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.

 

[knochgoon24]

The flaw with looking at compressor maps directly for a compound setup is that the airflow rates across the bottom of the maps assume approximately atmospheric pressure and 77*F intake temperatures at the entrance to the turbo; hence, the "corrected airflow" terminology you see on some maps.

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(Massively large compressor map that shows the correction factors at the bottom.)
http://www.vortechsuperchargers.com/maps/YSi-Trim_Compressor_Map.jpg

You don't have atmospheric pressure at the inlet of the second turbo. So don't look at the compressible maps for the smaller turbo and think that it will be what limits your max flow.



A small turbo feeding a larger turbo will eventually become a restriction. You'll end up with a 2.5" (or whatever the outlet size is on your smaller turbo) restrictor plate once the first small turbo runs out of steam. Don't think of it as the big turbo sucking air through the small one. That's not what happens.

Nothing sucks... everything blows. (That's why they call it a blowjob.)

The only thing pushing air through the first turbo is atmospheric pressure. You can spin it as fast as you want, but at best, you'll have 14.7 psi pushing air though it. The job of the compressor wheel is to get the incoming air out of the way as fast and efficiently as it can, so more air can be pushed in to fill the void.

Now if you put the smaller turbo after the bigger one, you'll have AT LEAST that same 14.7 psi, even when the big turbo isn't helping. But once the larger turbo starts to spool (presumably, before the smaller one chokes) it will start increasing the the pressure before that smaller turbo. If you're getting 22psig (gauge) after the larger turbo and before the smaller one, you'll have have 36.7psi pushing air though the smaller one. Now, even if that smaller turbo were not doing any work, you'll have 36.7psi pushing air through that 2.5" hole instead of just 14.7. Obviously, more flow.

Did that make sense?

You need to think in terms of pressure ratios.

 

[Boostdriven]

Yes it does make sense, so let's say I was to do it that way, how would I have the boost/vacuum lines connected to the wastegates, which one does what and would I have a boost controller running both wastegates before and after the big turbo?

 

[knochgoon24]

I think that Paul's build thread has info on that.

 

[Boostdriven]

So I've done a bit more brainstorming and I think that we r talking about two different goals in compound turbo setup. I can c how blowing a big turbo in to a small one would allow u to run higher boost which essentially is more flow. As far as I know compound turbo was first put in production on a diesel engine. For example a CAT c15 came factory with a compound turbo setup. But here is the difference, a diesel engine like c15 has a compression ratio of 18.1 and the fuel (diesel) does not ignite from spark like in a gas engine but from extremely high pressure, so more boost on a diesel engine is always welcome. More boost=more pressure=better ignition, so more fuel can be added which means more power.

Gas engine is a little different. U can run 25 psi on a 16g and get 300 to the wheels or u can run 25 psi on a gt35r and get 450, so I would say gas engine is more flow dependant then diesel because it spins at much higher rpms. Having said that, taking something that is designed to work on a diesel engine which is more pressure dependant and using it on gas engine which is more flow dependant would only work as designed. When I talked to a tech from boostlogic about their 2jz setup he told me that it was only efficient in high boost, in fact I think they discontinued that kit. I see the same results in Paul's case.

So I was thinking what could be done to maintain the spool up of a small turbo that I like, in my case hx40 and have the power of a big turbo, in my case hx52 which I already have. If I plum the hot side just like a diesel engine I have potential in keeping the egts and back pressure down. Now this is where the theory is put to the test. When I ran my hx40 I logged about 61 lb/min at 30 psi at whatever the turbo speed (rpm) According to what I found out about the hx52 is it will flow about 75-80 lb/min at 30 psi. Looking at those numbers it almost don't make sense to blow the small turbo in to the big one cause the big one will over run the small one. In my opinion that is only true if both turbos r working against the same pressure. If u take a turbo like hx40 that flows about 61 lb/min at 30 psi at let's say 100k rpms and blow it in to an open air (in this case hx52 that flows more) spinning it at the same rpms, that would make that hx40 flow more air because it would blow in to the big turbo that is consuming all that air and compressing it.

In my opinion with a set up like that I can get the spool up of an hx40 since it would start making boost first pushing the air through the big turbo, now to get the power and flow of the big turbo all the big turbo would need is at least an ambient pressure in from of it. So if the hx40 is big enough to bypass enough air to maintain at lease ambient pressure (14.7) before the big turbo (hx52) I will have a spool up of and hx40 and the power of hx52

I hope this make sense

 

[knochgoon24]

Well first, I'd like to see you fit a HX40 and a HX52 in the space you have between the engine and radiator.

