Turbine-Compressor dP

Fix_Until_Broke

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Turbochargers take energy from the engine, energy provided by the fuel. Fortunately they enable the engine to output more energy (torque & speed) than they consume (temperature, pressure of a mass flow), generally increasing energy output per unit time and thermodynamic efficiency of the engine. The amount of energy per time (power) consumed by the turbocharger relative to the amount of energy per time (power) it allows the engine to make over and above what would be made if there was no turbocharger (efficiency) depends on a lot of variables (mass air flow, fueling, injection timing, cam/valve timing, VNT position, engine load, etc) Just laying the groundwork here - feel free to correct any of the above as you may see fit.

I'd like to look at the effects of the turbine pressure, and more specifically the differential pressure between the turbine inlet and the compressor outlet. I've seen engines make more power after a turbo change running 10% less compressor pressure with the turbo B than turbo A. This was attributed to having 20% less turbine pressure for a net 10% increase in compressor pressure. The overall efficiency of this application increased. This was an IDI wastgated diesel application.

Has anyone measured the turbine pressure on a VNT TDI? I was considering installing a differential pressure gauge on the respective inlet/outlet ports of the turbo to evaluate this.

My thoughts on what you might see...Steady state, the turbine pressure would be a constant X psi higher than the compressor. For example - turbine @ 5 psi, compressor @ 2 psi, or turbine @ 13 psi, compressor @ 10 psi. Dynamically, It would be all over the map. The differential pressure could increase or decrease with absolute pressure depending on a lot of things (turbine/compressor maps, cam timing, valve overlap, etc). I don't know and was wondering if anyone has looked into this at all.

Specifically I would like to see what the turbine-compressor pressure versus absolue compressor pressure is for the stock VNT15, VNT17, and more interestingly would be to see how the hybrids compare. Absolue compressor pressure does not tell the whole story - you may gain power (absolue compressor pressure) but at the sacrifice of efficiency (increased turbine-compressor pressure) whereas with a different setup, you may also gain power (same compressor absolue pressure) but increase efficiency (decreased turbine-compressor pressure)

Clear as mud?
Worth the effort?
Anyone done it?
 

TDIMeister

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The improvement in the power output observed from different turbo matching is manifest in a couple of things. The biggest effect is, as you stated, by improving the delta-P between the intake and exhaust manifolds. This has the direct effect of reducing pumping losses which can be read as the lower work loop in an indicator or P-V diagram. The smaller the area of this negative work loop, the lower the pumping losses.

Secondly, better turbo matching results in the compressor operating in a more efficient operating point, meaning simply that the charge temperature going out of the compressor and into the engine is at a lower temperature and therefore higher density for a given absolute pressure. I won't go into the details as to why this is good as there should be pretty good intuitive understanding as to why this is so.

Now, here is the part is less well understood: Many people have the (erroneous) understanding that charge temperature and turbine backpressure are governed by the physical size of the turbocharger. I constantly hear terms such as "I get a cooler charge with a bigger turbo," or "I get less exhaust manifold backpressure with a bigger turbo." After hearing these for so long by so-called experts and reading the same over the Net, I started a thread some years ago in the Forced Induction forum at VWVortex that caused quite a stir.

The fact of the matter is, both charge temperature and turbine backpressure are related ultimately to efficiency and what effects efficiency. In the case of charge temperature, it can be calculated as nothing more than

T2/T1 = (P2/P1)^((k-1)/k)),



Where k is the specific heat ratio and approximated with the value 1.4, and the subscripts 1 and 2 refer to compressor inlet and outlet, respectively. All values of temperature and pressure must be absolute (Kevin or Rankine; kPa, bars or PSI absolute).

However, the calculation above assumes a perfectly isentropic compression process, which can never be achieved. We define an isentropic or adiabatic efficiency, whose limit of 100% would denote a truely isentropic or adiabatic process.


hs = (T2s - T1) / (T2 - T1 )

T2s denotes what the temperature would be at the compressor outlet if compression occured isentropically. T2 is the actual compressor outlet temperature and what we're trying to find.


What this equation shows is that as you approach an insentropic process (higher isentropic efficiency), the compressor outlet temperature reduces, with T2s being the lower limit.


