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arghx
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There will be no Taylor Lautner discussion in this thread. Basically I will randomly bring up whatever interesting [to me] shit I want to post about. Today we will talk about the original Honda NSX C30A engine with the original VTEC system.



The original VTEC system is way outdated now but at the time it was pretty revolutionary in a production car. By having two sets of valve lift, timing, and duration profiles it allowed the performance benefits of a "cammed" engine while still being docile on the street. Some modern engines can continuously vary valve lift (370Z can do it, and we all know Nissan Makes Some Junk). Honda has patented their own version of that technology but to my knowledge they haven't implemented it into production cars yet. Because they are cheap bean-counting assholes.



Those are specs on the original C30A (I believe it is the Japan version). For the low speed cam, I think the figures on the left are for the manual transmission. If I am doing the arithmetic correctly, the intake duration is 212.5 degrees and the exhaust duration is 202.5 degrees. When the high speed cam engages, intake duration increases to 230 degrees and exhaust duration increases to 220 degrees. Combine that with the increased lift and you get the following volumetric efficiency curves:



The NSX does not have a system to continuously advance the intake cam and retard the exhaust cam like most modern engines do. The i-Vtec system had that 10 years ago. To improve volumetric efficiency the NSX does have a variable intake plenum/runner system like the GS-R and a lot of other engines:



Nowadays I can get a variable intake system in a Dodge Charger rental car, so it shows how much technology trickles down.

[Edited on August 20, 2011 at 11:07 AM. Reason : .]

8/20/2011 10:52:18 AM

H8R
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8/20/2011 4:34:58 PM

catzor
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I <3 this kind of shit.

8/20/2011 7:44:05 PM

benXJ
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same here....i'll be checking back

8/20/2011 8:51:18 PM

tchenku
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I don't understand the "Open" pic

even with the butterflies open, it seems like more air would flow as in the closed configuration because it's the path of least resistance. couple that with the fact that the "open" config would be for low throttle --> less velocity --> less likely to pour into the chamber, slam to the bottom of the manifold, and finish the u-turn

8/20/2011 9:33:30 PM

arghx
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Quote :
"even with the butterflies open, it seems like more air would flow as in the closed configuration because it's the path of least resistance. couple that with the fact that the "open" config would be for low throttle --> less velocity --> less likely to pour into the chamber, slam to the bottom of the manifold, and finish the u-turn"


You've got some things reversed. There's nothing all that unique about this type of system, even though they tend to be used in higher-end engines. Here's one link to check out which discusses Porsche's system: http://www.autozine.org/technical_school/engine/tech_engine_2.htm

In this case, notice that this is the "chamber volume control valve." So what it does is increase or decrease the plenum volume, which isn't exactly the same as changing the runner length. The plenum is used as a sort of "reserve tank" of air and is also used for dynamic supercharging/resonance effects. Look up Helmholtz resonator. As random as it sounds, think of the plenum as the big chamber in an Ocarina instrument from Zelda. On a naturally aspirated engine, larger plenum = better top end but worse low end. On boosted engines I think also holds true but it is a little more complicated.

So on the NSX and GSR these are normally open butterfly valves with a diaphragm actuator. They need vacuum to be closed. When the engine is ON but under 4800 rpm, the ECU switches ground to the chamber volume control solenoid valve. This applies vacuum from the vacuum tank to the diaphragm actuator, pulling the butterfly valves shut and pretty much eliminating the plenum. The vacuum tank + check valve are used because the engine does not produce sufficient vacuum under heavy throttle to hold the butterflies shut.

At 4800 rpm, the ECU turns off the chamber volume control solenoid valve. Vacuum is released from the diaphragm actuator, and the butterflies open. A plenum opens up, allowing pulsation and resonance effects to increase volumetric efficiency. The pulsation effects can occur in two main instances:

1) As the intake valve closes, the intake air slams into the back of the valve and reverses direction. If the plenum volume and runner length are tuned correctly for the rpm range, a pressure wave will flow back into the next intake valve opening, but that air will be compressed a little bit so you get more volumetric efficiency.

2) IF there is sufficient overlap between the intake and exhaust stroke at a given rpm, when the intake valve opens there may be high exhaust pressure in the combustion chamber. When the intake valve opens, the air actually rushes backwards initially, causing a pressure wave that will reach another intake valve while it is still open. This causes that supercharging/resonance effect. The length of the runners, the volume of the plenum, the engine rpm, and the valve timing are very important for this.

