Exhaust Back Pressure - Dyno tested
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- เผยแพร่เมื่อ 28 ต.ค. 2021
- Increasing exhaust back pressure via a restriction and the effect on power
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Test engine:
Long rod 4AGE
Modified early bigport head
Kelford 193b 9.2/8.5mm 284/278 @ .3mm
Toda valve springs
Toda inlet cam gear
Redtop bigport block with 10.3:1 smallport pistons
Toda 3.7kg flywheel
Maxpeedingrods connecting rods
Link G4 ecu
47mm itb long runner
Garage4age Header and 3" exhaust - ยานยนต์และพาหนะ
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Remember this is only exhaust pressure. There is a whole lot of wizardry that goes on in the headers and the section after the collector. That needs to be tuned correctly to make good power. not just "make it big" . After said parts is what this video is about.
In motorcycles, such valve is sometimes used to improve the torque in the lower rev range (e.g. yamaha uses exup)
@@mateuszbarya9098 Yes, I own a Kawa ZX10r ´04 and has it, but years ago a red light was on in dash, after check with a wire to ground and read the code that exhaust valve was KO, was closed, removed the cables and blocked the valve in open position. Purchased new my bike, has 141.800Km, never engine valve adjustment made.
Since the valve is close ish to merge. might have some effect on scavenging. good chance its there for noise and/or emissions stuff also. The section I was talking about that needs to be right is basically the length of motocycle exhaust.
all im hearing is 3" straight through
@@tortron your hearing is perfect
You never need “back pressure”, what you need is efficient exhaust scavenging for the rpm you plan to run at.
Back-pressure is an indication of inefficiency. The reason why factory exhaust systems have back pressure is that it aids in noise suppression.
Exactly , with a multi cylinder engine you require spent exhaust gases to be sucked out by the vacuum from one or the other cylinders via a coupled exhaust system. Except with supercharged engines that can run separate pipes.
Don't need and back pressure at all , it jumps reduces power .
So u need back pressure.
@@jackdaniels2657 no you need scavenging
@@joshuabrown9398 OK so if u just run a dragster without an exhaust ur saying u will get more power. Then dragster like top fuel should ditch those exhaust all togeather
Far too many people confuse back pressure with exhaust scavenging. When you go too large on an NA exhaust you are not losing "back pressure" you are making the exhaust scavenging less efficient, because the exhaust diameter is too large for the flow of gas to produce a vacuum on adjacent exhaust runners. And if someone is telling you your turbo car needs back pressure, get better advice
And like that we all learned something today
Exactly. No engine needs backpressure. But proper scavenging and also resonance is key to making power.
People confuse that, because when they make their exhausts less restrictive (by changing their exhaust and/or remove mufflers) they lowered the backpressure (which is good). But also changed the scavenging and/or the resonance. If the car makes less power in the end they blame it on the backpressure. But the reason for the power loss is the messed up resonance tuning / the scavenging not working properly anymore.
Yes, do not confuse backpressure with exhaust gas velocity. The exhaust scavenging effect relies on the momentum of the exhaust gasses.
@@Chris-yy7qc 2 strokes need back pressure ;) But we get what you mean.
Back pressure in a turbo can generate more kinetic energy in the turbo, but it obviously has the downside of restricting flow.
I'm not tuner or anything, its just some general thermodynamics principles.
I hardly ever comment on TH-cam, but I always like to tell you how much I enjoy what you do. It's like watching all the stuff that runs through my head come alive. Great, simple illustration of backpressure. Keep doing what you do. Also, I swear that car gets better looking every time I see it.
Your editing keeps getting better and better.
These videos are great. Short, informative and straight to the point. Great work.
I dont even need to see the vid to like it already, you always do such good real world tests that are actually mostly unanswered thanks my dude!
Greetings from Bulgaria and keep going with good content!The limit for back pressure is arround 3-4 psi(0,25-0,30 bar).Everything above is causing losses or "disturbancies in the force" :) and it is clearly seen here.
What a simple and effective test and as simple as that test is this is the best test I have seen showing the difference in back pressure. All the other are just changing the size of the muffler and HP difference.
Good video for backpressure lovers hahahahah. Of course there will be a optimized exhaust diameter/gas speed for each setup.
Less pressure, more gases out, More gases out more in, more gases in equals more power... People keep telling me my car is going to burn valves with my resonator only exhaust. Don't know why its always old folks who tell me this but if the air fuel ratio is correct i dont think i need to worry. Btw love your vids man there's so much effort put imto these short vids. 👍
Correct, if the AF ratio is right but carbed cars can lean out with a less restrictive exhaust system but I have never seen burned valves because of straight pipes w/o adjustment.
