@@graham7513 He’s literally showing pressure differences with actual gauges in the video. I never said simulations weren’t accurate, it’s just nice to see a real world test done
@user-sj2zy3rp2p Yeah… I know that. All I’m saying it’s nice to see a way of doing it that doesn’t involve high end software. Where did I say simulations haven’t contributed to anything? I didn’t say one method is better than another. Of course simulations are better that whatever this guys is doing. Simulations rule everything. No one is expecting precise and accurate measurements using an air hose and some pressure gauges…
Primary scavenging occurs in the cylinder and valves at the end if the exhaust stroke and beginning of the intake stroke. This secondary effect is overrated, though can and does occur, but unless all parameters are the same between differing engines then the effects are largely reduced pumping losses masquerading at primary scavenging. In short people will say anything for money. It does occur and race cars operating in comparatively narrow power bands exploit the effect effectively.
Thanks mate, great work. I gained 28-29 whp on a Mainline dyno, going from twin 2.5" to twin 3" @ about 16psi - no loss down low. With sport cats. I appreciate you sharing your work.👍
Oooh that M52 motor sounded GOOD with the 3' system on it....much more like an M3 😍 Seemed to be visibly quicker as well. Imagine what it could do with decent headers too! This has got me thinking about what to do with the really crappy stock system on my E39...
I wouldn't say the stock exhaust is crappy. It's actually a high quality piece. It's made of stainless steel and fits better than any aftermarket or custom exhaust. But I can understand why people prefer louder exhaust.
@@tiitsaul9036 I didn't mean crappy in terms of quality - Yes it is well made and one of the few areas of the car immune to rust! But from a sound quality, weight and performance perspective, it is pretty crappy. It adds nothing to the enjoyment factor of the car at all, which is a shame because the engines themselves are great.
Interesting facts, ill add some of my subjective opinions... I could compare stock 328i with open valve all the time, 328i with 2l single pipe stock exh. and 328i with profesionaly made system. it was two cars with bone stock engines, just different exhaust. (1997 euro sedan, stock exhaus) ; (1996 euro coupe at first with 2l exhaust to pass technical inspection and than custom no cat with stock M52B28 stainless steel manifold) custom made felt rew happy and also pulled stronger in all the rew range, with a 2l it was deffinetly not as rew happy, torgue came in 3500rpm and ended soon . stock 328i exhaust felt much better than a 2l single pipe, car was pulling much smoother in higher rpm when VANOS kicked. in europe stock 328i exhaust is a valuable thing to have on the car with original catalitic convertors. we need more resreach on this topic (y)
What you mean, when vanos kicked? It's not vtec. Vanos turns on at ~1800 and turns back of at ~3500. With vanos broken you will have same Max power to the rev limit. Just less flexible car in city.
The 3 inch exhaust works better at scavenging not so much because of the larger dia but because the cross link in the BMW system is after the 1st restriction that reduces the strength of the pulses from each half of the manifold whereas the 3 inch system merges before any restriction. If you check the BMW system - dia's and lengths they may well have tuned the pipe for front and rear banks to match the resistance by the time they reach the cross link to get the best timed scavenging, certainly that's the case with my 2010 N52 car. ( dia into Cat/1st silencer on rear bank looks smaller?) On the 3" exhaust matching the lengths of the primaries will improve midrange and if possible don't merge untill just before the 1st silencer.
I'm not sure it matters much if restriction is before or after the merge. Either way, restriction is bad for scavenging. Cats in my stock exhaust may be not 100% healthy and starting to plug up. Yes you're right about one of the secondary pipe is smaller diameter. It's 325i piece. I believe they made longer pipe skinnier and shorter pipe larger in attempt to equalise pulse timing.
Just because the paper blows "in" to the header instead of "out" doesn't mean it's better at scavenging or anything. Scavenging works on reflected pressure waves in the system - so, a pressure wave reflecting "out" of the header will hit the back of exhaust valve and then once the exhaust valve opens there is a vacuum formed BEHIND that pressure wave, which acts to help fill the cylinder and pull exhaust out. This is an interesting comparison, but not sure the basic principles are entirely accurately described here. There is just a lot more going on in an exhaust when an engine is running than what can be realistically modelled by blowing compressed air into the exhaust.
yea blowing compressed air into the exhaust won't really show the reflection of the system. however what he showed here is the venturi effect of the system, which is also a style of scavenging, as the air (exhaust gases) coloum passes through the collector, it pulls the air out of the other runners, creating low pressure areas between the other exhaust runners.