On of the main advantages of port (or direct) fuel injection over a carburetor is that you have more flexibility in intake manifold design. With a carburetor and throttlebody-style injection, the fuel is flowing through the intake manifold and you have to make sure you get decent distribution among the runners and don't get too much pooling. With modern fuel injection you can use these more complicated intake manifold geometries because you don't have the same fuel flow, distribution, and atomization constraints as on a carb.

[Edited on August 21, 2011 at 9:41 AM. Reason : .]

8/21/2011 9:38:22 AM

arghx
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So check this out. Back in the mid 2000s Chrysler created a turbo version of their 2.4L 4 cylinder and put it in the PT Cruiser and the SRT-4 Neon. It's pretty interesting to read about all the modifications they made to the engine. But on the subject of intake manifolds, here is some info on the unique intake used for the PT Cruiser (due to fitment/packaging constraints):



and here is a diagram of manifold runner flow distirbution. Notice that it varies with the valve lift:

8/21/2011 9:48:31 AM

tchenku
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so basically you're saying this:



____________
| |
---------------' '--------------
---------------. .--------------- --->
| |
````````````


breathes more easily than

------------------------------------------------ --->
------------------------------------------------


reminds me of the bigger-fuel-filter-is-better and gutted cat debates, even though there's a push vs pull aspect

[Edited on August 21, 2011 at 9:57 AM. Reason : ]

8/21/2011 9:55:20 AM

arghx
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"Breathes better" maybe isn't the best word. You are thinking of the engine as a garden hose instead of a series of positive displacement pumps connected to each other. Air is constantly moving backwards inside the manifold as the valves close. But the whole point is to maximize the dynamic supercharging effects because of the pulsation. If I didn't work, Honda wouldn't have spent all that money to put it in the NSX and GSR.

8/21/2011 10:00:03 AM

arghx
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oversimplified youtube animations:





[Edited on August 21, 2011 at 10:04 AM. Reason : 2]

8/21/2011 10:03:26 AM

arghx
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Let's talk about fuel injection timing, something that is not widely understood. First, I'll start with a basic outline of how a carburetor works. I'm not a carburetor expert and I don't work on them much, but understanding the basics helps. Then we can discuss injection strategies for port injection and later on discuss gasoline direct injection. I've got this old Mazda carburetor training manual which will be a helpful source of diagrams.

Carburetors use pressure differences to create a sort of controlled fuel leak into the beginning of the intake manifold passages so that fuel will travel through the manifold.

Here is a basic carburetor:



The fuel sits in the float bowl and is drawn out into the intake system by the venturis. A venturi is basically a restriction that creates a pressure difference (vacuum). A carburetor is a restrictive intake system by definition. Here is a diagram showing vacuum under part load and full throttle conditions:



On the left you can see that at part throttle there is significant vacuum past the throttle valve at the bottom, with some vacuum in the venturis. At full throttle manifold vacuum disappears but vacuum in the venturis increase. There are also a whole bunch of orifices, hydraulic circuits, and other complicated crap to deliver different amounts of fuel under different types of driving. The fuel moves through the intake manifolds and thus flow distribution and fuel pooling could be a major issue. That can hamper the potential of carburetors due to the lack of flexibility in designing manifolds.

[Edited on August 23, 2011 at 12:27 AM. Reason : .]

8/23/2011 12:25:34 AM

arghx
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Skipping over throttlebody injection and some of the other less important designs, let's go right to multi-port solenoid injection. For now I will skip discussion of fuel pumps, fuel pressure regulators, etc. Here is a basic fuel injector:



A fuel injector is just a magnet and a valve. The magnet lifts the valve off its seat and allows fuel to flow. When a 12 volt circuit is complete, the solenoid coil energizes to pull the valve open. Normally the injector receives switched power from the electrical system, but it only turns on when the ECU pulses the ground signal through a transistor. Fuel pressure is kept constant through a fuel pressure regulator so fuel volume is regulated by the amount of ON time for a given pulse, in milliseconds. So 5 milliseconds delivers more fuel than 2 milliseconds. Some diagrams of port injection in a 4 valve overhead cam engine:





There are all sorts of variations in spray patterns and injector design. In the image immediately above, you can see that the injector has two holes in order to direct fuel on to the back of the two intake valves.

8/23/2011 12:42:43 AM

arghx
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For multiport fuel injection, there are three styles of control:

1. batch fired injection (all fire at once)
