[Amazinjoey]

Originally Posted by IMS-340C

Shouldn't be a debate really, it's a fact dropping timing too much will not produce more power.

I tune cars as a hobby and from my experiencing with B58 dropping timing below 8 degrees @6500 RPM will not add significant power if any.

This, if you need to drop timing and add more boost then there is way to much backpressure in the system or heat!. It's better to reduce the backpressure to get the same power with lower boost. People don't understand much diffrence lowering the backpressure does

[IMS-340C]

The cat makes the biggest difference I've seen many stock + downpipe compared to MPPSK + downpipe, not much of a difference.

Originally Posted by Amazinjoey

This, if you need to drop timing and add more boost then there is way to much backpressure in the system or heat!. It's better to reduce the backpressure to get the same power with lower boost. People don't understand much diffrence lowering the backpressure does

[weehe126]

Originally Posted by Amazinjoey

This, if you need to drop timing and add more boost then there is way to much backpressure in the system or heat!. It's better to reduce the backpressure to get the same power with lower boost. People don't understand much diffrence lowering the backpressure does

He has a catless dp and a full 3" exhaust with just a muffler. Why do you think he has back pressure issues? Do you want him to run a dump tube through the hood instead?

There are so many things the tuner could be changing that would mess with timing.

[weehe126]

Originally Posted by talontdone

https://www.bootmod3.net/log?id=61f1...90c60c0769c69a
https://www.bootmod3.net/log?id=61f1...90c609919ff44e

I think part of the problem is when I floor it, it takes a while for the throttle position sensor to show close to 100% ... here are two newer logs, I'm still not thrilled with the 30 psi and high load at ~3700 rpms, my tuner prefers to run higher boost and lower timing than others suggest like GLEM ... I will regap my plugs down to 0.020" as I think running 25 to 30 psi is too much for 0.022" .... my E85 estimated torque and MAF flow figures are not any higher than my 93 octane / 98 ron fuel tune right now ... but the car feels faster for sure.

Any suggestions?

I would go the opposite direction, put new plugs in and leave them at stock gap. This is a B58 not a N54, the coils are much better.

[Bdub440i]

What plugs are you running? My e30 tune was short on timing until i switchee back to the champion 9425. The ngk 94201 were not happy.

[Amazinjoey]

Originally Posted by weehe126

He has a catless dp and a full 3" exhaust with just a muffler. Why do you think he has back pressure issues? Do you want him to run a dump tube through the hood instead?

There are so many things the tuner could be changing that would mess with timing.

Yeah 100% sure this is backpressure issue, he should be able to run higher timing. So if it's not exhaust then it is probably his Exhaust manifold that is choking

I can take my friend car for example how opened my eyes to this, He is not running a BMW but a Saab 9-5, 4 cylinder with a TD04HL-19T. Which is a smaller turbo than what is on his B58.

He was doing 350hp with 1.7bar, running 3 inch catless to 2.5 inch exhaust, and the backpressure was a b*tch , but then he went 3.5 inch downpipe to 3 inch he could get the same power with 1.3 bar and higher timing

Now he is doing 450-500 HP with 1.3 bar and the same turbo, just by minimizing the Backpressure and optimizing the flow.

Here is video of him explaining, shitty audio but a really good explaination :

Acceleration video:

So Imaging if a 4 cyl car with a smaller turbo has this problem and needs a bigger exhaust then how will not 6 cyl with bigger turbo not need the same

[weehe126]

Originally Posted by Amazinjoey

Yeah 100% sure this is backpressure issue, he should be able to run higher timing. So if it's not exhaust then it is probably his Exhaust manifold that is choking

I can take my friend car for example how opened my eyes to this, He is not running a BMW but a Saab 9-5, 4 cylinder with a TD04HL-19T. Which is a smaller turbo than what is on his B58.

He was doing 350hp with 1.7bar, running 3 inch catless to 2.5 inch exhaust, and the backpressure was a b*tch , but then he went 3.5 inch downpipe to 3 inch he could get the same power with 1.3 bar and higher timing

Now he is doing 450-500 HP with 1.3 bar and the same turbo, just by minimizing the Backpressure and optimizing the flow.