This is stuff from the 1980's and i freaking love it xD . also those exhaust flaps just get rid of them if they get stuck shut they can really hurt your engine with excessive heat buildup. especially if you plan to drive enthusiastically
Due to the stock exhaust design, it's hard to measure AF ratio. The merge is after the catalytic converter. I could probe from one of the banks, but couldn't be bothered.
Yes ms41. I didn't have time to do any data logging. My butt dyno confirmed performance gains. With stock exhaust it doesn't spin in 1st gear. With 3" it lets loose. Also throttle response is much better with 3"(easier to down shift).
a little bit of back pressure is good, helps the engine breathe well and use all the torque it can get. too open means less torque and more hp. i know this with my subaru. but full throttle for long periods with back pressure can cause pressure build in the engine
Amazing job. I never thought N/A engine can gain so much power on higher rpms. As mostly mentioned, there is no power lose because of back pressure. Bigger is better!
@@tinuse3670 as mentioned that only applies to headers and collector. Properly sized header/primary pipes and collector (diameter and lengths, collector length starting point before tuning typically the same length as header pipe length from back of valve) exiting straight out with NO tail pipe is ideal even for everyday shopping/work car, lawn mower ect but very noisy. The only power loss you will get from a full exhaust system after this is from backpressure impeding flow or bad wave harmonics impacting tuning which can be seperated from the header/collector by a wave termination box at the end of the collector, basically a large empty chamber.
@@tiitsaul9036 Yeah i bought 6-7 of them 20 years ago when an online magazine from australia was mesauring Aerodynamics pressure and airbox restriction
So a 3 inch y pipe with single resonator and muffler gives ideal backpressure? My current plan is a y pipe 3" after long tube headers then double resonators ams a muffler. Should i omit one resonator?
Yes, in my case the 3" exhaust has the least back pressure. At this power level, I could probably get away with 2.5" I can't advise what you should do. My goal was to reduce weight, add simplicity and add power. It's mostly a track car. I've reinstalled the stock exhaust for driving on street.
Question ....what do you think of having a system that goes from 2" into a resonator out into 2" for a few feet then stepping up into 2.5 then into 3"....no muffler out thr back....what do you think the outcome would be ?
@@tiitsaul9036 oh sorry its for a smaller 4 cylinder....for a 6 it would be keeping the stock piping resonator then about 2 feet of a step up in size and step up again out the back. I have a sound clip on my page but I haven't done the 3" step up yet just up to the 2.5 as it's a stock single cam.
@@christopherdaniel2747 for a 4 banger single cam a 2" would be plenty. I wouldn't expect any power gains from stepping up in size. But if you like the way it sounds than keep it.
Interesting, But what the point of testing scavenging comparison seen that the stock system with separate pipes was not designed to do that ? The two pipes run along separated till the end ,there is no possible vacuum created unless you dump flow in a bigger section to create scavenging. The modified one is coupling both pipes cose to the manifold and dumping in a bigger section,and straight into an even bigger volume. You create a sudden loss of gases speed and increase its pressure in the system,so you will have a big scavenging. The MAF flow would have been great to see,it's the most important. Did you see some difference on air/fuel ratio ?
Stock exhaust is not twin pipe all the way through. It merges in the middle. AF ratio was not tested with stock exhaust. Pipes merge after catalytic converter. I could've installed O2 sensor in one of the banks, but couldn't be bothered. I'll do some data logs to learn more about performance gains when I find some spare time.
@@tiitsaul9036 If the pipes merge in a cross flow with same diameter pipes ,it will do nothing on scavenging relative to pressure effect,only on firing order pulses effet/ or a rpm range depending how far is the cross flow. You need what you did to gain scavenging : a pipe dumping in a bigger one to gain gas pressure ,so vacuum can build up upstream. It's Bernoulli effect if you don't know yet : for a same flow you increase pressure by increasing section area and reduce flwo speed. By reducing section area,you reduce pressure but increase flow speed. It's supposed to work on imcompressible fluids,but it works on gases too. Pretty neat testing,it's interesting to see.
@@michaelovitch Exhaust gas is pulsating. Each pulsation is followed by low pressure. Effective rpm range can be tuned with the merge distance from the exhaust valves.