2. grouped injection (two injectors fire before two pistons begin the intake stroke)
3. sequential injection (each injector fires separately)

Batch-fired and sequential injection are the most important.

Batch-fired is nice and simple and is common on early injection systems. The nice thing about batch fired (simulataneous injection) is that the ECU doesn't need to know exactly where a given piston is at a given time. The ECU calculates the required fuel volume for the engine to go through all four strokes, 720 degrees of crankshaft rotation in a normal piston engine. It then splits that total volume into two injection events where all injectors fire.



Grouped injection fires two cylinders at the same time, before the intake strokes of those cylinders. It's not really that important of a system so I'll leave it at that. Sequential multiport fuel injection is more advanced and it is still the most common fuel injection system used on production cars today:



Each injector fires separately before the intake stroke of its respective cylinder. Implementing this requires four separate transistors (injector drivers). The ECU also has to use a top dead center (TDC) signal as a reference point so that it knows when to fire the injectors.

8/23/2011 1:13:07 AM

arghx
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Let's digress for a second to talk about position sensors. The ECU needs to know:

1) the approximate position of the crankshaft in degrees to calculate engine speed

2) a reference point of TDC to synchronize injector firing

3) whether the engine is on TDC for compression stroke or the exhaust stroke

Here is a very simple crank position sensor trigger wheel, the Ford EDIS system. It has 35 teeth and 1 missing tooth, to each correspond to 10 degrees of crankshaft rotation. The missing tooth provides the TDC signal. The crank angle sensor produces an AC voltage for the ECU to interpret.



and here is the waveform:



So now the ECU knows engine speed and TDC reference, and a cam position sensor helps it figure out which cylinder is where and whether that cylinder is on the intake or exhaust stroke when it reaches TDC. That's how the ECU figures out how to fire the injectors in the proper order.

8/23/2011 1:24:13 AM

arghx
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Note that I am pulling some of these diagrams from different sources and these different engines do have variations in the design of their position sensors. Some of these diagrams are from early Mitsubishi designs which have all the position signals produced from one optical sensor on the cam, a design that requires a timing light for adjustment. The Ford EDIS system with the crank trigger wheel can actually be run without a cam position sensor altogether due to the design of the ignition system.

Almost all the newer engines use some kind of AC voltage trigger wheel on the crank pulley which has a few missing teeth. Then the cam position sensor uses a Hall Effect design (you can wikipedia it) to produce a square wave to allow proper fuel injection timing, spark timing & distribution, and valve timing on engines with variable camshaft timing.

Now during normal operation a modern sequential port injection system actually batch fires the injection under two types of conditions: cranking plus initial start up, and rapid opening of the throttle valve. There are some variations in injection strategies, but during cranking the ECU cannot immediately synchronize the crank position, TDC signal, and cam position signals. So it reverts to batch-firing the injectors based on the crank angle sensor signal, until everything synchronizes together and proper sequential injection can begin.



So this is on a Eclipse/Talon/Laser, which uses ON/OFF square wave pulses for position sensors as opposed to an AC waveform. Looking left across the chart, first the ECU receives a short 85 degree BTDC signal as a reference point. Then all 4 injectors initially fire at the end of the first crank angle sensor pulse, which signifies that the engine is at 5 degrees BTDC. This is a long fuel pulse to supply sufficient fuel for starting; it accomplishes the same thing as a choke on a carburetor. When the engine reaches the next 5 degrees BTDC signal, all 4 injectors fire again but the pulsewidth is much less because not as much fuel is needed. Finally, the number 1 cylinder TDC signal allows the ECU to synchronize everything in order to begin sequential fuel injection.

8/23/2011 3:25:07 PM

arghx
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The injectors may also be batch fired during a tip-in condition, where the throttle plate is opening and a carburetor would have activated an accelerator pump. This additional fuel prevents hesitations and lean misfires. There are two types of tip-in fuel: synchronous and asynchronous, and to my knowledge most port injected engines use both to some extent.

Synchronous fuel is additional fuel added to the normal sequential injection. So if I would have calculated 8 milliseconds of injector pulsewidth for cylinder #4, during tip-in condition I might instead deliver 9 milliseconds to cylinder #4. Synchronous tip-in is normally calculated based on:

-- the rate of change of intake airflow (on vehicles equipped with airflow sensors)
-- the rate of change of manifold pressure (on vehicles equipped with manifold pressure sensors)