Here is video of him explaining, shitty audio but a really good explaination :

Acceleration video:

So Imaging if a 4 cyl car with a smaller turbo has this problem and needs a bigger exhaust then how will not 6 cyl with bigger turbo not need the same

Right, only answer is back pressure. Couldn't possibly be any other normal issue for these cars. I means plugs, coils, injectors, clearly no possible issue with those normal wear items when trying to use 40% more fuel.

[IMS-340C]

My advice to you never compare totally different cars with different brands from different eras, if your friend's car has a restrictive exhaust doesn't mean all the cars in the world has a restrictive exhaust.

Originally Posted by Amazinjoey

Yeah 100% sure this is backpressure issue, he should be able to run higher timing. So if it's not exhaust then it is probably his Exhaust manifold that is choking

I can take my friend car for example how opened my eyes to this, He is not running a BMW but a Saab 9-5, 4 cylinder with a TD04HL-19T. Which is a smaller turbo than what is on his B58.

He was doing 350hp with 1.7bar, running 3 inch catless to 2.5 inch exhaust, and the backpressure was a b*tch , but then he went 3.5 inch downpipe to 3 inch he could get the same power with 1.3 bar and higher timing

Now he is doing 450-500 HP with 1.3 bar and the same turbo, just by minimizing the Backpressure and optimizing the flow.

So Imaging if a 4 cyl car with a smaller turbo has this problem and needs a bigger exhaust then how will not 6 cyl with bigger turbo not need the same

[talontdone]

Originally Posted by Bdub440i

What plugs are you running? My e30 tune was short on timing until i switchee back to the champion 9425. The ngk 94201 were not happy.

I'm running the NGK's ... so far so good. Not getting any misfires or anything like that.

[talontdone]

Originally Posted by Amazinjoey

Yeah 100% sure this is backpressure issue, he should be able to run higher timing. So if it's not exhaust then it is probably his Exhaust manifold that is choking

I can take my friend car for example how opened my eyes to this, He is not running a BMW but a Saab 9-5, 4 cylinder with a TD04HL-19T. Which is a smaller turbo than what is on his B58.

He was doing 350hp with 1.7bar, running 3 inch catless to 2.5 inch exhaust, and the backpressure was a b*tch , but then he went 3.5 inch downpipe to 3 inch he could get the same power with 1.3 bar and higher timing

Now he is doing 450-500 HP with 1.3 bar and the same turbo, just by minimizing the Backpressure and optimizing the flow.

Here is video of him explaining, shitty audio but a really good explaination :

Acceleration video:

So Imaging if a 4 cyl car with a smaller turbo has this problem and needs a bigger exhaust then how will not 6 cyl with bigger turbo not need the same

This is a fantastic post. Great videos too.

I used to have a 97 Eagle Talon TSI AWD back in high school that was a 2.0L 4 cylinder turbo and made 470 whp on a 3" inch exhaust .... it was a massive 60-1 turbo that flowed quite a bit of air up top (didn't hit full boost till about 4.5K rpms thx to the limited displacement ... but was still fun!).

I really don't know enough about required back pressure based on the amount of airflow produced by a turbo to opine with any level of credibility, but I have not yet read a single post on our cars that suggest our exhausts are bottlenecks... who knows! Not sure what size our cat back exhausts are, but aftermarket downpipes seem to be ~4 inches, which is absolutely massive. Think of the percentage difference between 3 and 4 inches for example ... its 33.3%. Meaningful delta.

That said, my car was like 340 whp stock ... it made 510 whp on 93 ... and im now dialing in on E85 with 3-5 PSI more boost, and almost 5 degrees more on timing ... so its a LOT of air ... maybe you are onto something here ....

What do you think guys????

[Wires]

Originally Posted by IMS-340C

My advice to you never compare totally different cars with different brands from different eras, if your friend's car has a restrictive exhaust doesn't mean all the cars in the world has a restrictive exhaust.

Agreed, and to carry that forward, don't assume your car will match anyone else's either. If you think of NASCAR racing, every engine is balanced and blueprinted. Basically clones of each other that perform identically.

On a production car, this is not true. They will all have slightly difference compression, slightly different flows, slightly different timing, etc. All of that impacts the power delivery.

The more cylinders the engine has the more this starts to get averaged out, and is very apparently when you are down in the 1-2 cylinder range.