It sure works with your setup. You might need to add a bung in the merge pipe for the probe. Give it a try and report back. I'd be interested in seeing the results.
Scavenging is not back pressure. Yes scavenging is good because the positive and negative pulse waves will be times for smoother operation. But it's not actually back pressure.
Yes it's just a clear tube filled with coloured water. Very primitive, but sensitive and effective. I used this device to measure the air filter restriction as well.
I would do a resonated / chambered resonator close to thr header to help with the low rpms and the drone up top I'll get the flow and thr best of both worlds
Low rpm performance is not an issue. This car is meant for weekend race track duty. Main considerations for my exhaust are weight, simplicity and top end power.
@@tiitsaul9036with that said, it's not only top end that is required for track duty, mid and top end are both heavily utilised. Based on my track car usage I would say mid range is 100% utilised more of the time, despite every gear change being made at or close to the limiter. In my case, I went from the OEM 328i to a single 3" decat exhaust after the downpipe and my butt dyno tells me that we lost torque and possibly top end (the Ecu has not been remapped with the decat exhaust). On home turf, lap times are 0.5s slower on average between a pool of 3 drivers and many laps before and a fair amount after. The weight loss and the cat loss however are definite pluses. Once hot cams are installed and the Ecu mapped to suit, I expect the numbers will change for the better. Time will tell. I do appreciate the content, that so for sharing. OEM Exhaust M52 manifold is crap, but better than M50. S50B3x is the best but very expensive in RHD drive now for a +10HP gain.
@@georgipetrov2203 yes, NA horse powers are expensive. Judging engine performance by lap time is tricky. Weather conditions affect lap time quite a bit each day. At my local track, typically we are faster in the morning at least 0.5 sec.
@@tiitsaul9036 Sure, I agree with you on all fronts, but our local is where we have all done 3 digits laps, so we have all conditions covered and various setups throughout the evolution of the machine. In essence it's our baseline for what the outcome is when we do changes, but I do get what you meant about variables being a significant factor too and only the dyno will prove one or the other.
@@georgipetrov2203 did you notice any improvement downshifting with custom exhaust? Mine free revs quicker with 3" exhaust which makes downshift quicker/easier. I was quite surprised.
I didn't measure power or performance. But I did notice a difference. I had more traction issues with 3" exhaust and throttle response was a lot better (quicker rev match when down shifting).
Is the intention of this video to show less is more? I'd argue scavenging effect of the exhaust is not measured with constant flow, rather with pulsating flow. As the OEM exhaust flow pushes against the closed valve on another cylinder, it actually creates a low pressure zone on its way back. This will work to increase the torque and driveability on lower rpm's. Put a low backpressure exhaust and all you do is ruin the low end performance with some added gain in the high end. Useful if you're doing track days mostly.
Please present some evidence to support your claims. I've heard this myth before, but never seen any evidence of back pressure improves low speed torque and drivability. Check out this video. Please note, increase in back pressure killed power the entire rev range. Only 6psi at 5krpm killed 20% power. czcams.com/video/V2Wv5-ZTOjM/video.html
@@tiitsaul9036 back pressure NEVER improves torque or power - but there is a lot more going on in an exhaust than what can be shown by the testing in this video. FWIW I am not claiming a drop in power with a larger exhaust, BUT, to claim that these testings show "scavenging" is imo, not correct.
Cylinder pressure is much higher than atmospheric pressure. When the exhaust valve opens, high pressure air from cylinder evacuates through exhaust to atmosphere. If exhaust system is restrictive, exhaust gases start building up in the exhaust system and increases pressure inside the exhaust pipe. That extra pressure works against cylinder pressure and hurts power output. I hope this helps.
Engines need backpressure, so you can't act like removing it is a good thing. It's always funny watching the sub 300whp group trying every little justification for an extra few horsepower.
@@carstennobody7047 this engine has 0 cam overlap. Most engines, built in last 30 years have no overlap. This time I was focusing on back pressure only. I'll do performance gains testing another time.
Finally someone who actually tests it. Instead of simulations and animations
But where is ACTUAL 0-100km test?
@@stefanvalchev8066I don’t think the goal of the experiment is to showcase speed or power
Simulations and animations are more accurate though... this really isn't accurately modelling anything.
