twin turbo's: help me day dream!!!

[rbsjnh]

I have been thinking alot about twin turbo's and hoping some of you might know some answers.

1.) when turbo's are run inline is the maximum amount of boost calculated though the combination of both turbo's flow, or is it decided by the maximum output of the larger turbo.

ex. small turbo maxes out at 7 psi, large turbo maxes out at 20....maximum boost 27 or in the low 20's?

I would think that because they only utilize 1 wastegate maximum pressure would be the combination.

2.) how difficult would it be to tune this, using a 3 bar map, I would tend to believe it would be much different than tuning for 1 turbo.

[rbsjnh]

http://videos.streetfire.net/video/t...ith_123302.htm

[h0ndab0yj0n]

bumppppp

[cali 18]

sounds fun to do for braggin rights

[jdm_risa]

i think one turbo should be efficient enough consider some factory twin turbo cars converting to single turbo upgrade

[rbsjnh]

Originally Posted by jdm_risa

i think one turbo should be efficient enough consider some factory twin turbo cars converting to single turbo upgrade

except a twin turbo should help make a broad powerband vs a peak powerband

[drhonda]

Originally Posted by jdm_risa

i think one turbo should be efficient enough consider some factory twin turbo cars converting to single turbo upgrade

This has already been discussed. not the point here. Questions in the first post are the ones at matter at this point.

[cali 18]

Originally Posted by rbsjnh

except a twin turbo should help make a broad powerband vs a peak powerband

very true. using a twin turbo setup on the circuit track would make SC guys hide. with almost 0 lag and the high top end of a turbo, considering this set up for road course use isn't to far fetch.
reliability would be my only concern.

[eddsi]

Originally Posted by cali 18

very true. using a twin turbo setup on the circuit track would make SC guys hide. with almost 0 lag and the high top end of a turbo, considering this set up for road course use isn't to far fetch.
reliability would be my only concern.

Reliability would depend on the tune. This seems like a serious question that i would like to see an answer

[1crazy93K]

Originally Posted by eddsi

Reliability would depend on the tune. This seems like a serious question that i would like to see an answer

x2



if a k20/k24 was in constant boost it would be mean. it wouldnt take much to make a manifold. i wouldnt think that it would be as hard to tune if anything maybe easier because if your in constant boost wouldnt the fuel ratios and air mixture be more consistant?

I would really like to see this done with some good documentation. i think that this could be really nasty!< in good way that is.

[Texasnick]

Originally Posted by rbsjnh

I have been thinking alot about twin turbo's and hoping some of you might know some answers.

1.) when turbo's are run inline is the maximum amount of boost calculated though the combination of both turbo's flow, or is it decided by the maximum output of the larger turbo.

ex. small turbo maxes out at 7 psi, large turbo maxes out at 20....maximum boost 27 or in the low 20's?

I would think that because they only utilize 1 wastegate maximum pressure would be the combination.

2.) how difficult would it be to tune this, using a 3 bar map, I would tend to believe it would be much different than tuning for 1 turbo.

I like this idea. I honestly would like to learn more about it. I don't know much about sequential turbocharging. The only experience I have in it is having driven a B4 Legacy when I was in Aus. It was a lot of fun. The smaller turbo had little to no lag, and carried the motor up to about 5k rpm. There was about a 500 rpm dip in power while the second, larger turbo started to spool (it was kind of annoying, actually) and that carried the car up to 8k rpm like a rocket ship.

But.....I digress. I'll take a stab at answering your questions....these are just educated guesses, so don't take them as truth.

1) If you think of it in terms of absolute pressure, the first turbo is able to achieve 14.7 psi + 7 psi = 21.7 psi, or 1.476 atm. This feeds the second turbocharger, so in effect the "atmospheric" pressure going into turbo #2 is really 21.7 psi, as opposed to 14.7 psi. If turbo #2 achieves 20 psi (relative), then at this point it is generating 41.7 psi abs as opposed to the 34.7 psi that it would if it were on it's own. In terms of boost, or guage pressure, this is 27 psi. Like I said, this is just an educated guess, but maybe someone can take it and run with it so we can get the ideas flowing.

I've just been sort of looking at this "sequential twin turbocharging" thing this morning before work, but it seems like there are 2 types of sequential turbocharging....

http://en.wikipedia.org/wiki/Twin-turbo

1)During low to mid engine speeds, when available spent exhaust energy is minimal, only one relatively small turbocharger, the primary turbocharger, is active. During this period, all of the engine's exhaust energy is directed to the primary turbocharger only, lowering the boost threshold, minimizing turbo lag, increasing power output at low engine speeds and providing the benefits of a small turbo. Towards the end of this cycle, the secondary turbocharger is partially activated (both compressor and turbine flow) in order to pre-spool the secondary turbocharger prior to its full utilization. Once a preset engine speed or boost pressure is attained, valves controlling compressor and turbine flow through the secondary turbocharger are opened completely (the primary turbocharger is deactivated at this point in some applications). At this point the engine is functioning in a full twin-turbocharger form, providing the benefits associated with a large turbo, including maximum power output, without the disadvantages such as increased turbo lag.