On the turbine side, it can be shown that the dP you ask about is a function of the net efficiency of the turbocharger, or simply the product of all the discrete efficiencies (isentropic efficiency in the turbine and compressor, and the mechanical efficiency).


dP a hTOT,NET = hMECH * hS,C * hS,T

Edit: In the above equations the letters come out incorrectly.
"a" that follows dP is supposed to denote the proportionality symbol, while "h" is supposed to the Greek letter "eta" that is synonymous with efficiency.

Note that the physical size of the turbo does not directly factor in to either the equations for T2 or dP at all. Where size would play a decisive role in dP is if the mass flow rate is approaching the choked region of the turbine. Here, a larger cross sectional flow area or a larger A/R turbine would certainly help.


Now, since you don't have the option of changing the efficiencies of the turbocharger at will, the practical question is, how can I minimize T2 and achieve the most favourable dP? The answer is by maximing the efficiency at which the turbocharger operates for each given operating point of the engine. That is the science of turbo matching. The parameters you have ample licence to play with are selection of wheel sizes, trims, and A/R ratios for both the compressor and turbine sides of the turbo. By proper selection, all you are doing is trying to make sure that mass flow and pressure ratio (boost) demands of the engine intake, and the mass flow and enthalpy (heat) of the engine exhaust are operating as much as possible in the most efficient parts of the turbo maps. The basis of turbo matching doesn't get any easier than that. It is NOT about stuffing the biggest turbo you can between the engine and the firewall!
 
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mojogoes

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Which usually means changing to either bigger wheels or turbo in 90% of most cases , maximising the efficiencies of a vnt15 other then changing/boring the housing and adopting larger wheels won't bag you much than it would by going up size to a 17 or 20.

Compromise is the key here especially with our tdi's only revving to 5000rpm and what you want to do with the car , the vnt15 is probably on its efficiency line through the tdi's rev range where its needed most but just lacks the flow/off its efficiency line/flapping the air=hotter intake air from 3200rpm on......and moving to a much bigger unit would make the setup then seem very peaky with this 5000rpm limited rev range .

If you watch 2 cars drag race one with 1200hp and the other with 600hp the one with 600hp will leave the bigger hp motor for dead every time and where even smaller powered motors race against such high hp cars they will even let the low hp motor get a 1/4 or a 1/2 way down the track before setting off and win as sometimes not to show this weakness up..............and THE big reason why the top guy's over hp there motors to make up for any losses that occur in the using of very very large superchargers........then there's no lag anywhere unless your racing at that level against other guy's which is all relative.

And yes these 1200hp or more motors are/seem monsters on the track but they get eaten alive on the street against the smaller hp cars.
 

Fix_Until_Broke

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TDIMeister said:
The improvement in the power output observed from different turbo matching is manifest in a couple of things. The biggest effect is, as you stated, by improving the delta-P between the intake and exhaust manifolds. This has the direct effect of reducing pumping losses which can be read as the lower work loop in an indicator or P-V diagram. The smaller the area of this negative work loop, the lower the pumping losses.

Secondly, better turbo matching results in the compressor operating in a more efficient operating point, meaning simply that the charge temperature going out of the compressor and into the engine is at a lower temperature and therefore higher density for a given absolute pressure. I won't go into the details as to why this is good as there should be pretty good intuitive understanding as to why this is so. Yes, this makes sense - more mass flow rate at the same pressure. The same thing should go for the turbine as well, more torque and/or speed for the same EGT or turbine inlet pressure. I've seen the same effect I described by just changing turbine wheels/housing.

Now, here is the part is less well understood: Many people have the (erroneous) understanding that charge temperature and turbine backpressure are governed by the physical size of the turbocharger. I constantly hear terms such as "I get a cooler charge with a bigger turbo," or "I get less exhaust manifold backpressure with a bigger turbo." After hearing these for so long by so-called experts and reading the same over the Net, I started a thread some years ago in the Forced Induction forum at VWVortex that caused quite a stir. My guess is (have not read your thread yet) that these things are consequential to the increase of efficiency.