@@graham7513 He’s literally showing pressure differences with actual gauges in the video. I never said simulations weren’t accurate, it’s just nice to see a real world test done
@user-sj2zy3rp2p Yeah… I know that. All I’m saying it’s nice to see a way of doing it that doesn’t involve high end software. Where did I say simulations haven’t contributed to anything? I didn’t say one method is better than another. Of course simulations are better that whatever this guys is doing. Simulations rule everything. No one is expecting precise and accurate measurements using an air hose and some pressure gauges…
I"ve never seen scavenging explained visually like that before. Very interesting stuff!
Primary scavenging occurs in the cylinder and valves at the end if the exhaust stroke and beginning of the intake stroke.
This secondary effect is overrated, though can and does occur, but unless all parameters are the same between differing engines then the effects are largely reduced pumping losses masquerading at primary scavenging. In short people will say anything for money.
It does occur and race cars operating in comparatively narrow power bands exploit the effect effectively.
Agreed.
I used to wonder what that meant as well.
Thanks mate, great work.
I gained 28-29 whp on a Mainline dyno, going from twin 2.5" to twin 3" @ about 16psi - no loss down low.
With sport cats.
I appreciate you sharing your work.👍
I'm glad you like it. I'd love to do much more testing if I had more time.
Thats a great gain!! What car and which mods? Thank you!
@agdwhite5421 BMW E46, M54B30 6cyl, 1.6L twin screw, 16-18psi, E85 fuel, 8k redline but taken to 8,5rpm regularly.
@@CosmosMBTS What a combo! It must be a monster. Do you keept stock cams?
@agdwhite5421 I used Schrick 272/256 cams.
It made 12psi boost around 2-2.2k rpm.
Ran semi-slicks on the streets to help with traction.
Thanks.
The BEST exhaust back pressure demonstration I've ever seen. THANK YOU for this contribution! This is awesome.
I'm glad you like it.
Thats how tests should be done, thank you!!
Cheers.
This reminds me a lot of the "old youtube" before 2013 and I love it!
amen
So cool, man. Thanks for testing. Presnetation was clear and straight forward. I didn't even have the sound on and I understood perfectly.
Cheers.
Oooh that M52 motor sounded GOOD with the 3' system on it....much more like an M3 😍 Seemed to be visibly quicker as well. Imagine what it could do with decent headers too! This has got me thinking about what to do with the really crappy stock system on my E39...
I wouldn't say the stock exhaust is crappy. It's actually a high quality piece. It's made of stainless steel and fits better than any aftermarket or custom exhaust.
But I can understand why people prefer louder exhaust.
@@tiitsaul9036 I didn't mean crappy in terms of quality - Yes it is well made and one of the few areas of the car immune to rust! But from a sound quality, weight and performance perspective, it is pretty crappy. It adds nothing to the enjoyment factor of the car at all, which is a shame because the engines themselves are great.
For good sound single pipe is the point :)
This person is on a level I can barely comprehend. Outstanding.
These motors sound musical past 5k rpm.
It's not the RPM it's the 3-1 headers. Should hear them on an old slant six or jeep 4.0
@@throttleblipsntwistedgrips1992 this guy is right
watching this after Garage 4AGE video was very enlightening! thanks
Cheers
tiki... your a bloody legend!!! this is in depth lad!!!
Thanks Ken.
I'll visit Brisbane soon. We should catch up.
Interesting facts, ill add some of my subjective opinions...
I could compare stock 328i with open valve all the time, 328i with 2l single pipe stock exh. and 328i with profesionaly made system. it was two cars with bone stock engines, just different exhaust. (1997 euro sedan, stock exhaus) ; (1996 euro coupe at first with 2l exhaust to pass technical inspection and than custom no cat with stock M52B28 stainless steel manifold)
custom made felt rew happy and also pulled stronger in all the rew range, with a 2l it was deffinetly not as rew happy, torgue came in 3500rpm and ended soon .
stock 328i exhaust felt much better than a 2l single pipe, car was pulling much smoother in higher rpm when VANOS kicked.
in europe stock 328i exhaust is a valuable thing to have on the car with original catalitic convertors.
we need more resreach on this topic (y)
Thanks
What you mean, when vanos kicked? It's not vtec. Vanos turns on at ~1800 and turns back of at ~3500. With vanos broken you will have same Max power to the rev limit. Just less flexible car in city.
Nice video! Would be interesting to compare dyno results!