Some modern cars (like Hyundai or Kia) with downscaled pistons and rings actually need SOME back pressure from stock catalytic converter. If removed, the engine starts to burn oil a lot.
Its more about resonances and velocities than anything else
yeah i mean having too low of ignition timing is more likely to burn valves
@@devl547 Most vehicles need some backpressure.
I think this is my fave channel on youtube & I might actually buy a t-shirt (I never buy merch ever). No BS intro/outro, no honeydicking "YOU WONT GUESS WHAT THIS MOD DID". Just pure awesome
Thank you so much for finally testing this. The next time someone tells me, "You need a little back pressure in your exhaust," instead of just shaking my head, I'll shake my head and refer them to this video.
*Old man shakes fist at Garage 4AGE*
good video ! never talk about backpressure but about optimum flow !
Yes ! Another great video as always !!!! 💪💪💪
Love the exhaustive testing.
under rated comment.
You've been a very busy 🐝 thanks for all the info dude😀
I love your content man. And the memes are awesome
I’m actually suprised that there is such a big difference in performance between 0.9 and 0.4 psi. Nice video!
I imagine you having a huge set of spread sheets with all these things you test so when you build a motor then set it up you could hypothetically select all the favorable parameters/components to have a tip top 4age. That would be pretty silly, in a cool way.
Thanks for you testing. Very good channel
This channel is so good
Changed my exhaust from 2.5 inch to 4 inch and boost went up 4 psi on average... nice!
Excellent demonstration, thanks.
Super grateful fot the videos!!
Again, super video.
Well done! Pretty much says it all. Keep On!
Man that car sounds GOOD
Wow, even tiny amounts of backpress make a difference!
Great work Mr 4age
Yup. The more cam overlap, the more sensitive to exhaust pressure. stock engine will get away with more.
@@Garage4age very interesting
@@Garage4age should try some kelford turbo cams in the hilux
I love this. Thank you.
Good videos very informative and fun.💯
If back pressure was a benefit wouldn't race cars have mufflers 🤔
Tbh, i never understood exhaust back pressure until finally i had a tuner explain it in the correct term, which is exhaust pulses. Since the pressure inside an exhaust isn't constant, it's spiking at the exhaust stroke in pulses. And that's why it's important to have a properly designed header that scavenges those pulses which in turn promote better breathing which equals power.
X Pipe testing would be very interessting too
Would love to see more 20v videos in the future!
I have a little update vid with some revisions on the stuff i done in the last 20v vids. Nothing to major, but its making decent power for whats been changed. probably be out in a week or so.
Not really surprising but love these tests
Love this content mate! I know the data is right in front of us but it would be great if you could voice over at the end to clarify the results as some people may not understand all the data. We like to hear what you have to say ✌️
Yep. I have no idea what the results were. Just tell me.
I fucking love this. Incredible.
No filler bullshit, just results. Lovely
just subbed! my favorite thing to argue at car shows! oh and claimed horsepower without dyno sheets 😂🤣
I must say that I LOVE this channel! In the description it says that the intake runners are 47mm but how long are they from the intake flange? Bets regards from Sweden :)
He has a video on the effect of differnt intakes and runner length.
It never made sense to me why the old guys always insist that you gotta have back pressure. But then they build a supercharged big block drag racer with straight pipes out the sides. Hey, where's the back pressure? Why would you want your engine to work harder to move exhaust out, even if it is just a regular car?
Nice channel, can you please do a video comparing 4-1 vs 4-2-1 design :)
Noticing the large spike in power in one spot with the higher back pressure settings, it might make for an interesting test to plot the throttle position that coincides with these peaks and the rpm that it happens at, then actually rig some sort of linkage that mimics the setting that is working at a particular rpm... might work even better with 2 or more of these exhaust throttles positioned at various points on the main exhaust tube, and find the throttle settings that work for each of these peaks... synched properly I think it would be the functional equivalent of a variable length exhaust pipe... heck of a lot of work, but cool to see how it would work.
Finally the myth has been busted! Thank you very much!
It has been busted for this specific setup. If you are running stock engine and you put in non restrictive exhaust it will be contraproductive without adjusting other parts...
@@vasek987 oh Jesus fuckin Christ! No it won’t!
