Do any of you guys have emap graphs / numbers verse rpm you are willing to share? Would need the associated WG spring pressure and likely need WG dome pressure also? Curves when running just wastegate spring would provide the cleanest, easiest to understand data. I'm curious as I don't have an EMAP sensor and based on MAP readings I think I'm seeing EMAP grow rapidly beyond MAP near 5200 rpm then fall more in line with it by 6500 rpm and beyond.

 

You are likely seeing peak VE and exhaust pulse energy combined with higher turbine/compressor efficiency throughthat flow range, when averaged/smoothed pressure will almost certainly be more at 6500rpm due to higher flow.

Fit an EMAP sensor, if it's just for diagnostics, even an old mechanical guage on a long line.


Edit: assuming VE/Fuel delivery is higher in that area, if lower I'd suggest your ignition is either retarded or you are having misfires and ignition on exhaust stroke causing increased charge carry over on overlap.

 

what is your setup wrt turbo, manifold, porting, intake, exhaust, etc (all the things that will influence the end result)?
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that's not possible. EMAP doesn't work that way.

 

13B large ports, Stock / Excessive Intake manifold, Coleman exhaust, 9180 turbo, 3 inch down pipe/exhaust to muffler, Tial V60 Wastegate with open dump. 9 lb spring in WG currently, have options for 6 and 15. Have used 15 in the past with similar results. Haltech 2500.

No EMAP port on exhaust manifold so no current option for setting up even a simple sensor. Haltech had a firmware bug they recently released a fix for so I'm reworking
the open loop boost control map as that is recommended as being a base for closed loop. I'm controlling boost by gear. The general WG duty cycle curve is high to help the tiny bit to get things started then down to is zero 4500 to 5000, then ramp up, slowly at first, then quickly in lower gears.

An example; last nights 1st gear pull, 3K to 6.5K. By 5K, DC is zero, MAP is 10, by 5750, DC was 18, MAP 17, by 6200, DC was 64, MAP 23, by 6500 DC was 78, MAP 27, then downhill from there as MAP dropped and the reverse spiral of dropping map and fuel leads to further drop in rpm / map. These DC values have been creeping up as I test changes. In the past, when using buggy Haltech firmware revisions, I have cases where 100 WG DC would not hold boost so I'm concerned I may be heading back to that situation. Tonight's test has the above values reaching 80% and 100% and 6250 / 6500 rpm respectively.

I was curious about EMAP curves as various examples I've seen would indicate they go up with MAP times some multiplier. Seen generalizations saying the good EMAP don't go beyond 1.3 X MAP but some go much higher. Once EMAP is past SPRING then MAP pressure must be added to keep WG valve closed. If EMAP goes past SPRING + MAP then the WG valve cannot be kept closed without adding additional pressure to WG dome such as CO2 based control or going to an electronic WG. Is this understanding incorrect?

 

you are overthinking it, you're also not considering the turbo. you just need to measure it. if you like start with the Post Turbo pressure, as you actually want to know that too

here is Mazda's chart, its stock port vs full peripheral.

 

^^that’s not really relative to this situation

am assuming 1.05 A/R turbine housing, but what muffler system?

did you try disconnecting the muffler just to see if it still happens the same way?
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Let me show some data in a graph from a piston engine (twin turbo with stock hardware, as measured on an engine dyno).




You can see the relationship between all the pressure drops in the system here. The turbine inlet pressure are by far the highest. This is p3 in a turbine map. Then there's a big drop after the inlet pressure and before the cat (basically, post turbine pressure) on each bank, which roughly corresponds to p4. Then there's another drop after the cat, then a way bigger one as it goes through the exhaust sytem and is measured right before main muffler (full exhaust system installed in the engine dyno cell).

On the intake side, there's an air drop at the airbox (after air filter), then another big drop before the compressor inlet (p1 on a compressor map), then the boost measured at the turbo is p2 on a compressor map (not shown here). You've got a pressure drop at the intercooler and another one as you get into the manifold.

Those are the fundamental relationships. The bigger your turbine hotside, the lower your turbine inlet pressure will be (larger A/R) and lower backpressure. You'll also make less boost at low rpm. By that I mean... if I take a .82 A/R hotside on the same turbo, and floor it in 5th gear (or on a loading dyno) at 2000rpm, I will make more boost than if I floor it in 5th gear on a > 1.0 A/R hotside. I'll also have higher turbine inlet pressure at high rpm with a smaller A/R. That's the best way to explain the relationship. It's a fundamental thing that characterizes the steady state performance of the system. It's not the same as say, switching to a ball bearing cartridge. That reduces inertia and transient response but it doesn't change the backpressure or turbine power at low rpm.

