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GUII ZD30DI Wgn
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Discussion Starter #1 (Edited)
@OldMav I would really appreciate it if you could spare a few moments to do a writeup on EMP, I'm specifically interested in the VNT turbo aspect for our 3L engines but you could also include bigger engines and turbos, we have touched on it in the past and I have measured mine a couple of times, the more I read on the subject the more confused I become, I read one 'expert' who said it takes a big turbo to get 1-1EMP, others say VNT units have much higher EMP than their larger wastegated cousins. The video series from Banks has no interest for me because he is not talking about what we are driving.

Could you also include items that can have a positive or negative effect on EMP.

I'm not going to attach any articles, not really worth the effort.

Peter feel free to chime in when you get the opportunity mate.
 

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My favorite subject..... :) having never personally done any testing with VNT and only gated turbos I only have opinions from my research but the theory is still the same. On the plus side VNT gives you so much more control over the EMP:IMP than what a wastegate could ever achieve so you're one up on us with that aspect but yes you do loose out in overall turbine efficiency to a gated/fixed geometry turbo.

Banks videos are great for wasting time but in most of the 20 minute plus videos there's normally only about 30 seconds of really decent info and the rest just basically an advertisement for his products/company.
 

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I remember this very detail reply from Peter in your build thread a while ago which I actually bookmarked at the time as I found myself reading it over and over again. I'm sure there would be lots who haven't read it due to being in a build thread so though I might post it here for others to read.

I will try and give an insight to the EMP/IMP gauge and how it is used. First an little understanding on the basics. With fuel mapping and fuel timing disregarded as for this exercise we cannot change those aspect. So we can only Tune the turbo for this aspect of fuel given within the confines of that the pump will adjust for its inputs and rpm values within the ECU. So we are essentially tuning the turbo to the fuel given with respect to the fuel pump modified adjusting criteria.

With this in mind we are trying to adjust an adjustable turbo to emulate the max criteria. For Ross we are looking for transitions and torque build, But i think for Ross economy is pretty high on the criteria as well. As i see it we should start at cruse speed adjustments (one thing at a time type of thing) to get a starting point to begin with.

How and why a EMP/IMP gauge is a good tool. Any real OEM engine engineer will tell you to get good cruise speed economy your want that turbo to be sized to give you the max density to the least EMP. I used the word density here because temperature is the biggest killer of air volume, boost pressure tells you nothing and is nothing except for a reference to density and PR. But because we have a turbo which has a fixed psi to a load and fuel delivery we will use IMP to do our ratio EMP:IMP. So for cruise we want to adjust the vanes down from full open to a point where we get our boost rising but our EMP staying under our boost psi. There will be a point somewhere in the vane range where EMP/IMP differential will be the greatest. So its not about what boost psi you have, its about the biggest differential point you can get is the best psi for cruise. But please dont forget density has a huge bearing on this differential. And density has the biggest bearing on your final cruise AFR which is a measure of economy. But for a 4 valve head we have good scavenging without having to have so much overlap so not too much cooling from the incoming cool air to lower EGT.

Which brings us to the very misunderstood EGT value. It not about the coolest that is totally wrong its about the most stable EGT and the fastest rise within the limits of the engine and turbo. So for cruise we want the highest possible EGT for that tiny fuel load. So we get the most heated exhaust air volume to drive not spin the turbine. This pushers the PR point on the compressor map into the better efficiency islands to get the highest AFR. What this is if you hadn't got it yet is density. Density on the comp map is those island percentage multiplied by the PR. More comp density with intercooler cooling is more economy with more torque at that fuel load so less fuel needed to push the cars air resistance. As a side note VNT tech is not good at doing high drive but matching to a good comp wheel is key for a VNT to get good drive flow against higher than expected EMP:IMP. So in conclusion for EGT we want the highest possible EGT for each fuel load for maximum Drive ratio on the turbine. The ideal obviously would be 750C pre turbo at every point of RPM at all times. So you see its not about boasting, i have the coolest EGT its about trying to get the highest EGT with the most stable temp rise for the complete rpm range. Now you know why those EGT threads annoy the crap out of me it shows complete ignorance to the workings of a turbo and engine.

