Sequential Turbo 3

[R34ztune]

Hi all,

I've been looking for a forum and place on sharing ideas about sequential turbo charging. Many forums I've seen on the Internet about turbocharging is mainly focusing on horse power. Sequential twin (or multiple) turbo setup goal is not just for high power but also taking care about low end grunt of an engine.

To make it sort, I will only talk about twin turbo setup to simplify the introduction of sequential turbo . The 1990's Mazda RX7 and Toyota Supra are well known setup of sequential turbo charging system. Tuners often change to twin parallel turbo or even one large turbo to replace the stock setup and achieve a high output engine. This doesn't mean the stock setup is no good, it is because tuner's goal is aim for high HP numbers with simplicity. Everyone who experience with turbochargers know that using a large turbo can achieve high horse power with sacrifice of low end torque. Sequential turbo charging is a way to optimize both low and top end power of an engine.

Take RX7 as an example, two turbo chargers exists in the system. These two turbo are the same size. The primary turbo works in all engine rev range. The secondary turbo only works in mid-high rev range. Since the 13B rotary engine is an engine having wide range rpm, it is an ideal motor to having a sequential setup to maximize the torque on each rpm range and deliver the most out of it. In low engine speed, both rotor's exhaust gas are pumped to the primary turbo, making the primary turbo spools up quickly so that the engine can have boost as soon as possible. When the engine speed goes higher, the primary turbo efficiency decreases and requires two turbo to work in parallel to generate enough boost for the engine. At this time, a flap in the exhaust manifold open wide and allow the exhaust gas of the second rotor to pump into the secondary turbo . At this stage, the engine just work as a parallel twin turbo system.

The disadvantage of sequential turbo setup is complication of piping work, control and known how of it. Nowadays we have a much better technology base then in 1990s. Does anyone know anybody in the world is doing some similar projects using a better design then the RX7 and Supra? I have been in this topic for many years, but I didn't have enough resources and time to build a prototype of it. I've done lots of design and research work in this area, but not seeing many of others is working on it. At the time I was studying, forum and blogs are not that common at all. Recently, I bought a R34-GTR, the engine revs from 1000 to 8500, with little modification it can go to 10000rpm. This engine is very tough. Currently, it is a parallel twin turbo setup and is missing low end grunt . I am looking to modify it to a sequential setup . I was trying to locate the Garret VNT (Variable Nozzle Turbine) turbochargers to achieve a similar goal, but can find very little information about it .

If anyone is in the field, please share.

 

[patprimmer]

Changing gear ratios, only happens in motorsport/race applications. How often a street car customer will do that?

I have and will again

Regards
Pat
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[gruntguru]

I believe everyone in this forum know that the usable area under the torque curve means deliverable power output.

Everyone except me - perhaps you should educate me? I would particularly like to know about "Selecting gear ratios to pickup largest area under the torque curve"

Engineering is the art of creating things you need, from things you can get.

 

[R34ztune]

If you look at the torque/power curve versus engine speed. Draw two vertical lines in your torque curve, the left line is the engine speed after shift, the right line is the max or shift speed. The deliverable power is the area under the power line and these 2 vertical lines. Then you can determine your gear ratios by moving these 2 vertical lines along the x-axis by maximizing the area under the curve.

 

[patprimmer]

gruntguru

While I have my doubts about the validity of this thread and the coherence of the OP, he is obviously English second language and I think we can cut some slack with regard to his use of terms that do not quite fit if we can clearly see what he means to say.

I think if this thread denigrates into yet another torque vs horsepower it will only detract from the thread and the participants and the forum.

Regards
Pat
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[Lou Scannon]

Pat, denigrates or degenerates?

 

[patprimmer]

Either. They both mean pretty much the same thing I think

Regards
Pat
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[gruntguru]

If you look at the torque/power curve versus engine speed. Draw two vertical lines in your torque curve, the left line is the engine speed after shift, the right line is the max or shift speed. The deliverable power is the area under the power line and these 2 vertical lines. Then you can determine your gear ratios by moving these 2 vertical lines along the x-axis by maximizing the area under the curve.

If you use a wider ratio gearbox the two vertical lines will be further apart and the area will be greater, so the widest possible ratios will yield the greatest area and there for the greatest acceleration? There is clearly something wrong with your method. So I repeat.

Gear ratios should be selected to maximise average power. ie move your two lines so they are either side of the power peak and as close to the power peak as possible.

Engineering is the art of creating things you need, from things you can get.

 

[R34ztune]

Thank you all.

 

[TDIMeister]

http://gt-suite.us/confarch/FEV2009.pdf

 

[yoshimitsuspeed]

Just found this a couple days ago.

http://www.aerocharger.com/aerochargers.php

Looks pretty interesting but some of their marketing is kind of hard to believe.
It is self contained, no engine oil and it looks like no coolant.
It has a small oil resivoir that mists the turbo and the oil needs to be checked once a year.
One thing that bothered me was in the FAQ.


