Compound turbo setup plumbed backwards

[Boostdriven]

Hello everyone, I have been doing a lot of research on this topic and everyone seems to be doing the same thing. From what I found the cold side of the turbos are plumed in such way that the big turbo blows air in to the small one which is factory set up on a cat diesel engine. Boostlogic they did a compounding turbo setup for a supra and its done that way too. I watched a YouTube video where Marcus with boostlogic explains how a compounding turbo works on his 2jz engine, he says that once the small turbo reaches a certain psi the wastegate goes wide open and and bypassed most of the exhaust gases to the big turbo which is making boost by then, so my theory is that since most of the exhaust gas bypassed the small turbo then its not being driven by the exhaust force so its not pulling the air in as it would being by itself and the air is being force in to it by the big turbo, so the big turbo has to push the air through the compressing of the small turbo. When I talked to a tech at boostlogic he told me that their setup is a good setup but its not that efficient unless u run high boost. I also seen a guy on these forums do that setup on his eclipse where he used a 16g and a 60-1 I think for a big turbo, he made a little over 600whp at like 47 psi, that's a lot of boost almost makes no sense to me, my car made 580awhp at 31 psi on pump gas with water injection using hx40 turbo.
My question is could the cold side of the turbos be plumed where the small turbo blows air in to the big one and still work? I plan on using hx40 and hx52 thank u for any input.

 

[black_gst]

I'm sure Paul will jump in here and answer your question better then I can, I think since turbos work off absolute pressure, feeding a smaller turbo compressed air from the larger turbo just means that the turbo is taking compressed air and further compressing it since the turbo doesnt know the difference, at least that was my understanding but I could be wrong.

I can tell you that an HX40 and HX52 combo wont really work, the point is to have a smaller turbo that will spool up quickly, a better combo would be a small 16G and and HX52

 

[Bud92gsx]

Learn how to use paragraphs and stuff please..All that reading hurt my head, ..


Pm 99_gstracer..He has a compound setup making over 600..He should be able to answer all of your questions..

 

[kngofbrknprts]

if you read through the whole thread he explains it, its something along the lines that the smaller turbo is actually the force multiplier, all it does is compound whatever air its presented with. im sure it would work the way you have listed but i dont think that it would be efficient

 

[hurricanecris24]

http://www.atsdiesel.com/ats2/templates/template_06.asp?p=2029422272&c=36. Hopefully that helps i dont have much info on the topic as im still learning, but i have a hahn 16g and hy35 im working with as the primary turbo still undecided on the secondary hx40 or hx52. A better combo would be a hy35 and hx52 from my understanding

 

[hurricanecris24]

No, the way compounding works is by having the bigger turbo feed the smaller turbo. The OP wants to run it backwards by having the small turbo feed the bigger.
http://www.dsmtuners.com/forums/custom-fabrication/336541-my-compound-turbo-set-up.html

 

[Boostdriven]

Hey bud92gsx I don't c how ## reply is helpful in any way I posted that off my phone with service cutting in and out so I'm sorry for the inconvenience, anyways here is my thing, if u take even a small turbo like a 16g and leave the wastegate wide open u will be lucky to c 5 psi of boost by 8k rpms, so how is that turbo be compressing the air from the big turbo when the wastegate in between the two turbos is wide open bypassing most of the exhaust flow from the small turbo? The only way to really c the pressure difference between the turbos is to have boost gauge before and after the small turbo and if the pressure after the small turbo is greater them before it then I would say that mean that its taking the air from the big turbo which is feeding it ad x amount of boost and compressing it even more but if the pressure is the same before and after then to me it looks like the big turbo just pushes the air through the small turbo intact I think that the small turbo like a 16g is a restriction for a bigger turbo, I would like to c a log from Paul's car to c what the pressure is before and after the small turbo, I might be wrong but I think there will be more pressure before it then after.

 

[black_gst]

Hey bud92gsx I don't c how ## reply is helpful in any way I posted that off my phone with service cutting in and out so I'm sorry for the inconvenience, anyways here is my thing, if u take even a small turbo like a 16g and leave the wastegate wide open u will be lucky to c 5 psi of boost by 8k rpms, so how is that turbo be compressing the air from the big turbo when the wastegate in between the two turbos is wide open bypassing most of the exhaust flow from the small turbo? The only way to really c the pressure difference between the turbos is to have boost gauge before and after the small turbo and if the pressure after the small turbo is greater them before it then I would say that mean that its taking the air from the big turbo which is feeding it ad x amount of boost and compressing it even more but if the pressure is the same before and after then to me it looks like the big turbo just pushes the air through the small turbo intact I think that the small turbo like a 16g is a restriction for a bigger turbo, I would like to c a log from Paul's car to c what the pressure is before and after the small turbo, I might be wrong but I think there will be more pressure before it then after.