Agreed
The 3 inch exhaust works better at scavenging not so much because of the larger dia but because the cross link in the BMW system is after the 1st restriction that reduces the strength of the pulses from each half of the manifold whereas the 3 inch system merges before any restriction. If you check the BMW system - dia's and lengths they may well have tuned the pipe for front and rear banks to match the resistance by the time they reach the cross link to get the best timed scavenging, certainly that's the case with my 2010 N52 car. ( dia into Cat/1st silencer on rear bank looks smaller?) On the 3" exhaust matching the lengths of the primaries will improve midrange and if possible don't merge untill just before the 1st silencer.
I'm not sure it matters much if restriction is before or after the merge. Either way, restriction is bad for scavenging. Cats in my stock exhaust may be not 100% healthy and starting to plug up.
Yes you're right about one of the secondary pipe is smaller diameter. It's 325i piece. I believe they made longer pipe skinnier and shorter pipe larger in attempt to equalise pulse timing.
Just because the paper blows "in" to the header instead of "out" doesn't mean it's better at scavenging or anything. Scavenging works on reflected pressure waves in the system - so, a pressure wave reflecting "out" of the header will hit the back of exhaust valve and then once the exhaust valve opens there is a vacuum formed BEHIND that pressure wave, which acts to help fill the cylinder and pull exhaust out. This is an interesting comparison, but not sure the basic principles are entirely accurately described here.
There is just a lot more going on in an exhaust when an engine is running than what can be realistically modelled by blowing compressed air into the exhaust.
yea blowing compressed air into the exhaust won't really show the reflection of the system.
however what he showed here is the venturi effect of the system, which is also a style of scavenging, as the air (exhaust gases) coloum passes through the collector, it pulls the air out of the other runners, creating low pressure areas between the other exhaust runners.
This testing is so jank, I love it.
Would love to see these measurements with equal length headers and a long collector of greater than 6 inches (long tube headers)🤓!
Amazing comparison, i have never seen this before, only theory, but no application in the real world.
What a sound.. That's why I'm BMW fan)
Great job no talk lots of visual proof
What an informative video!
God it sounds so good when it breathes!
This is stuff from the 1980's and i freaking love it xD .
also those exhaust flaps just get rid of them if they get stuck shut they can really hurt your engine with excessive heat buildup. especially if you plan to drive enthusiastically
Super
Good work
The hero we all needed
Impressive test work, good job !
Cheers
Great test!
I noticed when I changed exhausts my afr changed alot. I went to a more restrictive exhaust and I’m about 4-5% richer now.
Due to the stock exhaust design, it's hard to measure AF ratio. The merge is after the catalytic converter. I could probe from one of the banks, but couldn't be bothered.
great demo
would be intersting to know if your measurements transitioned into an increase at the MAF, are you on MS41? Its a 328i right?
Yes ms41. I didn't have time to do any data logging. My butt dyno confirmed performance gains. With stock exhaust it doesn't spin in 1st gear. With 3" it lets loose. Also throttle response is much better with 3"(easier to down shift).
a little bit of back pressure is good, helps the engine breathe well and use all the torque it can get. too open means less torque and more hp. i know this with my subaru. but full throttle for long periods with back pressure can cause pressure build in the engine
Is there any scientific proof of your claims?
Btw, at given rpm, more torque means more power.
Amazing job. I never thought N/A engine can gain so much power on higher rpms. As mostly mentioned, there is no power lose because of back pressure. Bigger is better!
I didn't measure power gains. It definitely gained something, but unsure how much.
Bigger is not better. To wide makes the gasses to slow and prevents good scavenging
@tinuse3670 thats only the case for the headers and the first few inches of exhaust
@@thelachsmith81 yep. Merge is around 2" and gradually expands to 3".
@@tinuse3670 as mentioned that only applies to headers and collector. Properly sized header/primary pipes and collector (diameter and lengths, collector length starting point before tuning typically the same length as header pipe length from back of valve) exiting straight out with NO tail pipe is ideal even for everyday shopping/work car, lawn mower ect but very noisy.
The only power loss you will get from a full exhaust system after this is from backpressure impeding flow or bad wave harmonics impacting tuning which can be seperated from the header/collector by a wave termination box at the end of the collector, basically a large empty chamber.
This is incredible!
Great work. This is good.
This is great!!
There are some sensitive pressure instruments from USA, they are called magnehelics....
