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SUI GENERIS UTE
GQ Ute 1990 Silvertop
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Discussion Starter #1
Just starting a thread on turbos and the whys etc.

I come across a pic of the compressor housing brand aside but i have seen this before on some Chinese examples. Its to do with anti surge holes and slot position and where they should be positioned and why.

I will put up this pic to see who can see why this housing cannot possible counteract surge.
 

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GUII ZD30DI Wgn
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Wild guess, the holes are too far away from the comp wheel? I look forward to being further educated.
 

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SUI GENERIS UTE
GQ Ute 1990 Silvertop
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Discussion Starter #5 (Edited)
Well done Geordie. Having the relief slot in the inducer or suction part of the blade cannot help surge at all. Logic should suggest the slot should be at least behind the second set of blade tips to at least release surge on those blades. But really this slot needs to be further back than this to be in the compression part of the wheel so when surge happens the pressure pulse can at least be dissipated at the compression point of the wheel as the surge pulse pushes high pressure back towards the inducer helping to release the stalling load of the wheel being backed up by the suction air being pulled in by the inducer section of the wheel.

Just to be clear on what surge can do to a turbo in the extreme condition. Blades can break off due to the pulse effect of surge but usually what happens with stronger billet wheels is the stalling force of the compressor wheel loading against the turbine wheel drive is the shaft will fatigue and break. The choof choof sound you hear is pulse forces which you would be aware is a pulsing load on the shaft which leads to fatigue. The blades of the wheel are aluminium and very thin and not the best material to counteract fatigue so will usually flex a few times and break off.

Positioning this slot is important and can be positioned to counter small surge effects or severe surge depending on how far back the slot is positioned. Most turbos are designed for petrol so the slot is usually positioned well into the compression area of the wheel to counter WOT surge without damage or big pulse loads of destruction. For diesel our lower rpm and turbo size and turbine ar we usually only see light surge pulses for example the choof choof low pulse width compared to high petrol engine speed surge where you don't hear the choof choof sound as the frequency is fast and continuous and destructive. Also usually we in diesel don't have a throttle body to start the process.

So for us we can have our surge slot a bit further out in the inducer area but not this far out lol.
By the nature of these slots we do loose some compressor efficiency, Not a lot but we in diesel are usually after every bit of efficiency we can get so we don't really want compression bleed off in our turbo compressor. Hence why EFR borg warner invented a blowoff recirc system in their compressor housings. This effectively senses surge in the charged area of the housing by differential pressure in the scroll to effectively release damaging pulse pressure safely in front of the comp wheel.

Now lets not get carried away here saying this pic it all wrong. The slots and holes are positioned in that position for another reason and its not surge reduction. The slot in the picture doesn't help surge at all it has zero effect on saving the blades from surge.

But what it does do is trick the inducer part of the wheel to pull more air into the compression part of the wheel so in effect can actually produce a bit more volume into the second set of blades without the front set of blades knowing sort of thing. The result is a little more volume in the spool part of the process.

Is it measurable you might ask? yeah well it is but usually not an amount that can be seen on a dyno run. It is measurable in the all important driveability transition part of our diesel power and response.

This is a really old trick done in WW2 on fighter planes operating at very high altitude where this slot position can help compress a lot more very thin air. For us down here at sea level yeah well not so much a measurable result.

A little drawing to help explain this idea.
 

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nissan
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Well done Geordie. Having the relief slot in the inducer or suction part of the blade cannot help surge at all. Logic should suggest the slot should be at least behind the second set of blade tips to at least release surge on those blades. But really this slot needs to be further back than this to be in the compression part of the wheel so when surge happens the pressure pulse can at least be dissipated at the compression point of the wheel as the surge pulse pushes high pressure back towards the inducer helping to release the stalling load of the wheel being backed up by the suction air being pulled in by the inducer section of the wheel.

Just to be clear on what surge can do to a turbo in the extreme condition. Blades can break off due to the pulse effect of surge but usually what happens with stronger billet wheels is the stalling force of the compressor wheel loading against the turbine wheel drive is the shaft will fatigue and break. The choof choof sound you hear is pulse forces which you would be aware is a pulsing load on the shaft which leads to fatigue. The blades of the wheel are aluminium and very thin and not the best material to counteract fatigue so will usually flex a few times and break off.

Positioning this slot is important and can be positioned to counter small surge effects or severe surge depending on how far back the slot is positioned. Most turbos are designed for petrol so the slot is usually positioned well into the compression area of the wheel to counter WOT surge without damage or big pulse loads of destruction. For diesel our lower rpm and turbo size and turbine ar we usually only see light surge pulses for example the choof choof low pulse width compared to high petrol engine speed surge where you don't hear the choof choof sound as the frequency is fast and continuous and destructive. Also usually we in diesel don't have a throttle body to start the process.