read the link hurricanecris24 posted, compound turbo charging has been around a long time in diesel applications, it doesn't make sense to you because you don't understand how it works, there's plenty of info on the web do a little reading and it will make more sense

 

[hurricanecris24]

Thought i would just copy and paste. http://dieselpowersource.com/index.php?route=information/information&information_id=6

There are certain facts and laws of nature that every diesel driver faces. Among these are 1. Ambient (atmosphere) air pressure is approx 14.7 psi at sea level. 2. Turbochargers only function at their best in a limited band of RPM's.

When you combine these two facts together you come up with some interesting problems. You have a few choices. You can either choose a small turbo, which functions very well with your engine at low RPM's, but limits high end power. You can get a large turbo which functions good at wide open throttle (WOT), but is horrible to just drive around town because it won't spool up (spool up refers to the amount of time it takes for the turbo to begin to produce boost), and has surging issues (trying to put more air into the engine then the inertia of the turbo allows, therefore causing the turbo to stop, reverse, and or slow down in pulses during operation). Or you can choose a medium sized turbo which spool's up relatively well, and at WOT still has some exhaust restriction but allows a lot more power and cooler EGT's than the small turbo. Yep, that's what your stuck with when you're choosing a single turbo. Sure there are much better choices than others, for example our D-Tech Turbocharger, which offers a huge increase in airflow and performance than the stock turbo, as well as has amazing spool up. But ultimately a single charger does have the restrictions listed above.

Part of the big problem is the ambient (atmospheric) air pressure, we mentioned earlier. If the boost pressure on your truck shows 35 psi, this is actually the gage pressure, or (psig), which means the zero on the gage is actually 14.7 psi (at sea level) or atmospheric pressure. The actual pressure is 14.7 psi + 35 psi = 49.7 psi, or actual pressure (psia). What this means is that the pressure trying to get into the turbo is only 14.7 psi, and despite how fast you spin the turbo, there is only 14.7 psi pushing air in, and if you spin the turbo too fast it becomes inefficient at bringing new air in, while it becomes increasingly harder to get exhaust out. To overcome this with a single turbo, people increase the sizes of turbines, housings, compressors, on and on, and may increase the amount of airflow, but ultimately hurt low end drivability and spool up, and all because they are up against those pesky laws of physics. A certain size of hole (the turbo air inlet) will only flow a limited amount of air at a given pressure. Atmospheric pressure becomes a huge limiting factor.

So what's the solution...Twins (turbos that is) also known as compound turbos or sequential turbos, actually two turbos placed sequentially (one flowing into the other). But not just any two turbos will work together, they must be sized correctly to complement each other or they can fight each other and not work properly. These two turbos will consist of a smaller charger, and a larger charger. The small turbo is the first to get exhaust from the engine, and the last turbo to touch the fresh air. Fresh air enters a large (slower spooling) turbo first , then is pressurized, and then fed into the small (quick spooling) turbo, which then multiplies the already pressurized air, and then feeds the air into the engine.

The beauty of the whole staged, two turbo concept is this. First of all you can have all of the benefits from a small quick spooling turbocharger, with more-than-all of the benefits of a very large turbocharger.

Turbos multiply atmospheric pressure, not add it, but function by multiplying it. Therefore if the small turbo as a single can take air at 14.7 psi, and produce 40 psi boost, it is multiplying the air by 3.72 times (14.7 psi x 3.72 = 54.7 psia, minus the 14.7 atmospheric gives 40 psig (gage pressure)). The large turbo can do a similar job. Therefore let's say that the large turbo multiplies by 2.2 times, it takes 14.7 psi (atmospheric pressure) and makes 17.6 psig (actual pressure 32.3 minus 14.7 atomspheric). (not taking into account adiabatic efficiencies), now the small turbo will see 32.3 psia at it's air inlet (instead of the 14.7 psia), but it think it's only seeing atmospheric pressure, or literally over double the amount that atmospheric would allow. So we can literally cram over double the volume of air into the same inlet hole size in the small turbo. So if the small turbo then multiplies the air by only 2.2 times you'll see 71.1psia - 14.7psia = 56.4 psig. (Note this does not take into account any of the efficiency losses, due to heat, etc., which do come into play, but that requires a much more lengthy discussion.)