Yes I've heard of them. I'll buy some if I find one cheap. It's hard to beat the coat of my homemade manometer though :)
@@tiitsaul9036 Yeah i bought 6-7 of them 20 years ago when an online magazine from australia was mesauring Aerodynamics pressure and airbox restriction
Doing Gods work.
it is very nice work
Beautiful vid. Looks like old gold YT. Straight forward. But I guess, you lost torque at low RPMs. Am I right?
Thanks for the comment.
I didn't measure the power difference, but according to my butt dyno 3" gained some torque throughout the rev range.
Them Civics better watch out now, Ka-Chow!
👏👏👏very interesting, nice work👍
Cheers
fantastic
More than back presure it´s scavening effect, and it´s quite better.
bigger exhaust pipes increase top end rpm power but KILL low end torque, it basically shifts the power band.
Do you have any evidence to support your claims?
@@tiitsaul9036 yes its called a dyno sheet AND its also called cfm air flow dynamics.
@@ACommenterOnCZcams I have yet to see dyno sheet showing torque improvement with smaller exhaust.
@@tiitsaul9036 you should look harder 🤷🏽♂️
@@ACommenterOnCZcams provide me with a link.
Fantastic video 👍🏼
When’s the turbo gonna kick in yo !!!
So a 3 inch y pipe with single resonator and muffler gives ideal backpressure?
My current plan is a y pipe 3" after long tube headers then double resonators ams a muffler.
Should i omit one resonator?
Yes, in my case the 3" exhaust has the least back pressure. At this power level, I could probably get away with 2.5"
I can't advise what you should do. My goal was to reduce weight, add simplicity and add power. It's mostly a track car. I've reinstalled the stock exhaust for driving on street.
Really cool setup
Thank you 👍
Cheers
Excelent video thanks , one question , from where did you do measurements in the exhaust? At the muffler? Regards
Back pressure was measured from exhaust manifold O2 bung.
@@tiitsaul9036 thank you .
Very noice😊 good stuff man!
Cheers
Question ....what do you think of having a system that goes from 2" into a resonator out into 2" for a few feet then stepping up into 2.5 then into 3"....no muffler out thr back....what do you think the outcome would be ?
Is it for BMW 6 cylinder?
Single 2" is smaller than factory twin system for m52b28. It would probably restrict some power.
@@tiitsaul9036 oh sorry its for a smaller 4 cylinder....for a 6 it would be keeping the stock piping resonator then about 2 feet of a step up in size and step up again out the back. I have a sound clip on my page but I haven't done the 3" step up yet just up to the 2.5 as it's a stock single cam.
@@christopherdaniel2747 for a 4 banger single cam a 2" would be plenty. I wouldn't expect any power gains from stepping up in size. But if you like the way it sounds than keep it.
Thanks for this
Cheers
Interesting,
But what the point of testing scavenging comparison seen that the stock system with separate pipes was not designed to do that ?
The two pipes run along separated till the end ,there is no possible vacuum created unless you dump flow in a bigger section to create scavenging.
The modified one is coupling both pipes cose to the manifold and dumping in a bigger section,and straight into an even bigger volume.
You create a sudden loss of gases speed and increase its pressure in the system,so you will have a big scavenging.
The MAF flow would have been great to see,it's the most important.
Did you see some difference on air/fuel ratio ?
Stock exhaust is not twin pipe all the way through. It merges in the middle.
AF ratio was not tested with stock exhaust. Pipes merge after catalytic converter. I could've installed O2 sensor in one of the banks, but couldn't be bothered.
I'll do some data logs to learn more about performance gains when I find some spare time.
@@tiitsaul9036
If the pipes merge in a cross flow with same diameter pipes ,it will do nothing on scavenging relative to pressure effect,only on firing order pulses effet/ or a rpm range depending how far is the cross flow.
You need what you did to gain scavenging : a pipe dumping in a bigger one to gain gas pressure ,so vacuum can build up upstream.
It's Bernoulli effect if you don't know yet : for a same flow you increase pressure by increasing section area and reduce flwo speed.
By reducing section area,you reduce pressure but increase flow speed.
It's supposed to work on imcompressible fluids,but it works on gases too.
Pretty neat testing,it's interesting to see.
@@michaelovitch mostly true, except, gas isn't flowing, but pulsating in exhaust.
@@tiitsaul9036 Yes,maybe at idle lol a bit less at higher rpm they tend to form a stream.