So for us we can have our surge slot a bit further out in the inducer area but not this far out lol.
By the nature of these slots we do loose some compressor efficiency, Not a lot but we in diesel are usually after every bit of efficiency we can get so we don't really want compression bleed off in our turbo compressor. Hence why EFR borg warner invented a blowoff recirc system in their compressor housings. This effectively senses surge in the charged area of the housing by differential pressure in the scroll to effectively release damaging pulse pressure safely in front of the comp wheel.

Now lets not get carried away here saying this pic it all wrong. The slots and holes are positioned in that position for another reason and its not surge reduction. The slot in the picture doesn't help surge at all it has zero effect on saving the blades from surge.

But what it does do is trick the inducer part of the wheel to pull more air into the compression part of the wheel so in effect can actually produce a bit more volume into the second set of blades without the front set of blades knowing sort of thing. The result is a little more volume in the spool part of the process.

Is it measurable you might ask? yeah well it is but usually not an amount that can be seen on a dyno run. It is measurable in the all important driveability transition part of our diesel power and response.

This is a really old trick done in WW2 on fighter planes operating at very high altitude where this slot position can help compress a lot more very thin air. For us down here at sea level yeah well not so much a measurable result.

A little drawing to help explain this idea.
WOW

My brains hurting.

Interesting though.

Franky.:)
 

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Just starting a thread on turbos and the whys etc.

Can we also ask our own questions relating to this topic, I'm sure a lot of us have had questions on there mind they would love answers/explanations for? Because I have one about compressor maps and boost control. I'm not even sure I've drawn the lines on the map correctly but I'm sure someone will be able to point me in the right direction. I didn't even no where the surge or choke was on the map a few months ago so I think I've learned a lot already but eager to learn more.

Why does everyone always strive to get to target boost pressure as quickly as possible? I think I understand that the fast increase in boost/airflow would certainly increase power/torque but would it not be beneficial from an efficiency point of view to slow it down to stay within the most efficient islands as long as possible? Or does the increase of boost/air flow outweigh the lower efficiency giving us more power?

quick vs slow boost.JPG

Second question. If we maintain the same target boost right through to our max RPM/airflow the shaft speed has to keep rising right? Does this mean we then start increasing the drive pressure needed to spin the shaft? Similar to first question, so does the steady higher boost/air flow outweigh the need for increasing drive pressure vs having boost taper off and keep shaft speed/drive pressure more constant? Or maybe we should have boost creep up to keep in the more efficient islands?

steady boost vs steady shaft speed.JPG

Third and final question which I'm sure will be completely laughed at by all and maybe a bit pointless depending on the answer for question 1 but, why do we try to hold it at a preset boost instead of letting it follow the best efficiency islands all the way up until we reach the max flow/rpm required? Probably a bad example with this map as I believe at max airflow boost would be well over 40psi having it follow the center of the islands all the way up.

linear boost.jpg

Sorry if my questions sound really dumb but sometimes the more I research to try to understand the more I get confused and have even more questions then before I started.

P.s - only just noticed when previewing my post that the compressor map image I stole from the Eclipse Turbos website has their logo pasted all over it. Sorry if it breaks some kind of advertising rule the forum has, I can find another one if it's a problem. I'm not even sure what turbo compressor that would be for or if it's even one they are using?
 

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SUI GENERIS UTE
GQ Ute 1990 Silvertop
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Discussion Starter #9 (Edited)
Hmm yeah well i will have to do this in sections starting with the first question. But first the thread was started because i have been sort of inundated over the years here with turbo questions. Seems fitting to have a thread on the subject.

So A bit of explaining your drawn lines on the comp map. The plot points are derived from engine displacement against rpm so lbs/min the engine can use, then against pr. Those pr points can move either way across the map depending on induction system resistance, exhaust system/muffler pressure, how efficient your intercooler is, intercooler pressure drop including the pipe work and lastly the expansion ratio of your turbine including ar and twin or single scroll efficiency and the turbine expansion ratio that your turbine housing can achieve with the engine displacement etc . but the starting point on the map is pr for the height and across the map is displacement rpm in lbs/min the engine can use corrected against all the bits mentioned above then including volumetric efficiency.

So the lines you see that most turbo enthusiasts draw like you have is arbitrary.

Boost pressure for some reason is easy to grasp so most joe blows see it as the only thing to measure a turbo by. As you are now well aware that isn't really the best approach for driving feel and actual real streetable power from your now experience. From this and some learned individuals build turbos to meet this odd boost super rising speed on the gauge to capture the unlearned in the market place. What happens doing this on a single scroll turbine open volute is your can have your boost gauge hit max boost very early in the rpm range but because its running up against the surge line and past it without actually hearing surge means its not moving the pr across the map so only increasing air volume pumped at a very small increase as the pr/boost rockets up the comp map.