2)Sequential twin turbo can also refer to a system where the output pressure must be much greater than atmospheric. In this case, two similarly sized turbochargers are used in sequence but with both operating all of the time. In this case the first turbo boosts pressure as much as it can (for example to three times the intake pressure) then the second turbo takes this charge and increases it further (for example to an additional three times intake pressure, for a total boost of nine times atmospheric pressure) to a pressure not possible by a single turbo. This is commonly found on piston engine aircraft which usually do not need to rapidly raise and lower engine speed (therefore turbo lag, while still present is not a problem) and where the intake pressure is quite low due to low atmospheric pressure at altitude, requiring a very high pressure ratio. High-performance diesel engines also sometimes use this configuration, since diesel engines do not suffer from pre-ignition issues and can use significantly higher boost pressure than Otto cycle engines.

http://www.absoluteastronomy.com/topics/Turbocharger

Some car makers combat lag by using two small turbos. A typical arrangement for this is to have one turbo active across the entire rev range of the engine and one coming on-line at higher RPM. Early designs would have one turbocharger active up to a certain RPM, after which both turbochargers are active. Below this RPM, both exhaust and air inlet of the secondary turbo are closed. Being individually smaller they do not suffer from excessive lag and having the second turbo operating at a higher RPM range allows it to get to full rotational speed before it is required. Such combinations are referred to as a sequential twin-turboTwin-turbo
Twin-turbo refers to a turbocharger internal combustion engine on which two turbochargers compress the intake charge. There are two commonly used twin turbo configurations; parallel twin-turbo, and sequential twin-turbo....
. Porsche 959 first used this technology back in 1985. Sequential twin-turbos are usually much more complicated than a single or parallel twin-turbo systems because they require what amounts to three sets of pipes-intake and wastegate pipes for the two turbochargers as well as valves to control the direction of the exhaust gases. An example of this is the current BMW E60BMW E60
The BMW E60 automobile platform is the basis of the 2003-onwards BMW 5-Series automobile, replacing the BMW E39. Before the recent restyling, the models available were the 520i, 520d, 525i, 525d, 530i, 530d, 535d, 545i, and the BMW M5....
5-SeriesBMW 5 Series
The BMW 5 Series is a mid-size car / executive car manufactured by BMW since 1972. The car, now in its fifth generation, is sold in sedan and station wagon body styles....
535d. Another well-known example is the 1993-2002 Toyota SupraToyota Supra
The Toyota Supra is a sports car/grand tourer that was produced by Toyota from 1979 to 2002. The styling of the Toyota Supra was derived from the Toyota Celica, but it was both longer and wider....
. Many new diesel engines use this technology to not only eliminate lag but also to reduce fuel consumption and reduce emissions.

Like I said, I'm quite retarded sometimes when it comes to things I know little about, but I find this really interesting, so hopefully we can maintain a decent technical discussion about it so we can ALL get our learn on

[Texasnick]

One thing I overlooked was compressor efficiency and boost pressure loss due to heat. So, I guess the end pressure should be less than 27 psi.

[archull]

I personally think this is a stupid idea. A Sequential setup would be pointless when a conventional setup works so damn well already. The cost will be considerable and the space just isnt there to fit 2 turbos and all the other stuff required to get this to work.

[drhonda]

Great minds discuss ideas. Average minds discuss events. Small minds discuss people.

[1crazy93K]

Originally Posted by archull

I personally think this is a stupid idea. A Sequential setup would be pointless when a conventional setup works so damn well already. The cost will be considerable and the space just isnt there to fit 2 turbos and all the other stuff required to get this to work.

theres plenty of space to make this work on a swapped car. but for your rsx or an ep3 it wouldnt fit.

it could get costly... but on the thread it says help me day dream. we are just talkin about how this would work. If money wasnt an issue id like to see what the outcome would be. just cause its different doesnt make it a stupid idea. lol

[scmil95eg]

Originally Posted by Texasnick

1) If you think of it in terms of absolute pressure, the first turbo is able to achieve 14.7 psi + 7 psi = 21.7 psi, or 1.476 atm. This feeds the second turbocharger, so in effect the "atmospheric" pressure going into turbo #2 is really 21.7 psi, as opposed to 14.7 psi. If turbo #2 achieves 20 psi (relative), then at this point it is generating 41.7 psi abs as opposed to the 34.7 psi that it would if it were on it's own. In terms of boost, or guage pressure, this is 27 psi. Like I said, this is just an educated guess, but maybe someone can take it and run with it so we can get the ideas flowing.

You are absolutely correct, and it makes total sense when you look at it from an 'absolute' point of view. The best and most extreme examples of this are in truck/tractor pulling where it's common to stage three turbos in line to achieve 150 - 300 psi of boost. The turbo at the end of the line would never spool without the other two forcing air into it. I think Dodge has a HD pick-up with two staged turbos on a cummins inline 6, if you want an OEM example.