@@vasek987 th-cam.com/video/24Z3TeMq69E/w-d-xo.html This vid i dropped the exhaust off after the header 2-1 section. It made a little more power everywhere. car basically stock other than aftermarket ecu, so i know its not the ecu doing weird stuff
@@Garage4age any chance you can run it without headers without damaging the car or setting anything on fire?
curious to see how much the power drops by removing the header completely
@@satanaz The time i ran it up with open header & megaphone. It was like the apocalypse had come. Silence and no wildlife as far as you could see. So not so keen for no header haha. the cam overlap makes them really loud. maybe i will find something else to try it on though.
You should make a UEL header for it, I bet it would sound amazing.
Such a simple test but love that it was all logged and put into one concise video.
You mentioned the AFR got richer with higher back pressure, which was expected, and curious if the VE/fueling changes scaled with the power losses or if the power losses were more significant than the VE drop alone would suggest. Essentially curious if pumping losses showed up- which seem to have more emphasis than they deserve in most cases, or if it was mainly the VE losses from reduced scavenging and more reversion.
Cheers
I didn't really work it out too precisely or get too picky on the high pressure runs for obvious reasons. but can say most of it come from ve or lack of. As i recall taking 15% fuel out of the map, plus some trimming here and there to get the afr ballpark.
Do you have an exhaust pressure reading using just a stock muffler? It's be interested to know how much back pressure one creates
Thanks!
You should dyno exhaust velocity with pipe size instead of a freaking butterfly valve. That way when you have a negative pressure wave behind each pulse it'll help in valve overlap instead of the vaccume being destroyed by the other half of the butterfly valve.
Its just showing what the wrong exhaust does on good header / collector combo. If i changed the pipe size after the collector it would do very similar thing. have done it before. All the power is in the header and collector. rest of exhaust just needs to flow enough to let them do there job or not be there at all.
@@Garage4age if what you think is true then exhaust leaks after the collector would have 0% impact of performance which isn't true at all
@@t_money_third9654 Can't say ive tested exhaust leaks. Maybe i will sometime, my money will be on it doesn't do anything. unless exhaust too small, then probably of benefit. What im calling the collector is more than just the merge btw, the size,shape and length needs to be right after the merge.
@@t_money_third9654 An exhaust leak will most definitely affect your performance - if it's meaning oxygen that isnt a combustion byproduct reaches the oxygen sensor.
My eyes were on the torque
The myth that an engine NEEDS back pressure to perform best is bunk! Engine masters did a test with various headers and complete exhaust systems and in a nutshell, the larger the headers and pipes, the more torque the engine would make, especially as the RPM came up. Think of it this way, you're running a foot race, would you want to be breathing through a mask or free air?
Very nice
Just curious - how many times a week is the engine in the starlet in pieces or even swapped out totally? :)
Love the content - this has to be the most informative dyno channel around :) Thank you :)
too many, lucky its pretty easy to work on
@@Garage4age about normal for a starlet
@@tortron how come?
@@weixianng when I was a teenager starlets were worth about $100 so we just thrashed k engines till they stopped, then swapped a box of beer for a new one. My mate swapped a $40 air pistol for a kp60
@@tortron wow. Thanks for the context. I was born in the 90's so I only got to know the Starlet when it's now being romantically looked at as a sought after classic RWD car.
People that still support the idea of backpressure, need to realize that the exhaust gases are pulsed and not a stable stream of gasses.
Picking the right diameter and length of the exhaust tubes means tuning the exhaust pipe to work best at certain RPM by maximizing scavenging, which in reality, minimizes exhaust pressure.
Thanks for the great video, I put a gasket on the connection between the muffler and the exhaust pipe for a better sound. It can be said that this part of the exhaust is leaking now, will it damage the car engine in the long run or not?
First off, love the content!
I’m curious if you’ve ever compared header termination types specifically 4-2-1 and 4-1 to see if there’s any benefit to having all the exhaust paths terminate together? I’m under the impression that there would be some sort of exhaust pulse overlap that would contribute to better power and torque.
What are your thoughts?
depends on the application or what power bias you want if we're talking N/A like straight pipes out of the heads it's more favorable to RPM but lower in torque whist on the other end of the scale a log manifold is great for torque but lower in RPM. The better the flow the higher it can rev the less it can flow the greater the torque. pulses are either cancel each other out if they colide or create a vacuum if they flow the same direction vacuum is better for RPM but doesn't beat straight piped exhaust systems for RPMS and colideing pulses are great for torque.
4-2-1 headers are also referred to as tri-Y headers. They will always make more torque than a 4-1 header because they pair up 2 cyl that are the furthest apart in the firing order to maximize scavenging. How long the Y legs are determines where the scavenging is most effective and you can move your torque peak around a fair bit.
