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

[Nz Nath]

Do our factory turbo diesel engines have much valve overlap? Would they not overlap when the piston is pretty much at TDC leaving little volume in the combustion chamber to be filled by exhaust gas?

The problem with 'seat of the pants' is how easily we can unwittingly be tricked. A louder exhaust, or more 'wooshy' induction sound often makes a car feel faster. An engine that makes no low down power may feel like it makes more top end power than one which makes more low down grunt but the same top end.

 

[Dougal]

So some results are in. I got the truck back today and want to share first impressions before zero tuning has been done. Was previously setup rather rich for the Grunter and definitely could use some more fuel now with this EFR. Upon driving I was shocked that it went quite well with how the pump is set up currently, despite seeing much lower numbers on the boost gauge compared to the grunter at certain RPM's and load. With the grunter my observation was a lot of power from 1200 - 2400 rpm and the engine always seemed to really fight itself past 2500rpm and power would fall very hard, EGT would rocket to 1000F. So on to the new one... the turbo is laggy if your perspective is the boost gauge - RPM - and X turbo gave me X amount of boost before this one ( in my case the grunter). Now down low in the rpm range I feel more useable power completely off boost 900-1200rpm ish range. This may be contributed to the divided manifold and its higher efficiencies with scavenging and prioritizing flow to the turbo. Rolling at about 1800rpm in 3rd giving it some decent fuel around 24:1 AFR just to test the waters I was seeing around 10-15psi around 2000-2200 rpm and while that may seem low the power was much linear and smooth and my AFR gauge is reading rather lean overall compared to the grunter at these boost values leading me to believe this turbo is pumping much more dense air or with the dramatic reduction in backpressure from the grunter my engine VE improved or both. I would describe it simply as 7-10 psi on this EFR turbo feels like 13-15 psi on the grunter with a much cooler EGT and leaner AFR. From the start, I had wastegate issues and knew my controller wasn't working and later found out that the compressor cover on the turbo has a threaded hole for boost reference but it's not.... Pre Drilled from Borg Warner so ill be doing that tomorrow. So I was driving on 19psi spring pressure in the wastegate but my gate isn't seeing boost pressure therefore unless backpressure was forcing the gate open then I had no boost control and this was evident as I hit 25psi rather easily a few times from an extra boost gauge at my inlet manifold and decided not to do that again. However, during these runs that normally on the grunter would have my EGT at 1000F, this turbo wouldn't move much past 800F and with a very lean AFR of course. Another very pleasant characteristic is the engine really wants to rev past 3000rpm now. The manifold and turbo have changed the exhaust note to be a tad quieter and much much smoother of a note almost a "tuned" sound. Again I'm guessing this is from the divided manifold.

Overall I'm extremely satisfied and there are still a few kinks to sort out and get it dialed in. It runs like a train on the highway but I'm curious to see the turbo characteristic on the trails. Once I get the wastegate fixed, fuel sorted, and boost dialed in ill be doing some backpressure testing and some other things and then hopefully on to a dyno.

The manifold is made out of schedule 40 pipe and is very thick.

Stay Tuned!

Sounds completely consistent with the divided manifold and turbine housing combined with a larger turbine. Basically you've dropped a lot of EMP and dropped a little boost.

Slower to build but free-er flowing and beathing easier at higher rpm. Trails at altitude will be the test for you.

 

[KiwiDingo]

Do our factory turbo diesel engines have much valve overlap? Would they not overlap when the piston is pretty much at TDC leaving little volume in the combustion chamber to be filled by exhaust gas?

The problem with 'seat of the pants' is how easily we can unwittingly be tricked. A louder exhaust, or more 'wooshy' induction sound often makes a car feel faster. An engine that makes no low down power may feel like it makes more top end power than one which makes more low down grunt but the same top end.

It has 13 degrees valve overlap on the HZ/DT, can't remember what the FT and FTE are. It really doesn't take much effort to find out all the data and info with evidence on the negative effects of high EMP. It's been known and well documented all over and the advantages of having EMP less than IMP at all times is very clear and why so many strive to achieve it

 

[KiwiDingo]

Yes, but lots of the reduced EMP benifits claim is unproven info unfortunately. Seriously, as many people here have said for ages, dyno graphs and real world data are needed, as seat of pants improvement cannot be measured. If we have evidence it helps everyone make a informed choice for a turbo for their application.

