MATH+Logic: An engineering approach in search for a perfect TURBO. (1 Viewer)

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If you've got time and you like listening to Gale i highly recommended watching his videos, especially this one where the second half of it clearly explains the downsides of high EMP with all the data to back it up including the change to engine volumetric efficiency which reduces with high EMP. There's plenty of other videos of his which goes into more detail about EMP if you have a free weekend to watch it all :)
Love me some Gale Banks. He does actually provide a lot of this data NZ Nath was talking about but for more modern diesels
 

Nz Nath

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I've seen a couple of that guys videos before, and found them a bit slow and tedious like a lot of glossy YouTube videos. However there was some interesting data in that video. However, not really controversial. We all know that bigger laggy turbos produce more high rpm power than small responsive ones. He said himself that you wouldn't want to fit that turbo to that engine without adjusting the TC to get into the revs quicker. They produced the same power from almost the same boost level, but the bigger turbo was more efficient at that power and rpm combo as you'd expect... That was also an extreme example where he had only 20psi emp to 30psi boost.
 
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They produced the same power from almost the same boost level, but the bigger turbo was more efficient at that power and rpm combo as you'd expect... That was also an extreme example where he had only 20psi emp to 30psi boost.
The only reason they made the same power at the same boost was because they wanted to show data for that very scenario, they reduced the fueling to show how efficient it was. If they actually kept the fueling the same on both tests the turbo with the lower EMP would have either made a lot more power at the same boost or the exact same power at much lower boost. I don't consider 20psi EMP to 30psi IMP which is 0.66:1 ratio very extreme, I can easily achieve 0.7:1 ratio myself and could easily go much lower depending on how I build my turbo and tune it. It'll be interesting to see what EMP ratio yours is running at @Socal81 when you test it?
 

Nz Nath

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If they actually kept the fueling the same on both tests the turbo with the lower EMP would have either made a lot more power at the same boost or the exact same power at much lower boost.
This is what all discussions on emp on this forum have come down to, I think I'm not alone in wanting to see a video showing him making the exact same power "at much lower boost".
 
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This is what all discussions on emp on this forum have come down to, I think I'm not alone in wanting to see a video showing him making the exact same power "at much lower boost".
I think maybe we aren’t quite making our point. The idea here is this Banks scenario described exactly the relation of EMP:IMP and how it effect power and efficiency and many other things. This is an extreme enough example to see the differences in turbos clearly that I’m sure he wanted to do for us to highlight these key details. Now what does that mean for me and maybe some others? It means if we apply what we learn in this video and other sources of info to what we can achieve for our own goals then their are many options in between these 2 turbos and even outside of them in more extreme options for example a very tiny turbo or very large that will produce many different performance characteristics or hurt them.

The way I see it we have a range of options let’s say it’s 5 turbos (hypothetically) and they all target different rpm ranges the 1st being very small let’s say a grunter and the 5th being very big maybe even a step or two larger than this one I have. If I apply what I learn that the pros are doing and what some of these gas laws are I can make an informed decision on what I’m willing to trade off on or not. I can target mid range rpm low or high or try and get something in between knowing though that high back pressure which is somewhat subjective it seems causes efficiency issues. I can then say ok well I would like to target 1:1 which is logical to me the closer I get to that the closer I get to a symbiotic relation between boost and EMP. So really this thread and the point of it all is to understand what goes into sizing a turbo, what causes certain characteristics and how those interact with others negatively or positively and then we ourselves can select what we know will work vs what some guys uncle said worked well on his truck. The latter thinking is what led me into the grunter in the first place and I was immediately disappointed which is my own fault but it’s what also led me here.
 
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The only reason they made the same power at the same boost was because they wanted to show data for that very scenario, they reduced the fueling to show how efficient it was. If they actually kept the fueling the same on both tests the turbo with the lower EMP would have either made a lot more power at the same boost or the exact same power at much lower boost. I don't consider 20psi EMP to 30psi IMP which is 0.66:1 ratio very extreme, I can easily achieve 0.7:1 ratio myself and could easily go much lower depending on how I build my turbo and tune it. It'll be interesting to see what EMP ratio yours is running at @Socal81 when you test it?
I just did a brief run. I rigged the wastegate to run a single port at the gate instead of the 2 I plan to run off my electronic controller. Until I tap the compressor cover I can’t hook it up the way it should be having a 3 port controller and 2 port gate for better gate control while getting to peak boost.

So with one port and only using the 19psi spring pressure in the can and the gate now working once I hit 20psi and the gate opens I lose boost to 15psi from the gate opening too far and the big hole BW has for the housing losing too much EMP. So I need to adjust spring preload on the gate higher to prevent that. I know this is true because before with no wastegate operation I didn’t observe this drop on boost on acceleration at 20psi. During this EMP:IMP was always within 1-3lbs of each other EMP tending to be a bit higher than IMP though. Which now makes me wonder how EMP:IMP relate during normal load driving and cruising.