And I wouldn't compare Saab to BMW as an apples to apples. There has been dyno tests (many of them) that shows upgrading our exhaust is mainly for sound, with very little gains (IE low change in backpressure).

[Bdub440i]

Originally Posted by talontdone

I'm running the NGK's ... so far so good. Not getting any misfires or anything like that.

I didn't have misfires either, just timing corrections like you.

[abbike18]

Originally Posted by talontdone

Think of the percentage difference between 3 and 4 inches for example ... its 33.3%. Meaningful delta.

warning - nerd alert.

Its actually a 77.7% difference. It's all about cross sections area, which is pi*r^2.

X-sectional area of a 3" pipe = 7 sq in
X-sectional area of a 4" pipe = 12.6 sq in

[Amazinjoey]

Originally Posted by talontdone

This is a fantastic post. Great videos too.

I used to have a 97 Eagle Talon TSI AWD back in high school that was a 2.0L 4 cylinder turbo and made 470 whp on a 3" inch exhaust .... it was a massive 60-1 turbo that flowed quite a bit of air up top (didn't hit full boost till about 4.5K rpms thx to the limited displacement ... but was still fun!).

I really don't know enough about required back pressure based on the amount of airflow produced by a turbo to opine with any level of credibility, but I have not yet read a single post on our cars that suggest our exhausts are bottlenecks... who knows! Not sure what size our cat back exhausts are, but aftermarket downpipes seem to be ~4 inches, which is absolutely massive. Think of the percentage difference between 3 and 4 inches for example ... its 33.3%. Meaningful delta.

That said, my car was like 340 whp stock ... it made 510 whp on 93 ... and im now dialing in on E85 with 3-5 PSI more boost, and almost 5 degrees more on timing ... so its a LOT of air ... maybe you are onto something here ....

What do you think guys????

Sorry Forum notification here sucks

Here is a more detailed explaintion of backpressure, in the forum there is also some simulation showing backpressure and flow
Source:
https://www.trionictuning.com/forum/...p?f=46&t=11945

Understanding Backpressure and importance of exhaust size


Gonna start with saying.. Yes, your exhaust might function for the power you have, but do you really know how much backpressure you have or know if it is even near optimal? Something worth looking into if doing max effort setups.

Understanding backpressure and importance of exhaust dimensions, this is a very heated subject across all brands and many knows a very very little on the subject, even many professional tuners which is quite worrying.

Most might think their exhaust system flows enough, like these aftermarket 3'' and 3'' to 2.5'' systems. However it is far more complicated than that and most dont even suit the stage 5-6 tunes in reality without tuners having to lower torque peak a whole bunch to lower backpressures and reduce risk of choke out. There is this big myth trending worldwide in the car scene that 3'' works for everything and flows enough for 700hp or even as high as 1000hp which makes no sense.

Since mid 2019 until now I have probably done a well over 400 hours worth of CFD research on the subject established from a tone of physics calculations along with a few real-world scenario tests to get a perfect template to predict flow, velocity and backpressures for various setups. What I found most might find it very surprising and everything is leaning towards the same conclusion, bigger is always better. Anything behind the turbine is just waste gasses to no use.



Real-world scenario backpressure testing


The car: 2008 Saab 9-5 2.3t Biopower wagon.
The exhaust side setup consisted of: 3'' downpipe with race cat to 2.5'' cat back exhaust, running tubular manifold and ported TD04HL-15T 6cm2 turbine housing. I also fitted an 60mm wastegate to the downpipe on the first bend in the line of flow so it could work its magic, ran it as an boost activated exhaust cutout valve which opens at 0.7 bars of MAP.

Power figures were into the 350hp region and plenty of torque. The fuel that were used was E85.

I bought a backpressure testing kit which was based on using O2 bungs and there was this O2 plug with a threaded hole for a brake line and fitting to go in. In the bottom of it is there an calibrated hole(1.5mm) that the pressure can pass through and is small enough so it cancel out the cylinder pulses. EMAP and exhaust system backpressure were measured. I welded on a O2 bung on the manifold collector in such manner that it is not in the direct line of flow of any of the cylinders for highest accuracy hooked it to an analog 3 bar boost gauge. The exhaust system I took the existing 1st O2 sensor bung on the downpipe and ran the car in open loop during all tests. All pics attached in the end of the post.