It's all proven and all true. Dyno graphs and real world data is all over the place which proves the benefits

 

[Magic Spool Bus]

Instead of disagreeing to disagree let's try and solve these questions and keep in mind, this is in no way me trying to convince someone to do it. This was a very expensive setup and I know most wouldn't want to fork it over and quite frankly it's not needed right? It's all about what we want out of our engine. I learned a lot about turbos and attempting to size one while making this choice for nearly a year I read a lot of tech articles and played in match bot for a stupid amount of time. Lets take a look at how temp affect air density. This is from an article with Gale Banks and if you don't like him, science can prove this anywhere if you look.

"Air density is the mass per unit volume. It can be calculated using a formula that relates pressure and temperature, two key variables affecting air density.

As air flow (pressure) increases, density goes up. You can pack more air into a given space if you push it in with a turbo, supercharger, or ram-air system. But pressure alone does not make power. It’s the relationship between the two variables-temperature and pressure-that determines air density.

Logically, as temperature goes down, density increases. With colder air, it becomes possible to get more into a given volume. Anything that cools air, such as an intercooler, is essentially a density machine."

Inversely if we have psi stay the same and air temp goes up air density goes down depending on the heat increase. An example of this would be a turbo way outside its efficiency island at that psi and rpm. So temp and psi are directly related in term of air density.

So with this in mind, if we have x turbo with a small compressor nearing its choke point at 20psi and another turbo and its compressor are near the middle of the efficiency island at 20psi then the latter turbo will be more efficient meaning pumping cooler air at 20 psi. Now, this is just the compressor side what about the exhaust side? Well if we have a turbo pumping 20psi into an inlet manifold on one side and we have 60psi on the exhaust side what side do you think will win during valve overlap getting into the chamber? Obviously the exhaust side. Now let's take a turbo with 1.5:1 now we have 30 in the exhaust and 20 in the intake... which is much more ideal and still not perfect but much less competition for gasses to compete during valve over lap. I compare 3:1 to 1.5:1 because the 3:1 was what the grunter was near. 1.5:1 being what most want as an acceptable EMP but on the higher side.

Hopefully in another month or so I can get this on a dyno and track some more things to better give an understanding of if this a turbo someone else may want to use. Dougal I'm concerned about the altitude as well. At sea level, it's doing quite well even with a lack of fueling.

The turbo does indeed sound like a jet engine and I agree with others we cant operate off the seat of the pants feel if want to prove a point or provide data to someone to make an informed choice. However, this is not a race truck and if my seat of the pants got my pee-pee hard driving this thing around with no fuel and no wastegate then I'm happy.

I will do my best to provide unbiased information on this setup as I go along.

 

[Magic Spool Bus]

From what I've read, I'm a bit skeptical that EMP can make that much of a difference. I'd love to read some more theory. If a typical diesel compresses normal air to 450psi on each compression stroke, is say 30psi (example of bad emp, 1.5:1, 20psi boost) of back pressure on the exhaust stroke really going to make that much difference to power output? And how do air temperature and pressure play off against each other in terms of air density. Sure lower air temperature probably means lower egt/combustion temperature, so the ability to burn more fuel. But could you realistically get the equivalent of 5psi worth of air density from slightly lower inlet temperature from the 2 turbos in question?

Not trying to be a naysayer, just curious to read the science/theory.

diesel_exh_pres.php

turbo-tech-how-to-turbo-and-the-difference-an-a-r-makes-for-optimizing-your-turbo-system

keep in mind chasing low emp with a better flowing exhaust side will shift your spool up time to the right. I was very very worried about the lag everyone spoke about doing this. Now that I have driven it on low fuel and no wastegate control, im 95% confident that the lag I was worried about is a non-issue and far outweighed but how easy and quitely my engine revs. I haven't taken it past 3k rpm and at that rpm or anywhere from 2200-2800rpm it feels as if I'm stretching a rubber band and it's starting to let go (cheesy way to explain it yes but the grunter felt more like whiplash to 2300rpm and then hitting a big wall. I don't know what adequate fuel and more revs will feel like once I get the gate and fuel sorted. Still much more to find out. I give these seat of the pants comparisons because I truly hated the way the grunter behaved and it's exactly why I went down this road. Now i have to admit i could have probably achieved near similar results with a red or blue wheel and been happy but I was obsessed with twin-scroll manifold and turbos as they are a bit more effecient.