Once the gate and fuel is working properly. I plan to video both my tach and my gauges at the same time clearly so that I can overlay them and get accurate readings and relations.
 
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This is what all discussions on emp on this forum have come down to, I think I'm not alone in wanting to see a video showing him making the exact same power "at much lower boost".
There is videos of him showing exactly this, I just don't have the time to watch them all too link the exact one sorry. There's also hundreds of other diesel guys on YouTube and other social media showing this exact scenario and plenty of research and white papers on Google scholar and similar that go into more technical depth too which is great
 
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Just an anecdote to fuel the fire a bit more.

In the past I've run a lot of different T2/T25/T28 combinations on my Isuzu 4BD1T. None intercooled (apart from a brief stint with a home-made water-air setup).

T2 turbo (far too small), fast boost rise but not as big a difference as I expected. Top end performance completely missing. EMP spiking to 4x boost (15psi boost, 60psi EMP) over 3000rpm.
Note the 4BD1T doesn't like to rev anyway. It's a slugger, not a dancer.

T25 turbo (Nissan CA18DET spec) with 0.49 A/R turbine and 40/51.3mm compressor.
Great boost response, pulls really well from 1500-2500rpm where I drive. Top end tapers off fast.
Below 2000rpm with EGT above 600C this turbo produces more boost than EMP.
Best fuel economy. Best drivability.
Compressor maps out well for cruise and max torque.

T25/28 compressor (Nissan SR20 I think) with 0.64 T25 A/R turbine and 60mm 60 trim compressor.
Terrible response off idle, but pulled great from 2000rpm on up.
Towing and altitude work sucked.
Lower boost and EMP at 2000rpm cruise.
Fuel economy lost about 15%. Partly due to lower efficiency at cruise, partly because I had to use lower gears more often for hills and passing.

T25/28 Hybrid with 0.49 A/R (T25 turbine, T28 60mm compressor).
It had surge issues. The turbine tried to drive the compressor to make boost at flows where it couldn't.
Towing and altitude sucked but not as bad as the straight T28.
Big drop in power compared to the same compressor with the T28 turbine.
Drivability and torque didn't improve enough. So this turbo wasn't used for long.

All these turbos ran exactly the same fuelling. Differences in drivability and power were enormous. Differences in EGT weren't big.

I went back to the T25 and have run that turbo for about 15 years now. I have a freshly built MHI TD04HL-19T with 11 blade turbine and extended tip compressor wheel sitting here in a box for a couple of years now. I still haven't had the time to fit it.

I need to bury some other projects.

The mathmatical modelling I did afterwards backed up all these observations.
The T25 compressor is a good match for most of my driving (it falls over at altitude) and the T25 0.49 A/R turbine drives the compressor up the middle of it's map on this engine.
The T25 turbine with 0.49 housing drives the T28 compressor wheel up the left edge of it's map where efficiency sucks.
The T25 turbine with 0.64 housing drives the T28 compressor wheel closer to the middle of the map where they and build together for best power but the low rpm wasn't there.

The MHI I have built has a compressor wheel with a far better surge margin so it can build boost in that area with decent efficiency on a smaller turbine. Taking care of spoolup and driveability while doing better at higher rpm and at altitude.
 
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mudgudgeon

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Just trying to give a idea of normal driving here, before on this hill the grunter was so annoying to drive I would have to rev out very high and try to keep revs between 1800- 2200 in gear shift to feel any decent power. This setup doesn’t seem to mind as much what gear your in and as long as rpm doesn’t drop below 1600rpm on the shift pulling the hill the power is there even with only 7psi on the gauge.
this video quality is bad sorry. This is at 2000rpm in 4th giving it about half throttle only gets to 23:1 AFR but hits 20psi here but it cut off the boost gauge in the v

Dang that sounds sweet! Makes me miss my diesels :frown:
 
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Just trying to give a idea of normal driving here, before on this hill the grunter was so annoying to drive I would have to rev out very high and try to keep revs between 1800- 2200 in gear shift to feel any decent power. This setup doesn’t seem to mind as much what gear your in and as long as rpm doesn’t drop below 1600rpm on the shift pulling the hill the power is there even with only 7psi on the gauge.
You don't need a radio when you can listen to turbo whistle like that! :D
 
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You don't need a radio when you can listen to turbo whistle like that! :D
My radio hasn’t been on since I picked it up 😂. Getting a little closer to gate control. I’m running 19psi in springs in the actuator but as soon as the wastegate hits full stroke around 19psi the gate opens and I lose boost to around 16-17psi. As I have worked from 2mm preload on the gate to now around 5mm this issue is becoming less and less by limiting how far the gate can open.

The truth is the truck is driving so great that I’m rather lazy about tuning it at the moment. School and life getting in the way.
 

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