-- perhaps both if the engine has both types of sensors, like a lot of GM's and Subarus.

Asynchronous fuel is additional fuel added in a completely separate batch-fired injection event, where all injectors fire at once outside of the normal sequential fuel injection. This injection event does not depend on the crank angle signal, TDC signal, or cam position signal. It is typically calculated based on the rate of change of throttle valve position. Here is a graph showing asynchronous tip-in fuel:

8/23/2011 3:26:27 PM

arghx
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So with sequential fuel injection, does the injection timing advance (fire earlier) as rpms increase, just like spark timing usually does? The answer to that is yes, but little easily-attainable information exists on how this is calculated on modern engines. One interesting source does explain how an Rx-8 Renesis engine calculates the CA (crank angle) for the start of injection and end of injection. Rotary engines are a little weird because they go through all four strokes in 360 degrees of crank rotation instead of 720 degrees like a piston engine. TDC is always on the compression stroke, instead of a piston engine where TDC could be on the compression stroke exhaust stroke. So here is the formula.



It's not as confusing as it looks. The ECU begins with a starting point, the "standard position" for injection. Then it adds injection timing advance (ends the injection event earlier in terms of CA) based on engine speed. The higher the engine rpm, the earlier the injection event will end. After calculating the injection end position, it calculates the start position based on the injection pulsewidth which is proportional to engine fuel requirements. The longer the injector fires the more fuel will be delivered and the earlier the injection event will begin.

-- At high rpm and heavy load, injection will end early and start early. The injector will fire for a long time.

-- At high rpm and light load, injection will end early, but start later than it would under a heavy load condition. The injector will fire for a short time.

-- At low rpm and heavy load, injection will end later than it would under high rpm, but injection will still start relatively early. This is because the injector will be firing for a long time due to fuel requirements under heavy load.

-- At low rpm and light load, injection will end late and start late. The injector will fire for a relatively short time.



And that covers the basics of injection timing on multiport fuel injection.

[Edited on August 23, 2011 at 4:15 PM. Reason : .]

8/23/2011 4:12:13 PM

sumfoo1
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post so you know i'm reading.

8/23/2011 4:17:16 PM

Hiro
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8/23/2011 10:50:58 PM

arghx
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Found this overview of suspension geometries today...



8/24/2011 2:55:53 PM

Quinn
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can you explain why VWs 5 valve head doesnt flow for shit?

8/24/2011 6:39:17 PM

sumfoo1
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Can't put any lift on the intake cam without interference.
That and the engine only displaces 1.8 liters...

and no one has the balls to put a turbo on it that's correctly sized and won't choke it out on the big end.


Are there any cars for around 10k with full a-arm suspension rwd and an easily boosted engine ?

(and why do you bitch about that so much?)


[Edited on August 24, 2011 at 8:46 PM. Reason : .]

8/24/2011 8:37:25 PM

arghx
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^sounds like you need to get an AP1 s2000... not exactly cheap to boost though

Without specs on the VW engine in question, it may be that the intake ports and heads are optimized for tumble motion instead of total flow capacity. They are two competing design requirements. I know VW likes to use tumble generation valves on some engines so it would make sense that they would optimize for tumble flow. I've got some shit here about tumble generation valves and the aspect ratios of tumble maximizing intake ports vs flow capacity maximizing intake ports.

8/24/2011 9:52:00 PM

Wyloch
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This is a cool thread. Thanks, keep it up.

8/24/2011 10:18:52 PM

arghx
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So the high flow port is on the left and the high tumble port is on the right. High flow is going to help engine output provided that everything else is optimized. High tumble motion is better for combustion stability, emissions, and knock resistance. The port on the right is the high-tumble port. It's a little hard to see, but if you look at the bottom/lower left side of the valve a tumble zone forms there.



The level of tumble flow is mostly determined by the two dimensions shown above. That's unless you use tumble generation valves like VW and Subaru use. Here are the tumble valves on a VW 2.0T engine:





I really don't know much about the VW 5 valve engines though. The poor flow might have more to do with cam and valve design as sumfoo1 suggested.

[Edited on August 24, 2011 at 11:50 PM. Reason : .]

8/24/2011 11:44:52 PM

ncsufanalum