 

[chelo]

I was leaning towards that turbo after following this thread and or the eclipse dbb. I also want to change manifold . I like how you say you feel the linear power.
I just came back from crossing the grapevine, drove through mojave and the Tehachapi on my way back and I'm in need of more power. It's interesting to hear that the grunter falls flat after certain rpm and the temperature spike. I really like this setup.

 

[Magic Spool Bus]

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

 

[Nz Nath]

Instead of disagreeing to disagree let's try and solve these questions and keep in mind, this is in no way me trying to convince someone to do it.

Exactly, we're all searching for truth? Surely someone can quantify how much exhaust gas might end up in your cylinder due to EMP. Does the exhaust pressure actually push exhaust gasses into the inlet manifold during valve overlap? And if so by how much? What percentage of cylinder charge would end up as exhaust gas at the given examples? How does that play off against higher boost? Eg with less EMP you might get less hot exhaust gas in your charge but with less boost you'll also get less air density from the inlet. How do pressure pulses come in to play? The main benefit of twinscroll is that the pressure pulse from the piston expelling exhaust gases doesn't push against the next exhaust stroke in the engines cycle, do these pressure pulses or waves overcome an overall average emp?

The temperature vs boost thing for air density should be an easy one to quantify? I'll research it if nobody knows, I was hoping someone like dougal would already know the answers.


I'm also keen to try a twinscroll setup, I've been waiting for a cheap td04hla to come up for sale so I can use the turbine housing with my holset he221w.

 

[Magic Spool Bus]

The Borg-Warner match bot could simulate this for you I'm sure. When I get some time later ill try it out and see if we can make any approximate number about density, psi, and temp.
In my opinion and this is in no way a shot at you but the numbers you are looking for to me are irrelevant. I say that because unless we are an engineer and have access to an engine dyno and loads of money at fancy equipment it would be very hard to test this but I'm willing to bet Eclipse has done a bit of this or they are doing it currently to develop their turbo. In reality this is science and gas laws and we know from the previous conversation that these laws are true.

To expand on how exhaust gas would re-enter the combustion chamber it would do this back through its own exhaust port pushing back in already burnt fuel air mix during overlap of the valve. If we understand pressure difference for example 20 psi on one side of a bottle and 60 on the other... if you open both sides briefly which will enter the bottle? The exuast side primarily. This would, in turn, dilute, so to speak the next compression stroke robbing you a what could have been much more dense fuel air mix in the chamber. Lowering this value to 1:1 would allow you to fill the chamber easier and with more clean air and fuel. This is how I understand it simple. I could be wrong slightly.

Again I say irrelevant values because I'm not trying to set a record racing or have the highest HP and Torque so operating from these laws and principles I'm heading to a more efficient direction with the engine and for now that's enough for me. However, I also wish I or someone else would go this far with this engine but its highly doubtful someone will invest that time and money into a 25 year old diesel.

 

[Magic Spool Bus]

To your other question about lowering EMP and lowering boost and losing air density... this can be true yes but it’s entirely possible for one turbo to give you more dense cooler air at say 7psi then another one giving you 10-12 psi and have the same power at those boost levels. This comes down to how efficient is the compressor and hot side of the turbo. If you have a huge compressor capable of it but a tiny hot side then you CANT use all the air it’s pumping due to high back pressure and over spinning the turbo with the small hotside causing the turbo to mainly pump hotter air. I wish I could give people a ride in this because it truly is something that might not make much sense until you feel it in the truck and see it on the gauge. I went down this same road with a STI years ago. A lot of people are scared to get away from the stock Subaru turbo due to lag. I was scared just like I was here hoping I wouldn’t make it un “fun” to drive. Yes there will be lag but until you feel the benefit of having higher RPM power you may never know how green the grass can be over here

 

[IanB]

How do you feel this would translate to an auto trans truck, where you spend more of your time at those low rpm, and have little control over when the trans upshifts? Do you think you can maybe get away with a bigger turbo due to the manual trans without paying the full price on the low end response like an auto might?