Only works well when you can make your own and test. Most are just tuned for where ever the engine they are ment for makes peak torque.
Want a small engine to make much more torque way down low? Make the legs as long as a 4-1 header then Y up the cyl that make sense. 1342 firing order would pair up 1,4 and 3,2.
Bet you get a 5-10% spike in torque below torque peak with no loses up top if sized appropriately.
Found out Tri Y style turbo headers apparently spool a large turbo noticeably better. The owner of the "KC Maxx" Firebird built a set and is very happy with them 💁
Air in and air out with as much thermal expansion possible during the power stroke will equal the highest power
Garage 4age FTW. Now try out vacuum :D
Use some other engine to power a turbine which sucks in the exhaust of that red car and makes vacuum in it haha xD
Now seriously, great video as always. Simple, short, sometimes funny, and informative. GJ!
You just got a sub from me mate.
what if, if you can create some sort of a vacoum insinde the exaust? will it increase power? Like with venturi effect or air pressed towards the rear end?
how did you measure it? At idle , at certain rpm or under load(WOT)?
Would like to see the result of one of those vortex type silencers, and also do two catalytic converters in series clean up a performance engine enough to meet recent emissions limits? E.g can you clean up a Cammy performance engine with exhaust after treatment and mapping to make them clean enough to meet emissions limits.
This I gotta see! I've always considered back pressure to be as necessary as waiting 30 minutes to swim after eating to prevent cramps. I guess today we find out!
You can't swim can you?
@@johncameron6864 I can swim fine. That's why I think back pressure as a necessity is a myth and anyone who believes back pressure is important has back pressure in their brain. No offence btw
both are myths. You can swim after eating, but there's no need to do so because your body is trying to prioritize blood flow to the digestive muscles. Take a casual walk for 10 minutes after each meal and you'll gain digestive health, nutrient partitioning, and insulin sensitivity. Any real activity after eating or sleeping after eating is a big no.
man i love tihhis shit
MotoIQ has a great video on this topic
Yes, you are best
I wonder how 1 cylinder engines would respond, as there is no exhaust scavenging as such so what would be the most efficient exhaust setup?
This is actually an extremely interesting test.
Given the data it’s looks very much like the idea of backpressure is only related to minor amounts or torque below 3,500rpm.
It’s probably likely that the idea probably started somewhere where they were developing cars for non performance street uses
The idea probably stemmed from 2 stroke gas engines which do benefit from a certain amount of back pressure to prevent fresh air/fuel mixture from being sucked out the exhaust port. 4 stroke engines on the other hand benefit from the exhaust exiting the cylinder at a high velocity, creating a strong vacuum in the cylinder at whatever rpm the exhaust header was designed for.
thank You :-)
Thanks 👍🏻😊
Very cool stuff man! I am really interested in the positioning of X pipe in the midpipe and the different effects.. I got bmw 2.5 inline 6 with 3 2 2 exhaust, but i dont think i would be translateble from your engine..
I got a M52 2.8 and recently made my own stainless exhaust. I still have the factory 3-2 headers with a cat which merge in to a 2-1 collector after the cats to a 3" pipe up till just after the diff. I noticed the car is much more responsive on throttle and pull slightly harder between 3 and 4.5k and starts to fall off after 5.5k rpm (3.5k VANOS opens)
Can you do some part throttle tests as well ?
People don't understand it's the resonance frequency that offers more scavenging at lower rpm.
Back pressure myth is painfully believed by way too many.
Would be interesting to see a full wave tuned exhaust effect on hp though.
I recall that being around 45' or so for resonance on an engine at peak rpm
So... exhaust diameter then affect hp?
Flow / resonance?
that is why even stock restrictive exhaust does not reduce power for more than 10-15%, or gain with good exhaust is about 10-15% and bigger difference is on lower rpm than on higher rpm
Good shit. It's not about backpressure, it's about flow. Flow and pressure are intertwined but separate, but people can find it counterintuitive how one affects the other.
I've said this many times before and i'll say it again, 4stroke motors dont NEED backpressure to make power the way a 2 stroke needs it.
You certainly not chek the video hehe les backpressure make the most power 🤣
Sorry i mis read sir haha
Thanks for this. Now I have something to show to the old heads who think backpressure is everything. Lol
Hey just wondering does anyone know how to tell if a kp60 starlet is a trd is there a badge on the chassis somewhere
Hey, have weird request to test, everyone knows about 4-2-1 n 4-1, but what about 4-4 exhaust and 4-2 exhaust on inline 4 engine, i guess that could be quite interesting
Lots of debate still with pipe size and length...