But what is your goal with all of this? I wouldn't exactly call the spool of a HX40 quick, so why are you going to wait for that to spool? Why not run something a little smaller? That's the great part of compound setups; you get the quick spool of the small turbo with the flow of the larger one. At the very least, why not use a 50-trim? Or a TD06H 20g w/ 10cm2 housing?

If u take a turbo like hx40 that flows about 61 lb/min at 30 psi at let's say 100k rpms and blow it in to an open air (in this case hx52 that flows more) spinning it at the same rpms, that would make that hx40 flow more air because it would blow in to the big turbo that is consuming all that air and compressing it.

You'd still be better off going the other way, big into small. Make the pressure ratios work in your favor.

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If you really wanted to make both these turbos work to their full potential, you'd run them at the pressure ratio that produces the peak flow. So the HX40 would have a 2.5PR and the HX52 would have a 3PR.

Full boost:
14.7 * 2.5 * 3 = 110 psia -> 95 psi.

Now you see how those diesel guys get such high boost for pulling competitions. You'd have a lot of flow at 95psi with those two.

Of course you aren't going to run 95psi.

So you see, you can run a smaller small turbo, get the quicker spool, and as long as you have a wastegate to bypass enough exhaust around the turbine of the smaller turbo so that it doesn't become a restriction, you get the best of both worlds: say the spool of a 16g with the flow of a HX52.

Bypass enough flow, and you end up with what is essentially a sequential setup. Where one turbo takes over and the other "shuts off".

 

[91vr4galant]

Every one of you on here has alot more knowledge than what I know, I would just like to chime in on something.

If you could run a small turbo (say a 16g) with a bigger turbo (lets say a GT4094R that is on my car now) When you put them on in the sequence that is normal blowing the big into the small I would think the small turbo would be over spinning with all the air flowing from the bigger turbo. obviously it does not hurt the turbo itself but it has to hurt the power of the engine right? What if you were to run the small turbo into the big one, with some sort of valve/flap between the small turbo and big turbo, so when the gt40 would spool a pressure controlled valve would open right infront of the big turbo then smaller turbo would not choke the intake flow of the bigger turbo. With the exhaust side running to the small turbo first with a wastegate, Maybe 2 so the smaller turbo would actually become completely bypassed and feed the big turbo without the flow restriction of the smaller (16g) turbo housing.

I have always wanted to discuss this subject with compounds on cars, I have seen it done on diesels the normal way but never figured out how the small turbo doesn't choke the flow of everything.

 

[Fejery4491]

The small turbo doesn't spin any faster that it would if it was pulling in atmospheric pressure. It just takes the pressurized air and pressurizes it further.

 

[Boostdriven]

Fitting those two turbos is half the problem and that can done. And yes blowing the big turbo in to the small one would work better if I wanted to run 70+ psi and it would work fantastically, that is if I was installing it on a 5.9L cummins.

My thing is when we build an engine, rods-pistons-cams-springs-retainers and so on, when u did all that u end up with an engine that is capable of making power past 8k rpms. When ## at the track racing ## car, would u shift at 6800 or would u shift at 8500 since ## peak power is let's say at 8200. I have not seen yet a compound turbo setup make power at high rpms with out having to run ungodly amount of boost, but I have seen many single big turbos do just that at lower boost.

So here is my goal, I don't care to have a really fast spooling turbo, but I also don't want to start seeing boost at 6k so my hx40 does just fine for spool up for me. If I go smaller I'm afraid it would be to small and cause the big turbo to pull vacuum on the small one and that's what I don't want, so if the big turbo never sees any vacuum but ambient or few pounds of boost it will work just as if it was by itself still flowing 75-80 lb/min at 30 psi. So now I have a spool up of my hx40 and the power of hx52, in theory that is

 

[knochgoon24]

Every one of you on here has alot more knowledge than what I know, I would just like to chime in on something.

If you could run a small turbo (say a 16g) with a bigger turbo (lets say a GT4094R that is on my car now) When you put them on in the sequence that is normal blowing the big into the small I would think the small turbo would be over spinning with all the air flowing from the bigger turbo...

It doesn't spin any faster. That's the beauty of turbochargers. They work using pressure ratios. That's why PSI or BAR isn't listed up the left side of the chart.

If you look at the left side of the compressor map that I linked to in the post where I have the flow numbers from the bottom, you'd see that it says "Pressure Ratio P2c/P1c". (Post #26)

P1c is the absolute pressure at the turbo inlet, not ambient. This is why well flowing intakes are important.
P2c is the pressure at the outlet.

In the stuff across the bottom:
BP is the barometric pressure. This chart was made with 99kPa at the turbo inlet. Standard atmosphere is 101.1kPa. (Edited to fix my error, 11 months later...)
T1c is the temperature of the air at the turbo inlet.
Ti is the ambient temperature. It's almost the same as T1c, but not exactly. If there's a pressure drop before the turbo (there is) then P1c =/= Patm. As such, T1c =/= Ti.