@@michaelovitch Exhaust gas is pulsating. Each pulsation is followed by low pressure. Effective rpm range can be tuned with the merge distance from the exhaust valves.
Very nice video!
Turbo Sound 🤤
So straight pipe for the win
Always.
Meanwhile, knowledgeless mappers keeps saying that exhaust flow doesn't matter for remaps
Thank you for this nice and informative video! Will this also work on stock M20B25 E30 with aftermaket headers?
It sure works with your setup. You might need to add a bung in the merge pipe for the probe. Give it a try and report back. I'd be interested in seeing the results.
Good job
Backpressure is only needed on 2-Strokes
Good job :)
what about 5sfe when you heabily port those heads am i going to have to do this :( i was hoping max I would have to use is 2.75
I don't think mine needs 3". I used it because I had some 3" bits available.
2.5" is plenty big for 5sfe.
nice :)
Scavenging is not back pressure. Yes scavenging is good because the positive and negative pulse waves will be times for smoother operation. But it's not actually back pressure.
I never said scavenging is back pressure.
Stock exhaust appears to have intact cats so no wonder the scavenging test didn't work.
Stop, in the stock muffler there ia a catalytic converter.
In the 3" there is no catalytic converter.
!!
You're not wrong
This date is very important !.
Mabby my question is stupid but why single pipe not using two like original ?
Why would I use double pipe? Double the work for no benefit.
The exhaust gases escape faster with the 3'' one
Ghetto testing FTW!! 👊
That's how it's done 👍
what affect would no exhaust at all have? just straight dump from the exhaust manifold on a m54 with cats still in
Based on some dyno tests I've seen, I'd expect to lose low/medium torque.
Good tests mate, interesting stuff
Cheers
Looks like it's header time
Id love to build a set of headers if I had more free time.
very interesting, do you not have 328i tubular headers to test against the cast ones?
I didn't feel like removing 328i manifolds and used 325i manifolds for testing.
@@tiitsaul9036 haha fair enough, it can be a pain xD
does anyone know what would be the implications of leaving the valve always open all the time, because i'm thinking of doing it to my car.
Flap open would increase the noise levels.
What is the device you made to measure pressure? Is it a home made manometer
Yes it's just a clear tube filled with coloured water. Very primitive, but sensitive and effective.
I used this device to measure the air filter restriction as well.
So, that back pressure is good or bad for the engine? Having backpressure it helps or restricts the flow&power?
Less backup pressure = better efficiency and more power.
@@tiitsaul9036 Nm attacked below ,low and medium range work engine ? txh
0:55 actually it doesn't, and that's the problem
Where did u measure pressure? Dp or end of exhaust?
Pressure probe was in exhaust manifold, replacing O2 sensor. All configurations were probed from the same location.
@@tiitsaul9036 thats great result
I would do a resonated / chambered resonator close to thr header to help with the low rpms and the drone up top I'll get the flow and thr best of both worlds
Low rpm performance is not an issue. This car is meant for weekend race track duty.
Main considerations for my exhaust are weight, simplicity and top end power.
@@tiitsaul9036with that said, it's not only top end that is required for track duty, mid and top end are both heavily utilised. Based on my track car usage I would say mid range is 100% utilised more of the time, despite every gear change being made at or close to the limiter.
In my case, I went from the OEM 328i to a single 3" decat exhaust after the downpipe and my butt dyno tells me that we lost torque and possibly top end (the Ecu has not been remapped with the decat exhaust). On home turf, lap times are 0.5s slower on average between a pool of 3 drivers and many laps before and a fair amount after.
The weight loss and the cat loss however are definite pluses. Once hot cams are installed and the Ecu mapped to suit, I expect the numbers will change for the better. Time will tell.
I do appreciate the content, that so for sharing. OEM Exhaust M52 manifold is crap, but better than M50. S50B3x is the best but very expensive in RHD drive now for a +10HP gain.
@@georgipetrov2203 yes, NA horse powers are expensive.
Judging engine performance by lap time is tricky. Weather conditions affect lap time quite a bit each day. At my local track, typically we are faster in the morning at least 0.5 sec.
@@tiitsaul9036 Sure, I agree with you on all fronts, but our local is where we have all done 3 digits laps, so we have all conditions covered and various setups throughout the evolution of the machine. In essence it's our baseline for what the outcome is when we do changes, but I do get what you meant about variables being a significant factor too and only the dyno will prove one or the other.
