Autoblog

Two words: Turbo Lag.

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Three words: Variable Turbo Geometry

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Turbos are the new sliced bread lol

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There's no such thing as a no-lag gas turbo engine. The throttle plate does more damage than the air inlet (what is modified in a VGT). I think it's also likely there can't be a no-lag Diesel in the real world either, due to low air volumes at low revs.

Anyway, VGT is not the revolution you act that it is. VGT just a continuously adjustable system that lets you best utilize the energy present in the exhaust gas stream to spin the turbo shaft. This sounds great, and it is. But a simple twin-scroll or dual entry turbo also can do this, it just isn't continuously adjustable. That is, it'll have a low-volume mode and a high-volume mode. These systems do work well to reduce lag from a standing stop. But the presence of these systems in the mass market already (Toyota shipped dual-entry in the MR2 in the early 90s and Mazda shipped twin-scroll in the RX7 in the late 80s) has stolen most of VGTs thunder.

Turbos are a reactive system, working from the exhaust gas of the combustion of the engine, they'll never truly be lag free unless anti-lag systems like in the WRC are adopted.

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why not the LS2/LS7? : "There's no such thing as a no-lag gas turbo engine."

Actually, that's not true in R&D: electrically-assisted turbos coming down the engineering pipeline will be lag-free.
http://www.autospeed.com/cms/A_1250/article.html

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That would be under the last paragraph of my post. "anti-lag systems".

Depending on your opinion of the "free energy" aspects of turbos, I would think that having an electric motor on a turbo charger is pointless when you can just use an electric motor to run a supercharger instead.

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@ why not the LS2/LS7 -

twin scroll volutes and the VGT are separate and compatible technologies.

The point of the former is to eliminate exhaust manifold crosstalk, which would otherwise occur in banks of four or more cylinders in a four-stroke engine. Crosstalk implies poorly controlled hot EGR, resulting in poor combustion stability and fuel economy in low part load. Avoiding it means smoother running and better dynamic response at very low RPM. You can also reduce the idle speed.

The point of a VGT is to reduce the effective throat cross-section of the turbine inlet when mass flow is low. This improves response dynamics but also increases stationary low-end torque without affecting rated power. This is especially relevant for manual transmissions, because the drivetrain controller cannot effect an automatic kickdown. In fuel economy terms, extra low-end torque means you can use longer gear ratios, forcing the engine to run at higher load and lower speed. This reduces internal friction losses, which are relatively high at low power levels.

The trouble with a true, continuously variable VGT is that the mechanism requires very tight clearances between stator and the movable vanes. This is a manageable issue for diesels, whose exhaust is relatively cool even at full power because CI combustion is always lean. Stoichiometric gasoline engines feature higher temperatures, so the VGT mechanism has to be made from expensive exotic alloys. To date, the current 911 turbo model is the only production car with a gasoline engine sporting VGTs.

A robust and much cheaper option, the VST, uses a sliding muff instead of vanes. This gives you two stable settings for the throat: either one scroll or both scrolls open. The downside is that you can no longer use the two scrolls to avoid exhaust crosstalk.

A third option proposed by Ricardo is to use 20-30% of low-pressure externally cooled EGR, effectively leaning down the gasoline engine so an affordable VGT turbo can be applied. In addition, throttling losses are much reduced and there is no need to enrich the mixture at high load. Both measures save fuel but the net effect is that rated power is no better than the naturally aspirated base engine and possibly, lower.

A fourth option is to use a small and a large turbo in sequence, as BMW has done on two of its diesel engines. This is more expensive than a single VGT but reduces turbo lag to a nearly imperceptible 0.15 seconds. Rated power is almost double that of the naturally aspirated base engine. In gasoline engines, achieving such low lag times means using a tiny turbo for the high pressure stage. Unfortunately, you cannot buy twin-scroll units below ~30mm turbine diameter. This re-introduces the crosstalk issue, which is why the TU Dresden suggests a bank size of 3 cylinders.

A fifth option proposed by Swissauto Wenko is to use a single Hyprex pressure wave supercharger a.k.a. wave rotor instead of sequential turbos. The emissions and load step response issues with the original Comprex design have been solved with a more advanced control strategy. The technology is now viable for gasoline engines. Crosstalk can be avoided by splitting the wave chambers radially at a suitable diameter.

Of course, you can always combine a mechanical supercharger with a large turbo as VW has done in the 125kW version of its 1.4L TSI, but this is very expensive option with modest fuel economy benefits at low RPM.

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Can you even read?? The article clearly states DAIMLER is going to be developing them. Daimler is the name of a company that makes: Mercedes-Benz, Smart, Freightliner, Sterling etc... NOT Chrysler, which is now Chrysler LLC.

Comprehension my friend....

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You really are that slow. It's almost sad.

Can you read? Honestly, can you read or do you just look for cognitive shapes based on object/name association?

Daimler means the Daimler Benz Group of companies, not Chrysler anymore.

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i thought Daimler /= Chrysler anymore...

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Aaron,

Not only is Chrysler separate from Daimler (except for 20% because they want access to the new v6 engines and DSG tranny that Chrysler is developing (but Daimler will NEVER, EVER say that publicly)) - But, Chrylser turbos have been very reliable historically. Part of the reason is water the cooled jacket they designed around the turbo to cool the lubricating oil. Chrysler built more turbo powered models and cars than anyone for the US market in the '80's. Unfortunately head gaskets were another story, but they have nothing to do with turbos. Maybe your particular ride had a problem but that doesn't mean it happened with the many millions of happy turbo powered cars (myself included).

see this link:
http://www.allpar.com/mopar/22t.html

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Frank

Yeah, I used to work for a Chrysler Dodge Jeep Eagle Mazda Subaru dealership in the 90s, mechanic, and I will bash Chrysler till the day I die.

I have respect for the Chrysler Corp. of the 60s and 70s, and even their comeback in the 80s, but but after working for them in the 90s I lost all respect for the Chrysler Corp. which is once again in the toilet where they rightly belong.

Daimler jettisoned them because the division was dragging the company down, but it may have been too late, the mutated Chrysler gene can destroy any company, checked my comment below.

I watched Chrysler screw up Jeep, which made a pretty good product until they started redesigning them. Now some of their jeeps are at the top of the Consumer Reports list of vehicles which have the least satisfied customers.

Grand Cherokee (V6, gas)

Jeep Commander (V6)

The original Jeep Cherokee was an excellent vehicle, and that in-line six 4.0 L was a rocksolid motor that you could count on. Even the Grand Cherokees of the 90s which Chrysler redesigned, were pretty good because they retained a lot of the parts from the Cherokee, like the engine. But then Chrysler started putting the 318 in them, which was once one of the best V8's on the market, then they started failing left and right because of shoddy assembly-line procedures. Now these vehicles are total junk. It's a crying shame.

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KW Mann? Ocean going diesel?

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