So if you want to know how well the compressor of a the second turbo in a compound setup would work, you could calculate a new x-axis by changing those numbers.

On the turbine side, you just need to be able to bypass enough flow past the smaller turbo so that it doesn't become a choke point in the system.

So here is my goal, I don't care to have a really fast spooling turbo, but I also don't want to start seeing boost at 6k so my hx40 does just fine for spool up for me. If I go smaller I'm afraid it would be to small and cause the big turbo to pull vacuum on the small one and that's what I don't want, so if the big turbo never sees any vacuum but ambient or few pounds of boost it will work just as if it was by itself still flowing 75-80 lb/min at 30 psi. So now I have a spool up of my hx40 and the power of hx52, in theory that is

You also haven't seen too many twincharged DSMs, but I digress.

You seem pretty set on the doing this the your way. You don't have to run both turbos at that peak flow PR. You could run them at whatever combo gets you the boost for the flow you desire. It would be really wise to choose turbos where you were in the peak efficiency islands so the air charge was cooler.

 

[Boostdriven]

So bottom line question is, would it be totally crazy and off the wall for me to set up the turbos I have the way I talked about or would u say there is potential light at the end of the tunnel

 

[mindset]

So I've done a bit more brainstorming and I think that we r talking about two different goals in compound turbo setup. I can c how blowing a big turbo in to a small one would allow u to run higher boost which essentially is more flow. As far as I know compound turbo was first put in production on a diesel engine. For example a CAT c15 came factory with a compound turbo setup. But here is the difference, a diesel engine like c15 has a compression ratio of 18.1 and the fuel (diesel) does not ignite from spark like in a gas engine but from extremely high pressure, so more boost on a diesel engine is always welcome. More boost=more pressure=better ignition, so more fuel can be added which means more power.

The second diesel engines run lean they blow. More fuel is welcomed on a diesel engine, not necessarily boost. That's why they blow so much smoke. They have to run rich so it don't blow!

 

[Boostdriven]

Diesel engine will smoke a lot mostly before the fuel/boost optimized, once its rolling there is not that much smoke. If u do a little bit of research online u might find Google to be ## best friend diesel engine under load will run leaner then a gas engine.
Here is something I copied from this page ( Banks Power | Understanding Today's Diesel )
Gasoline engines operate within a narrow air/fuel ratio range of approximately 12:1 to 15:1, although some modern "lean-burn" technology engines have been able to achieve significantly leaner air/fuel ratios.Diesels can operate with a broader range as rich as 15:1 or as lean as 60:1, however, going richer than about 22:1 to 25:l produces excessive temperature, soot, smoke, and poor fuel economy. Some aftermarket diesel chip manufactures simply dump in excessive fuel for power, causing the engine to operate in the undesirable rich range, as evidenced by plumes of black smoke. Thermal efficiency of diesels can be, and is, further enhanced with turbocharging to increase the available air (oxygen) to support combustion of more fuel. Gasoline engines cannot tolerate significantly higher cylinder pressure from turbocharging without creating preignition and/or detonation unless high-octane or ultra-high-octane gasoline is used.

So looking at all that u can probably guess how they get a 5.9L cummins to get 18-20 mpg where Ford f150 5.7L v8 can barely get 13
That is my point with this whole compound turbo set up stuff. Diesel engines run different then gas and applying something that is designed for a diesel to a gas engine will only work as designed.


I'm not trying to argue with anyone, I'm only asking a question, do any of u guys thing that doing it the way I describe in this post might actually work?

 

[knochgoon24]

I'm not trying to argue with anyone, I'm only asking a question, do any of u guys thing that doing it the way I describe in this post might actually work?

Work? Yes.

Work as well as it could? Not at all.

 

[Boostdriven]

I guess I'll have to do it to find out

 

[Andre Du preez]

Thought i would just copy and paste. http://dieselpowersource.com/index.php?route=information/information&information_id=6
Thx for the explanation. It makes sense in a way. I just compounded my toyota vigo 3.0l d4d and still battling. I have stock turbo with a 4mm bigger billet wheel with a t3 turbo on. I do need some help hurricane I'm still getting confused. I got with stock turbo 1.6bar boost alone.
I compound it now.
Final boost on intake manifold 1.7bar with a limiter. Compounds
Secindary turbo is only 0.7bar.
Exhaust manifold I get 44psi /1.6bar boost
Exhaust manifold I get 24psi /1bar boost
Exhaust manifold I get 13psi /0.5bar boost


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.

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.

I need some advise