MATH+Logic: An engineering approach in search for a perfect TURBO.

[Magic Spool Bus]

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]

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.

 

[KiwiDingo]

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]

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".

 

[Magic Spool Bus]

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.

 

[Magic Spool Bus]

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.

 

[KiwiDingo]

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

 

[Dougal]

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.

 

[mudgudgeon]

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

 

[MonsterCruiser]

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!

 

[Magic Spool Bus]

You don't need a radio when you can listen to turbo whistle like that!

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.

 

[Magic Spool Bus]

Wanted to update this a bit after some time driving and tuning.

Some quick observations are :
- Fuel mileage went from 16mpg previous with the green wheel to 19mpg with slightly more fuel and both with 35's and 4.10 gears.
- Cruising flat or slight grades the turbo sits at 600-750F pre turbo EGT with about 5-7psi gauge pressure 2200-2600rpm.
- Pulling a grade EGT loves to live at 800F and about 10-13psi Gauge 2200-2600rpm.

I attribute the fuel mileage increase primarily from the divided manifold and probably a little to do with decreasing EMP and the turbo on average is making much less boost if we displayed this on a graph with time in hours yada yada.

Cruising low load conditions like stated above it is not making much boost. EGT being so cold is a slight issue when tipping into power below 1800RPM in 4th or 5th gear as usually I'm seeing 500-650F. This characteristic I'm sure is what most do not like about larger turbos. However, my opinion now is that I probably do not mind this as much because of the divided manifold improving my diesel N/A horsepower off boost and this lag never produces a situation where I need to downshift due to low power at low rpm no boost situations. The only RPM + gear situations I avoid is below 1800rpm in 4th or 5th gear as it feels like its approaching a lugging situation which I don’t see why I should want to operate at the rpm and gear anyways. I'm sure re gearing would solve this a bit but I like my highway cruise speeds.

I plan to pull the manifold soon to have it sent out to be ceramic coated, I will also be putting on a manifold blanket from a cummins I picked up in hopes to keep a little more heat in the system. I did install a turbo blanket and this helped marginally.

Pulling a step grade or highway driving this thing is a monster, I can pull a step grade at 10psi and 800F around 30:1 AFR and if I get into hard down to 24:1 boost is around 20psi and EGT has never gone over 1000F.

I have some fueling issues I'm sure, currently I have maxed out my fuel screw to the point I have lost adjustment at my throttle linkage on the intake manifold.

A big question I have is what is a safe AFR to see during spool up? I understand not to operate below 18:1 is usually a safe bet. If I dip into 15:1 or below for a moment to light the turbo is this asking for an explosion? Or do I still follow the rule of EGT temperature? Currently I limit this value to around 17:1 on the bottom but have hit 15 or even 14:1 briefly which obviously help the turbo spool up much better and gets more heat in. Once I feel I'm happy with fuel Ill be hitting a dyno for some numbers just for fun.

 

[AussieHJCruza]

My 80 spooled at 16:1 (and I'd say still does) - no concerns as it's only for a short time.

Edit: some more context - live 300m above sea level and virtually never did towing

 

[Dougal]

15:1 will just make annoying smoke unless you're stuck pulling a grade stuck in that rpm/load band for long enough for EGT to climb. It's hard to get EGT up without boost.

I think that your EGT temps are reading too low. Does the probe reach the middle of the exhaust stream?

 

[Magic Spool Bus]

Wanted to update this a bit after some time driving and tuning.

Some quick observations are :
- Fuel mileage went from 16mpg previous with the green wheel to 19mpg with slightly more fuel and both with 35's and 4.10 gears.
- Cruising flat or slight grades the turbo sits at 600-750F pre turbo EGT with about 5-7psi gauge pressure 2200-2600rpm.
- Pulling a grade EGT loves to live at 800F and about 10-13psi Gauge 2200-2600rpm.

I attribute the fuel mileage increase primarily from the divided manifold and probably a little to do with decreasing EMP and the turbo on average is making much less boost if we displayed this on a graph with time in hours yada yada.

Cruising low load conditions like stated above it is not making much boost. EGT being so cold is a slight issue when tipping into power below 1800RPM as usually I'm seeing 500-650F. This characteristic I'm sure is what most do not like about larger turbos. However, my opinion now is that I probably do not mind this as much because of the divided manifold improving my diesel N/A horsepower off boost and this lag never produces a situation where I need to downshift due to low power at low rpm no boost situations. The only RPM + gear situations I avoid is below 1800rpm in 4th or 5th gear as it feels like its approaching a lugging situation. I'm sure re gearing would solve this but I like my highway cruise speeds.

I plan to pull the manifold soon to have it sent out to be ceramic coated, I will also be putting on a manifold blanket from a cummins I picked up in hopes to keep a little more heat in the system. I did install a turbo blanket and this helped marginally.

Pulling a step grade or highway driving this thing is a monster, I can pull a step grade at 10psi and 800F around 30:1 AFR and if I get into hard down to 24:1 boost is around 20psi and EGT has never gone over 1000F.

I have some fueling issues I'm sure, currently I have maxed out my fuel screw to the point I have lost adjustment at my throttle linkage on the intake manifold.