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Yes, arghx, I'd say its safe to say you should be exercising this knowledge/passion on a daily basis via working in the auto industry in some capacity.

8/25/2011 9:29:10 AM

sumfoo1
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yeah i love this stuff but i don't know where you find all the tech papers on them... its awesome.

8/25/2011 11:19:21 AM

arghx
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Who in the Garage has a dual clutch transmission? I've been reading a lot about them (and other automated manuals) and watching videos but I have not actually driven one. I'd love to drive all the different variations to get a feel for them. I believe Lamborghini uses the single plate dry clutch (automated manual) on some models which are known for hard "sporty" shifts. VW is using BorgWarner dual clutch units on the R32 and Mitsubishi has a Getrag DCT on the Evo X. Now I think Porsche is using a ZF 7 speed.

Some Youtube videos on DCT transmissions:



8/25/2011 1:13:19 PM

arghx
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Here is a chart from a 2005 BorgWarner study comparing different transmission configurations.



BW went on to make some interesting observations and in some cases rosy predictions about DCT adoption, but they are definitely growing in popularity.

8/25/2011 1:42:52 PM

sumfoo1
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Does the hydraulically actuator negate that the inner clutch should have a lower torque rating then the outer? (i guess do they bump up the pressure on the inner clutch?)

8/25/2011 2:08:57 PM

arghx
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Well the inner clutch is connected to a narrower diameter input shaft so maybe it all works out? The two clutch diameters might be the same. I'm sure they have precise control over hydraulic pressure controlling a bunch of solenoids in the valve body. I've torn apart regular manual and regular automatic transmissions but not a dual clutch, since you can't exactly get your hands on a cheap junkyard one yet. Here is a diagram of the Getrag 6 speed unit on the Evo X:

8/25/2011 2:44:20 PM

sumfoo1
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I mean they're concentric so one has to be a smaller diameter then the other.. i guess they could do it with # of disks in the pack too. like inner has 4 sets outer has 3 or something along those lines.
I also figure 1st and 7th would probably see the most torque and they're both on the outter clutch pack.

8/25/2011 3:10:25 PM

sumfoo1
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GRR why does tww keep DPing me.!!

[Edited on August 25, 2011 at 3:10 PM. Reason : .]

8/25/2011 3:10:25 PM

arghx
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Here's some discussion of pulse turbocharging including monoscroll turbo, twin scroll turbo, and twin turbo configurations. Monoscroll is a conventional turbocharger. A monoscroll turbo has one big open inlet for the turbine housing:



These work best on applications when there is a steady steam of exhaust flow with minimal pulsation effects and load changes. They're also cheap and simple to implement because they allow the most flexibility in exhaust manifold design. A twin scroll turbo (and also twin turbo configurations) utilize pulse turbocharging. Pulse turbocharging has been around on diesel engines for decades and has been slowly adopted on passenger car gas engines beginning in the 80s. Pulse turbocharging takes advantage of the engine's firing order to reduce backpressure and residual gases in the manifold. This can improve transient response. Here is an example of a twin scroll inlet:



Notice the two inlets. So the key is to divide up the exhaust pulses according to the firing order. On a regular inline 4 cylinder engine, the easiest way to do this is with a twin scroll manifold like on most Evos:



If you look carefully you will notice that cylinder #1 and #4 are paired to one scroll, while cylinder #2 and #3 are paired to another. Now a typical firing order on an inline 4 is 1-3-4-2. So the engine is alternating between pulsing each scroll. This keeps residual exhaust from building up in the manifold. That not only reduces backpressure, it can also help scavenging effects in the combustion chamber during valve overlap:



In the image above you can see the reduction in exhaust gas backpressure on an inline 4 cylinder engine utilizing twin scroll pulse turbocharging. If both the intake and exhaust valves are open at the same time, a high intake pressure and low exhaust backpressure can help improve with filling the cylinder. Here is another graph showing boost pressure improvements for the same engine mentioned above:

8/26/2011 9:39:17 AM

arghx
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Older rotary engines (pre Rx-8 Renesis) produce very strong pulsations and thus benefit greatly from turbo systems that take advantage of those pulsations. The torque produced by the turbine side of a turbocharger, which is used to drive the compressor wheel, is proportional to the square of the exhaust gas velocity (Tashima, Development of Sequential Twin Turbo System for Rotary Engine, 1991). Any kind of high pressure, high velocity exhaust gas will improve response on a turbo. Here is a comparison between the exhaust pressure and exhaust port area of an older rotary vs a piston engine:



The higher pulsation effects are due to the fact that the exhaust ports open much faster on this type of rotary and there is no valvetrain to absorb heat or slow the exhaust down. Utilizing these unique characteristics, Mazda adopted a twin scroll/divided turbocharger for the 1989 model year Rx-7. This yielded the following benefits over a monoscroll design:





Now, getting back to piston engines we can compare single turbo monoscroll, single turbo twinscroll, and twin turbo concepts. Twin turbos are also going to take advantage of the engine's firing order, by directing one set of pulses to one of the two turbos. On an inline six, the front three and rear three cylinders alternate in their firing order and packaging twin turbos is straightforward. BMW did a study to understand their relative capabilities on an inline 6 cylinder engine. The did this during the development phase of the N54 twin turbo engine utilized on many BMW's today. This engine has been replaced with a twin scroll twin turbo on the N55 engine.



You can see that the twin turbo configuration has better overall capabilities than a single turbo, but obviously they are going to cost a lot more. Here are the BMW twins:



Toyota utilized a similar twin turbo configuration on their 1JZ-GTE engines 20 years ago but it used older manufacturing processes. Here is the twin scroll turbo from the BMW N55 engine:



And here is the twin scroll turbo from the new 4 cylinder BMW N20 engine:

8/26/2011 9:44:41 AM

arghx
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Now here's a real oddball design. This is from a prototype 5 cylinder diesel for marine applications. 5 cylinders have a firing order of 1-2-4-5-3 with 144 degree interval. This creates weird uneven pulsation effects. The particular prototype I am talking about here used a triple-scroll turbo and a complicated valving system.





So on the three scrolls it worked like this

scroll 1) single cylinder
scroll 2) two cylinders
scroll 3) two cylinders

At low rpm/load, they are all divided up among the three scrolls like that. At high rpm, two valves open to connect scroll #2 and #3 with the single cylinder scroll #1. That effectively turns it into an undivided manifold with less pulsation in order to improve turbine efficiency. The whole point of this configuration was to ultimately reduce diesel smoke emissions as part of a marine diesel emissions reduction study.

8/26/2011 9:50:55 AM

sumfoo1
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It makes the a/r of the turbo act small during spool and large during WOT a .86 ar twin scroll will choke at the same time as a .86 single scroll housing on the same turbine but will spool much earlier. Twin turbos work similarly confining pulses to smaller manifolds where they cannot dissipate pre turbine. The disadvantage of twin turbos is the compressors push against each-other making the compressor lose efficiency.

Most twin scroll turbos are high a/r turbos because that is where they can gain the most, spooling like a .63 but not reaching choke flow till when a 1.0+ would. Also operating with dual wastegates gives another way to make sure excessive back pressure is kept in check.



[Edited on August 26, 2011 at 9:59 AM. Reason : .]

8/26/2011 9:52:36 AM

arghx
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Quote :
"Most twin scroll turbos are high a/r turbos because that is where they can gain the most, spooking like a .63 but not reaching choke flow till when a 1.0+ would. Also operating with dual wastegates gives another way to make sure excessive back pressure is kept in check."


On aftermarket performance applications with free float housing (no internal gate) the manifold design can get complicated when you have to incorporate the wastegates. The twin scroll design is almost like "free spool" though. I noticed a significant improvement in transient response on my Rx-7 when I switched from single scroll to twin scroll.

These new OEM twin scroll turbos like Hyundai, BMW, and Ford are using have an integrated exhaust manifold and are meant to have a ton of low end torque.

8/26/2011 9:58:13 AM

sumfoo1
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Yes I disagree with that article on the twin turbo moment of inertia aspect. Moment of inertia effects response more than it does boost threshold. I consider boost threshold to be the larger portion of spool. I think twins on an inline are a bad idea because they have the needless loss of pushing against eachother. On a v motor the increased pulse density of having a much shorter manifold is well worth the loss of compressor efficiency.

8/26/2011 10:04:35 AM

sumfoo1
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i mean moment of inertia is an r squared function, and so is flow rate right.

8/26/2011 11:12:28 AM

arghx
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It's tough to form my own opinion on that because I do not have access to the prototypes, proprietary models, and modeling software that these engineers are using.

8/26/2011 11:15:00 AM

sumfoo1
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does the bmw twinscroll only dump 1 scroll through the wg?

8/26/2011 11:18:39 AM

arghx
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for the N55 from that angle of the diagram it appears to only come off one scroll. I'm not sure about the N20.

8/26/2011 1:15:38 PM

arghx