Would a few sets of Zoomies be easy enough to make and test?
And wake the dead...
Its not about back pressure as much as it is resonance tuning (for N/A).. and no, you don't want really any back pressure on turbo.
Cam timing is important to match higher air flow also a silenced system delivers more low down torque.
thats because a silenced system creates more backpressure as expanding gasses volume increases with rpm.
Obviously the next test is going to be adjusting for cam overlap in the presence of back pressure at various amounts.
I wonder the effect on a NA car.
2-strokes the exhaust pipe is the turbo. The expansion chamber design lets unburned gas fuel mixtures back into the engine for a turbocharging effect. I wonder if you can apply this to 4-strokes. With a little expansion chamber on each header.
This is an NA car, so you don't have to wonder..
Most people confuse back pressure with exhaust velocity.Exhaust velocity can change the power band of a motor.
U all over the internet homie?!
Good stuff here.
Yea I remember on my turbo dart when I made my own down pipe 3 inch straight dump to the ground now cat or muffler he was lecturing me on back pressure while I'm trying to explain my turbo needs to breath out as good as she breaths in back pressure used to be a way to start a argument lol.
So it's about Heather flow and collector and some back pressure
i know that sometimes not going crazy with the diameter of the exhaust system, can increase the velocity of the exhaust which in turn can decrease the resistance the engine sees. But im very curious as to where this urban legend of exhaust back pressure comes from? surely having back pressure just for the sake of back pressure , will do nothing except increase resistance for the engine
It's much more complicated than this. This experiment proves very little, if not that the throttle plate bounced back the pressure wave, changing the dyno graph curve, insignificantly. Back pressure is a derivative of a chosen design that diminish the exhaust gas to return into the cylinder.
Of course is to be kept at minimum, to limit the pumping loses..
More power means more air mass, more everything, bigger ports, no way a small section will produce big power. The sections are determined by the diameter of the valves.
It just shows what a restrictive exhaust will do on a otherwise good header/collector. which is where all the power is. changing pipe sizes after said items will do very similar
I was always told that in N/A cars you need to get rid of the back pressure for more HP, but you will sacrifice TQ by getting rid of the back pressure, now this is what I was told in the 90s, today's car's are different do to technology and with a simple tune you can balance things out, I'm old school and I like at least the most minimum back pressure possible from my experience running lots of exhaust setups on cars that I have owned, not to mention that if you have straight through piping you will make some ears bleed with the 100% cabin drone that will make you regret your decision for more HP, not to mention the check engine light and the emissions on the state that you might live in.
I got a 2.5" tip reducer for my 4" exhaust it won't even rev past 3k but it's quiet
Back pressure is a myth thats not what happens. The length of the exhaust itself can tune the out going exhaust pulses which helps get the exhaust out faster creating differences in power band. This video proves that 100 percent.
Is that 130hp or 130 kw , what size exhaust is it running. My vehicle makes 158kw at the wheels using 2 1/2" single system . However I think it could benefit from 2 3/4 "
130kw. yeah kinda depends on the engine setup to a point. an engine with big cams and overlap will benefit more than something with stock/smaller cams
i love power in the middle .. try that with straight pipe bigger than it should !!!!! cant ? i know~~~~~ the how long you gonna push it , spooling or lag is another chapter!!!! this is why turbo group cars have tight setups!!! sorry to kill the dreams of many turbo guys in this chat i saw some comments about turbo already ...this is why i mentioned something about charged ones
damn 18 psi of exhaust pressure is more than the 14psi atmospheric pressure trying to get into the engine
Yes, but it's irrelevant. The main goal, on N.A. engines, is to keep the flow running, just like when you're emptying a tank of liquid, with a hose. The secret is to keep the flow, even if closed and opened repeatedly, do to inerzia and correct speeds, determined by the section, shapes and... luck...
During the 18 psi run, could the torque spikes be an indication of detonation?
Most likely misfire,
If you block off the exhaust, the power output goes down.. Now who would've guessed it. But, there was one interesting spike on the curve, that is a clue to the "back pressure" conundrum. The thing has nothing to do with psi, but pulses. Is the exhaust draining the combustion chamber, or filling it, when the valves are @ the overlapping phase, which one it should do, where the torque is needed and how it's used. The exhaust is a tuning element, just like the intake, and these two need to work in unison to really make power.
Yes, read my pinned comment
I did some back pressure measurements and I discovered mine developed slight vacuum during deceleration. Is it normal? I recorded it on video and it's on my channel. Please check it out if you have a spare moment.