The fact of the matter is, both charge temperature and turbine backpressure are related ultimately to efficiency and what effects efficiency. In the case of charge temperature, it can be calculated as nothing more than

T2/T1 = (P2/P1)^((k-1)/k)),



Where k is the specific heat ratio and approximated with the value 1.4, and the subscripts 1 and 2 refer to compressor inlet and outlet, respectively. All values of temperature and pressure must be absolute (Kevin or Rankine; kPa, bars or PSI absolute).

However, the calculation above assumes a perfectly isentropic compression process, which can never be achieved. We define an isentropic or adiabatic efficiency, whose limit of 100% would denote a truely isentropic or adiabatic process.


hs = (T2s - T1) / (T2 - T1 )

T2s denotes what the temperature would be at the compressor outlet if compression occured isentropically. T2 is the actual compressor outlet temperature and what we're trying to find.


What this equation shows is that as you approach an insentropic process (higher isentropic efficiency), the compressor outlet temperature reduces, with T2s being the lower limit.


On the turbine side, it can be shown that the dP you ask about is a function of the net efficiency of the turbocharger, or simply the product of all the discrete efficiencies (isentropic efficiency in the turbine and compressor, and the mechanical efficiency).


dP a hTOT,NET = hMECH * hS,C * hS,T

Edit: In the above equations the letters come out incorrectly.
"a" that follows dP is supposed to denote the proportionality symbol, while "h" is supposed to the Greek letter "eta" that is synonymous with efficiency.

Note that the physical size of the turbo does not directly factor in to either the equations for T2 or dP at all. Where size would play a decisive role in dP is if the mass flow rate is approaching the choked region of the turbine. Here, a larger cross sectional flow area or a larger A/R turbine would certainly help.


Now, since you don't have the option of changing the efficiencies of the turbocharger at will, the practical question is, how can I minimize T2 and achieve the most favourable dP? The answer is by maximing the efficiency at which the turbocharger operates for each given operating point of the engine. That is the science of turbo matching. The parameters you have ample licence to play with are selection of wheel sizes, trims, and A/R ratios for both the compressor and turbine sides of the turbo. By proper selection, all you are doing is trying to make sure that mass flow and pressure ratio (boost) demands of the engine intake, and the mass flow and enthalpy (heat) of the engine exhaust are operating as much as possible in the most efficient parts of the turbo maps. The basis of turbo matching doesn't get any easier than that. It is NOT about stuffing the biggest turbo you can between the engine and the firewall!
TDIMeister - I agree with what you have said (I trust you on the deails of the equations, Thermodynamics was a few too many years ago;) ). To summarize - get the highest mass airflow rate out of the compressor with the minimum dP across the turbine. This may not be accomplished as you say by stuffing the biggest turbo in that will fit. There is some seperation in goals here - maximum efficiency or maximum power. An increase in efficiency will likely come with an increase in power, whereas an increase in power may not necessairly come with an increase in efficiency. (my goal is an increase in efficiency or an increase in power without a decrease in efficiency).

So, can we make a rough evaluation of turbo (turbine and compressor) efficiency by looking at mass airflow (which we can get via vag com - assuming intercooler performs the same during all tests (not a great assumption I know - can we mount a MAF on the outlet of the turbo?)) and turbine-compressor pressure? The metric would be (mass/time)/dP and a more efficient setup would yield a higher number.
 

GoFaster

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You need the performance maps of the turbochargers in question, in order to be able to do that. If you have the mass-flow and pressure ratio data, it is possible to see where this ends up on the compressor map and find the compressor efficiency. It is important to do this not only at maximum engine RPM, but also at the *lowest* RPM that the engine will be expected to deliver maximum torque at. Failing to do that last step, and simply picking a compressor based on maximum RPM only, might result in a bigger turbo selection and a bigger peak horsepower number, but it is likely to result in a "peaky" torque curve due to poor matching at lower engine RPM. The question about what RPM range the engine is to be used at, and what its intended purpose is, is an extremely important one.

The mass flow rate through the engine can be estimated even if sensor data is not available. In SI units, displacement must be in cubic metres (divide litres by 1000), temperatures are all absolute (add 273.15 to the degrees Celsius), and the outcome will be in kg/sec.