First run measuring in the downpipe with the exhaust cutout closed it peaked at 0.5 bar of backpressure.

Second run measuring in the downpipe with the exhaust cutout open it peaked at 0.2 bar of backpressure.

Here is the interesting part on how it affects the EMAP(Exhaust manifold absolute pressure).

First run measuring in the manifold collector with exhaust cutout closed on the downpipe it peaked out at 3.3+ bars of EMAP, the 3 bar analog gauge has an mechanical stop at about 3.2-3.3 bar and the pressure continued to build past that for a little while so made the assumption of it atleast reaching 3.40bar of EMAP.

Second run measuring in the manifold collector with exhaust cutout open on the downpipe it peaked at 2.6 bars of EMAP.

The difference in EMAP by removing 0.25-0.30 bar backpressure post-turbine makes for an 0.8 bar difference in EMAP which is a quite drastic change.

Video of the gauges while testing here:

You might now ask yourself how the hell could the EMAP differ that much?! Well this is due to pressure ratio. The turbine and turbine housing works through pressure ratio in order to be able to get turbine drive, in other words an pressure release for the turbine to be able to spin/accelerate to those extreme RPMs and be able to have enough energy for the compressor side to draw in air and compress.
So this means if you have the scenario of a pressure ratio where it is 3.0:1, the pressure from the downpipe will triple into the EMAP automatically in order to overcome the restriction of the exhaust system. Also take note the more the wastegate flap is closed for example with an stiffer wastegate spring(or running excessive pwm% on boost controller without gaining anything) the more the pressure ratio while make itself known with backpressure so finding the correct balance with wastegate spring is essential especially on these small turbos to make them flow optimal.

You now see that slightest elevated pressure present in the downpipe can have drastic changes on the EMAP and the EMAP affect the overall engine flow a whole bunch, will come to that in a bit.

After all this my car felt so much more alive on the top end like it just wanted to go, before it was like hitting a brick wall and it would just stop accelerate even tho the airmass was almost the same. What's funny was that it was even noticable in the acceleration times. However my intake side of the turbo was not up to spec during this so didnt see any major increase in airmass. But I have since mounting that cutout been able to push it into 373hp on the hubs with a basic Saab OE 15T with cast wheel and 12 blade turbine combined with ported OE exhaust manifold, because it is basically free flowing and only needing to boost 1.49 bar at the most with this close to optimal ignition. The screampipe I previously had on the 60mm cutout during this test I removed and now I have no backpressure present at all in the downpipe so might have dropped the EMAP down to barely 2 bars now even on OE manifold.

Calculating the cross-section area of my exhaust and combined with that 60mm wastegate as cutout valve and taking into account of the pressure drop that early, my 3'' to 2.5'' now flows better than any regular 3''. CFDs were made on this aswell and it truly adds an whole new dimension of flow, more like in to the region of a slightly restrictive 3.5''.



How it affects the engine and turbos performance


So how does this backpressure and EMAP affect the engine and turbos performance?
Lets start with the turbine while keeping backpressure present in the exhaust system.

What happens is that you are working against the pressure ratio in the turbine and turbine housing from being able to function as it should so you decrease the drive of the turbine, basically loosing turbine efficiency as it is harder to make that pressure release. The exhaust manifold flow decreases due to velocity cannot be maintained so ending up choking out that's why you can see certain setups starting loose boost. But also this is something that can occur due to too high entry velocity aswell, because the energy transfer doesnt function. The exhaust gasses escapes over the turbine blades faster than what the energy can be transfered. Sometimes it is choking, sometimes it is too high velocity and sometimes it is an combination of both things happening at the same time. Backpressure mainly halts overall flow and velocity, the gasses take the fastest way out of least resistance like out the wastegate and ramming it open the flap on internal wastegate applications or escaping the turbine wheel too fast with pressure being too high closest to the blades and the inner turbine wheel core.

This excessive backpressure around the turbine does also increase the thrust bearing wear by a lot on many journal bearing turbos. The reason why so many TD04HL that has been pushed very hard end up with a tone of axial shaft play but the radial play is still just fine.