So what exactly does this all mean...Most compressor maps for turbos end between a 3.5:1 and 4:1 ratio because the efficiency of the compressor drops beyond that point so dramatically. Most compressors have their highest efficiency at below 2.5:1 ratio. Efficiency is the amount of energy which is converted into heat during the compression process. The higher the efficiency the less heat is made from compressing the air. Our D-Tech 62mm will run at 78% efficiency below 2.3:1 ratio, which is where it typically will run on twin turbos, running appx. 55 psi boost. Whereas at 40 psi boost when ran as a single turbo the ratio is 3.7:1 and the efficiency drops to 70%, or 8% less than at 2.3:1 ratio (which is still very efficient at that level compared to most other turbos but is significantly lower than the twins at a much higher boost level, the stock turbo at this same ratio 5% is less than that). By 45 psi most single turbos are running off the compressor map at efficiency below 68%. In other words our Twin Turbo Kit at 55 psi boost is 10% more efficient than any single turbo running at only 40 psi boost. This translates into more usable, cool air entering the engine. To show the increase in compressing efficiency, our Twin Turbo Kit at 58 psi of boost produces compressed air temps (before the intercooler) of appx. 375 degrees F, while at 35 psi the stock turbo produces air temps of appx. 465 degrees F.

But don't forget that because of the low ratio required by the small turbo, we can wastegate it much earlier on our Twin Kit vs. as a single. By allowing the small turbo to wastegate early, the exhaust (drive) pressure goes way down. Less drive, or back pressure also raises the horsepower while lower exhaust temps (EGT's).

So exhaust pressure drops by 10-15psi, while boost pressure is 55-60psi, this is 157% more air going into the engine, while allowing the exhaust to escape 20-30% easier, then with a single turbo. On our properly engineered Twin Turbo Kit, all of these details translate into much more horsepower, much lower EGT's, better fuel mileage, a much broader RPM range (quick spool up, with huge high end WOT potential), and overall a much more drivable, high performance truck.

 

[Boostdriven]

I do understand how it works and I've done my share of reading, but I think a 60-1 by itself running 47 psi would have made more power then 600 whp, my car made 580 at 31 psi on pump gas with hx40 t3 .70 ar exhaust housing which is about the same size as 60-1 I'm sure if I ran 40+ psi on my car it would have made close to 680 awhp, don't get me wrong, I have seen Paul's car and that is some impressive work, but I guess ill just have to do it to find out

 

[black_gst]

I do understand how it works and I've done my share of reading, but I think a 60-1 by itself running 47 psi would have made more power then 600 whp, my car made 580 at 31 psi on pump gas with hx40 t3 .70 ar exhaust housing which is about the same size as 60-1 I'm sure if I ran 40+ psi on my car it would have made close to 680 awhp, don't get me wrong, I have seen Paul's car and that is some impressive work, but I guess ill just have to do it to find out

its not about making more hp, its about response look at Paul's dyno sheets sheets, he makes good hp low in the range. its about having the power of a big turbo with the response of a small turbo. you ever driven a DSM with a 60-1? I have, its a slug, spool up at like 5k

 

[JusMX141]

I think a 60-1 by itself running 47 psi would have made more power then 600 whp

Keep in mind there was a slipping ACT2600 on the car in question, and many 60-1 owners never reach 600whp no matter what the boost level is, and none EVER get near 541tq. I'm willing to bet your HX40 torque numbers are a good 100 lb/ft less. That's where the magic of the compound setup really shines- below 5250rpms, where all of the torque is made.

To compare, find me a single-turbo 16G car that made anywhere near 609/541, and likewise find me a single-turbo 60-1 car that made the same.

 

[hurricanecris24]

More power to you if you can make it work, theres a reason why diesels have been running compounds this way cause its more efficient. I havent read anyone trying to run it backwards(small turbo feeding big bigger) but im sure if it was a better way to compounding more diesel people would be running it that way.

 

[99gst_racer]

he says that once the small turbo reaches a certain psi the wastegate goes wide open and and bypassed most of the exhaust gases to the big turbo which is making boost by then, so my theory is that since most of the exhaust gas bypassed the small turbo then its not being driven by the exhaust force so its not pulling the air in as it would being by itself and the air is being force in to it by the big turbo, so the big turbo has to push the air through the compressing of the small turbo.

That's not a very accurate statement. It almost any situation, the small turbo's wastegate will never bypass "most" of the exhaust. Once the small turbo hits it's target boost, the gate is working overtime, but it's not realistically bypassing "most" what what comes out of the head. Most of the exhaust is still required to pass through it's turbine housing to maintain the work that it's doing. The rest is bypassed, and the rest is usually far less than half of the total exhaust output (but that will depend on the specific set-up). The small turbo doesn't stop working just because it hits it's target boost.