A big question I have is what is a safe AFR to see during spool up? I understand not to operate below 18:1 is usually a safe bet. If I dip into 15:1 or below for a moment to light the turbo is this asking for an explosion? Or do I still follow the rule of EGT temperature? Currently I limit this value to around 17:1 on the bottom but have hit 15 or even 14:1 briefly which obviously help the turbo spool up much better and gets more heat in. Once I feel I'm happy with fuel Ill be hitting a dyno for some numbers just for fun.

15:1 will just make annoying smoke unless you're stuck pulling a grade stuck in that rpm/load band for long enough for EGT to climb. It's hard to get EGT up without boost.

I think that your EGT temps are reading too low. Does the probe reach the middle of the exhaust stream?

EGT is definitely low. Currently the bung is placed properly deep but it is reading from the front 3 cylinders. I could swap it for the rear bank and see if there are any deviations. I have no reason to believe it is not reading correctly but I’ll verify this.

I was contributing it to such a higher flowing turbine and it being larger. Steady state conditions at 2400rpm usually get me 800F on the highway but temp falls very fast obviously off throttle.

Even on boost hard at 22psi and 25:1ish AFR 3000rpm 4th or 5th it will not touch 1000F but it’s getting close if I’m pulling a grade. I do believe I could benefit greatly from some custom injection work at this point.

EDIT: I was reading my gauge wrong. It’s never touched 1100F pre turbo under the hard acceleration even up steep inclines.

 

[Magic Spool Bus]

EGT is definitely low. Currently the bung is placed properly deep but it is reading from the front 3 cylinders. I could swap it for the rear bank and see if there are any deviations. I have no reason to believe it is not reading correctly but I’ll verify this.

I was contributing it to such a higher flowing turbine and it being larger. Steady state conditions at 2400rpm usually get me 800F on the highway but temp falls very fast obviously off throttle.

Even on boost hard at 22psi and 25:1ish AFR 3000rpm 4th or 5th it will not touch 1000F but it’s getting close if I’m pulling a grade. I do believe I could benefit greatly from some custom injection work at this point.

My 80 spooled at 16:1 (and I'd say still does) - no concerns as it's only for a short time.

Edit: some more context - live 300m above sea level and virtually never did towing

Same I live at sea level but occasionally maybe 1 time a year find myself at 10,000+ feet. I’ll just need to remove some fuel on these trips. I never tow but I imagine this turbo would love to pull a load.

 

[Magic Spool Bus]

15:1 will just make annoying smoke unless you're stuck pulling a grade stuck in that rpm/load band for long enough for EGT to climb. It's hard to get EGT up without boost.

I think that your EGT temps are reading too low. Does the probe reach the middle of the exhaust stream?

I swapped the bung but realized I was confused and my EGT probe was already in cylinders 4-5-6 but swapped to 1-2-3 just to get values and I could not notice any difference in EGT values vs front and rear bank. I cant for the life of me find any data about what AFR is safe on spool up. Again I understand full load safe AFR to be 18:1 or above.

Let me paint a scenario to further describe what I'm stuck on. Lets say I tune to hit 15:1 AFR full pedal at 1600rpm in 4th gear. Then as boost and rpm rise I lean out almost instantly 20:1+ AFR. Does this scenario sound dangerous? I have while playing with spring tension and pin profile hit 14:1 and obviously the response feels great EGT is still a non issue as its so brief and once the turbo is making anything above 5 psi EGT is stable. BUT what might cylinder pressures be doing in this moment? With that rich of a AFR briefly am I even concerned of cylinder pressure or only EGT?

I'm guessing since not much info about this specific scenario during tuning is being talked about or discussed it may be a non issue and I'm asking silly questions.

One observation here is currently I have spring tension set to not allow anything lower than 17:1 if I floor it from 1600rpm in 4th gear with minimal smoke until boost rises. This setup produces AFR to be max 22:1 on a 3rd to 4th gear shift and leaning out rapidly to above 30:1 and maybe an EGT of 600-700F (normal street driving) and these values aren't exact but close. So I'm overly curious about how far I can go with AFR to raise EGT a bit on cruise conditions. I have played with multiple pin profiles, many different spring tensions but mostly I feel under fueled on the bottom end.

My logic with tuning the compensator could be flawed here so appreciate any advice and experience from the salt dogs

 

[Indestructible 47]

Dumping fuel in it at a low rpm puts a ton more stress on your internals. There is no real set value or figure that tuners use, mostly they will base tune it at around 18:1 and go from there. Some rough tuners bring it on boost at 14:1, no way I'm going that low.

 

[KiwiDingo]

Stop worrying about the AFR number, it's just a number which can't be compared against other people's numbers. EGT is so much more important.

I've done nothing but a simple turbo change with no change to the tune running the same boost. The smaller turbo made 800 degrees C pre-turbo EGT at 22:1 and the larger turbo only made 550 degrees EGT at the same AFR. I no longer care about what the AFR number is because it means nothing without context. There is no safe or bad AFR number to run at, it's all setup dependant.

 

[Magic Spool Bus]

Stop worrying about the AFR number

Thanks for confirming this .