The stock twins on an FD specifically worked on that principal. To relieve the backpressure at higher rpm, the exhaust A/R effectively increased by spooling two turbos (similar on the Quick SPool Valves and the original 87-88 Rx-7 turbo hotside with the switching actuator).

Naturally at higher compressor speeds you will have higher compressor outlet pressure (boost) and more turbine inlet pressure. That's just how a turbo works. The ratio between intake manifold pressure and turbine inlet pressure is kind of a weird internet thing that people argue about.

 

The graph shows the basically exponential relationship between exhaust outlet pressure and rpm, but it's not for a turbo engine. So it's relevant in a general sense. Mean effective pressure is just another way of saying torque. It doesn't necessarily correlate to intake manifold pressure.

 

yep, on a turbo engine its pre turbo pressure (P3) vs intake pressure (p2), but the relationship stays the same. the turbo also has the post turbo exhaust (P4), which should be as low as possible

we are a little lucky in that Mazda tells us how much backpressure we can have without loosing power, we just have to bake that into the turbo recipe

 

There is no objective way you could know that without an EMAP sensor for your application.

WG spring pressure means different things to different people....some could run a 7psi WG spring...and never have any issues with EMAP. where as another could be running 32psi and EMAP is what will likely dictate the restriction for boost level.

What boost pressure are you running? What Turbo setup, engine ports etc etc?

Like Raceonly has already stated, you're not going to find any meaningful data unless someone else has an identical setup to your own.

The relationship between EMAP, MAP, and RPM can provide insights into how efficiently the turbocharger is working and how well the engine's air and exhaust flow are balanced. Here's how to interpret the scenario you've described:

1. EMAP vs. MAP: In a well-functioning turbocharged engine, the EMAP will be higher than the MAP because the exhaust gases leaving the engine are at a higher pressure compared to the atmospheric pressure entering the engine. At low RPMs, the EMAP might be slightly higher than the MAP due to less exhaust gas restrictions on the turbine side. Most engines will operate at a 2:1 ratio. For rotaries you want to get as close to 1:1 without ending up with a lag monster, usually not possible unless you run a massive turbo. Too many variables here.
   
2. EMAP Growth and Drop: The rapid growth of EMAP beyond MAP around 5200 RPM could indicate a point where the turbocharger is fully spooled up and producing significant boost pressure. The drop in EMAP to align more closely with MAP at higher RPMs (around 6500 RPM and beyond) could suggest that the engine is reaching its peak efficiency point, where the air and exhaust flows are balanced, resulting in less divergence between EMAP and MAP. Again this is merely a guess as you need an EMAP sensor to confirm what is actually happening.

 

so, you never saw any actual emap data before? Because I saw plenty where emap is lower than imap.

that old PP vs side port data is not relative to what is actually going on here for the specific issue he brought forward (it’s just showing how sensitive pp is to emap and the affect on it’s performance), any more that data on a twin turbo. This is an EFR9180. It should not be running out of boost (and low boost at that) at 6500 rpm unless there are other things causing it.

not wanting to assume things, you did determine no boost leaks and such right?
.

 

I believe arghx graph with the blue and red lines is part of what I'm looking for. It seems to show a similar trend to what I thought may be possible in that MAP can be higher than EMAP (which I'm using as the term for exhaust gas pressure prior to turbo) for a portion of the early rpm range. The MAP appears to stay ahead of EMAP in these lines until about 1600 mbar. The hard right turn of the blue line at about 3100 rpm and 1820 mbar would appear to be boost control happening. At that point the EMAP is just a small amount higher than MAP thus small wastegate pressure + MAP would appear to have the ability to keep a WG closed, if desired. If the wastegate would have been kept closed I would expect MAP to roll over more gently and follow the red line at least for a while, slowly falling more and more behind, such as by 30% in the 1.3X ratio difference case. What I was curious about is if anyone has mapped that type of roll over or MAP / EMAP cross over point up further thru the rpm range such as when using a strong spring and not MAP assist to spring, i.e. spring only?

Another consideration, at a similar roll over point for my situation, I was at 27 MAP with a 9.5 spring, thus the maximum possible push to keep the WG closed was 36.5. If I happened to be lucky enough to have a 1.3X EMAP ratio climb then the WG valve would be have to resist 27 X 1.3 = 35.1 EMAP and thus WG should stay closed as 36.5 > 35.1. If I happen to have 1.35X ratio climb then EMAP and MAP + spring would be equal and anything 1.36X or high it would be impossible to keep WG closed based spring + MAP. Another factor, the WG control had not reached the 100% "push the WG closed" setting yet as duty cycle was 78%, thus the about of push available to help the spring was less than MAP (for example 27 X 0.78 = 21 (the 0.78 is a generic for example value), thus 21 + 9.5 = 30.5 is less than 27 X 1.3 = 35.1)

Based on the curve differentials in the blue/red lines, the ratio number is not constant and thus various ratio numbers tossed around the internet a likely approximations for given situations, such as max torque, max flow, etc. Based on my VE numbers and comparisons to other shared tables for similar (enough) setups it appears max torque and thus max combustion pressure, which would seem to lead to max EMAP, is around 6K rpm. If this is a reasonable approximation then I'm in the rpm range where EMAP value would appear to have the potential to climb most quickly and make boost control more difficult.