Now that we have cruise sorted to a point we now adjust the transitions off Cruise as this is what we do in our 4x4's travelling to our destination as a tourer. So again our fuel map and timing is set so limiting our ability to dump instant fuel. But we can adjust our VNT to give the best possible transitions of cruise rpm's. So its reversed to cruise we want to dump the vanes closed to build EMP and EGT To force the turbine wheel to spin as quick as possible to generate as much initial rise in EGT and EMP to over come inertia issues from the turbine and comp wheel. Then we want the EGT to go stable and EMP:IMP to drop back below 1:1 to generate faster boost rise but also to drive the PR point across the comp map. YEAH yeah i hope you get this now more of that density stuff to build faster torque rise. The faster this happens the faster the spool and more the PR moves across the map for faster density rise to get the highest transition possible. As you can see its not about the speed boost rises or really how high it gets to like a few turbo re constructors think. So again the adjustment you can use is EMP:IMP differential as the measure of transition and how much you can adjust into that electronic gismo.

Now for acceleration Torque rise. Pretty much the same as transition with a few exceptions. To begin, We want the same dump of fuel which is dialled in with the ECU and its mapping and adjusting from intake air so more air velocity and measured MAF the more fuel dump on a DI. So we want that turbo to spool with density so same as transition closed vanes build EMP and EGT to drive the comp PR across the map to get best density. But this time we dont want the emp to drop, we want the EMP:IMP to build to 1:1 or a max of 1.4:1 as quick as possible and then open the vanes progressively to hold that max 1.4:1 EMP:IMP all the way through to max RPM in all gears so it a compromise because that gismo doesn't have the ability to adjust fuel with its MAP but it should be able to adjust the vanes to compensate the different gears as a product of load. So again you can see the ability of a EMP gauge as a tool for tuning the VNT. It's no different really from a fixed turbine just a bit better at transition adjustment over a fixed turbine i use with a gate flap. I adjust creep to do what a VNT does with its vanes.

A note of interest, to get good torque rise and peak and a holding peak you adjust EMP:IMP to get the highest differential just before peak torque RPM. Remember we do have a delay with a turbo the comp wheel has to react to move its PR across the comp map. so turbo comp wheel sizing and shape etc etc all that math crap needs to be compensated for to each engine and fuel load. But you will find with enough recorded data from a data recorder to get the turbo adjusted to get its best point of vane angle to produce the best EMP:IMP to hit that ideal fuel given load for best torque rise and peak values.

Not forgetting power here we still need that stuff to drive torque so in the above peak torque RPM we need the fuel mapping which is fix for us to keep the least EMP:IMP ratio with boost to keep power rising right to the end of our rpm range. I do understand the idea we dont rev past a certain point but this sort of thing is about engine flexibly so the power needs to be at least rising after peak torque otherwise the engine will feel very flat. At a minimum you dont want to see power dropping at all after peak torque, to at least 200rpm of max engine rpm or if you have that concept of not using your engines flexibly and drive like my old man you want power rising to your proposed usage max rpm. The power rise holds that torque curve on a diesel after peak torque RPM. There are other factors in this obviously that being your fuel mapping and fuel timing are critical in this process for absolute best results.

I assume you have noted my bias of top mounts to give an insight of my belief's, no matter how good they are their heat reaction time is woeful to say the least and very unstable. Can you now understand the importance of a cooler and its stability to our really REALLY important density and the bonus of them being stable for transitions and cruise flexibility or driveability. Yeah yeah we inject water it works to a point but you need lots and lots to overcome the top mounts instability. But we do get a bonus from the steam engine effect from water which compensates a heap. And a note not that you Ross have even come close but if you inject too much water at cruise speeds after turbo you will see a drop in torque due to turbine drive from cooling the EGT's to much below the expansion threshold of air. I have hit that point in an experiment. Its not the case with pre turbo hence why it is sooooooooooooo good because it increases air density and nothing else regardless of what efficiency island the PR is in. It doesn't effect EGT because the effects to EGT is at cam overlap time when the gas is cooled by the incoming cool air charge and the differential amount the tiny bit heat the water absorbs for more volume in the end. Its a balance of course i am sure you know this stuff anyway.

Hope this helped you and the other members following your experiment in tuning the VNT gismo.

sorry about the wall of text.
 

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GUII ZD30DI Wgn
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Discussion Starter #4
I remember this very detail reply from Peter in your build thread a while ago which I actually bookmarked at the time as I found myself reading it over and over again. I'm sure there would be lots who haven't read it due to being in a build thread so though I might post it here for others to read.
Yes I re read that the other day, but what I'm after is a bit more detail on what is good and what is bad and exactly why and how we can relatively easily influence it. As said there is a lot of conflicting info out there.
 

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I remember this very detail reply from Peter in your build thread a while ago which I actually bookmarked at the time as I found myself reading it over and over again. I'm sure there would be lots who haven't read it due to being in a build thread so though I might post it here for others to read.
That was a really damn succint read about a range of subjects we've touched on lately here at P4x4 over the last 6 months. Thanks for reposting it.
 