Now the EMAP(exhaust manifold absolute pressure) the higher the pressure and dependant on exhaust cam duration when the exhaust valve opens, just a little or a lot of pressure escapes in to the cylinder bore and chamber. The longer the duration of the camshaft the more pressure will get in and the pressure difference between bore and exhaust manifold will level out making the engine flow horrible if a lot of backpressure and high EMAP is present. Like if you would run a obnoxiously large exhaust cam like 300 degree duration you can end up almost having 1:1 pressure between cylinder bore/chamber and exhaust manifold. This is why it is so important in understanding what camshafts for what setup and the balance between exhaust cam and backpressure. Upwards 300 degree duration exhaust cam is rarely ever used on turbo setups even over 1000+hp, because most people end up loosing power.

The point here is if you have higher EMAP from backpressure when it is time to close that exhaust valve again the pressure remaining in the chamber is trapped. This pressure remaining starts immediately work against the new air and fuel trying to enter the chamber as intake valve starts to open. This is what causes us to gain boost pressure as we try to push more and more power on the same turbo. You now see how this can potentially make the power very limited with a lot of backpressure and high EMAP.

But there is more to it, this elevated pressure causes the disturbance of fuel atomization as the intake ports has to be over-sprayed with fuel to get fuel in efficiently against this backpressure leading to less efficient combustion etc. More heat gets trapped within the cylinder aswell which changes the ability of how much ignition timing advance you can run before knock on petrol or on E85 just that the optimal ignition point is lowered because the burn cannot get anymore efficient due to poor fuel atomization and many other factors.

Now you kind of see where this is heading, the compressor on the turbo is kind of self-explanatory of what happens, the whole chain is affected by this. The backpressure acts against the compressor wheels ability to flow and draw in air as you have to raise the boost more for the same work while it is getting hard to even get more airflow out of the compressor wheel. This can also cause the turbo to get heavy compressor surge in some cases.
This is why many get disappointed when their new fancy turbo specified for like 750hp only makes between 600-700hp before boost pressures and choke out starts occurring. Good example is the trend of internal wastegated gen 1 GTX3071/76Rs always choking out around 500-550hp for everyone while running 3'' turbo back(In the region of 0.8-1.1 bar backpressure in the downpipe).



External wastegated setups and exhaust system backpressure


There are many running an external wastegate with screampipe and still using their 3’’ turbo back exhaust system while still going up in power. There are a few complications with this, think of the turbine housing and pressure ratio that was mentioned earlier and how the backpressure affects the EMAP. While running an too small exhaust system you now get all the backpressure directly through the turbine housing and turbine causing it to get that more prenounced multiplication from present pressure ratio. This is much like what happens as mentioned earlier running too stiff wastegate spring/too high boost controller PWM% while not still getting anymore out of it on internal wastegated setup. The pressure on an internal gated housing shares the same outlet which levels out this phenomena a little bit.

I made an quick CFD analysis of this showing how the pressure changes in the exhaust manifold also how the flow and velocities pick up. Can be found in attachments aswell, you may notice the 3’’ lower bend of the downpipe is quite sharp. Left it as it is as I noticed that didnt do much difference as the restrictions were already so high. Like 0.02 bar decrease in the downpipe making a more sweeping bend.

Running an GTX30 turbine size and 700hp worth of flow combined with an 40mm external wastegate with screampipe. I was trying to mimic the og9-3 exhaust routing and during this test EGT was set to 800 degrees C. Only changes that where made was the turbo back exhaust system. 3’’ which causes backpressure vs 4’’ to 3.5’’ which has no backpressure present. Even due to the very design of the beginning 4’’-3.5’’ we get an little act of bernoulli’s principle where actually pressure drops below atmospheric pressure because velocity picks up so much.

What can be noticed is how the velocities picks up as backpressure decreases and something standing out significantly is that the wastegate gains an additional 100m/s worth of velocity meaning it can function properly. One thing we must understand is that wastegates are not meant to flow exhaust mass, they are meant to hold enough pressure to just stabilize turbine drive to get boost pressure. Therefore the theory of running excessive wastegate size to add flow is an poor way to actually add flow as you get very limited results in the end compared to just bump up the turbo back exhaust size.