Mass flow rate = (displacement / 2) x (RPM / 60) x (volumetric efficiency) x (air density at the engine intake manifold)

In this equation, the air density can be calculated from the gas laws, or simply proportioned from known air density (1.2 kg/m3) at standard temperature and pressure:

Density = 1.2 x (Intake manifold pressure / Ambient pressure) x (Tambient / Tintake)

What is commonly called "boost pressure" is the intake manifold pressure less the ambient pressure. Intake manifold pressure = ambient pressure + boost pressure. The temperatures Tintake and Tambient are absolute (degrees Kelvin).

The volumetric efficiency is generally not known. In the absence of test data, an estimate of 80% at the peak-power point and 90% at the peak-torque point will be close enough for the intended purpose here.

The relationship Tambient / Tintake will depend on the pressure ratio, the compressor efficiency, and the intercooler efficiency. This one is easy to use test data; the TDI engine has an intake temperature sensor (after the intercooler) and VAG-COM can display it.

The turbine side is a lot more difficult to deal with.
 
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TDIfreak

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Measured the exhaust manifold pressure today.
GT22V turbo with AHU manifold.
60mm exhaust with the cat still in place.
12mm pump with Race injectors.
Boost is 1.5 bar.
WOT EMP is about 1 bar at 2000 rpm and rises to 1.5 bar at 4000 rpm (4 th gear).

My friend tested recently his otherwise very similar package but GT2052V turbo. He got 2 bar EMP at 4500 rpm, with the same pressure gauge I used.

On another car, VNT-17 made 2.3 bar EMP at 1.5 bar boost and he did not have the cat anymore but he had a 260 degree cam which may make some additional EMP.

I can see no reason to try even bigger turbo than GT22V to get the EMP to stay lower than boost at 4000...5000 rpms. GT23v turbine and 56 or 59 mm compressor with low trim number and small a/r of the housing should be a fine set.
 

TDIMeister

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This should illustrate that a well-matched turbocharger can, in fact, operate such that the compressor outlet pressure is greater than that at the turbine inlet. This answers some people's assertion that the turbo is a net efficiency (not power) drag on the engine because it adds backpressure to the exhaust (this is a question on the TDI quiz).

I would say, that a turbine with slightly larger A/R will have a greater effect on EMP, particularly at high RPM, than say moving a step in turbo size from a GT17 to GT20, for example will help. This preassumes that a given frame size is not already operating near choke conditions, where really only an increase in the flow cross sectional area (bigger wheel diameter and/or trim). What I'm basically saying, is that at 4500 RPM, going to a turbo of the same frame size but with a higher turbine A/R (e.g. from 0.64 to 0.70) will have a greater effect on EMP than going to a larger frame size and maintaining or even reducing the A/R. Both will certainly help, but we're talking in relative terms here. However, increasing the A/R means you will have a less responsive turbo at the low-end...

And here is where I want to defend the statement that lower EMP measured with the bigger turbo is not explicitly because of the size, but because at high engine RPM (high mass flow), higher efficiency is implicit from the larger turbo, both is gross terms (larger turbos generally have higher peak efficiency values), and in terms of where the turbo is operating on the map at the given pressure ratio and mass flow rate. For a given boost pressure and engine RPM, the engine is going to only accept a certain mass flow of charge (unless you improve intercooling or increase the volumetric efficiency of the engine). What this means is that if you don't do anything else, a 1.9 TDI operating at 1.5 bar boost at 4500 RPM will take in the roughly (in the order of ~10%) the same mass flow of air regardless of what turbo is connected to it. I say roughly because there will be differences due to the actual charge temperature in the intake ports as well as residual gas content due to pressure differences between the exhaust and intake ports. This is the concept that is lost when people think that turbo selection is completely separate from any consideration of the engine. The only way to effect a large increase in the mass flow of air are: better volumetric efficiency, larger displacement, more cylinders, faster engine RPM, higher boost pressure, etc.
 