Now that's only half the story and i am trying to make this as simple as possible. But the engine has only a certain volume space it can pump at each rpm so pressure can increase volume but air temp reduces that volume so hence we have efficiency islands which is about density. So basically the islands means more density for a given pr point across the map more density is more air volume crammed in the same space in the cylinder for a given rpm. So you see its not about boost pressure so much but about density because density is calc by multiplying pr X island percent. So boost pressure is only half the equation even then its not corrected so even less value to us as a measure of a turbo.

Using your chosen map the start point on that map is much closer to the 5 lbs/min mark actually about 3 for us at 1000 rpm, so a line running along the surge line with lots of boost or PR rise with not a lot of volume compared to the green line on the first map running up the max efficiency islands.

Knowing that comp map intimately and its associated wheel its impossible in maths to get the pr to run up the surge line, with a 4.2 litre displacement diesel with an open volute single scroll turbine housing. You should have chosen a much more petrol type map to propose this boost surge discussion point. If the map is a lot more straight up and down you would see the difference clearly. this map suggests red line at peak boost at 20 lbs/min green line 35 lbs/min. With another map without names you would see a very different line showing boost starting at 3lbs/min and peaking at about 12 lbs/min so the turbo has to make full boost before volume can generate to make torque and move the heavy 4x4 forward at a reasonable speed. Compared to the green line on this map you posted producing 15lbs at 1.5 pr about 1300 rpm and 35 lbs/min at 2.7 pr at about 2000 rpm having a lot more volume during the spool to have a very linear feel in acceleration.

Remember all of this and the ability to drive these pr and map position points is fuel dependent of course with diesel. Its very different with petrol.

So to answer your first question. Time to max boost can be a good thing but doing it with huge turbine emp pressure is not how you do it for driveability. The other thing you just cannot see on these maps or a dyno graph is transitions. To trick the turbine into instant torque build and good light throttle response is to have high volume build to boost pressure or PR with density ratio. So a line something like your first map green line suggests this volume build. Hence your experience of linear drive feel.

I try the next questions tomorrow.
 

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I tried to read all this on my phone last night, but the pictures just weren't working then. Geez kiwi, you went to a lot of effort to get that picture when google images has just about every compressor map known to man. That aside, great information in your response peter.
 

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What I can tell you, from having a turbine speed gauge, and accurate boost readings, is that I have never observed anything like the red line in the first graph, or any of those plots in real world street acceleration tests. It would kinda be a combination of all.
Personally I believe it is a assumption by most when they use plots like that.
I would have to go back through some data I have to map out what my compressor does.
And with the new engine, I would need new data to do it, as it responds a lot differently, it may be identical across the compressor map. I shall work it out at some stage.
 

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Thanks, Peter. Way more information than I was expecting! It's hard not to get caught up and focus on boost at times when that's all everyone talks or wants to hear about, I guess you would have classed me as one of those "Joe Blows" too before I started thinking for myself and wanting to learn what was actually happening under the bonnet . I'm really glad I've started to educate myself to gain a bit more understanding of this topic in which most people just follow the "boost is king" methodology. My mindset is changing into the "density is king" way of thinking, but I can sometimes be a bit of a slow learner and revert back to my old ways. Maybe one day I'll even get rid of my boost gauge on the pillar pods which is just too easy to get distracted by and tricks me into focusing on the wrong part of the equation.

Haha Technician, wasn't much effort at all when I had already download that image onto my work computer and had already started drawing lines all over it to try to understand how compressors maps worked before this thread was even started. The Turbo Terminologies page on that website only has already taught me more than I ever knew previously and I found on the Garrett website a downloadable PDF on turbo tech with some good info for the uneducated like myself which only made me want to learn more so when I saw this thread pop up when I already had these questions going around in my head I jumped at the chance! I'll make sure I'll use a map with another companies name on it if I ever post one again to avoid anyone thinking it's just an advertising post.
 

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SUI GENERIS UTE
GQ Ute 1990 Silvertop
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Discussion Starter #14 (Edited)
Second question or part 2.

Before we go forward maybe i should quell the speculation of comp wheel to surge like the first map plot lines. The map displayed is a 7x7 wheel with a few tricks in the blade angle to produce a map bent over and the shaft rpm required to produce those pr to lbs values drive force required to do those shaft rpm is not accounted for. First the comp map is a fixed entity produced from a series of tests with some flashy software for a prediction of what that particular wheel will do. Secondly the displacement of the engine at set rpm plots the position on the map using lbs/min it can use in absolute if you dont account for all the engine pumping losses. So the map shows density at the pr you think you can drive.

The first pic is a real map with displacement point plotted with pr on a 4.2 using a 7x7 wheel. It from the BW matchbot simulator. Easy to use and probably the best about without me trying to math plot points. this plot is using a intercooler with 100% efficiency.