Or do you guys think I'm not getting it yet?

 

At higher compressor flow you need more turbine flow to drive it, you can only achieve that by increasing the pressure differential across the turbine.

People generally state intake to exhaust pressure ratio around peak power, it absolutely changes across the entire operating range and as you increase boost.

 

The more common practice of analyzing a system's sizing being adequate is something like this:



Above: Purple Trace is RPM Climbing.
Middle: Green Trace is TPS.
Below: Red Trace is MAP, Orange Trace is EMAP.

There's a crossover point at a given RPM point in which MAP:EMAP Ratio surpasses 1:1 at 6000 RPM. EMAP is below MAP before that point, and EMAP is above MAP after that point. At the PEAK of the 7500 RPM run, the turbo is only 1.124 Ratio of EMAP:MAP, which is very close to ideal for most road-course applications.
Extremely minimal "extra" backpressure in the system and a nice balance of response, cooler exhaust temperature, and overall power.
Some of you will forget that with higher EMAP, our exhaust temperature rises as it's unable to naturally extract from the system as easily. Larger Exhaust = Cooler EGTs, every time. Less Exhaust Restriction ALSO builds more boost AND improves turbo response (to a point).

Something to note is that with changing pressure ratios, the accuracy of the wideband sensor continues to shift and expand tolerance.
I've attached a video explaining this from Evans Performance Academy, as well as my personal tune file with modeled change from a Bosch Motorsports Pre-Turbo Lambda Sensor. Changing this compensation for our wideband sensors is needed to maintain accuracy with larger pressure differentials.





Notice how the accuracy for the wideband moves around at either end of atmospheric pressure...

If I were a betting man, which I am not, I would say something to the effects of you being unhappy with either the configuration's response or unsure if you're finding limitations of it in some form.

Your approach of tracking data is going to be invaluable for making these decisions, but MOST of the time a tuning problem is actually giving you this sort of thought in the back of your head and CAN be resolved or worked around without the setup changing.

I think it pays off dearly to take a step back and start asking the right questions first. What are you truly trying to accomplish here?

 

you just need to measure the actual manifold pressure. you might start with the post turbo pressure, just because you can make a fitting that screws into the o2 sensor bung.
while you could get fancy and have a map sensor and log it, you can also just use a old boost gauge and just see where it is.

it would answer a lot of questions, it did for me.
i think i can unscrew the o2 plug and it will thread in the manifold on my car, but tbd on that.

 

Beyond understanding the basic concepts of exhaust pressure, what is your end goal here? Are you trying to figure out if you need a different spring pressure, or a different wastegate duty cycle? If you're tired of dealing with spring pressure and its relationship to boost control with pneumatic wastegates, you could switch to an electronic wastegate. Those have been common factory parts for 10 years on a lot of cars. Are you trying to figure out "do I need a bigger turbine A/R" ? Bigger A/R is going to give you lower exhaust manifold pressures, but diminishing returns always come into play as you go bigger. At some point you won't be able to build any boost at lower rpm. Bigger exhaust system will help spool and make the turbo more efficient, but fitment and noise constraints do exist.

 

I had originally posted a stupid comment regarding the 1:1 (plus spring) calculation of MAP vs. holding capacity.

This ratio would assume the wastegate valve and piston/diaphragm are the same diameter.
I'm not sure that is the case in practice, I seem to think the diaphragm may be larger in some cases and that could extend the holding capacity of the wastegate. Just something to consider if it hasn't been factored in.

 

it’s easy to think that, seeing the data makes it clear though.

you can likely find some on here by doing the S-word thingy
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Garrett has a really nice PDF on their wastegates, https://www.atpturbo.com/info/Garret...ll%20Sheet.pdf

 

I wont argue about a wastegate working as intended at the rated spring pressure.

Just trying to say theres more to consider when your target is above or below the spring pressure.

There is a reason there are so many spring options.. I’d assume its because there is a relatively small window for accurate control.

 

or dump the old way of doing it and go electronic, all that spring crap goes bye bye.

 

A lot of models in a range will share the same diphragm diameter against different valves, you are correct that the smallest valve that gives you stable control at your lowest target boost will give you the widest control range due to the area ratios, will take more emp to "blow open" with atmosphere on both sides of the diaphragm for the same base spring pressure.