An example on how much that can be gained. With these CFDs I helped my buddy design an properly flow exhaust system for his 700+hp 2.3L 9-5 build, running 46mm precision wastegate and 4’’ downpipe to 3.5’’. This was combined with an GTX3076R gen 2.
He accidentally put in a little bit too stiff spring in the external wastegate and reached about 1.3bar. Like no mans business during baseboost testing we exceeded 2000mg/c of airmass on E85 with only 1.3bar of boost. That is in to the 600hp region on E85, oh boy that car moved out on baseboost. It was faster than his old 580hp setup with and IRX600 turbo with internal wastegate which he had to boost 2 bars with and had him locked out due to backpressure so boost started dropping with high rpms.



Ignition timing and boost curve how it affects backpressure build up


How you setup your boost curve/power curve has an big effect on the backpressure how you much EMAP you end up building before reaching your RPM limiter.

If you go all out max boost/airmass in the low RPMs you start building up pressure a lot earlier and it continues to build much harder as you reach the top end of the powerband. As we already know by now that will interfere with the ability to get the most power out in the higher RPMs or even cause complete choke out where it just stops making power no matter what you do.

If you have trouble with backpressure you can reduce the early torque peak a bit and induce a slight ramp on the airmass/boost pressure, this will slow down the build up so you peak with a much lower EMAP in the higher RPMs. Can lead to an overall increase in power gain as mid to high RPM experience much less restrictions.

How does ignition have a roll in this? Well ignition timing advance is quite important timing the burn of the combustion to get an as complete burn as possible. If you have too low ignition advance you have an low temperature combustion occurring, but the setback is that you now can continue to burn the fuel as piston tries to push it out the exhaust port. This increases EGT significantly in some cases going out in to the exhaust manifold, with heat comes gas expansion so meaning you are reducing flow as it starts to build the EMAP higher. One more thing that reduces flow and velocity is that the piston doesnt get to push out the full exhaust volume at once, this is why spool up/response out of the turbo and setup gets so hurt by sluggish ignition.

Like running close to MBT/optimal ignition(maximum brake torque) we get an very energetic high temperature combustion which completes the burn much better. We get the full volume exhaust before the piston has pushed the exhaust gasses out the exhaust port and leaves us with much higher velocity/flow. The exhaust gas heat drops aswell reducing the expansion while you still gain more response and less pressure.

I did some testing on my own 15T setup on the daily 9-5 going down in ignition timing to what is more commonly used and then I went closer to the MBT ignition, I saw an difference in up to 0.2-0.3 bar EMAP from just going to better ignition. Also adding to this the MBT ignition makes so much more power that I could even lower the boost/airmass further down in low range and lower midrange and still maintain a good torque peak without causing build up. Ultimately having an very low EMAP peak and backpressure on the top end.
This is how I am able to push so much power with this small turbo and still maintain flow without choke out..




Engine displacement


Engine displacement have an effect on the exhaust sizing, EMAP and backpressure.
Many try to argue when this subject get brought up that the 2.0L 4 cyl engines doesn’t need larger exhaust because of the engine volume, but that is sort of incorrect in terms of 2.0L 4 cyl not needing larger, but correct that the larger engine can cause more build up.

Lets say you have an GTX3076R on a 3 liter engine and the same turbo on a 2 liter engine. Both engines will take the same amount of air to make the same power theoretically. In reality it differs from friction and more moving parts inducing losses etc.

What makes them both different even tho they make the same power with almost the same air is that the initial pressure build up is higher on the larger displacement engine as you pump much more volume with per combustion. Much like having an crazy torque peak with a lot of boost on our small saab engines. This makes the larger engine peak slightly higher in EMAP and backpressure as it chokes things out earlier. However the pressure can be very close to eachother on the top end as the 3 liter engine ends up outflowing the GTX3076R compressor faster meaning that it most likely end up with the EMAP peak building very very slowly towards the top end. While the smaller 2 liter engine is catching up further up in the RPM. This makes the larger engines more sensitive to small exhaust systems because it builds so much faster down low so more of their powerband gets affected by higher backpressure earlier. But as mentioned earlier boost curves and such have an drastic change in the behavior of pressure build up.