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As said there is a lot of conflicting info out there.
Curious as to what conflicting information have you found? I've spent countless hours on Google scholar download every article and white papers on the subject I could find and they all pretty much came up with the same conclusions and strategies for EMP.
 

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Personal experience not ZD related - I did a lot of stuff many years ago with a Garrett 2871, wasn't much left of the original turbo in the end.
It did work pretty good however. Hmmmm stretching my memory now, but was essentially 1:1 up until gate opening (30psi at the time), would drop to .9:1 at gate opening and then climb to 1.3:1 or so at 3800rpm.
It was no slouch, 200 - 220rwkw and 700-740nm or so. Made its 30psi at 2000rpm easily enough, and above that rpm point was great to drive.
However, if I was to graph the time it took to hit those results, and the drive ability off the bottom that every one desires, then the reality is that it was lacking.
All the number looked awesome on paper, from the power produced to the EMP:IMP etc etc.
Personal preference I guess, but i would happily trade the last few % of efficiency for the drive ability that might come with that sacrifice.
 

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Abbreviation "PR" is that the pressure ratio, as calculated from EMP:IMP?
 

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No separate things, the "PR" referred to by oldmav was in relation to a point on a compressor map.
Thanks, had to ask the question keen to learn. Gather U have been researching subject a lot, is there a good read that you could refer me to check out? Be appreciated.
 

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Thanks, had to ask the question keen to learn. Gather U have been researching subject a lot, is there a good read that you could refer me to check out? Be appreciated.
Yeah sorry that was probably my fault, I stole that reply from another thread so was taken a bit out of context when read on its own.

There's plenty of info on this very site, just use the search function for "EMP" or "EMP:IMP". Won't take you long to work out who the guys are you want to take note of and then you can use advance search to just read all their posts. Oldmav, bambill, dieseltuner etc. I've even gone to the extent of blocking everyone on this forum except those people to read entire threads with only their replies 👌
 

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Yeah sorry that was probably my fault, I stole that reply from another thread so was taken a bit out of context when read on its own.

There's plenty of info on this very site, just use the search function for "EMP" or "EMP:IMP". Won't take you long to work out who the guys are you want to take note of and then you can use advance search to just read all their posts. Oldmav, bambill, dieseltuner etc. I've even gone to the extent of blocking everyone on this forum except those people to read entire threads with only their replies 👌
I have read this post from Peter re EMP previously and even then the abbreviation puzzled me. Was interested in viewing a document that did cover/explain Compressor function/performance map. Thanks will look around.
 

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I have read this post from Peter re EMP previously and even then the abbreviation puzzled me. Was interested in viewing a document that did cover/explain Compressor function/performance map. Thanks will look around.
Honestly for a really great guide for beginners started from scratch I highly recommend the turbo tech education info on the Garrett website. There's three separate papers to read basic/advanced/expert. Gain Turbocharger Technology Expertise from Garrett Motion
 

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As I have explained in other posts, only MAF value matters.
If you build-up too much boost too quickly, you get automatically high EMP and a poor turbo efficiency (i.e less air in).

What you can do, if you don't want to put an EMP sensor in your exhaust manifold :
Record MAF and RPM vs time with ECUTALK. Then use Excel to get an XY graph with MAF on Y axis and RPM on X axis, since you cannot get MAP value with the ZD30 unless you use an adequate acquisition system.

Then try and reduce boost down low using several valves (explaoined elsewhere) , and get the same graph out.
Reduce boost until you get the maximum MAF value for a given RPM. that will de facto reduce EMP.

Getting the two curves on the same graph will make your comparative analysis easier (and you setting too).
With a stock turbo, you will see that a lot more air can be gained with less boost ( and less EMP vs IMP).
 

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Discussion Starter #17
What's that showing, it's all blurry on my end when I enlarge it? I can see gauges but can't read anything. I'm guessing that's your EMP gauge sitting in the middle of the bonnet though, did you have any footage while driving? What pressure range gauge did you use?
It wasn't meant to be read, just showing how I quick and easily tested.
 

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It wasn't meant to be read, just showing how I quick and easily tested.
Fair enough, I'd been having issues with loading images yesterday so thought there might have been something of interest on the gauge displays. I'm curious to hear what readings you're getting, especially during spool/at peak boost/at max rpm?
 

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On my Navara i'm getting 32 psi emp for 24 psi of boost. Turbo is a GT2360V with an upgraded comp wheel 49/65 from 42/60. 3 inch exhaust.
 
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