Fix_Until_Broke

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TDIMeister said:
TDIMeister - That is exactly what I'm talking about on the exhaust side. If you take the same turbo back example of how back pressure effects VE and apply it to the turbine and compressor as an assembly one would get turbine-compressor differential pressure, and since what we are interested in doing with a turbocharger in the first place is increasing the mass airflow through the engine (not increasing absolute manifold pressure), we should be able to get a rough idea of efficiency of the whole operation - Mass airflow per unit of compressor-turbine differential pressure. Take all of the speeds and maps and trims and A/R ratios etc out of the picture and I believe what we are looking to do is get the most mass airflow for the least turbine-compressor dP.

With no means of boost control this is pretty straight forward, when we add in a variable exhaust geometry or wastegate we have just added another dimension to the analysis. Is there another sensor that the ECM reads that we could put another manifold pressure sensor on without otherwise messing up the engines operation? Then you could do all of this via VagCom - record MAF, manifold pressure and the other paramater, subtract the two pressures (have to convert one from it's native untis to pressure) and divide by MAF. I can do it with a differential pressure gauge and VagCom, and just do point by point at different steady state conditions (50, 60, 70, 80, 90, etc MPH?) but dynamically would be great.
 

TDIMeister

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After all is said and done, nothing new is brought to the table. If one looks at the turbocharger as simply a black box energy conversion device, taking thermal energy from the turbine side and doing work (compressing) charge air in the compressor, the maximal work done per unit of dp, if you want to use that term, is just a function of the efficiencies as have already been stated...

After all, efficiency is merely defined as the amount of work you get out for a given amount of work input. Applied to a turbine, the efficiency is the amount of work that is extracted out of a mass and heat content (enthalpy) of the exhaust flow going through it, and this work must be equated to the work required to raise a given mass flow of air on the compressor to a given pressure ratio. In any case, the minimum work, and the highest possible mass density of charge air, occurs when the compressor efficiency is at it's highest. And the maximum extracted work on the turbine from a given mass flow and pressure ratio of exhaust gas also coincides with the maximum efficiency of the turbine.

At the end, the equation I posted for the overall dp being proportional to the product of the efficiencies hold. I didn't make this equation up. The source for this comes from the book, "Diesel Engine Handbook" by Baranescu and Challen, published by SAE. I don't have the book at the moment (it's all the way back in Canada), but from my recollection, chapter 2 deals with turbocharging and turbocompounding, and there is a nice little graph that shows differential pressure as a function of the efficiencies and EGT with explanation that goes to more detail than I have posted.
 

mojogoes

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BLAH BLAH So with all that said Meister just give us the best turbo a/r , wheel sizes , housing etc with no lag and 300hp on the ve setup so i can go to bed cheers.
 

mojogoes

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I know what you could/can do see if you can get hold of one of the turbo's on the new twin turbo'd Porsche's which have vnt's , one of them's bound to be the right size for our tdi's and would be able to take the temps as there being used in a gassa setup.
 

TDIMeister

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Posted in another thread:

(BorgWarner has new turbocharger technology that supposedly allows more reliable VNT operation at high EGTs, which means it is being looked at again for gasser engines, the new Porsche 911 Turbo being the notable example -- 480 hp vs. 420 in the previous model with the same 3.6L displacement; 457 lb.ft of torque from 1950-5000 RPM in a gasser DAYUMM!! :eek:).
 

im570rm

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Acording to turbomaster.info here are the turbo's part number(s):
911 Turbo 2005 997 Top (der) 480 3.6/V6 G BV50 5304-988-0060 997.123.014.72
911 Turbo 2005 997 Top (izq) 480 3.6/V6 G BV50 5304-988-0061 997.123.013.72
 

Scott_DeWitt

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shortysclimbin said:
hmmm interesting. The car or the turbos dont show up in BW website. Must be they dont have the info up yet?
It takes a couple years until the OEM allows specs to be released to the public. I ran into this with a pair of Audi RS6 turbos I was modifying for a customer.
 

nicklockard

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bump.

revisit FUB's topics?


3 things to consider:

1.


Meaning of this plot from BorgWarner?