 

[chelo]

I'll message you for that ride. Would you be able to do a video where you get in the higher rpm say in 3rd gear? From below 1500, how does it feel? Would you mind if I asked what that manifold cost?

 

[Nz Nath]

How do you feel this would translate to an auto trans truck, where you spend more of your time at those low rpm, and have little control over when the trans upshifts? Do you think you can maybe get away with a bigger turbo due to the manual trans without paying the full price on the low end response like an auto might?

I would have thought it would be the other way around? You give it some jandle in an auto and the TC starts slipping to get you into the revs, or the box instantly drops a ratio to do the same. In a manual you want the low down torque to be able to 'lug' at lower rpms to save rowing between the gears, and because you can't slip the clutch to minimize time spent accelerating at lower rpms. I've only driven modern autos though, so maybe those older auto boxes are pretty different?

 

[Magic Spool Bus]

How do you feel this would translate to an auto trans truck, where you spend more of your time at those low rpm, and have little control over when the trans upshifts? Do you think you can maybe get away with a bigger turbo due to the manual trans without paying the full price on the low end response like an auto might?

It’s hard to say and I was thinking of that on the way home. The auto usually does love to boost earlier than a manual or so I thought and this turbo would I imagine work even better on a auto if you could control your shift points.... I was under the impression you guys could do that on the auto to a point? The next step up is the EFR 7064 with a smaller compressor but larger exhaust turbine it flows less air on the compressor side but more on the exhaust. Or even bigger would be the EFR 7670 which may be too big for my taste. So far I’m happy I went with the 7163 because it is BIG compared to most others flowing about 60lb/min which is wayyyy more than enough to blow this engine I’m sure, but it’s exhaust turbine is so light and the MFT turbine wheel I believe help compensate a lot for lag. If you want a EFR and concerned about lag the EFR 6758 would be it and I actually bought that one first and canceled it days later for the 7163 version (devil in my ear ). Even the 6758 flows 53lbs/min which is good for over 200hp at the crank. The TD42 boys love both of these and more so the 6758 for a responsive turbo and they get about 1.2:1 EMP IMP which is good. Full boost around 2000rpm 25-30psi and on a 10mm pump sometimes

 

[Magic Spool Bus]

I'll message you for that ride. Would you be able to do a video where you get in the higher rpm say in 3rd gear? From below 1500, how does it feel? Would you mind if I asked what that manifold cost?

Yea once I get the fuel and wastegate sorted I’ll do some good videos and overlay the gauges to the tack so everyone can see at what RPM I’m getting X boost and X AFR and EGT and what not. Right now I can’t get into very hard because it wants to swing by 25psi too easily with no gate control

 

[Magic Spool Bus]

I'll message you for that ride. Would you be able to do a video where you get in the higher rpm say in 3rd gear? From below 1500, how does it feel? Would you mind if I asked what that manifold cost?

This was an expensive venture and I’m embarrassed to say how much. The turbo cost around 3k but I bought a turbo shaft speed sensor gauge, the lighter aluminum CHRA and coated the CHRA and Turbine housing 2000F coating.

The manifold + new down pipe + fabing nice coolant and oil feed lines cost me 3.5K so yeah this is a very expensive setup.

 

[chelo]

What is the stall speed on the torque converter? I have a manual but in the days when I messed with my turbo syclone. It was a 4.3 gas, we would up the stall for faster spool.

 

[KiwiDingo]

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

 

[KiwiDingo]

I would have thought it would be the other way around? You give it some jandle in an auto and the TC starts slipping to get you into the revs, or the box instantly drops a ratio to do the same. In a manual you want the low down torque to be able to 'lug' at lower rpms to save rowing between the gears, and because you can't slip the clutch to minimize time spent accelerating at lower rpms. I've only driven modern autos though, so maybe those older auto boxes are pretty different?

This is also my findings in the cruiser autos I've driven, the auto usually needs a bigger turbo than manual due to the TC and higher engine rpm it generally sits at compared to manual