Exhaust sizes for optimal flow at different power levels, internal and external wastegate


Here are some guideline for you people who have desire for max efforts and want the backpressure staying at minimal or basically having zero backpressure. Based on the testing I have done from real-world scenario and CFD data, this is mainly for 1.8-2.3L engines. This is with taking the exhaust routing of our Saabs into account as piping length and where the bends are placed affects backpressure significantly.

If you manage to keep the EGTs down on petrol/pump gas you get sometimes a tiny bit more head room here on exhaust system sizing as the exhaust mass produced by E85 is 50.6% larger than petrol/pump gas.

External wastegate with screampipe setups.

340-400hp: 3’’ downpipe to 2.5’’
400-475hp: 3’’
475-550hp: 3.5’’ downpipe to 3’’
550-650hp: 3.5’’
650-750hp: 4’’ downpipe to 3.5’’
750-850hp: 4’’

One thing to address from what has been mentioned earlier here, even tho you have an external wastegate with screampipe drops EMAP and some exhaust mass to the exhaust system. You can still in some cases use larger than mentioned here and benefit from it as flow can still stagnate by poor pressure drop behind turbine outlet due to exhaust pipe routing still allowing for an slight pressure build up. Also as we know from before the full backpressure now goes directly through the turbine housing so even the slightest pressure increase will be able to stagnate flow to an certain degree. Once again external wastegate is only there for one thing and it is pressure control, not for great deals of exhaust mass flow.

Internally wastegated setups.

275-310: 3’’ downpipe to 2.5’’
310-360hp: 3’’
360-450hp: 3.5’’
450-550hp: 4’’ downpipe to 3.5''
550-650hp: 4’’(4.5'' downpipe can even be of use here.)
650+hp: 4.5''

Cross-section area/flow area of each pipe dimension.

Showing how every half inch increases the flow area.

2’’ = 3.14159 in2 / 2026.8282 mm2
2.5’’ = 4.90874 in2 / 3166.9227 mm2
3’’ = 7.06858 in2 / 4560.3651 mm2
3.5’’ = 9.62113 in2 / 6207.1682 mm2
4’’ = 12.56637 in2 / 8107.3193 mm2
4.5’’ = 15.9043 in2 / 10260.8182 mm2
5’’ = 19.63495 in2 / 12667.6843 mm2



Gonna end this post with saying if bottlenecks exists elsewhere in the setup while going up in exhaust size you might not see as much of a big difference, every setup if different and keep in mind on how you build so you dont get bottlenecks.

If anyone wanna see more CFD content just message me.

Incase someone missed while reading, video of the real-world backpressure testing showing the gauges here again:

As mentioned CFDs in attachment show 3'' vs 4''-3.5'' exhaust at 700hp combined with 40mm external wastegate.
Also take note that all CFDs are made with atmospheric pressure present so withdraw 100000 pascal off what's showing. 100000 pascal is 1 bar of pressure.

I hope you guys like this gigantic wall of information!


EDIT:

2020-09-13

I forgot to mention that the filling of the cylinder bore is increased as EMAP is so much lower combined with no exhaust backpressure which make us increase our volumetric efficiency a whole bunch. This means we have an stronger combustion event every cycle, automatically making the engine make more power without having to pump a lot of air through it.

An great example of this is how little air is used in my car when doing its 373hp/570nm at the hubs with an TD04HL-15T turbo. The 15T compressor is rated up to 33lb/min of airflow at 170000rpm while at 1.3 bar of boost(2.3 pressure ratio). My car only used max 29.65lb/min(224 grams/sec) according to the airmass. What I have done by everything mentioned above is that I have moved the turbo in to its happy place in the compressor map due to volumetric efficiency is so greatly increased so the car doesnt have to pump a tone of boost and air to make power. This means that I am still somewhat within the compressor maps lines and not really exceeded the turbos capacity.

I have 3000rpm 1.32(1300mg/c) -> 4000rpm 1.49 bar(1470mg/c) -> 4250rpm 1.49bar(1490mg/c) -> 4500rpm 1.47bar(1480mg/c) -> 4750rpm 1.42bar(1425mg/c) -> 5000rpm 1.32bar(1355mg/c) -> 6000rpm 0.97bar(1150mg/c). Yet still manage to make this incredible power, because really high volumetric efficiency combined with MBT ignition.