2.) Add: like this quote form Meister's whoretex thread

Meister said:
It can be shown from a first law derivation that -- choking flow aside -- backpressure is a function of the total efficiency of the turbochager (i.e. the combined sum of compressor-, turbine- and mechanical efficiencies), not of its physical size. Therefore the designer endeavours to design the turbo/engine combination to operate at the highest turbo efficiency over the widest, most prevalent operating range for the application.
Therefore, differential pressure EMP-IMP is a more-or-less direct measure of overall turbocharger net efficiency, right? And, knowing that MAF in + fuel mass in = exhaust mass out, we can figure things out. One thought and question on this: can we also say that backpressure on the turbo is a measure of stored potential energy; therefore, EMP-IMP is a measure of the extra energy available for accelerating the car, roughly?

Finally

Honeywell-Garrett makes mention of the "third generation VVT turbo technology as applied to trucks and other vehicles (http://www.honeywell.com/sites/servlet/com.merx.npoint.servlets.DocumentServlet?docid=DAB2CE61C-DB65-7AA4-02B3-ED98A50F34D4&userID=npointadmin)

Note the Passat is listed.

More mentions: http://www.honeywell.com/sites/servlet/com.merx.npoint.servlets.DocumentServlet?docid=D123FB792-9C3D-889C-8946-436B8EBF84EE&userID=npointadmin

Which of these turbos (available to us) apply to or can be adapted to Golf/Jetta platforms?
 
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Rub87

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BV50 is also used on the audi 3.0L tdi.. too bad it will not be the high egt resistant version as found on the 911 :/
 

StingrayRT

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Scott_DeWitt said:
It takes a couple years until the OEM allows specs to be released to the public. I ran into this with a pair of Audi RS6 turbos I was modifying for a customer.

just ask what you want

Porsche 997?

5304 970 0061 - look at third and four number if 04 meant as K04 if 16 = KKK16......

ok and now go for complete specification

BV50-2277DCB405.10BVAXO

22 = 2.2" compressor main diamter exducer
77 = 77% of 2.2" inducer

this turbo is K04 so a bigger compressor can be fitted to this turbo......K04 has Audi RS6, RS4......you can use also a K06 compressor
 

StingrayRT

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Rub87 said:
BV50 is also used on the audi 3.0L tdi.. too bad it will not be the high egt resistant version as found on the 911 :/
BV 50 from audi 3.0 is good options but be sure that it comes from 233hp car

look:

225HP car = 5304 950 0003 / BV50-2080DYB426.12BVAXC
233HP car = 5304 970 0043 / BV50-2277DYB426.18BVAXC

bigger compressor 2080 and 2277
 

TDIMeister

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I had a document that explains how to decipher Borg-Warner turbocharger designations. I'd have to look for it though, I think I only have a paper version.
 

TDIMeister

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TDIMeister said:
I had a document that explains how to decipher Borg-Warner turbocharger designations. I'd have to look for it though, I think I only have a paper version.
Found it. To use the following as an example:
BV50-2277DYB426.18BVAXC

22 is the exducer diameter in 1/10 inch (2.2 inches = 55.88 mm)
77 is the trim d/D in percent (this is different from the method by which Garrett calculates trim, which is (d²/D² multiplied by 100).
DYB4 are compressor design characteristics; I can't get full correspondence with the document I have, but to the best that I can decode it:
D = 4th development level
Y = combination of "Frequenzerhöhtes Verdichterrad mit 7° Schräge am Eintritt
KSM im Verdichtergehäuseeintritt" (increased frequency compressor wheel with 7° inlet taper; I don't really know what KSM is but I assume it to be a shrouded port).
B = KSM-Nutlage für O-Verdichterrad.
4 = no idea...

26 = throat cross-section in cm²
.1 = single-entry housing
8 = SA-contour (no idea what this means)
B = unknown; no correspondence to what I have in my document
V = VTG with moveable vanes, single-entry
X = development/revision level
A = identification letter of turbine entry flange
C = turbine housing material, in this case GGV (vermicular graphite cast iron) SiMo 4.5 0.6

I don't have maps for these specific turbos, but I do have a 2277DCB and 2280DCB. However, I'm not at liberty to disclose them due to NDA.

Here's what I can post:
 
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TDIMeister

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All that does is increase the trim and moves the map toward the right to higher mass flow rates. It's directionally the right thing for more air flow at a given boost pressure as long as you ensure a surge margin.
 
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