"Does the Aerocharger require a turbo timer?
A:
No turbo timer is required with the Aerocharger. Since the Aerocharger does not use hot engine oil, hot shutdowns are not an issue. The drag on the bearings is so little in fact, that the Aerocharger will slowly spool down on it’s own when the engine is shut off. Whereas conventional turbos suffer from engine oil heat and are stopped almost abruptly after the engine is shut off due to a flooded bearing design. This is very damaging over time and is exactly why the Aerocharger does not use and oil source from the engine."

Seems funny since the coking problems conventional turbos have is not from the hot engine oil but from the even hotter turbo. How does their turbo not have this problem with no water or outside oil cooling?

It is still interesting though. I could see playing with something like this at some point.

 

[gruntguru]

The Aerocharger looks a lot like the turbos from Aerodyne in the 1980s. The bearing is located on the end of the shaft furthest from the turbine. This reduces heat soak to the bearing.

I had almost forgotten Aerodyne. They made a kit for something (I think it was a Mercedes diesel) with the turbo shaft vertical and the turbine housing integral to the exhaust manifold, with the runners feeding directly to the periphery of the turbine nozzle. Very innovative I thought.

Engineering is the art of creating things you need, from things you can get.

 

[yoshimitsuspeed]

I noticed the bearing location after I posted. It does seem like a very good idea but it still bothers me that wasn't their answer to the question.
It could be more of an issue with marketing though. I see that way more often than I'd like.

 

[patprimmer]

Once I see marketing hype in one piece of technical literature it tends to create fruit from the poisoned tree type reactions to all their claims in my mind.

Or put another way, 15 years to build a reputation, 15 seconds to blow it.

Regards
Pat
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[patprimmer]

While I can see advantages to removing the bearing from the area of the hot side, I also see a few disadvantages and problems, being:-

1) The wheels being out on cantilevered shafts greatly decreases the strength and stability and makes it a lot more sensitive to out of balance especially on the hot wheel.

2) Wear or slack in the bearing causes exagerated clearance problems due to the extra distance from the bearing to the wheel/housing interface area.

3) You still need shaft seals between the hot and cold sides and these should be cooled.

4) The air inlet to the compressor wheel has to have a shaft across it and this disrupts airflow.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

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[gruntguru]

Since this is technology that was developed in the 1980s and the IP has obviously changed hands, it is likely the new owners are not as conversant with it all.

Engineering is the art of creating things you need, from things you can get.

 

[bradvr4]

What about a compound turbo setup? Your I6 arrangement lends itself nicely to this. Google for 'eclipse compound turbo' and you'll find a thread of someone doing exactly this to an I4 2.0 making a massive amount of low down torque and spooling up the big turbo very quickly.

 

[simple77]

R34ztune, I am cannot agree more with you on you initial post.

1. It can be done and already been done. OEM's do not like it as it's costly. Power-train developers had those systems drawn out and tested decade ago, mainly for racing applications and high power staff like tracks / generators engines.

2. EGT are NOT a problem, even if one want to use two VGT's / VNT's. If you worry so much about EGT - run E85, it runs 200C cooler. Very close to diesel temperature. You will also get more HP from E85 due to high octane rating. Will use more fuel, but it cost

3. One may want to have variable boost pressure delivery across the RPM range. When engine VE (volumetric efficency) peak (usually 3000-4000RPM) you will need to reduce boost to keep torque curve flat. This will save engine and maximize utilization of strength of internals. They are rated by max load.

4. Good set up will have one smaller turbo to spool from idle and larger to take care of the rest. You can and want to have more boost after 4000RPM, therefore larger turbo.

5. There was the point mentioned about opening the vanes of VNT to aid engine efficiency at cruise: same can be done by keeping the wastegate open. I do not think it will be much help, exhaust gas flow is minimal under cruise, there will be very little restriction from the turbine.

6. One may wonder if two sequential VGT's will be an ultimate answer.The problem is that those turbos are made in the limited range and may prove hard to find two suitable petrol units. Diesel models may not be optimal due to different flow/PR configurations. Maybe units scavenged from Porsche can be used.

Thoughts?


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[TDIMeister]

"6. One may wonder if two sequential VGT's will be an ultimate answer."

Being done:

http://forums.tdiclub.com/showthread.php?t=270527

 

[simple77]

TDIMeister, very nice thread. Watching it.




Manufacturing parts in China

http://www.pa-international.com.au

 

[zcchene46]

R34ztune,
Have you thought about making a twin turbo system where a bigger feeds charged air to a smaller turbo? The system will go like this
Hot side: Exhaust Manifold>Big Turbo>Small Turbo>Exhaust
Charge side: Air Filter>Big Turbo>Small Turbo>Cooler>Throttle Body>Intake Manifold
The small turbo is basically compound-charging whatever the big turbo spits out to it. The boost pressure multiplies. The small turbo picks up the low to mid-end while the big turbo shines in top-end.
It is essentially the same as twincharging only change the supercharger into a smaller turbo.. Comparing to a twin charge system, this might still lose a tiny bit of low-end.. However, it will not have the hassle of dealing with the bypass for SC when part throttle or idle..
And I believe some cummins diesel engines use this setup