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Here's an interesting comparison between an oil-cooled turbo, which is a turbo without coolant lines attached to it, and a water-cooled turbo which does have coolant lines. This is a study Mazda did when developing their turbo 13B rotary engine for the 1987 and later Rx-7.



The "temperature of metal" is presumably the bearing housing. In this chart the temperature is the same with the oil and water cooled turbos until the ignition shuts off. Then the oil cooled turbo shoots up in temperature, with a max of 150C/302F temperature difference between oil and water cooled. There's also remarks here about the coolant reducing oil deterioration. After shutdown the coolant lines cool the bearings through a process called thermal siphoning, explained here on an Ford Ecoboost engine:



A fully electric waterpump gives even greater cooling ability for the turbo. On the BMW N54 engine for example the the waterpump can run after shutdown in order to assist in cooling the turbochargers:

8/27/2011 2:31:32 PM

arghx
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Here's a chart comparing the torque output of an R35 GT-R VR38DETT engine (early model) when the air-fuel ratio is stoichiometric (14.7:1 on pure gasoline) vs the torque output in enrichment mode. The engine was designed to have a lot of usable torque in the stoichiometric range to limit fuel economy and emissions.

[Edited on August 28, 2011 at 1:50 PM. Reason : .]

8/28/2011 1:48:58 PM

sumfoo1
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Ok so here is what i don't get... if you richen up the mixture to 12.2 instead of stoich you get power but that fuel is "extra" and shouldn't be burning. So, does the extra power come from the inter-cooling effect of the extra evaporation and mass absorbing pre combustion energy and thus allowing for more timing or, is it because even at stoich some fuel doesn't get burned so the extra fuel just ensures complete combustion with all the air in the combustion chamber.

8/28/2011 6:45:45 PM

arghx
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Quote :
"is it because even at stoich some fuel doesn't get burned so the extra fuel just ensures complete combustion with all the air in the combustion chamber."


I think that's the main reason why enriching the mixture produces more engine output. Here is a study on a single cylinder naturally aspirated research engine. It shows engine torque output vs throttle position vs air fuel ratio vs ethanol blend.



Lambda on the x axis has to do with the air-to-fuel ratio, where 1.0 is the stoichiometric ratio of air to fuel for the particular fuel. So with E0 (0%) ethanol, a Lambda of 1.0 is 14.7:1 AFR. A lambda higher than 1 is a leaner mixture and a lambda lower than 1 is considered an enriched mixture. Each graph is for a different throttle position. Here's some explanation of the trends:



There are a few inflection points in the relationship between Lambda and torque output. That means that with extremely rich or extremely lean mixtures you get a fast drop off in torque. Here's a graph showing brake specific heat consumption:



This is measuring how much heat is being absorbed in the engine. You can see that as the mixture enriches, the heat consumption shoots up which ultimately results in cooler exhaust temperatures. That's another reason why the mixture is enriched under heavy loads. High exhaust temperatures decrease component life, especially catalytic converters.

8/29/2011 11:24:26 AM

arghx
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Here are some good videos showing continuously variable lift & duration systems. This one is the Nissan system:



Here is an animation of BMW's Valvetronic system. Skip ahead to about 0:35 :



In both systems basically you are adding an extra arm. Normally the rocker arm opens the valve. Now you have an additional shaft connected to another arm that is then connected to that rocker arm. Changing the shaft angle ultimately changes to valve lift and duration.

This is definitely more complicated than the old NSX VTEC system, but instead of having two fixed valve lift and duration settings you can change them continously to increase engine output and reduce emissions.

8/30/2011 2:58:48 PM

sumfoo1
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wasn't there a bmw (i can't remember if it was production or concept i think it was the concept m5) that didn't use a throttle body and only used infinitely variable lift valves.

8/30/2011 3:55:56 PM

arghx
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yeah that's what Valvetronic is. It has a throttle valve but the valve is normally held in a wide open position so that there is negligible restriction and thus negligible loss of pumping efficiency.

The early Valvetronic engines were port injected, just like a 370Z which has port injection + its VVEL system. The latest Valvetronic engines like the N55 on the BMW 335 and the N20 on the BMW Z4 use gasoline direct injection. The current BMW gasoline direct injection system is different than most others out there. Among its many differences, it uses more expensive injectors and has more injection events per cycle.

http://www.bmw.com/com/en/insights/technology/technology_guide/articles/mm_valvetronic.html

8/30/2011 5:05:28 PM

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