explanation of exhaust flow dynamics.
In my experience I ran a truck with no back pressure correct diameter straight piped. One thing you missed was how the back pressure pulse affect piston rings. Unless you have a turbo(which produces back pressure).
This is the perfect video to explain to someone why it’s unnecessary who always says, “but you need back pressure!” As long as they have the intelligence and attention span to pay attention to all of this.
I’m no engineer but understand what he is saying. It’s like some people tacking fart cans on their Honda’s claiming power increases. Headers, intakes, mufflers, it’s all good, BUT baffles in the muffler(if that), exhaust pipe sizing, and actual tuned exhaust is a different animal. My own truck I figured easy air in and easy air out it’ll run great. It does. Runs strong, not quite like a V8, but it has a lot of heart.
Inertial scavenging ; same can be said about the intake manifold in a naturally aspirated engine. This is why you really have to know what you are doing if you want to tune stuff like that. It's not always bigger equals better.
Might be wrong, but my understanding of pressure wave scavenging is that it's designed to help the other cylinder(s) connected at the collector, not the cylinder that generated it...?
years ago racing snowmobiles, we learned that proper exhaust design gave the equivalent of super/turbo charging. You pulled air fuel mixture into the exhaust, and then the pressure wave pushed the mixture back into the cylinder. Made good power but also polluted a bunch. (And they were louder than heck, I don't hear as well as I should because of it). ;)
Serious question. I've been trying to wrap my head around the idea of removing all back pressure post turbo exhaust. My idea was to include a reed valve (a valve only allowing one way flow direction) after the muffler. 2-stroke engines use to reed valve and I thought four stroke engines could somehow benefit from this, particularly turbo charged engines. Could this work? Would it hurt?
Personally I like my setup. 2.5 inch stainless pipes bolted to factory manifolds. The engine itself is a Chevy 350 with 305 heads that have been machined to a larger exhaust valve. The results are more power.
Thew dislikes are because this is not all of the story. You CANNOT change from the factory exhaust without harming your cars performance. This has to do with all of the air flow sensors and exhaust sensors that are all set in the computer to make the engine run at its best. You replace just the muffler with one that is more open, and it will take away from the cars performance. If you do change ANYTHING with the exhaust, you MUST take your car ot someone with the correct equipment and know how to change the settings in your cars computer, to make the engine work right with the new exhaust. Now his explanations as to how ti all works is fine, but when you change anything in that exhaust, you just have your computer reset for your vehicle to run properly. This is why you see cars with new loud exhausts installed and they backfire and shoot sparks out the back. This will RUIN a good engine quickly. So yes, the exhaust needs the proper back pressure so your engine runs as it was set up at the factory.
@@valkman761 he does make a valid point that on ECU engines with EFI you do need to reprogram your ECU to get the best performance with the new exhaust. Just like you have to adjust the carburetor on an old-school hot rod when you make big changes to the exhaust.
And just to clarify the crackle and pop you hear from some aftermarket exhausts is not a backfire, stop talking absolute rubbish. The only sense you made was about tuning your car to suit your exhaust
You're right, Dragsters just have short, unbaffled 3ft pipes coming straight out of the engine. I'm sure if complicated, slower exhaust systems would give the engine more power the engine builders would use that.
It would, except that you need to power that somehow. It would take more energy to run the "reverse turbo" (essentially a vacuum cleaner) than you would gain from the more efficient exhaust, however, so you'd have a net loss of power.
Well I thought that a concept such as that already exists sort of. You can place a turbo on the exhaust side which uses the exhaust to boost an engine where most people place turbos on the intake side using the engines power to boost the amount of airflow.
Ethan McLeod turbo is powered by the exhaust gases. It spins a turbine which is connected to a compressor on the intake side. I dont think you quite understand the design of a turbocharger.
LOL!!! Turbo charger is a combo of gas turbine and compressor... It's an energy recycling process lol... If you don't use exhaust gas to power it then it's not a recycling process
Most "car guys" are idiots is the problem so bad information floods the iinternet. Being an engineering myself makes talking with most of them impossible. Engine masters does a good job shutting people up with the dyno even if there tests are sometimes not perfect.
i heard back pressure is good 20 years ago in high school auto shop and about how new cars (1997) needed it to help performance because of the computer. i have remembered that for 20 years and it never EVER made sense to me except that maybe the o2 sensor somehow will dump more fuel or ????....but i dont think it can dump more fuel than my right foot so it is finally reassuring that it doesnt make sense to you either.
Car guys, even mechanics, are not engineers. They have not studied physics. They see something like a slight performance decrease from a poorly modified exhaust and start making assumptions about the cause. I can't tell you how many supposedly knowledgeable car guys insist a venturi in an exhaust draws the gases out faster. That's wrong and would be perpetual motion. That's what is great about this channel - he explains how it all really works.
The first thing is you're listening to a "engineer" na cars need mufflers turbo / supercharged 10000hp drag car need no mufflers ! if I have to explain further just go ahead and remove your exhaust from head and go have some no back pressure fun
The exhaust system with "back pressure" can be designed to create pulses/waves of pressure that can assist in evacuating the exhaust from the cylinders at the right times. this can help for example to create better torque at low rpm for a particular engine. A fully free flowing exhaust with zero back pressure would not allow for this type of optimization since you cannot create any kind of pulses of vacuum to help evacuate more exhaust than atmospheric and will always leave more noncombustible exhaust inside the combustion chamber in comparison (there would be a point of optimization). Once you have forced induction none of this matters because the power gained per added flow overcomes any other effect so more free flowing the better. I would imagine a similar case may hold true for non-FI but just overwhelmingly powerful engines or engines running at very high RPM.
07 Ram single cab with a v6 motor and a 6 speed transmission. Cats were deleted, muffler deleted, cold air intake installed, AirRaid Throttle body spacer. Went from Oklahoma City to Waco Tx on less than 1/2 a tank. Roughly 1/3. Over 300 miles. Mileage calculated rough guesstimate was around 40+ average speed was 65mph. Truck ran great after getting rid of the emissions crap, before all this i was lucky to get 200 miles a full tank on a v6. Check engine light always on, but what ever, i knew what it was for. It was for upstream 02 sensors below temp and pressure because no cats on the heads.