The second pic is the same plot points but i simply changed intercooler efficency to 65% or about what a top mount is capable of on a GU.

The 3 pic is the same everything except i changed the air cleaner resistance from .2 psi to 1 psi resistance which is about what it is on a TD4.2 at 3500 rpm using a ZD airbox with std element.. You can see the number 6 plot point has mover a long way up the map but i haven't changed the pr at all its still set at 28 psi and 3500 rpm.

The 4th pic is all the same values as the first pic 100% intercooler efficency except i have changed the map to a 6x6 wheel with pretty much the same end volume capacity wheel. You can see the map width is not as wide as the 7x7 wheel so surge can happen and does for a TD using this compressor wheel.

The 5th pic is the start values i used for the exercise the displacement and rpm and the control points to set where the plot point really are in a spool up condition.

This pretty much answers your second question and fixes the assumptions i assumed with the first post above.

The best way to lean some of this stuff and the relationships is to have a play with this turbo match program and plug in some values and try and see the relationships. Then when you have that sorted you can play with the turbine part of matchbot to see how far you can drive the comp wheel. then if you get all that have a play with the fuelling and see how it all changes.

Just google "matchbot" to find the link. In the end its a simulator and only a prediction of what can happen or an idea of what can happen.
 

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Thanks Pete, This simulator is fantastic and very helpful to visualize what's going on. Thanks for the data in pic 5, I would have had no clue on those otherwise. I'm loving being able to see the percentage of wastegating and also seeing how much drive you can get from the turbine. I can answer a lot of my crazy questions now by plugging in all the random scenarios I think of.

I'm pretty sure I've also found my own answer for my original question 3 now that I can see the other half of the equation and not just focusing on the compressor. I can see that the turbine stops flowing at a certain point and from then onwards it just increases drive pressure. I increased turbine size to combat this but then I couldn't maintain boost at the same rpm early on. Also on my question 2, having boost taper off does reduce these drive pressures quite substantially but you also lose out on air flow so It's a bit of catch 22! Bloody glad I'm not the one designing these things.

I can see I'll be spending many hours playing around with variables seeing how it affects certain things. Once again thanks, I had no idea a tool like this even existed.
 

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SUI GENERIS UTE
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Discussion Starter #16 (Edited)
As you get use to what happens and the reference it all comes back to fuel then it will make a lot of sense. You will need to lower turbine temps as well i left petrol numbers in there use 1200 as max temp at about 2000 rpm. Heat in the turbine is drive so that fuel effected which effect gating for turbine drive etc..

Have fun but remember to get real result from this you need to plug in correct assumptions. If you get far enough down the path to changing fuel and how to convert lbs/hr into or from cc/1000 shots just ask.
 

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I'm loving being able to see the percentage of wastegating and also seeing how much drive you can get from the turbine.

I can see that the turbine stops flowing at a certain point and from then onwards it just increases drive pressure.
Are you sure your only new to this? Because that's pretty impressive that you can pick all that up so fast.
 

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Then you can also see the mechanical limitations of actuator springs for internal waste gate designs. Once the maximum boost pressure is achieved, there is no more control of the gate. Unless its fed from a different pressure source. Mostly, the turbine back pressure is taken at peak boost and left to run its course for the duration of the rpm, unlike vacuum actuators that can run close to the entire engines rpm. Which is why some companies spend millions of $$ to design a turbine wheel that has the correct flow and pressure eliminating the equation all together. Cheaper companies use a massive waste gate to try to create a "buffer zone" for flow. Which leads to them just losing a lot of control.
 

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Then you can also see the mechanical limitations of actuator springs for internal waste gate designs. Once the maximum boost pressure is achieved, there is no more control of the gate. Unless its fed from a different pressure source. Mostly, the turbine back pressure is taken at peak boost and left to run its course for the duration of the rpm, unlike vacuum actuators that can run close to the entire engines rpm. Which is why some companies spend millions of $$ to design a turbine wheel that has the correct flow and pressure eliminating the equation all together. Cheaper companies use a massive waste gate to try to create a "buffer zone" for flow. Which leads to them just losing a lot of control.
I most certainly can and already did come to my own conclusions that the wastegate control was limited only using boost pressure! You sure you're not spying on me because I no joke spent most of my days at work last week researching this exact problem. I came to the conclusion that I needed to use my on board air compressor so I can use more than max boost pressure to control the gate or to find an electronic actuator with a standalone controller of some description. I even toyed with the idea of using EMP instead of IMP to supply pressure to the gate.
 

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I guessed, that was the path you where headed next. EMP for control has been done many times before, its great in theory but not the greatest in application. It works but reliability is a problem. Most closed loop electronic controllers give no aspect to EMP. Maybe at the end you will come to the same conclusion (JUST GET A BETTER TURBO).
 
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