[archull]

Originally Posted by 1crazy93K

theres plenty of space to make this work on a swapped car. but for your rsx or an ep3 it wouldnt fit.

it could get costly... but on the thread it says help me day dream. we are just talkin about how this would work. If money wasnt an issue id like to see what the outcome would be. just cause its different doesnt make it a stupid idea. lol

The way I look at it, you wouldn't be gaining usable power with this setup. If you are using the car for a road race setup you want a small turbo because the power comes on too violent with a big turbo and the more power you are pushing the most likely you are to break the tires loose and lose control, a sequential setup will lower the drastic nature of the boost kicking in but it will still have the same effect, too much power = you in the wall.

On a drag setup you want a big ass turbo to get you there as quick as possible. On slicks and using antilag you are building full boost off the line so there is no need for a smaller turbo. The smaller turbo will actually hurt you as it is a restriction in the system and has too much back pressure.

Like they always say, if something isn't broken don't fix it and I think this really rains true with this setup

[zaider]

I, too, am basically just thinking out loud here so if someone knows more and wants to correct me, give'r.

So, there are two scenarios to consider:
a) True Sequential: Small turbo provides boost at low rpm. At mid-rpm, Small Turbo feeds Big Turbo. Once the big turbo is spooled up, there is no bypassing the smaller one. Both turbos are providing boost.
b) Usual Sequential: Small turbo provides boost at low rpm. At mid-rpm, Small Turbo feeds Big Turbo some boost, as rpms increase, small turbo is phased out until only the big turbo is providing boost.

For the usual sequential case, you're not going to get any summation of the boost pressures as your max PSI. Max psi occurs at high rpms, therefore only the large turbo is providing boost, with the small turbo being bypassed. This means that the inlet air pressure is still 14.7 and the outlet would be that plus the relative change of the large turbo (20psi) for a total of 34.7psi.

I dont think that the total output of true sequential turbochargers would be the sum of their outputs due to the following reasons:

1) Temperature. PV = nRT. This formula states that Pressure is proportional to Temperature. Raising the pressure by passing the air through the small turbo would increase the temperature of the air that gets passed through to the larger turbo.

Tout = Tin + Tin x [-1+(Pout/Pin)^0.263]
.............................efficiency

An increase in temperature makes the second turbo a lot less efficient. This could be partly dealt with by placing an intercooler between the turbos, but that restricts flow in, and you lose power by decreasing your Intake Air Flow.

This brings me to my next issue:

2) Intake Air Flow. From a general standpoint, more air in and more air out means more power. A small turbo is good because it is designed to pass a lower volume of air at a lower pressure than a large turbo. It spools up faster due to these design characteristics, so it is more efficient at lower RPM. A large turbo is good because, once it has spooled up, it can pass a larger amount of air at a higher pressure.

However, most sequential turbocharger designs that I have seen use the small turbo at low rpm, then use some of the airflow from that to spool up the bigger turbo and then switch the airflow to the larger turbo, bypassing the smaller one at high rpm. I believe this is due to the fact that the smaller turbo can pass a limited amount of air flow.

At higher rpms the smaller turbo becomes less efficient due to its size. In our case, it simply cannot pass enough air through it's smaller inlet as opposed to the larger turbo. To produce its higher output pressure, the large turbo needs to intake a specific amount of air through its inlet and I dont believe that the smaller turbo is capable of supplying that air at the necessary pressure. Basically, the larger turbo, when spooled up, would be "sucking" the air through the small turbo. The small turbo loses efficiency and can either supply the desired air flow or the desired pressure, not both. You might be able to achieve a small gain from operating the small turbo before the larger turbo, but I couldn't see it being more than 1-2 psi.

Now, I've been discussing this with Texasnick (we work together) and i've gotten very confused about flowrates, conservation of mass, etc so Im going to post this and see what the thoughts are...

[1crazy93K]

Originally Posted by archull

The way I look at it, you wouldn't be gaining usable power with this setup. If you are using the car for a road race setup you want a small turbo because the power comes on too violent with a big turbo and the more power you are pushing the most likely you are to break the tires loose and lose control, a sequential setup will lower the drastic nature of the boost kicking in but it will still have the same effect, too much power = you in the wall.

On a drag setup you want a big ass turbo to get you there as quick as possible. On slicks and using antilag you are building full boost off the line so there is no need for a smaller turbo. The smaller turbo will actually hurt you as it is a restriction in the system and has too much back pressure.

Like they always say, if something isn't broken don't fix it and I think this really rains true with this setup

yeah you are correct i see your point, but what about a street setup what would you say for that?

[Texasnick]

Originally Posted by archull

I personally think this is a stupid idea. A Sequential setup would be pointless when a conventional setup works so damn well already. The cost will be considerable and the space just isnt there to fit 2 turbos and all the other stuff required to get this to work.

It may be to you, but this type of FI setup has been used on production cars, and they obviously saw a point to doing it. Besides, k20a.org is hardly a "follow what works" forum. This is a site full of innovators (see....honda based v8....pacman's quest for 1000 hp). It's just an idea to throw around. Maybe something cool will come out of it. If everyone listened to the "just do what works" school of thought, we'd all still be running around in b16 hatches running 14 second 1/4 miles.