When I talked to a tech at boostlogic he told me that their setup is a good setup but its not that efficient unless u run high boost.

By nature, a compounded configuration is designed to run more boost. It's impractical to go through the effort to set it all up and run low boost. You won't receive the full benefits of compounding until both compressors are being pushed up to and/or beyond their efficiency ranges, and you can't do that running 10 psi on each turbo.

I also seen a guy on these forums do that setup on his eclipse where he used a 16g and a 60-1 I think for a big turbo, he made a little over 600whp at like 47 psi, that's a lot of boost almost makes no sense to me, my car made 580awhp at 31 psi on pump gas with water injection using hx40 turbo.

Ohh, not that crazy guy again...

The neat part was that that's using an old school 57 lb/min turbo (60-1) running at only 27 psi. But keep in mind that "PSI" and horsepower are not relative. PSI is restriction. Don't let the numbers fool you. It's entirely possible to turn up the boost and lose power. For example- try running 47 psi on a 60-1 and let me know how that goes for you.

As mentioned in the other thread a hundred times, compound turbocharging isn't for peak power. The benefit is the wider powerband, torque down low, and no huge, sudden power hit that scatters drivetrain parts.

If you don't mind, please link to your dyno sheet.

 

[Boostdriven]

Again don't misunderstand me I'm not picking on Paul, he did a great job with his set up, and ## right a lot less torque but it don't drop off till 7200 rpms on my car and it was only 412 foot pounds, but holly sh!t 47 psi u rattle the lug nuts of a semi truck with that kind of pressure

 

[99gst_racer]

but it don't drop off till 7200 rpms on my car

I'm working on that part. My original configuration wasn't optimized by any means. It was made with the stuff that I already had in the garage and it worked very well for what it was. But, there was room for improvement and the results of my next one should show this.

 

[Boostdriven]

I'm not really sure how to do the whole link thing, but I can email my dyno sheet if my email is provided

 

[TofastForU_99]

What about feeding the larger turbo the exhaust first in a twin scroll situation and then feeding the smaller. It seems back pressure is a major issue.

 

[Boostdriven]

I just added a picture of my dyno sheet to my profile, u can look at it there

 

[99gst_racer]

What about feeding the larger turbo the exhaust first in a twin scroll situation and then feeding the smaller. It seems back pressure is a major issue.

I really don't know how that would pan out. I can't find any reason why it wouldn't work, but in the same token, I can't find anyone who has done it either.

With the turbine housings that I'll be using, I'm really hoping I'll have backpressure in check this time. And I'll be datalogging it this time around too.

 

[Boostdriven]

Let me ask u guys this, let's say a turbo spinning at 100k rpms making 30 psi flowing 60 lb/min if u were to take that turbo still spinning at 100k rpms but blowing it in to an open air would it flow more air then 60 lb/min ?

 

[knochgoon24]

Yes. It's easy to see if you just follow the turbo's RPM line down and to the right from any point. Flow will increase with the turbo at a steady RPM (and PR dropping) until you hit choke flow.

 

[Boostdriven]

Well in that case that kind of support my theory of running a small turbo in to the big one, all the small turbo would have to do is displacing the air to the big one and the big one would be doing all the work, obviously u couldn't use to small of a turbo cause the big one would over run it, but with close enough ration big turbo wouldn't have to work for that air cause the smaller one is supplying air to it making the big turbo more efficient making more power at lower boost, just like having a small fuel pump in the tank and a bigger one in line, that actually works very well, I have 255 in tank and Bosch 044 in line in the engine bay

 

[knochgoon24]

Almost.

The problem is, you'll hit the choke line at a lower flow rate with a PR that is too low.

You must be logged in to view this image or video.

See how a 1.5PR will choke at 475CFM, with the turbo spinning at just 90k? But if you run it at a 2.0RP, it won't choke until 640CFM and just under 120k.

The turbo needs to be spinning a sufficient rate to actually move the air out of the way so more air can flow in behind it.

Your goal is to keep the turbos in their efficiency islands.

 

[Boostdriven]

Agree but that's if the turbo is spinning at slower speeds, I'm talking about the big turbo sucking air out of it not it pushing against pressure in the engine, so that smaller turbo would be spinning way faster trying to keep up the flow supply to the big turbo, so there would be bare minimum pressure between the small turbo and the big one but let's say 30 psi between the big one and the engine, just like the fuel pump set up, my friendly has the same fuel pump set up, he sees 5 psi of fuel between small and big pump but 43 psi between big pump and regulator