I also forgot to mention about ignition timing advance. As we have lowered EGT, increased flow in and out, increased our volumetric efficiency we have completely changed how the engine responds to ignition timing so we are able to run more ignition timing without complication. We do also see that it start to change the location of the MBT ignition as we have more air and fuel per combustion event combined with consistency in the combustion events so even more power can be made. And one thing is for certain.. We all sure like more power I have been able to run a very very good amount of ignition advance due to this very reason even as high as 19.5 degrees of advance past 5500rpm and still havent gone past the point of power dropping out due to over-advanced ignition timing.

[talontdone]

Originally Posted by Bdub440i

I didn't have misfires either, just timing corrections like you.

I spoke too soon ... latest revision and getting timing pull and car is completely cutting out at 6K rpms (not sure if its misfire or fuel cut). Have been advised to get new plugs and gap down to "0.020 .... sad part is I just put new plugs in maybe 4K kms ago (~3K miles) ... this E85 thing is getting frustrating.

[weehe126]

Originally Posted by talontdone

I spoke too soon ... latest revision and getting timing pull and car is completely cutting out at 6K rpms (not sure if its misfire or fuel cut). Have been advised to get new plugs and gap down to "0.020 .... sad part is I just put new plugs in maybe 4K kms ago (~3K miles) ... this E85 thing is getting frustrating.

Try not gapping them down first. Also make sure you aren't buying counterfeit plugs.

[talontdone]

Originally Posted by weehe126

Try not gapping them down first. Also make sure you aren't buying counterfeit plugs.

So you're saying buy new NGK's and keep them at "0.022 ? I suppose I could do that. I just put NGK's in a few month ago and it's such a pain in the ass for me to gap cyl 1 and cyl 6. Ughhh!

I really hope I'm not getting counterfeit plugs ... I get them from an extremely reputable BMW performance shop here in Calgary.

[G.Newt]

Originally Posted by talontdone

So you're saying buy new NGK's and keep them at "0.022 ? I suppose I could do that. I just put NGK's in a few month ago and it's such a pain in the ass for me to gap cyl 1 and cyl 6. Ughhh!

I really hope I'm not getting counterfeit plugs ... I get them from an extremely reputable BMW performance shop here in Calgary.

Everyone in B58 Discussion group on FB told me to switch to Champions and run stock gap. Replaced my 6 month old NGK's with Champions since I got a DS2 put in at the same time. Stock gap has a much smoother idle than my NGK's at 0.022". I run Champion at 0.030"

[weehe126]

Originally Posted by talontdone

So you're saying buy new NGK's and keep them at "0.022 ? I suppose I could do that. I just put NGK's in a few month ago and it's such a pain in the ass for me to gap cyl 1 and cyl 6. Ughhh!

I really hope I'm not getting counterfeit plugs ... I get them from an extremely reputable BMW performance shop here in Calgary.

The stock gap is closer to 0.032". Was just pointing out the chance for the counterfeit plugs.

It's funny that people are saying to go with Champion plugs when they were stock and everyone had issues with them. Not even a year ago everyone was switching to NGKs because of it.

[talontdone]

Originally Posted by weehe126

The stock gap is closer to 0.032". Was just pointing out the chance for the counterfeit plugs.

It's funny that people are saying to go with Champion plugs when they were stock and everyone had issues with them. Not even a year ago everyone was switching to NGKs because of it.

Absolutely agree with you on both points. I just swapped in some new NGKs at "0.020 gap and this is a completely different animal. Runs smooth, no more misfires, and literally pulls like a raped ape. I also replaced my stock charge pipe with a VRSF cp. What a bitch to install ... i have a bms wmi kit with a spacer for the dual nozzles pre throttle body and so the cp wouldnt fit ... had to take a saw to it haha.I've been on borrowed time with the stock cp. Hitting the dyno next Wednesday.... my guess is 610 to 630 whp.

[340TBD]

Originally Posted by IMS-340C

Not doubting your tuner but I find it strange that he prefers to run high boost low timing as their is absolutely no benefit by doing so, but the downside is risking knock, more wear on the turbo and higher fuel consumption.

Normally higher boost lower timing is safer, that is why tuners choose that path out of the others you can use.