@@georgipetrov2203 did you notice any improvement downshifting with custom exhaust?
Mine free revs quicker with 3" exhaust which makes downshift quicker/easier. I was quite surprised.
Can you tell more about silencers?
Just generic straight through mufflers.
did you notice an increase in power?
I didn't measure power or performance. But I did notice a difference. I had more traction issues with 3" exhaust and throttle response was a lot better (quicker rev match when down shifting).
@@tiitsaul9036 thanks for your reply, and thanks for this experiment! :)
@@tiitsaul9036 If you had more traction issues, then you must buy the best tires that you can pay.
what are the modifications ?
I have a video describing all modifications some years old.
Basically, 240 degree cams, high CR and M50 intake. Some other minor mods as well.
But cat converters where fine? Oil consumption get's them blocked, missfire get's them melted :v
I seriously diagnosed those problems in not tuned cars with exactly those readings
Good question. I don't know. I'd have to cut cats open to verify.
Is the intention of this video to show less is more? I'd argue scavenging effect of the exhaust is not measured with constant flow, rather with pulsating flow. As the OEM exhaust flow pushes against the closed valve on another cylinder, it actually creates a low pressure zone on its way back. This will work to increase the torque and driveability on lower rpm's. Put a low backpressure exhaust and all you do is ruin the low end performance with some added gain in the high end. Useful if you're doing track days mostly.
Please present some evidence to support your claims. I've heard this myth before, but never seen any evidence of back pressure improves low speed torque and drivability.
Check out this video. Please note, increase in back pressure killed power the entire rev range. Only 6psi at 5krpm killed 20% power.
czcams.com/video/V2Wv5-ZTOjM/video.html
@@tiitsaul9036 back pressure NEVER improves torque or power - but there is a lot more going on in an exhaust than what can be shown by the testing in this video. FWIW I am not claiming a drop in power with a larger exhaust, BUT, to claim that these testings show "scavenging" is imo, not correct.
this is absoluty true....Valkman761
Can you do cold intake to
It has cold air intake from factory. Every BMW since 90s have an excellent air intake that's hard to beat.
Did it affect AFR Readings?
I don't know. Stock exhaust merge is after cats. I could've tapped in to one of the banks, but it's too much hassle.
scavenging is not happening with air,but with sound pulse.
What creates the exhaust sound? Pulsating air.
@@tiitsaul9036 the sound that you can hear at the end it is not the sound that creates scavenging.
3in pipe is for 700km XD
That thing hauls ass
I don't understand what I'm watching here! I've always heard about back pressure but never actually understood what it is.
Cylinder pressure is much higher than atmospheric pressure. When the exhaust valve opens, high pressure air from cylinder evacuates through exhaust to atmosphere. If exhaust system is restrictive, exhaust gases start building up in the exhaust system and increases pressure inside the exhaust pipe. That extra pressure works against cylinder pressure and hurts power output. I hope this helps.
@@tiitsaul9036 oh! That was a great explanation! Thank you so much! Thumbs up
That engine is not stock either 😂
Engines need backpressure, so you can't act like removing it is a good thing.
It's always funny watching the sub 300whp group trying every little justification for an extra few horsepower.
Yeah right. Those 1000+HP cars on the dragstrip with open headers don't seem to mind lack of back pressure.
If engines needed backpressure then top fuel dragsters would not run open primaries ;)
But 1.8 is better 😂
Now show dynograph because low pressure in exhaust is not that good in NA engine
Elaborate please
Back pressure is bad in any situiation. It a myth that back pressure make power
@@jdmboyscout7947 (unless its a 2 stroke)
The whole idea of a good flowing exhaust is to have as little backpressure as possible without losing gas velocity
@@carstennobody7047 this engine has 0 cam overlap. Most engines, built in last 30 years have no overlap.
This time I was focusing on back pressure only. I'll do performance gains testing another time.
Interesting vid.
What mods are done with that M52B28? M50 manifold, remap etc? Looks to go well.
240 degree cams and 11.6 CR. Stock fuel and ignition map. I've been meaning to tune it, but haven't have time.
Holy fuck...that welding. That's horrific.
If it works it ain't stupid.
@@tiitsaul9036 the dots of "welding" on the hangar will not work very long.
You don't need backpressure, the less the better.
Agreed. I'm yet to see dyno results prove otherwise.